a. Review capnography data in the patient’s chart (Code: IA7e) [Difficulty: ELE: R; WRE: Ap]

Capnography is the analysis of graphic and numeric data from a patient showing the pattern and amount of exhaled carbon dioxide (CO₂). It is wise to look for previous capnography data before measuring the patient’s exhaled CO₂ level again. Look for numeric values as well as a printout of the tracing of exhaled CO₂. Be prepared to compare the previous information with the new data to help evaluate the patient’s condition. It is also useful to compare the patient’s pressure of CO₂ in arterial blood (PaCO₂) with the capnography information, even though they should not be expected to be the same.

b. Recommend capnography to obtain additional data (Code: IC10) [Difficulty: ELE: R, Ap; WRE: An]

There are three main reasons to recommend capnography. The first reason is to assess a patient’s ventilation. General anesthesia and even conscious sedation can result in a blunting of the patient’s normal drive to breathe. Several clinical or pathologic situations (discussed later in this chapter) can result in an abnormal increase or decrease in the carbon dioxide level. Second, capnography helps evaluate the effectiveness of cardiopulmonary resuscitation efforts. See the discussion in Chapter 11. Third, capnography can be used to help identify the proper placement of an endotracheal tube. If the tube is within the patient’s trachea or a main stem bronchus, the exhaled tidal volume will contain carbon dioxide. See the discussion in Chapter 12.

c. Perform the bedside procedure (Code: IB9c and IIIE3d) [Difficulty: ELE: R; WRE: Ap, An]

The capnometer is a device that measures the concentration of CO₂ in a gas sample from a patient. The principle of operation of most bedside units is based on carbon dioxide’s absorption of infrared light in a narrow wavelength band (4.3 μ). Infrared light at this wavelength is passed through the gas sample to a receiving unit. The difference between what is transmitted and what is received is directly related to how much carbon dioxide is in the gas sample. In other words, the greater the difference between the sent and the received infrared light, the greater the concentration of carbon dioxide in the gas sample.

The capnometer is calibrated by comparing a gas sample without carbon dioxide (possibly room air) with a second gas sample containing a known amount of carbon dioxide. The first gas sample without CO₂ should give a “zero” reading. Adjust the calibration control to zero if needed. The second sample usually contains 5% to 10% carbon dioxide. The capnometer should display a CO₂ level that matches the amount in the known gas sample. Adjust the calibration control as necessary. The carbon dioxide level can be documented as a percent or fraction (F_ACO₂) or as a partial pressure (P_ACO₂).

The capnograph is a strip chart recorder that provides a copy of the patient’s exhaled carbon dioxide curve. There are at least two paper speeds that are useful for different purposes. The fast speed is most useful for evaluating sudden changes in the patient’s condition. Each individual breath is easily seen (Figure 5-1). The slow speed is most useful for trend monitoring (Figure 5-2).

Figure 5-1 Normal capnograph tracing taken at a fast speed. The percentage of exhaled alveolar CO₂ is shown on the left vertical scale as F_ACO₂. The partial pressure of exhaled alveolar CO₂ is shown on the right vertical scale as P_ACO₂. The tracing of exhaled gas can be divided into these four components: A, the beginning of exhalation, which shows no carbon dioxide in the upper airway anatomic dead space; B, the addition of alveolar gas, rich in carbon dioxide, to the anatomic dead space gas causes a rapid rise in measured CO₂ level; C, pure alveolar gas with a stable amount of CO₂ causes a plateau—the end-tidal CO₂ point is shown at C just before inspiration; and D, inspiration with a rapid drop in carbon dioxide concentration to zero. Compared to a slow-speed tracing, a fast-speed tracing is more useful for determining the cause of a patient’s changing condition.

Figure 5-2 Normal capnograph tracing taken at a slow speed. The percentage of exhaled alveolar CO₂ is shown on the left vertical scale as F_ACO₂. The partial pressure of exhaled alveolar CO₂ is shown on the right vertical scale as P_ACO₂. The slow speed results in a blending of parts A, B, and C of the fast-speed tracing (Figure 5-1). Each spike is part C of the curve and marks an exhalation. A slow-speed tracing is more useful in trend monitoring of a patient than a fast-speed tracing.

Two different gas sampling methods exist: mainstream and sidestream. The mainstream method involves having the infrared sensing unit at the airway; usually it is attached directly to the endotracheal/tracheostomy tube. If the patient is on a ventilator, the sampling adapter must be placed between the endotracheal tube and the ventilator circuit (with or without mechanical dead space). All inspired and expired gas passes through the sensor (Figure 5-3).

Figure 5-3 Schematic drawing of a mainstream exhaled carbon dioxide analyzer sensor. The infrared sensor is attached to the patient’s airway so that all of the exhaled and inhaled gas passes through it.

Rights were not granted to include this figure in electronic media. Please refer to the printed book.

(From Szaflarski NL, Cohen NH: Heart Lung 20:363-374, 1991.)

The sidestream method employs a capillary tube placed so that a small sampling of the patient’s exhaled gas can be drawn into the capnometer for analysis. It is not necessary for the patient’s entire breath to pass through the sampling adapter; therefore it can be used in an unintubated patient by taping the sampling catheter a short distance into a nostril. If the patient is on a ventilator, the sampling adapter must be placed between the endotracheal tube and the ventilator circuit (with or without mechanical dead space). Remember that the patient’s exhaled tidal volume (V_T) and minute volume (_E) are reduced by the amount that is drawn into the capnometer (Figure 5-4).

Figure 5-4 Representation of a sidestream capnometry system. A capillary tube is placed into the ventilator circuit to sample the exhaled and inhaled gases.

d. Interpret the results from the procedure (Code: IB10c, IIIE4e) [Difficulty: ELE: R, Ap; WRE: An]

It is known that carbon dioxide diffuses from the higher concentration in the tissues to the venous blood and to the lungs to be exhaled. Figure 5-5 shows the normal physiology behind capnography. This diffusion or “flow” of CO₂ results in a measurable gradient or difference. In a healthy, upright sitting person, a close relationship exists between carbon dioxide levels in both venous blood and arterial blood and the amount of exhaled carbon dioxide gas. The carbon dioxide level at the end of exhalation is most frequently monitored during patient care. This is called the end-tidal carbon dioxide pressure (PetCO₂). When ventilation and perfusion match well, as in a healthy upright person, the gradient between the arterial carbon dioxide level (PaCO₂) and the PetCO₂ is between 2 and 3 torr, with a range of 1 to 5 torr. The gradient will show the PetCO₂ level to be less than the PaCO₂ level. This is because the PetCO₂ value is an average of exhaled carbon dioxide levels from all lung areas.

Figure 5-5 Representation of the alveolar-capillary membrane showing the diffusion of oxygen and carbon dioxide and the arterialization of venous blood. Also shown are alveolar CO₂ values measured by capnography.

Box 5-1 lists normal values of capnography. Three factors influence capnography’s use and the interpretation of the results. (1) The first factor is the patient’s metabolism. The average resting adult produces about 200 mL of CO₂ per minute, and fever and exercise increase this value. Hypothermia, sleep, and sedation decrease CO₂ production. Exhaled CO₂ is monitored during a cardiopulmonary resuscitation (CPR) attempt to determine the effectiveness of circulation and ventilation attempts and to decide if the efforts should be continued or stopped. If no carbon dioxide is being exhaled despite proper CPR procedures, the physician may conclude that the patient’s metabolism has stopped altogether and death has occurred. There would then be nothing to gain by continuing cardiopulmonary resuscitation (CPR) efforts.

(2) Although not a major factor, the patient’s cardiac output is another factor that influences the use of capnography. Sepsis, which might double a patient’s cardiac output, reduces the PCO₂ level only a few torr (millimeters of mercury [mm Hg]). Cardiogenic shock, which reduces the cardiac output, raises the partial pressure of CO₂ (PCO₂) only a few torr.

(3) The third and most important factor is alveolar ventilation. A doubling of alveolar ventilation, under steady-state conditions for carbon dioxide production, results in a halving of the PCO₂ levels in arterial blood and alveolar gas. However, a reduction of alveolar ventilation to half of its previous level will result in the PaCO₂ and P_ACO₂ levels being doubled (Figure 5-6).

Figure 5-6 Relationship between alveolar ventilation, PaCO₂, and exhaled percent CO₂.

(From Pilbeam SP: Mechanical ventilation: physiological and clinical applications, ed 4, St Louis, 2006, Mosby.)

Tidal volume (V_T) and respiratory rate are directly related to alveolar ventilation. Of the two, tidal volume is more important because it relates to the patient’s dead space (V_D) to V_T ratio (V_D/V_T). A decrease in the patient’s V_T level results in less alveolar ventilation and a rise in PCO₂ level. Conversely, an increase in the V_T level results in more alveolar ventilation and a drop in the PCO₂ level.

Capnography is most accurate and correlates best with the PaCO₂ level if the patient’s ventilation and perfusion match. The more ventilation and perfusion mismatching there is, or the more unstable the pulmonary perfusion, the wider or less reliable is the gradient between the patient’s arterial carbon dioxide and alveolar carbon dioxide levels. The following procedures should be performed to help understand the patient’s condition and interpret the capnography results.

