CHAPTER 1 OXYGEN AND MEDICAL GAS THERAPY
PRETEST QUESTIONS
1. A patient is receiving oxygen from an “E” cylinder at 4 L/min through a nasal cannula. The cylinder pressure is 1900 psig. How long will the cylinder run until it is empty?
2. After setting up a partial rebreathing mask on a patient at a flow of 8 L/min, the reservoir bag collapses before the patient finishes inspiring. The respiratory care practitioner should do which of the following?
3. A patient with carbon monoxide (CO) poisoning can best be treated with which of the following therapies?
4. The following blood gas levels have been obtained from a patient using a 60% aerosol mask.
What should the respiratory care practitioner recommend at this time?
5. Given the following data, what is the patient’s total arterial O2 content?
6. A patient is using a 30% Venturi mask at an O2 flow of 5 L/min. The total flow delivered by this device is which of the following?
See answers and rationales at the back of the text.
REVIEW
I. STORAGE AND CONTROL OF MEDICAL GASES
CRT Exam Content Matrix: IIA9a
There are 28.3 L in 1 cu ft.4. Valves on the cylinder allow attachment of regulators that release the gas at various flow rates. Cylinder and regulator safety systems dictate that the valves be constructed to allow the connection of only one type of gas regulator. For example, an O2 regulator cannot be attached to a helium cylinder.
a. Large cylinders use the American Standard Safety System. Each type of gas cylinder valve has a different number of threads per inch and a different thread size, and the cylinder may require either a right- or left-hand turning motion for attachment to the regulator.
b. Small cylinders use the Pin Index Safety System. Each cylinder valve has two holes drilled in unique positions that line up with corresponding pins on the appropriate regulator. There are six different hole placement positions.
5. Safety relief devices on cylinder valves allow escape of excess gas if the pressure in the cylinder increases. There are two types of safety relief devices:
b. Fusible plug—melts at 208° to 220° F (caused by high ambient temperature or high pressure, which increase the temperature)
| Gas | Color of Cylinder |
|---|---|
| Oxygen | Green; white (internationally) |
| Helium | Brown |
| Carbon dioxide | Gray |
| Nitrous oxide | Light blue |
| Cyclopropane | Orange |
| Ethylene | Red |
| Air | Yellow |
| CO2/O2 | Gray and green |
| He/O2 | Brown and green |
b. Cylinders are hydrostatically tested every 5 or 10 yr, depending on the cylinder marking. A “star” next to the latest test date means the next test must be done 10 yr from that date. Hydrostatic testing determines the amount or number of
a. 1 cu ft of liquid O2 expands to 860 cu ft as it changes to a gas. Liquid O2 is much more economical than gas.
b. The liquid O2 is stored in Thermos containers at a pressure not to exceed 250 psig and a temperature below −297° F (the boiling point of O2).
1. Regulators are devices attached to the cylinder valve to regulate flow and reduce cylinder pressure to working pressure (i.e., 50 psig).
a. Single-stage, which reduces the cylinder pressure directly to 50 psig and has one safety relief device
b. Double-stage, which reduces the cylinder pressure to approximately 150 psig and then to 50 psig and has two safety relief devices
c. Triple-stage, which reduces the cylinder pressure to approximately 300 psig, then to 150 psig, and finally to 50 psig and has three safety relief devices
a. Dust or debris entering the regulator from the cylinder valve may rupture the diaphragm. Always “crack” the cylinder before attaching a regulator. This is accomplished by turning the cylinder on and back off quickly to blow out the debris from the cylinder outlet.
b. Constant pressure “trapped” in the pressure chamber after the cylinder is turned off may rupture the diaphragm. Always vent pressure in the regulator by turning the flowmeter back on after the cylinder is turned off.
c. A hole in the diaphragm will result in a continuous leak into the ambient chamber and out the vent hole (see diagram of regulator), causing failure of the regulator.
d. A weak spring can result in diaphragm vibration and inadequate flows that are caused by premature closing of the inlet valve.
e. When attaching a regulator to a small cylinder, make sure the plastic washer is in place or gas will audibly leak around the cylinder valve outlet and regulator inlet.
One liter of liquid oxygen weighs 2.5 lb (1.1 kg).
(1) The needle valve is located proximal to (before) the float; therefore atmospheric pressure is in the Thorpe tube. Any back pressure in the tube affects the rise of the float.
(2) When a restriction, such as a humidifier or a nebulizer, is attached to the outlet, back pressure into the tube forces the float down and compresses the gas molecules closer together so that more molecules go around the float than what the float indicates. Therefore the flowmeter reading is lower than what the patient is actually receiving.
(1) The needle valve is located distal to (after) the float; therefore 50 psig is in the tube. Only back pressure that exceeds 50 psig will affect the rise of the float.
(2) The flowmeter reads accurately with an attachment, such as a humidifier or nebulizer on the outlet, or with any obstruction downstream. If the oxygen tubing is completely obstructed with no gas flowing to the patient, the flowmeter will reflect that with a flow reading of near zero.
(4) Flowmeter outlets use the Diameter Index Safety System, as do all gas-administering equipment that operate at less than 200 psig, so that attachment to the wrong gas source is avoided.
(5) If the flowmeter is turned off completely but gas is still bubbling through the humidifier or is heard coming from the flowmeter, the valve seat is faulty and the flowmeter should be replaced.
(1) The Bourdon gauge flowmeter is a pressure gauge that has been calibrated in liters per minute. It is uncompensated for back pressure.
(2) When a humidifier or nebulizer is attached to the outlet of the Bourdon gauge, back pressure is generated into the gauge (which measures pressure) and the gauge reading is higher than what the patient is actually receiving.
(3) Gas enters the hollow, flexible question mark–shaped tube, which tends to straighten as pressure fills it. A gear mechanism is attached to the tube, and as the tube straightens, it rotates a needle indicator that shows the pressure (flow).
(4) The advantage of the Bourdon gauge is that it, unlike Thorpe tube flowmeters, is not position dependent. It reads just as accurately in a horizontal position as it does in a vertical position.
(5) Because this gauge actually measures pressure, an obstruction to flow through the tubing attached to a Bourdon gauge flowmeter resulting in back pressure will cause the gauge reading to increase slightly. In other words, the gauge will indicate flow to the patient while the patient is receiving little or no oxygen.
8. Air compressors are used to provide medical air through either portable compressors or large medical air piping systems. Two types of air compressors are generally used:
Air is drawn into the compressor, where it travels to a reservoir tank. From this tank, the air passes through a dryer to remove moisture and on to a pressure-reducing valve, which reduces the pressure to 50 psig to power a compressed-air wall outlet. As the piston drops, gas is drawn in through a one-way intake valve. On the upstroke, the intake valve closes and gas exits through a one-way outflow valve. Piston air compressors are seen most commonly on large medical air piping systems.
A diaphragm is used instead of a piston. On the downstroke, the flexible diaphragm bends downward, drawing air through a one-way intake valve. On the upstroke, air is forced out the one-way outflow valve. Diaphragm air compressors are commonly used on O2 concentrators and portable air compressors.
CRT Exam Content Matrix: IIA1a-c, IIA9a-b, IIA12a-b, IIID2d, IIID6, IIIE10, IIIF2d1-2, IIIG2c
RRT Exam Content Matrix: IIA4b
1. Respiratory depression: The patient with chronic obstructive pulmonary disease (COPD) who is breathing with the “hypoxic drive” mechanism is most affected. Maintain PaO2 between 50 and 65 mm Hg for these patients.
Exam Note2. Atelectasis: High O2 concentrations in the lung can wash out nitrogen in the lung and reduce the production of surfactant, which may lead to atelectasis. Maintain FiO2 below 0.60.
3. Oxygen toxicity: High O2 concentrations result in increased O2 free radicals and therefore lung tissue toxicity. This may lead to acute respiratory distress syndrome (ARDS). Maintain FiO2 below 0.60.
4. Reduced mucociliary activity: Maintain FiO2 below 0.60. The beating of the cilia in the mucociliary blanket is not as active when high FiO2 levels are used.
5. Neonatal retinopathy (retinopathy of prematurity): This is caused by high PaO2 levels in infants and results in blindness. It is more common in premature infants. Maintain PaO2 below 80 mm Hg. Normal level of PaO2 in infants is 50 to 70 mm Hg.
| Age (yr) | Normal PaO2 |
|---|---|
| ≤60 | 80 mm Hg |
| 70 | 70 mm Hg |
| 80 | 60 mm Hg |
(3) Diffusion defects (i.e., pulmonary edema, atelectasis, and pulmonary fibrosis): administering O2 alone may not be beneficial.
b. If a normal PaO2 level cannot be maintained with a 60% O2 mask, a large shunt is probable and should not be treated with higher O2 concentrations. CPAP should be administered provided that the PaCO2 is at normal or below normal levels. If the PaCO2 level is elevated in a patient with hypoxemia, mechanical ventilation should be initiated.
Exam Note
(b) The PaO2 level may be normal, but because of the blood’s reduced capacity to carry O2, the tissues may be deprived of O2. The Hb value must be determined to assess the patient’s oxygenation status.
(a) CO affinity for Hb is 200 to 250 times faster than O2 and therefore occupies the iron-binding sites on Hb before O2 can. This causes tissue hypoxia.
(b) Because Hb releases the CO more readily when levels of PaO2 are high, the patient should immediately be given 100% oxygen, usually via a non-rebreathing mask, which delivers high O2 concentrations.
Exam Note(c) Elevating the PaO2 even higher to further increase the dissociation of Hb from CO may be achieved with hyperbaric O2 therapy (discussed later in this chapter).