Remember that mm Hg (millimeters of mercury) and torr (Torricelli) are equivalent units of pressure. The National Board of Respiratory Care (NBRC) uses these two units for different items in its questions. It uses mm Hg for blood pressure measurements and torr for blood gas values (such as PaCO₂ and PO₂). However, in questions regarding capnography, the NBRC has used both mm Hg and torr in its questions that relate to exhaled CO₂ (such as P_ACO₂ and PetCO₂).

a. Perform the bedside procedure (Code: IB9c and IIIE3d) [Difficulty: ELE: R; WRE: Ap, An]

The arterial–end-tidal carbon dioxide gradient [P(a-et)CO₂] is useful, because once it is reliably determined the patient’s ventilatory condition can be monitored by capnography alone. Drawing an arterial blood sample to measure the PaCO₂ level is less necessary if the patient is stable.

The normal gradient is 2 to 3 torr, with a range of 1 to 5 torr. However, most patients using capnography are not normal. The possible gradient ranges from 6 to 20 torr in unstable patients with cardiopulmonary abnormalities. For example, the patient who is breathing shallowly may have an end-tidal CO₂ level that is greater than the arterial CO₂ level. This is because the patient is not exhaling completely to empty alveolar gas. Therefore determining each patient’s own gradient is important.

Follow these steps:

b. Interpret the results from the procedure (Code: IB10c, IIIE4e) [Difficulty: ELE: R, Ap; WRE: An]

Review the components of a fast-speed capnography tracing in Figure 5-1 to understand a normal person’s expiratory pattern. Figure 5-7 shows eight different abnormal fast-speed capnography tracings. See the figure legend for an explanation of each problem. As the patient returns to normal, the tracing should approach that shown in Figure 5-1.

Figure 5-7 A series of abnormal fast-speed capnography tracings. A, A mechanically ventilated patient with a malfunctioning exhalation valve. Note that the baseline CO₂ level is elevated because the patient’s exhaled breath is measured during an inspiration. Correction of the exhalation valve should result in normal inhalation and exhalation. B, This rapidly rising baseline gas pressure and failure to return to baseline is usually seen when moisture or secretions block the capillary tube. Clearing the obstruction enables the patient’s gas to again reach the analyzer. C, Distortions in the tracing from incomplete exhalation. These may be caused by hiccups, chest compressions during CPR, or inconsistent tidal volume efforts during an asthma attack. D, An obstructive lung disease patient with ventilation and perfusion mismatching. There is no alveolar plateau with a stable CO₂ level. Inhaling a bronchodilator should result in the tracing returning closer to normal. E, A patient with restrictive lung disease showing no plateau of alveolar gas emptying. This is because the alveoli do not empty evenly. F, A sudden drop in carbon dioxide level in the middle of an exhalation indicates that the patient attempted inspiration. This “cleft” is usually seen when a patient who has been pharmacologically paralyzed begins to regain movement. G, Uneven carbon dioxide levels seen at the end of exhalation can be caused by the following: (1) the patient’s heartbeat pumping fresh blood and CO₂ to the emptying lungs; the cardiogenic oscillations should match the heart rate; (2) the ventilator’s exhalation valve is fluttering open and closed. H, The alveolar plateau is biphasic. This has been seen in patients with lungs that are different in compliance and ventilation/perfusion matching (e.g., single lung transplantation).

(From Shapiro BA, Peruzzi WT, Templin R: Clinical application of blood gases, ed 5, St Louis, 1994, Mosby.)

a. Perform the bedside procedure (Code: IB9c and IIIE3d) [Difficulty: ELE: R; WRE: Ap, An]

Have a cooperative patient exhale maximally to residual volume (RV) through the capnography unit. The graphic results will be similar to that shown in Figure 5-8. The usual P(a-RV)CO₂ gradient in a healthy person is about 3 to 5 torr, and should be less than 7 torr. The wider the gradient, the greater is the ventilation to perfusion (/) mismatching. A gradient of more than 13 torr is considered to be markedly abnormal. This may be the case in patients with chronic obstructive pulmonary disease (COPD), pulmonary emboli, left heart failure (LHF), or hypotension.

Figure 5-8 Comparison of several fast-speed capnograph tracings showing how the exhaled carbon dioxide level changes as the patient exhales to residual volume. A normal tracing is matched against abnormal tracings of pulmonary emboli, left heart failure (LHF), and chronic obstructive pulmonary disease (COPD). The normal patient has the same end-tidal CO₂ level as residual volume CO₂ level, showing good matching of ventilation and perfusion. LHF and COPD patients have a narrowing of the gradient as residual volume is approached. The patient with a pulmonary embolism keeps the same gradient at the residual volume as that found at the end of the tidal volume.

(From Pilbeam SP: Mechanical ventilation: physiological and clinical applications, ed 4, St Louis, 2006, Mosby.)

b. Interpret the results from the procedure (Code: IB10c, IIIE4e) [Difficulty: ELE: R, Ap; WRE: An]

When comparing the normal (solid line) tracing in Figure 5-8 with the / mismatching (dashed line) tracing, note the increased gradient at end-tidal CO₂. With continued exhalation to residual volume, the left heart failure and COPD patients have a narrowing of the gradient. This can be used clinically to follow these patients’ progress and response to treatment. The patient with a large pulmonary embolism will not have such a narrowing of the gradient as he or she exhales to residual volume. This patient’s gradient will narrow to normal as the embolism is resolved and the physiologic dead space returns to normal.

Past exams have often had one question that requires the interpretation of capnography results, especially the end-tidal CO₂ value (PetCO₂). Examples include a change in alveolar ventilation, shallow breathing, and CPR attempt.

a. Determine the decimal fraction or percentage of dead space

Place both carbon dioxide values into this formula, which is derived from the original Bohr formula:

In which:

V_D/V_T or V_D the patient’s physiologic dead space

PaCO₂ = the patient’s arterial carbon dioxide pressure

PĒCO₂ = the patient’s average exhaled carbon dioxide pressure

The following example is based on an abnormal adult:

The patient’s V_D fraction can be recorded as 0.6 or 60%. (Note that this equation must be used when the patient’s tidal volume is not known.)

b. Determine the dead space volume

Place both carbon dioxide values into this formula, which is derived from the original Bohr formula:

In which:

V_D V_T or V_D the patient’s physiologic dead space

V_T = the average exhaled tidal volume

PaCO₂ = the patient’s arterial carbon dioxide pressure

PĒCO₂ = the patient’s average exhaled carbon dioxide pressure

The following example is based on a normal adult:

The patient’s physiologic V_D volume = 150 mL. (Note that this equation must be used when the patient’s tidal volume is known.)

In addition, the preceding equation allows calculation of the patient’s V_D/V_T ratio. In this example, it is 150/500, 0.3, or 30%, depending on how it is written.

The recent advent of volumetric capnography technology allows the patient’s dead space to be rapidly determined. These units can simultaneously measure the patient’s exhaled tidal volume and the variable percentage of carbon dioxide found during the exhalation (Figure 5-10). The computer that is integrated with the volumetric capnography unit then calculates the volume of dead space as a fraction of the exhaled tidal volume. Figure 5-11 shows how volumetric capnography can be set up to measure the dead space of a patient requiring mechanical ventilation. This technology permits the rapid assessment of a patient as treatment is being performed. For example, if a patient had a large pulmonary embolism resulting in significant dead space, a clot-dissolving medication such as streptokinase (Kabikinase or Streptase) or alteplase (Activase) would be given. These “clot buster” medications will rapidly dissolve the patient’s pulmonary embolism. With volumetric capnography, the dead space volume can be monitored as it normalizes when blood flow through the lungs is restored.

Figure 5-10 A graphic representation of the factors involved in the calculation of a patient’s dead space volume, or dead space to tidal volume (V_D/V_T) ratio, through volumetric capnography. These units can measure exhaled carbon dioxide (by pressure or percentage) at time intervals as the patient’s tidal volume is exhaled. Review Figure 5-1, as needed, for a normal capnograph tracing.

Figure 5-11 Measurement of volumetric capnography on a patient receiving mechanical ventilation. All measurements are taken between the patient’s endotracheal tube and mechanical ventilator circuit. The mainstream capnograph sensor sends data on exhaled carbon dioxide concentration to the computer within the capnograph monitor. The pressure and flow sensors send data to the computer to determine the exhaled volume. The computer integrates the information to determine anatomic dead space (white area) and alveolar dead space (black area). With areas q and p being calculated as equal, the shaded area is alveolar volume where gas exchange occurs.

a. Decreased V_D/V_T ratio

b. Increased V_D/V_T ratio

c. Increased dead space effect with ventilation greater than perfusion ( > )

Many clinicians believe that a dead space/tidal volume ratio of 0.6 (60%) or more is an indication for mechanically ventilating the patient. A person who is wasting 60% or more of his or her ventilation will soon tire from the work of breathing and go into ventilatory failure.

a. Review blood pressure data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

Systemic arterial blood pressure (BP) is the force exerted against the walls of the arteries when blood is pumped through them. As one of the vital signs, the patient’s BP should be found in the chart. Review it to know the patient’s normal blood pressure reading, and if it has been stable or variable with the patient’s changing condition.

b. Recommend blood pressure measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

The patient’s blood pressure, and other vital signs, should be monitored as often as clinically prudent. If the patient’s cardiovascular or pulmonary condition is changing frequently, the blood pressure should be measured frequently, even continuously.

c. Perform blood pressure measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]

The general steps in measuring blood pressure were described in Chapter 1. The BP is usually measured on either of the patient’s arms. Necessary equipment includes the proper size of blood pressure cuff, a sphygmomanometer to measure the pressure, and a stethoscope to hear the sounds of bloodflow returning through the brachial artery. Figure 5-12 shows the basic elements of the procedure. The cuff is inflated to a pressure that is greater than the patient’s systolic pressure. As the pressure in the cuff is gradually decreased, the first sound heard (Korotkoff sounds) is the systolic pressure. The pressure reading at which this sound ceases is the diastolic pressure. Blood pressure measurement can usually be performed manually by a respiratory therapist or other trained health care professional. If BP measurement is needed on a frequent basis, an automated blood pressure measurement system can be set up on the patient’s arm. This unit can be programmed to measure the BP on a schedule and can also have high and low blood pressure alarm limits established as a safety feature.

Figure 5-12 Arterial blood pressure is most commonly measured with a sphygmomanometer cuff that is inflated to a pressure greater than the patient’s BP. When that happens, no palpable pulse can be felt. As the cuff pressure is gradually decreased, a respiratory therapist can listen, with a stethoscope placed over the brachial artery, for the return of blood flow. The first sound heard is systolic pressure (in this case 110 mm Hg) and the last sound heard is diastolic pressure (in this case 80 mm Hg).

(Modified from Rushmer RF: Cardiovascular dynamics, ed 3, Philadelphia, 1970, Saunders. In Wilkins RL, Dexter JR, Heuer AJ: Clinical assessment in respiratory care, ed 6, St Louis, 2010, Mosby.)

d. Recommend the insertion of an arterial line (WRE code: IC12) [Difficulty: WRE: R, Ap, An]

Recommend that an arterial line (catheter) be inserted in the following situations: (1) the patient needs continuous monitoring of blood pressure, (2) frequent arterial blood samples are needed for blood gas analysis. The arterial line is usually placed into the radial artery of an adult; a newborn will have the line placed into the umbilical artery.

e. Interpret the results of the blood pressure measurement (Code: IB10m, IIIE4c) [Difficulty: ELE: R, Ap; WRE: An]

Review the general discussion on blood pressure in Chapter 1. The following are normal blood pressure values:

Patients who have values that are higher or lower than these should be further evaluated. Know the following values since they represent a serious patient problem:

a. Review central venous pressure measurement data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

The central venous pressure (CVP) is the pressure measured in a patient’s superior vena cava, just above the right atrium. See Figure 5-13. Review previous patient data to understand whether there is an abnormality. Compare the current data with the earlier information to determine if there has been a change in the patient’s condition. See Box 5-2 for normal values.

Figure 5-13 Proper position of a central venous pressure (CVP) catheter with its distal tip located in the superior vena cava, just above the right atrium. The catheter can be inserted through the internal jugular vein (as shown) or the subclavian vein. This traditional, single-lumen CVP catheter can be used to measure the pressure on the right side of the heart and to administer fluids or medications.

b. Recommend the insertion of a central venous pressure catheter to obtain additional data (WRE code: IC12) [WRE Difficulty: R, Ap, An]

A single-lumen central venous pressure catheter (also called a CVP line) is inserted into many patients for one or more reasons: (1) to monitor the patient’s right-sided (right atrium) heart pressure, (2) to rapidly administer a large volume of intravenous fluids, and (3) to administer cardiac medications during a CPR attempt (preferred route). Recently, the development of a triple-lumen CVP catheter with integrated fiberoptic channel (Edwards Lifesciences, LLC) has enabled the continuous monitoring of central venous oxygen saturation (ScvO₂), in addition to the previously mentioned uses. See Figure 5-14.

Figure 5-14 New triple-lumen CVP catheter that can be used to continuously monitor the patient’s oxygen saturation of central venous blood (SCVo₂) in addition to measuring the right heart pressure and administering fluids and medications.

(From Edwards Lifesciences LLC, Irvine, Calif.)

c. Recommend central venous pressure measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

The CVP is measured in order to know the pressure in the right atrium of the patient’s heart. This information is used to help evaluate a patient’s fluid status and to guide the administration or restriction of more fluids.

d. Perform central venous pressure measurement (Code: IB9e) [Difficulty: R, Ap, An]

The catheter is usually inserted into the right jugular vein or right subclavian vein and advanced to just above the superior vena cava. When set up for monitoring pressure, it measures the right atrial pressure (see Figure 5-15 for how to perform the procedure). Note that the stopcock must be kept at the midchest (midheart) level. Usually a mark is placed at this location (on the patient’s chest) for consistency. Raising the stopcock above the mark results in an incorrectly low reading. Lowering the stopcock below the mark results in an incorrectly high reading. See Figure 5-16. Clinical practice is very important in learning how to perform this procedure. It is important that the patient breathes spontaneously if at all possible. Peak pressures during inspiration on a mechanical ventilator may artificially raise the CVP reading. Positive end-expiratory pressure (PEEP) may also raise the CVP reading. If the patient cannot be removed from the ventilator, take the reading during exhalation. Make a note of the settings and that the reading was taken with the patient on the ventilator. Record the data in the patient’s chart or flow sheet.

Figure 5-15 Procedure for determining the central venous pressure (CVP) with a manometer. A, Water-column manometer marked in centimeters, IV tubing, and patient in place. The patient must be placed in a horizontal position with the stopcock located at the midchest (midheart) point, as shown by the dashed line. B, Turn the stopcock so that the manometer fills with fluid above the expected pressure. C, Turn the stopcock off to the IV so that the fluid flows from the manometer into the patient. Look at the stable fluid level for the CVP reading. D, Turn the stopcock so that the fluid flows from the IV into the patient.

(From Daily EK, Schroeder JS: Techniques in bedside hemodynamic monitoring, ed 5, St Louis, 1994, Mosby.)

Figure 5-16 The effects of patient position compared to position of the pressure transducer. A, When the patient’s midchest (midheart) is above the pressure transducer, the measured pressure will be higher than actual. B, When the patient’s midchest (midheart) is below the pressure transducer, the measured pressure will be lower than actual. C, True pressures will be measured when the patient’s midchest is the same height as the pressure manometer. All hemodynamic pressures (CVP, arterial pressure, pulmonary artery pressure, and pulmonary capillary wedge pressure) will be adversely affected if the patient and manometer heights do not match, as shown in A and B.

(From Oblouk Darovic G: Hemodynamic monitoring—invasive and noninvasive clinical application, ed 3, Philadelphia, 2002, Saunders.)

Past exams have asked about the proper placement of the CVP stopcock or arterial pressure transducer at the midchest (midheart) location to ensure accurate pressure measurements. Usually a mark is placed on the patient’s chest for a consistent measurement point. Review Figure 5-16 for the effects of misplacement.

e. Interpret the results of the central venous pressure measurement (Code: IB10m, IIIE4c) [Difficulty: ELE: R, Ap; WRE: An]

As noted earlier, the CVP is a measure of the pressure in the right atrium. The two main factors that influence the right atrial pressure are the blood volume returning to it and the functioning of the right ventricle (see Box 5-2 for normal CVP readings).

A decreased CVP reading usually indicates that the patient is hypovolemic. Hypotension confirms this. An increased CVP reading may suggest one of the following possibilities:

Memorize the values listed in Box 5-2. Expect to see several questions in which these values are used as patient data or as options to answer a question. The normal values must be understood to identify abnormal values and know why they are abnormal.

a. Review pulmonary artery pressure data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

The pulmonary artery pressure (PAP) is the systolic and diastolic pressure found in either pulmonary artery. It can be measured only through a pulmonary artery catheter. (The NBRC often refers to this as a flow-directed pulmonary artery catheter.) Review the patient’s previous values before taking another pressure reading to make a comparison. Box 5-2 shows normal cardiopulmonary values.

b. Recommend the insertion of a pulmonary artery catheter for additional data (WRE code: IC12) [WRE Difficulty: R, Ap, An]

To read the PAP, a pulmonary artery catheter (PAC) must be inserted through a vein and passed through the right atrium and right ventricle into the pulmonary artery. The common insertion sites, in descending order of preference, are the basilic vein in either the right or the left arm, the right internal jugular or subclavian vein, or the right or left femoral vein. The pulmonary artery catheter is also commonly called a Swan-Ganz catheter after the inventors who gave their names to a particular brand. The catheters are available in different lengths and diameters for pediatric and adult patients. See Figure 5-17 for a typical adult catheter.

Figure 5-17 A 7-French quadruple-lumen thermodilution pulmonary artery catheter. A, Distal port goes to the tip of the catheter. It is used for measuring PAP and PCWP and for sampling blood for PO₂ determination. B, Balloon inflation port is used to inflate the balloon for inserting the catheter and for obtaining a PCWP reading. C, Proximal port is used for measuring central venous pressure and for injecting iced saline for a thermodilution cardiac output study. The iced saline exits from the right atrial opening. D, Thermistor connector attaches to the cardiac output computer. A bimetallic wire runs through the catheter to the thermistor opening, where it is exposed to temperature changes of the blood and cold injectate. (NOTE: Not all catheters are capable of measuring cardiac output. Some catheters have other special features such as continuously measuring venous saturation or cardiac pacemaker leads.)

(From Oblouk Darovic G: Hemodynamic monitoring—invasive and noninvasive clinical applications, ed 3, Philadelphia, 2002, Saunders.)

c. Recommend pulmonary artery pressure measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

The PAP is important to measure in patients with severe pulmonary or cardiovascular problems, pulmonary hypertension, myocardial infarction, congestive heart failure, hypertension, and hypotension.

d. Perform pulmonary artery pressure measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]

Figure 5-17 is an illustration of a 7-French quadruple-lumen thermodilution pulmonary artery catheter. Besides measurement of PAP, it is capable of being used to measure cardiac output. Figure 5-18 illustrates how a pulmonary artery catheter could be arranged with a pressure transducer and pressure monitor. Figure 5-19 shows a representation of the series of pressure waveforms seen as the catheter is advanced through the heart and into the wedged position in a branch of the pulmonary artery. Figure 5-20 shows a larger cutaway view of the heart with a PAC and normal heart chambers and related pressures.

Figure 5-18 The various components of the pulmonary artery monitoring system. It includes a fluid source such as normal saline that is pressurized to 300 mm Hg to maintain a flow of fluid through the tubing system. The continuous flush device (made by Sorenson) is designed to allow three drips of fluid per minute through the tubing system; pulling on the fast-flush valve gives a continuous flow of fluid to clear air or blood from the system. The transducer converts a pressure signal to an electrical signal that is sent to the monitor for display as numeric data and a pressure waveform. The high-pressure tubing transfers the patient’s pressure accurately to the transducer. The double stopcocks are used to close off the tubing system or sample blood from the patient. This then connects to the distal port of the pulmonary artery catheter. This same monitoring system can be used with an arterial catheter for continuous pressure monitoring and blood sampling.

(Adapted from Smith RN: Invasive pressure monitoring, Am J Nurse 9:1514, 1978. Copyright 1978 The American Journal of Nursing. Used with permission in Oblouk Darovic G: Hemodynamic monitoring, Philadelphia, 1987, WB Saunders.)

Figure 5-19 Sequence of pressures and pressure waveforms seen as the pulmonary artery catheter advances through the right atrium, right ventricle, and pulmonary artery until it wedges. Be observant of premature ventricular contractions (PVCs) as the catheter is advanced through the right ventricle.

(From Wilkins RL, Dexter JR, Heuer AJ: Clinical assessment in respiratory care, ed 6, St Louis, 2010, Mosby.)

Figure 5-20 Pulmonary artery catheter (PAC) through a heart with normal chamber pressures. SVC, Superior vena cava; IVC, inferior vena cava; RA, right atrium; RV, right ventricle; PA, pulmonary artery; PCWP, pulmonary capillary wedge pressure; LA, left atrium; LV, left ventricle; and Ao, aorta.

To obtain an accurate pulmonary artery pressure measurement, the equipment must be set up and calibrated properly, the distal lumen of the catheter must be patent with a continuous fluid-filled channel from the patient’s bloodstream back to the transducer, and the catheter’s balloon must be deflated. Clinical practice is important in understanding how to perform this procedure. Record the PAP data in the patient’s chart or flow sheet.

e. Interpret the results of pulmonary artery pressure measurement (Code: IB10m, IIIE4c) [Difficulty: ELE: R, Ap; WRE: An]

Again, the PAP is the systolic and diastolic pressure found in the pulmonary artery (see Box 5-2 for normal values). Elevated PAP values are usually seen with the following conditions:

Decreased pulmonary artery pressure values are not frequently seen. Patients with hypovolemic shock, anaphylaxis (allergic shock), or excessive use of vasodilating drugs may have a decreased pulmonary artery pressure. The most obvious clinical sign in these patients is a low systemic blood pressure.

Expect to see at least one question requiring the calculation of the PAd-PCWP gradient and at least one question requiring the result to be interpreted.

a. Review pulmonary capillary wedge pressure data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

The pulmonary capillary wedge pressure (PCWP) refers to the pressure measured in the pulmonary capillary bed under no-flow conditions. It is important to review previous patient data before measuring another pressure. Normal values are listed in Box 5-2.

b. Recommend pulmonary capillary wedge pressure measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

Measuring the PCWP is important in patients with severe pulmonary or cardiovascular problems, including pulmonary hypertension, myocardial infarction, congestive heart failure, fluid overload, dehydration, hypertension, and hypotension.

c. Perform pulmonary capillary wedge pressure measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]

A pulmonary artery catheter must be placed into a patient’s pulmonary artery for the PCWP to be measured. The PCWP is obtained by inflating the balloon at the tip of the catheter. This obstructs that branch of the pulmonary artery so that the downstream pressure from the left ventricle is seen on the monitor (see Figures 5-19 and 5-20). The balloon volume varies with the diameter of the catheter. The necessary volume is printed on the catheter near where the air is injected into the balloon. For example, the 5-French catheter balloon holds 0.8 mL of air and the 7-French catheter balloon holds 1.5 mL of air. It is important to inject only the required amount of air. Overinflating may burst the balloon or rupture the pulmonary artery. If the balloon wedges at less than the required volume, the catheter is probably too far down in the artery and may need to be withdrawn a short distance. The balloon is only inflated long enough to obtain the PCWP and then the balloon is deflated. Pulmonary infarction will occur if the balloon is left inflated and the blood in the pulmonary artery is stagnant and allowed to clot. Record the PCWP value in the patient’s chart or flow sheet.

d. Interpret the results of pulmonary capillary wedge pressure measurement (Code: IB10m, IIIE4c) [Difficulty: ELE: R, Ap; WRE: An]

As noted earlier, the PCWP refers to the pressure measured in the pulmonary capillary bed under no-flow conditions. This pressure reflects downstream pressure from the left side of the heart. At diastole, in the patient without pulmonary hypertension or mitral valve disease, the PCWP parallels left atrial pressure (LAP) and left ventricular end-diastolic pressure (LVEDP). The literature reveals that a variety of terms and initials are used to describe the same physiologic value. Do not be confused by reading about the pulmonary capillary pressure (PCP), pulmonary wedge pressure (PWP), pulmonary artery wedge pressure (PAWP), or wedge pressure.

Elevated PCWP is generally considered to be greater than 10 mm Hg and can indicate the following conditions:

These conditions result in serious problems for the patient’s lung function. When the PCWP reaches 20 to 25 mm Hg, fluid begins to leak into the pulmonary interstitium. This makes the lungs less compliant and increases the patient’s work of breathing. A PCWP of 25 to 30 mm Hg results in frank pulmonary edema and dramatically decreases the patient’s Pao₂ level.

Decreased PCWP is generally considered to be less than 4 mm Hg and can indicate the following conditions:

a. Review cardiac output data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

Cardiac output (CO) is the volume of blood pumped in 1 minute. It is calculated as the product of heart rate (HR) for 1 minute and stroke volume (SV): (CO = HR × SV). CO is a measurement of the heart’s pumping ability to meet the body’s needs. As always, review previous data before repeating the test. Box 5-2 lists normal values.

b. Recommend a cardiac output measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

A cardiac output measurement is performed on patients with serious cardiovascular disease to assess the condition of the heart. A major change in vital signs or new cardiovascular treatment justifies a measurement. See Figure 5-21 for the interplay of factors that can impact a patient’s cardiac output. To measure CO, the patient must have a pulmonary artery catheter in place that is capable of measuring cardiac output.

Figure 5-21 Factors that influence cardiac output (CO). CO is the product of heart rate and stroke volume. Stroke volume is determined by preload (blood volume), contractility of each ventricle, and afterload (arterial resistance).

(From Wilkins RL, Dexter JR, Heuer AJ: Clinical assessment in respiratory care, ed 6, St Louis, 2010, Mosby.)

c. Perform a cardiac output measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]

At the time of this book’s publication, there are several cardiac output methods that are commonly utilized in the cardiac catheterization laboratory. They will not be presented here. This discussion is limited to intensive care unit bedside procedures where a respiratory therapist is likely to be involved. A thermodilution cardiac output study involves using one of two special four-lumen pulmonary artery catheters. Both catheter types require additional hardware and supplies, including a computer designed to calculate the CO.

The first type of thermodilution catheter is used to inject a cool solution into the heart. This cool solution is diluted with the patient’s blood. As the blood and cool solution mix passes a thermistor at the catheter tip, the computer calculates the patient’s cardiac output based on the time required to pump the cooler blood past the thermistor (see Figure 5-17).

This procedure requires an injectable saline solution or a 5% dextrose, ice-water bath to cool the injectate, necessary tubing and connections, thermometer, 10-mL syringes, and injector system (Figure 5-22). It is beyond the scope of this text to describe all of the steps in the different types of adult and neonatal thermodilution cardiac output procedures. Hands-on experience is necessary. Only the most important and common features are presented here:

Figure 5-22 Complete system for performing thermodilution cardiac output studies.

(From Edwards Lifesciences LLC, Irvine, Calif, 1985.)

The “cool solution” thermodilution cardiac output procedure has been available for more than 20 years and is widely used clinically. Its main disadvantages are that the CO value is available only intermittently, it is a time-consuming procedure, and patients with heart failure are given significant amounts of additional fluid for each cardiac output calculation.

The second type of thermodilution cardiac output catheter uses a thermal filament (a heated wire) that wraps around the catheter (Figure 5-23). With this catheter, the computer periodically directs electricity to the filament. This results in periodic warming of the blood from the heated wire. The computer calculates the patient’s cardiac output by determining the time needed to pump the heated blood past the thermistor at the tip of the catheter. The advantages of the “heated wire” cardiac output catheter are that it gives an updated cardiac output value every 30 seconds, requires no additional time from the nurse or respiratory therapist after the initial setup, and does not add any additional fluid to the patient’s intake.

Figure 5-23 View of the right side of the heart showing a continuous cardiac output thermodilution pulmonary artery catheter in proper position. Note the thermal filaments that heat the passing blood. The resulting temperature change is detected by the thermistor in the pulmonary artery.

(From Daily EK, Schroeder JS: Techniques in bedside hemodynamic monitoring, ed 5, St Louis, 1994, Mosby.)

d. Calculate the patient’s cardiac output value (ELE code: IB9l) [Difficulty: ELE: R, Ap]

The following formula can be used to calculate a predicted cardiac output for the adult patient. This value can then be compared with the actual patient cardiac output.

BSA is the body surface area and can be calculated mathematically or determined from a data table (Figure 5-24). See the following discussion on cardiac index for information on calculating BSA.

Figure 5-24 DuBois Body Surface Chart (as prepared by Boothby and Sandiford of the Mayo Clinic). Directions: To find the body surface of a patient, locate the height in inches (or centimeters) on scale I and the weight in pounds (or kilograms) on scale II. Place a straightedge (ruler) between these two points, which will intersect scale III at the patient’s surface area value.

(From Boothby WM, Sandiford RB: Boston Med Surg J 185:337, 1921.)

The following two methods can be used to calculate the patient’s cardiac output:

In which:

Therefore:

e. Interpret the results of the patient’s cardiac output measurement (Code: IB10l) [Difficulty: ELE: R, Ap; WRE: An]

As listed in Box 5-2, the healthy, resting adult has a cardiac output in the range of 4 to 8 L/min and a healthy, resting neonate has a cardiac output in the range of 0.6 to 0.8 L/min.

Cardiac output can increase markedly in a person with a healthy heart who is stressed or exercising, has a fever, or has any other reason for an increased metabolism. All these conditions increase the person’s demand for oxygen, which is primarily met by increasing cardiac output. (To a lesser extent, the tissues extract more oxygen from the blood.) Sepsis is the one serious condition that results in a high cardiac output.

There are many possible causes of a decreased cardiac output. The most common are hypovolemia, increased peripheral resistance, and heart failure. A patient with low cardiac output often has a low blood pressure. If the cardiac output and blood pressure are too low, the patient will develop metabolic acidosis from peripheral hypoxemia. Death can result if this is not corrected.

a. Review stroke volume data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

Stroke volume (SV) is the volume of blood ejected with each heartbeat. It is the difference between the volume of blood in each ventricle at the end of diastole (preload) and the volume left in the ventricles at the end of systole (after ejection [afterload]). It is helpful to review the patient’s previous cardiac output and stroke volume data before performing another SV measurement.

b. Recommend a stroke volume measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

A stroke volume (and cardiac output) measurement is performed on patients with serious cardiovascular disease to assess the condition of the heart. A major change in vital signs or new cardiovascular treatment justifies a measurement. As shown in Figure 5-21, preload, contractility of each ventricle, and afterload can impact a patient’s stroke volume.

c. Calculate the patient’s stroke volume (ELE code: IB9l) [Difficulty: ELE: R, Ap]

The normal stroke volume is based on a person’s age. See Box 5-2 for normal values. Stroke volume can be determined through a cardiac ultrasound procedure or can be calculated from the patient’s heart rate and cardiac output measurements.

For example, calculate an adult patient’s stroke volume when the heart rate is 100 beats/min and cardiac output is 8 L (8000 mL):

The stoke volume is not the entire preload volume. The stroke volume portion of the preload that is pumped out of the ventricle is referred to as the ejection fraction. Under normal conditions, an adult will have an ejection fraction of 0.6 to 0.75. This means the ventricle ejects a stroke volume that is usually 60% to 75% of the preload volume.

d. Interpret the results of the patient’s stroke volume calculation (Code: IB10l) [Difficulty: ELE: R, Ap; WRE: An]

The stroke volume is the same for both ventricles except under pathologic conditions. Usually, however, only the left ventricle is of concern. The Frank-Starling curve shows us that as the heart muscle is stretched with greater volume, it contracts and pumps more completely, resulting in a larger stroke volume. A left ventricle that has been damaged by a myocardial infarction does not pump as effectively and the stroke volume decreases. A drop in stroke volume results in a decrease in cardiac output unless the heart rate can increase to compensate for the difference. This is seen in many patients with heart disease. In addition, when a healthy right ventricle continues to pump more blood than the damaged left ventricle, the unpumped blood backs up into the pulmonary circulation and results in pulmonary edema (congestive heart failure).

a. Review cardiac index data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

The cardiac index (CI) is the cardiac output per square meter of body surface area. Review any previous information on CI before performing another calculation.

b. Recommend a cardiac index measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

If cardiac output is being determined, the CI should also be calculated for additional information on heart function.

c. Calculate the patient’s cardiac index value (ELE code: IB9l) [Difficulty: ELE: R, Ap]

Since CI is the cardiac output per square meter of body surface area, both cardiac output and body surface area must be known. Cardiac output is usually measured by the thermodilution cardiac output method via a special pulmonary artery catheter. The body surface area (BSA) can be determined from the DuBois Body Surface Chart as shown in Figure 5-24. The body surface area can also be determined with the following equation:

d. Interpret the results of the patient’s cardiac index calculation (Code: IB10l) [Difficulty: ELE: R, Ap; WRE: An]

A normal, resting cardiac index is 2.5 to 4 L/min/m² of BSA. The cardiac index is a much more accurate way of determining if the patient’s oxygen demands are being met than by simply looking at the cardiac output. For example, a resting cardiac output of 4 L/min is considered normal. This cardiac output might be fine for a small adult but not for a large one. The CI takes into account the difference in body sizes. A normal cardiac index indicates that the patient is receiving enough oxygen to meet the body’s needs. A low cardiac index should be a cause for concern; it usually indicates that the patient is not getting enough blood and oxygen to his or her tissues. Check to see if the patient’s cardiac output and blood pressure are also low and if the patient has hypoxemia or acidemia. If these conditions exist, they must be corrected as quickly as possible to prevent dire consequences. A high cardiac index indicates that the patient is pumping more blood than appears necessary. Investigate why this is occurring. See the earlier discussion on cardiac output and the factors that affect it to understand the factors that affect cardiac index as well.

a. Review mixed venous oxygen data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

Mixed venous blood sampling involves taking blood from either the pulmonary artery or the superior vena cava. The gold standard for this procedure involves the analysis of true mixed venous blood taken from the pulmonary artery through a pulmonary artery catheter. The pressure of mixed venous oxygen (PO₂) and the saturation of mixed venous oxygen (SO₂) represent tissue oxygenation. This is because the blood has returned from the body after having some of its oxygen extracted. (Remember that Pao₂ and Sao₂ represent the supply of oxygen to the tissues.) Another option involves the use of a CVP catheter equipped with fiberoptic technology for the measurement of the saturation of central venous oxygen (ScvO₂). As always, the PO₂ or ScvO₂ value(s) should be reviewed before performing another measurement.

b. Recommend a mixed venous oxygen measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

Recommend a mixed venous oxygen measurement if it is clinically important to know the patient’s level of tissue oxygenation. Low PO₂, SO₂, and ScvO₂ values are often seen in patients with heart failure because the slow flow of blood through the tissues results in more oxygen being extracted. In addition, PO₂ and SO₂ values are needed to calculate a patient’s arterial-venous oxygen content difference or shunt percentage.

Because of technical difficulties and increased risks associated with the placement of a pulmonary artery catheter, the placement of a triple-lumen CVP catheter with fiberoptic channel for ScvO₂ monitoring may be recommended. This CVP catheter has been found useful in monitoring patients with increased intracranial pressure, heart failure, heart surgery, and severe sepsis. Information from either catheter is very helpful in managing these critically ill patients.

c. Perform mixed venous oxygen measurement (Code: IB10m, IIIE4c) [Difficulty: ELE: R, Ap; WRE: An]

A patient with a functioning pulmonary artery catheter (PAC) can have a sample of blood withdrawn through it and analyzed for the mixed venous oxygen (PO₂) value (and the other blood gas values as well). There are currently three methods of performing the bedside procedure.

2. Use a pulmonary artery catheter with reflectance oximetry capability

These catheters have fiberoptic bundles built into them and use technology similar to that used in pulse oximeters. See Figure 5-25. The processing unit sends two narrow wavebands of light down the transmitting fiberoptic bundle to be illuminated on the passing blood in the pulmonary artery. Oxyhemoglobin in the red blood cells absorbs some of the light. The rest is reflected. The receiving fiberoptic bundle picks up some of this light and transmits it back to the monitoring unit.

Figure 5-25 Mixed venous oxygen saturation (SO₂) can be monitored continuously by reflection spectrophotometry (spectroscopy) in the appropriate pulmonary artery catheter. (Note that the same technology is used in a CVP catheter that measures continuous central venous oxygen saturation [ScvO₂].) A, Detail of the fiberoptic bundles in the catheter. Specific wavelengths of light are directed at passing blood. Some of the light is absorbed by the passing red blood cells and some is reflected back to the photodetector. The microprocessor calculates the percentage SO₂. B, Components of the system include (1) microprocessor that connects to the catheter, displays the SO₂ % values, and has high and low saturation alarms; (2) strip-chart recorder to copy the saturation values over time; and (3) fiberoptic reflective spectroscopy-type pulmonary artery catheter. The catheter can also be used for measuring pulmonary artery pressure, pulmonary capillary wedge pressure, and cardiac output; and for obtaining a mixed venous blood gas sample.

(A, from Rupple GL: Manual of pulmonary function testing, ed 9, St Louis, 2009, Mosby. B, Courtesy of Abbott Critical Care Systems, Mountain View, Calif.)

SO₂ is determined by the monitoring unit based on the light waves that were transmitted and received. Care must be taken when using this catheter in patients with elevated carboxyhemoglobin or methemoglobin levels. As with pulse oximetry, COHb and MetHb will be interpreted as oxyhemoglobin. Thus inaccurately high readings will be seen.

An actual mixed venous blood sample can be taken with this catheter through the distal lumen as described next. The advantage of the reflectance oximetry system is that it provides continuous monitoring of the patient’s venous oxygen level. In addition, high and low saturation alarms can be set. If the tip should become lodged in the wall of the artery or if a clot should form at the tip, the SO₂ value will drop or fluctuate dramatically. The alarms should warn the clinician of a problem with the equipment.

d. Interpret the results of the mixed venous blood measurement (Code: IB10m, IIIE4c) [Difficulty: ELE: R, Ap; WRE: An]

This topic is discussed in some detail in Chapter 3. The normal values follow:

True mixed venous blood oxygen values are useful for monitoring the patient’s oxygen consumption. The most accurate methods of calculating percent shunt and cardiac output (Fick method) use mixed venous blood oxygen values with arterial blood oxygen values. A PO₂ value of less than 30 torr or an SO₂ value of less than 56% is considered to show tissue hypoxemia. Quick steps must be taken to reverse this. Increase the inspired oxygen percentage as needed. Low stroke volume and cardiac output measurements can be increased by giving digoxin (Lanoxin) or other inotropic agents. Low blood pressure can be increased by administering vasopressors such as dopamine hydrochloride (Intropin).

a. Review arterial-venous oxygen content difference data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

The arterial-venous oxygen content difference [C(a-v)O₂] is a calculation of oxygen consumption by the body. It is the difference between the oxygen content of arterial blood and the oxygen content of mixed venous blood. Box 5-2 lists normal values. As always, check previous values to compare with present values to determine if the patient’s condition has changed.

b. Recommend an arterial-venous oxygen content measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

The C(a-v)O₂ measurement should be recommended when it is necessary to know a patient’s oxygen consumption, such as with heart failure or sepsis management.

c. Perform the arterial-venous oxygen content difference measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]

The following steps must be performed to make the arterial-venous oxygen content calculation:

d. Calculate the patient’s arterial-venous oxygen content difference (ELE code: IB9l) [Difficulty: ELE: R, Ap]

As mentioned in the previous discussion, the arterial-venous oxygen content difference is found by subtracting venous blood oxygen content from arterial blood oxygen content. These two values must first be calculated separately and then subtracted as shown in these three steps:

2. CO₂ = the content of oxygen in mixed venous blood = vol % of oxygen in mixed venous blood:

Co₂ =(Hb ×1.34 ×So₂) + (Po₂ × 0.003)

e. Interpret the results of the patient’s arterial-venous oxygen content difference (Code: IB10l) [Difficulty: ELE: R, Ap; WRE: An]

The normal range for the C(a-)O₂ difference is 3 to 5.5 vol %. Measurements in this range show normal levels of oxygen consumption by the tissues, cardiac output, and cardiopulmonary function. (See Figure 5-26 for a graphic presentation of C(a-)O₂ on the oxyhemoglobin dissociation curve.) A C(a-)O₂ difference of greater than 5.5 to 6 vol % is seen in patients with a low cardiac output. As the blood flows more slowly than normal through the tissues, more oxygen is consumed per mL of blood. The SO₂ and PO₂ values drop and the C(a-)O₂ difference widens.

Figure 5-26 Oxyhemoglobin dissociation curve showing normal oxygen saturations and pressures in arterial and venous blood. From these, the normal C(a-v)O₂ difference of 4.6 vol % can be calculated.

A C(a-)O₂ difference of less than 4 vol % in the healthy patient commonly indicates good cardiovascular reserve with an increased cardiac output. As the blood flows more quickly than normal through the tissues, less oxygen is consumed per mL of blood. The SO₂ and PO₂ values increase and the C(a-)O₂ difference narrows. The septic patient may have a narrowed C(a-)O₂ difference because of peripheral shunting and decreased oxygen consumption by the tissues caused by the infection. The C(a-)O₂ difference is necessary to accurately calculate the percent of pulmonary shunting as discussed next.

a. Review shunt study data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

Shunt (s/t) is the amount of blood pumped by the heart that passes through the lungs but does not participate in gas exchange. A pulmonary artery catheter must be inserted into the patient for a shunt study to be performed. Review previous (s/t) study results and compare with current information to see if there has been a change in the patient’s status. See Box 5-2 for normal values.

b. Recommend a shunt study measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

A shunt study is very useful to find out how much ventilation to perfusion mismatch a patient has. Most patients with refractory hypoxemia and requiring mechanical ventilation have an increased amount of pulmonary shunting. When an optimal positive end-expiratory pressure (PEEP) study is performed, a shunt study should be done with each change in the PEEP level.

c. Perform a shunt study measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]

Steps in the bedside shunt procedure include:

d. Calculate the patient’s shunt percentage (ELE code: IB9l) [Difficulty: ELE: R, Ap]

To date, the NBRC has not had an examination question that requires all of the calculations needed to determine a patient’s shunt percentage. However, examinations have had questions that relate to calculating components of the shunt equations. These have included calculating CaO₂, CO₂, and C(a-)O₂.

There are a number of possible variations on the methods and equations for calculating shunt percentage. Only the two most commonly used equations are presented here.

1. Modified clinical shunt equation

In which:

PAo₂ = The partial pressure of oxygen in the alveoli calculated from the alveolar oxygen equation

Pao₂ = The partial pressure of oxygen in the arterial blood

0.003 = The oxygen-carrying capacity of blood plasma per mm Hg Po₂

C(a-)o₂ The oxygen content of arterial blood minus the oxygen content of mixed venous blood

This formula requires that the patient’s hemoglobin be 100% saturated. This does not happen until the Pao₂ level reaches 150 torr at any given FiO₂. An obvious clinical limitation is that very ill patients never reach 100% saturation even when breathing 100% oxygen. Also, putting patients on more than 80% oxygen, even for just the duration of the test, may lead to some denitrogenation absorption atelectasis. This results in an incorrectly high shunt percentage calculation.

EXAMPLE

Modified clinical shunt equation

The subsequent example shows the modified clinical shunt calculation with the following environmental and patient information:

P_B = Localbarometricpressure;760torr for sea level inthisexample

PH₂O 47 torr; water vapor pressure in the lungs at normal body temperature

FIo₂ = inhaled oxygen percent of 100% or 1.0

Pao₂ = 155 torr

Paco₂ = 40 torr

Sao₂ = 100% or 1.0

Po₂ = 40 torr

So₂ = 75% or 0.75

0.8 = The normal respiratory quotient (An exact value can be determined by a metabolic study.)

15 g/dL = The patient’s hemoglobin concentration

0.003 = The oxygen-carrying capacity of blood plasma per torr Po₂

1.34 = mL of oxygen/g of Hb in the patient (The value of 1.39 mL of oxygen/g of Hb is occasionally used.)

Preliminary calculations:

1. Oxygen content of arterial blood

2. Oxygen content of mixed venous blood

3. Partial pressure of oxygen in the alveoli: the alveolar oxygen equation is used for this. (Review Chapter 3 if necessary.)

Final calculation:

d. Interpret the results of the patient’s shunt study calculation (Code: IB10l) [Difficulty: ELE: R, Ap; WRE: An]

As noted earlier, shunt is the amount of blood pumped by the heart that does not participate in gas exchange through the lungs. It is wasted cardiac output and wasted effort by the heart. The healthy person has a shunt of 5% or less of cardiac output. This shunted blood has a low oxygen content and dilutes the oxygen content of all the blood. The larger the percentage of shunted blood, the more the heart and body are stressed. Many clinicians believe that an indication for mechanical ventilation is a shunt of 15% to 20%. Most agree that a 30% or more shunt can be life-threatening. The ventilator is used to reduce the patient’s work of breathing and oxygen consumption. Also, supplemental oxygen can be more carefully controlled, and PEEP may be added to increase the patient’s functional residual capacity (FRC) as needed.

a. Review pulmonary vascular resistance data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

Pulmonary vascular resistance (PVR) is the total resistance of the pulmonary vascular bed to the blood being pumped through it by the right ventricle (afterload). This value may be calculated when other cardiopulmonary studies are performed.

b. Recommend a pulmonary vascular resistance measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

It is valuable to know the PVR in any case where restricted blood flow through the lungs is known or suspected. This could include a patient with COPD, a pulmonary embolism, or persistent pulmonary hypertension of the newborn (PPHN). If therapeutic procedures are effective, the patient’s PVR should be decreased toward normal. For example, inhaled nitric oxide (iNO) therapy has been shown effective in reducing the PVR of a newborn with PPHN.

c. Perform the pulmonary vascular resistance measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]

Cardiac output, mean pulmonary blood pressure, and pulmonary capillary wedge pressure must be known to determine the PVR. To gather the necessary hemodynamic information, the patient must have a thermodilution-type cardiac output pulmonary artery catheter. Measure the CO, PAP, and PCWP as described earlier.

d. Calculate the patient’s pulmonary vascular resistance (ELE code: IB9l) [Difficulty: ELE: R, Ap]

The patient must have the mean pulmonary artery pressure (PAm), pulmonary capillary wedge pressure (PCWP), and cardiac output (CO) measured and placed into this formula:

The answer will be in units of dynes/sec/cm⁻⁵.

e. Interpret the results of the patient’s pulmonary vascular resistance calculation (Code: IB10l) [Difficulty: ELE: R, Ap; WRE: An]

The normal range for PVR in an adult is 1 to 3 mm Hg/L/min. Multiplying this value by 80 changes the result to units of dynes/sec/cm⁻⁵. PVR is listed this way in some cardiology studies. The normal range of PVR in an adult is between 80 and 240 dynes/sec/cm⁻⁵.

With a normal PVR, the difference between the pulmonary artery diastolic pressure and the pulmonary capillary wedge pressure is 5 mm Hg or less. Any of the following can cause an elevated pulmonary vascular resistance:

Additional clinical data must be gathered to confirm the diagnosis. An increased PVR is a serious problem because it can lead to right ventricular hypertrophy. The COPD patient is at risk for developing cor pulmonale—right ventricular failure secondary to lung disease and increased pulmonary vascular resistance.

a. Review systemic vascular resistance data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]

Systemic vascular resistance (SVR) is the total resistance of the systemic vascular bed to the blood being pumped through it by the left ventricle (afterload). This value may be calculated when other cardiopulmonary studies are performed.

b. Recommend a systemic vascular resistance measurement to obtain additional data (Code: IC11) [Difficulty: ELE: R, Ap; WRE: An]

Recommend an SVR measurement in a clinical situation where there may be abnormally increased or decreased resistance to blood flow through the body. This may include a patient with hypertension or vasodilation from an anaphylactic reaction.

c. Perform a systemic vascular resistance measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]

Cardiac output, systemic blood pressure, and central venous pressure must be known to determine the SVR. To gather the necessary hemodynamic information, the patient must have a thermodilution-type cardiac output pulmonary artery catheter, arterial line, and central venous pressure line (if this cannot be measured from the pulmonary artery catheter).

d. Calculate the patient’s systemic vascular resistance (ELE code: IB9l) [Difficulty: ELE: R, Ap]

The patient must have mean arterial pressure (MAP), central venous pressure (CVP), and cardiac output (CO) measured and placed into the following formula:

The answer will be in units of dynes/sec/cm⁻⁵.

e. Interpret the results of the systemic vascular resistance calculation (Code: IB10l) [Difficulty: ELE: R, Ap; WRE: An]

The normal range of SVR in the adult is 15 to 20 mm Hg/L/min. Multiplying this value by 80 changes the result to units of dynes/sec/cm⁻⁵. SVR is listed this way in some cardiology studies. When multiplied by 80, an adult’s SVR ranges between 770 to 900 and 1400 to 1500 dynes/sec/cm⁻⁵.

A patient with hypertension will have an elevated SVR. It will also increase if the patient is given a vasoconstricting drug and decrease if the patient is given a vasodilating drug. Some allergic reactions result in anaphylaxis with a dramatic drop in the SVR and blood pressure despite an increase in the cardiac output.

Know the normal values for pulmonary and systemic vascular resistance. To date, the NBRC has not expected the examinee to perform all of the calculations to determine a patient’s PVR or SVR. Know that a patient with COPD or PPHN will have a chronically increased PVR and a patient with a large pulmonary embolism will have a sudden increase in the PVR. With proper treatment, the PVR will decrease toward normal.

There are several ways that the cardiology version of the PVR or SVR values can be found. The preferred versions have units listed in “dynes/sec/cm⁻⁵” or “dyne sec/cm⁻⁵.” However, the NBRC has also listed these values in units of “dynes seconds cm⁻⁵,” “dynes·seconds·cm⁻⁵,” and “mm Hg/L/min.”

a. Get the necessary equipment for the procedure

As discussed earlier, a capnograph is used to measure a patient’s exhaled carbon dioxide level and expiratory pattern. There are two different types of capnography systems. Their main difference is in how the gas is sampled from the patient. Figure 5-3 shows the patient connection for a mainstream capnograph. Figure 5-4 shows a sidestream capnograph. Both work equally well if the patient is intubated. The capnography connector is attached between the endotracheal tube and the ventilator circuit or T-piece (Brigg’s adapter). The sidestream unit may also be used with a spontaneously breathing patient because the capillary tube may be taped into a patient’s nostril for gas sampling.

b. Put the equipment together and make sure that it works properly

The following are components of a capnography system:

c. Troubleshoot any problems with the equipment

Capnography systems cause relatively few problems. The sidestream capnometer units must be kept dry. An external water trap is located between the capillary tube and the capnometer itself. Make sure that the water is drained periodically. Either capnography system can be disconnected from the patient. This is seen as a drop in the exhaled carbon dioxide level to zero. The alarm should activate if it has been set.

d. Perform quality control procedures on capnography equipment (Code: IIC7) [Difficulty: ELE: R, Ap; WRE: An]

As discussed earlier, both capnography units are calibrated using two points. Room air is used to set the zero point, and either 5% or 10% carbon dioxide from a cylinder is used to set the high point. Follow the manufacturer’s guidelines regarding how much adjustment for low or high point can be tolerated. Do not use a machine that cannot be properly calibrated.

a. Get the necessary equipment for the procedure

Hemodynamic monitoring requires a transducer that converts a blood pressure signal into an electrical signal. Select a strain gauge type transducer to do this. The strain gauge transducer uses a fine wire screen that bends proportionately to the pressure put against it.

b. Put the equipment together and make sure that it works properly

Check to see that the wire screen of the transducer is not bent, damaged, or contaminated with old blood or other debris. The transducer’s wire cable and monitor-connecting prongs should not be bent or damaged. Carefully insert the prongs into the receiving jack on the monitor.

A disposable, sterile, clear plastic dome should be firmly attached to the transducer. Noncompliant pressure tubing should connect the transducer with the patient’s arterial or pulmonary artery catheter. The automatic fluid drip system (Sorenson) should be pressurized to 300 mm Hg. Heparin must be added to the fluid (usually normal saline) to prevent clotting in the patient’s catheter. Because this is a continuous fluid “plumbing” system, all connections must be tightly joined to be watertight. There must be a continuous flow of fluid through the tubing system and into the patient’s blood vessel. Any air bubbles must be removed or the measured pressure reading will be lower than the actual reading (see Figures 5-18 and 5-27).

Figure 5-27 Schematic diagram of a strain-gauge pressure transducer. The wire mesh resistance wires are arranged like a Wheatstone bridge so that a pressure change results in a proportional change in the electrical resistance.

(From Armstrong PW, Baigrie RS: Hemodynamic monitoring in the critically ill, Philadelphia, 1980, Harper & Row.)

The transducer must be kept at the patient’s midchest (midheart) level during calibration and measurement. Calibrate the electronics in the monitor by placing known pressures against the fluid system. The electronics should first be adjusted to “zero” pressure by opening the transducer to room air (atmospheric pressure). Adjust the electronic controls as needed. A sphygmomanometer is then used to pressurize the fluid system. A pulmonary artery catheter system is pressurized to relatively low pressures such as 30 and 50 mm Hg. An arterial system is adjusted to higher pressures such as 100 and 150 mm Hg. The monitored pressure should match the sphygmomanometer pressure. If not, adjust the electronic controls on the monitor to match.

c. Troubleshoot any problems with the equipment

As mentioned previously, all connections must be watertight. If not, the IV solution will drip out when it is pressurized. This can also result in the patient’s measured pressure readings being less than the true readings. Stopcocks must be opened or closed properly to allow the patient’s pressure to be measured by the transducer. Electronics that will not calibrate to match the known pressures should not be used.

a. Get the necessary equipment for the procedure

Obtain the catheter type and gauge that are requested by the physician. Additional equipment includes a water-column manometer, stopcock, intravenous tubing, and IV solution system. A triple-lumen fiberoptic channel CVP catheter will be needed to measure the patient’s ScvO₂ values.

b. Put the equipment together and make sure that it works properly

See Figure 5-15 for the traditional assembly of the equipment and the procedure for measuring the central venous pressure (CVP). The equipment must be properly calibrated to ensure that the data are accurate. Calibrating a central venous pressure water-column manometer usually involves only making sure that it reads zero at atmospheric pressure.

c. Troubleshoot any problems with the equipment

Make sure that all connections are watertight. Check the position of the stopcock if the CVP cannot be measured.

a. Get the necessary equipment for the procedure

As discussed earlier, a neonate can have its umbilical artery catheterized. An adult usually has the radial artery catheterized. Following are the general supplies necessary for catheterizing either of these arteries for drawing blood gases and continuously monitoring blood pressure:

b. Put the equipment together and make sure that it works properly

See Figures 5-18 and 5-28 for illustrations of how the pressure transducer, connecting tubing, stopcocks, infusion system, and monitoring electronics are assembled. See Figure 5-29 for a completed radial artery system. Clinical experience is needed with these types of systems.

Figure 5-28 Common steps in the assembly of the tubing circuit and pressure transducer to attach to an arterial or pulmonary artery catheter. Sterile technique must be maintained at all times. (NOTE: Individual institutions will vary these steps. Clinical practice is very important in this assembly.) A, Obtain a 250 to 500 mL bag of sterile, normal saline. Add 1 to 2 units of heparin per mL of solution. Attach an IV line with a macrodrip chamber. B, Insert the solution bag into a pressure bag. Inflate the pressure to about 100 mm Hg to force the fluid through the IV tubing. The pressure bag will be inflated up to 300 mm Hg at the end of this procedure to ensure that 3 drops of fluid flow through the tubing per minute to keep it patent. C, Attach the strain gauge pressure transducer to an IV pole. Let it and the monitor warm up. D, Attach the IV tubing to the continuous flush device (Sorenson Intraflow). E, Screw the continuous flush device into the transducer stopcock. F, Backflush the continuous flush device and transducer, with open stopcocks, so that all air is removed and replaced with the saline solution. G, Zero and calibrate the pressure transducer and monitor. H, Attach high-pressure tubing to the continuous flush device. Flush the air out of it. I, Attach the high-pressure tubing to the patient’s arterial line or pulmonary artery catheter. Ensure that no air bubbles are present and that there is a continuous saline to blood connection. Accurate patient pressures should now be seen on the monitor.

(From Oblouk Darovic G: Hemodynamic monitoring, Philadelphia, 1987, WB Saunders.)

Figure 5-29 Example of a complete setup for monitoring the arterial pressure.

(From Daily EK, Schroeder JS: Techniques in bedside hemodynamic monitoring, ed 5, St Louis, 1994, Mosby.)

The process of calibrating the monitor for systemic artery pressures was briefly discussed earlier. Regardless of whether the catheter is placed into a systemic artery, pulmonary artery, umbilical artery, or superior vena cava, the equipment must be properly calibrated to ensure accurate data. When performing two-point calibration, all pressures should read “zero” when exposed to atmospheric pressure. This is the low point. The high point pressure for arterial pressure monitoring is commonly 100 mm Hg.

c. Troubleshoot any problems with the equipment

Table 5-1 lists problems, causes, prevention, and treatment for inaccurate pressure measurements with arterial or pulmonary artery catheters. Table 5-2 specifically lists problems with arterial lines. Figure 5-30 shows common problem areas with arterial lines. Pulmonary artery catheters can have problems in the same areas.

Figure 5-30 Common problem areas with arterial and pulmonary artery catheters.

(From Oblouk Darovic G: Hemodynamic monitoring—invasive and noninvasive clinical application, ed 3, Philadelphia, 2002, Saunders.)

d. Perform arterial line insertion (Code: IB9s) [Difficulty: ELE: R, Ap; WRE: An]

The most widely used arterial line insertion site is the radial artery in the patient’s nondominant hand. The procedure for inserting a radial arterial line is very similar to the procedure for drawing a blood sample from the radial artery. See Chapter 3 to review the procedure. As presented previously, the necessary fluid infusion system and pressure monitoring system must be assembled and working properly. A significant difference is the use of a needle with covering catheter, rather than a needle and syringe, to puncture the artery (Figure 5-31). As the needle and catheter enter the artery, bright red blood will pulse out. In rapid succession, withdraw the needle and advance the catheter into the artery (Figure 5-32). Place a gloved fingertip over the proximal hub of the catheter to stop the bleeding. Next, screw the prepared three-way stopcock and high-pressure tubing to the hub of the catheter. Flush some heparinized saline solution through the arterial catheter to prevent any blood from clotting. Make sure the automatic drip system and arterial pressure monitoring system are working properly. The patient’s blood pressure should be displayed on the monitor (see Figures 5-28 and 5-29).

Figure 5-31 Proper positioning of the patient’s hand enables the respiratory therapist to insert a needle and covering catheter into the radial artery for the continuous measurement of blood pressure. The therapist is about to insert the needle with catheter (cannula) into the patient. Steps in the cannulation procedure are very much the same as those for an arterial puncture as described in Chapter 3.

Figure 5-32 Steps in the procedure for the percutaneous insertion of an arterial catheter (cannula) for the continuous measurement of arterial pressure. Once the needle and catheter are inserted into the artery, the needle is withdrawn and the flexible catheter is advanced into the artery. The proximal end of the catheter is connected to a tubing circuit and pressure transducer as shown in Figures 5-28 and 5-29.

(From Oblouk Darovic G: Hemodynamic monitoring, Philadelphia, 1987, WB Saunders.)

e. Interpret the results of the insertion of arterial monitoring lines (Code: IB10s) [Difficulty: ELE: R, Ap; WRE An]

As discussed previously, if the equipment is properly assembled, the pressure readings will be accurate. If the pressure readings are transmitted to a display monitor, the blood pressure waveform can be seen.

a. Get the necessary equipment for the procedure

Pulmonary artery catheters are available in several diameter sizes. The smallest can be advanced into a pediatric patient’s vein. Most adults will have either a 5-French or a 7-French catheter inserted. Once the appropriate size is determined, select a catheter that provides the information that is needed. A standard 5-French catheter can be used to measure pulmonary artery pressure and pulmonary capillary wedge pressure, and a mixed venous blood sample can be withdrawn from it for analysis. A 7-French thermodilution cardiac output catheter can perform all the functions just mentioned and in addition provide a central venous pressure measurement and measure cardiac output through the computer (see Figures 5-17 and 5-22). A 7-French fiberoptic catheter can measure continuous SO₂ as well as PAP, PCWP, CVP, and cardiac output by the thermodilution method. Mixed venous blood can also be sampled for analysis.

b. Put the equipment together and make sure that it works properly

The 5-French and 7-French catheters are packaged self-contained as a single unit. The general assembly of the related tubing circuit and pressure transducer was discussed earlier and illustrated in Figures 5-18 and 5-28. Clinical experience is needed. Make sure that all connections are watertight, the transducer calibrates accurately, and the balloon inflates and deflates properly.

The process of calibrating the monitor for pulmonary artery pressures or systemic artery pressures was briefly discussed earlier. Regardless of whether the catheter is placed into a systemic artery, pulmonary artery, umbilical artery, or superior vena cava, the equipment must be properly calibrated to ensure accurate data. When performing two-point calibration, all pressures should read “zero” when exposed to atmospheric pressure. This is the low point. The high point pressure for pulmonary artery pressure monitoring is commonly 30 mm Hg.

c. Troubleshoot any problems with the equipment

See Table 5-3 for a listing of the problems seen with pulmonary artery catheters and their causes, prevention, and treatment. Figure 5-30 shows common problem areas with the related pressure tubing and equipment.

a. Get the correct cardiac output computer for the procedure

The manufacturers of cardiac output pulmonary artery catheters (e.g., Edwards Laboratories LLC) also make thermodilution cardiac output computers. However, the computer is usually designed only for use with their brand of catheter. Make sure that you have a compatible catheter and computer.

b. Put the equipment together and make sure that it works properly

Figure 5-17 shows a thermodilution cardiac output pulmonary artery catheter. Note the thermistor connection to the cardiac output computer and the proximal port where the cooled solution is injected. See Figure 5-22 for the assembly of the cardiac output computer to the catheter. In addition, the computer must be programmed with the size of catheter, injectate volume, and injectate temperature.

c. Troubleshoot any problems with the pulmonary artery catheter equipment and cardiac output computer

An error in the cardiac output value can be caused by an error in programming the computer or by not injecting the cooled solution through the proximal port in the required 4 seconds.

a. Get the correct monitor for the procedure

The manufacturers of continuous mixed venous oxygen saturation pulmonary artery catheters (e.g., Edwards Laboratories LLC) also make the required monitor. However, the monitor is usually designed only for use with their brand of catheter. Make sure that you have a compatible catheter and monitor.

b. Put the equipment together and make sure that it works properly

See Figure 5-25 for a photograph of a continuous mixed venous oxygen saturation pulmonary artery catheter and its connection to the required monitor and analyzer. Make sure the monitor is properly connected to the catheter. Calibrate the equipment as directed by the manufacturer so that accurate patient values will be measured.

c. Troubleshoot any problems with the monitor

Errors can result from the catheter and monitor not being properly connected or the analyzer not being properly calibrated.

a. Determine the appropriateness of the prescribed therapy and goals for the patient’s pathophysiologic state (Code: IIIH3) [Difficulty: ELE: R, Ap; WRE: An]

b. Review the planned therapy to establish the therapeutic plan (Code: IIIH2a) [Difficulty: ELE: R, Ap; WRE: An]

c. Recommend changes in the therapeutic plan when indicated (Code: IIIH4) [Difficulty: ELE: R, Ap; WRE: An]

d. Terminate the procedure based on the patient’s response to therapy (Code: IIIF1) [Difficulty: ELE: R, Ap; WRE: An]

e. Recommend discontinuing the procedure based on the patient’s response to therapy (Code: IIIG1i) [Difficulty: ELE: R, Ap; WRE: An]

A catheter should be withdrawn if the patient develops signs or symptoms of infection at the insertion site.

a. Record and interpret the following: heart rate and rhythm, respiratory rate, blood pressure, body temperature, and pain level (Code: IIIA1b4) [Difficulty: ELE: R, Ap; WRE: An]

b. Record and interpret the patient’s breath sounds (Code: IIIAb3) [Difficulty: ELE: R, Ap; WRE: An]

There is a risk of puncturing the right lung during the insertion of a central venous catheter by way of the subclavian vein (see Figure 5-13). Assess the patient for equal, bilateral breath sounds after this procedure has been attempted. Know the signs and symptoms of a pneumothorax. Review them in Chapter 1, if needed.

c. Recheck any math work and make note of incorrect data (Code: IIIA1b2) [Difficulty: ELE: R, Ap; WRE: An]