(d) Patients who have been involved in fires or who have been breathing car fumes must be treated immediately for CO poisoning.
(e) PaO2 and Hb saturation (SaO2) readings (discussed later in this chapter) may be within a normal range even though the patient has severe hypoxia.
(f) The level of CO bound to Hb (carboxyhemoglobin) may be determined with CO oximetry (discussed later in this chapter).
(g) The patient usually presents with a normal PaO2 level and a low or normal PaCO2 level. The pH level is usually low as a result of lactic acidosis (metabolic acidosis), caused by severe hypoxia. Lactic acid is produced as the body goes into anaerobic metabolism trying to provide more oxygen to the tissues.
(3) Excessive blood loss also may result in anemic hypoxia. Administering blood (RBCs) is the appropriate treatment.
(4) Methemoglobin may cause anemic hypoxia and is most commonly a result of nitrite poisoning. Treat by administering ascorbic acid or methylene blue, which removes the chemical (nitrite) from the system.
(5) Iron deficiency leads to anemia and is treated by increasing iron intake and administering blood.
(1) Bound to Hb: 1 g of Hb is capable of carrying 1.34 mL of O2. To determine the milliliters of O2 carried by Hb, use this formula: (1.34 × Hb × SaO2).
(2) Dissolved in plasma: 0.003 mL of O2 dissolves in plasma for every 1 mm Hg of O2 tension (PaO2), or (.003 × PaO2).
Exam NoteEXAMPLE:
Given the following information, calculate the patient’s total arterial O2 content.
| Arterial Blood Gas Study Results | |
|---|---|
| pH | 7.42 |
| PCO2 | 41 mm Hg |
| PO2 | 90 mm Hg |
| SaO2 | 98% |
| Hb | 15 g/dL |
*
19.97 mL/dL may also be expressed as 19.97 vol%.
* Exam Notea. The O2 content and carrying capacity is normal but capillary perfusion is diminished as a result of
b. May be seen as a localized problem, such as peripheral cyanosis resulting from exposure to cold weather
1. Low-flow O2 systems: an O2 delivery device that does not meet the patient’s inspiratory flow demands; therefore room air must make up the remainder of the patient’s tidal volume (VT). The normal inspiratory flow rate is 25 to 30 L/min. The following devices are connected to humidifiers; however, in some institutions, humidifiers are not used if less than 5 L/min is being delivered.
Exam Note
(1) The catheter is inserted directly into the midtrachea through an incision between the second and third tracheal rings to deliver low flow rates (1 to 3 L/min) of O2.
(2) Conserves O2 for home patients by bypassing anatomic dead space, which results in a reduction in the work of breathing.
(3) Possible complications include accidental removal of the catheter and irritation or infection at the insertion site and in the trachea.
(4) The catheter should be cleaned routinely by instilling saline and inserting a cleaning wire into the catheter. The catheter should be replaced every 3 months before it becomes kinked, cracked, or obstructed by dry mucus.
(1) Delivers 24% to 40% O2 at flow rates of 1 to 5 L/min (at about a 4% increase for every 1-L/min increase).
Although a flow of 6 L/min is acceptable, according to the American Association for Respiratory Care Clinical Practice Guidelines, the maximum oxygen percentage obtainable with a nasal cannula is 40%.
FIGURE 1-11 Nasal reservoir cannula.
From Scanlan C, Wilkins R, Stoller J: Egan’s fundamentals of respiratory care, ed 8, St Louis, 2003, Mosby.
(1) The reservoir, which is positioned just below the nose, stores approximately 20 mL of O2 that the patient inhales during the early part of inspiration.
(2) Because the patient receives more O2 with each breath, the flow needed for a prescribed level of O2 may be decreased, thus conserving O2.
FIGURE 1-12 Pendant reservoir cannula.
From Scanlan C, Wilkins R, Stoller J: Egan’s fundamentals of respiratory care, ed 8, St Louis, 2003, Mosby.
(1) The pendant reservoir cannula uses a pendant-shaped inflatable reservoir that expands as the patient exhales, which forces the stored O2 out of the pendant and up the cannula tubing to the patient.
(2) For this device to function properly, the patient must exhale through the nose so that the exhaled air passes through the cannula tubing to inflate the reservoir.
(3) Because the pendant may be hidden beneath clothing and the nasal reservoir is much larger than that of typical cannulas, the patient may prefer the pendant cannula.
Exam Note
(3) Ensure that the patient is not positioned so that the reservoir bag gets kinked or cuts off flow, which results in a lower FiO2.
(4) Only the first part of the patient’s exhaled gas enters the reservoir bag. This is gas that was left in the upper airway from the previous inspiration and is therefore high in O2 and low in CO2. It is gas that did not participate in gas exchange at the alveolar–capillary level.
(3) The non-rebreathing mask is equipped with a one-way valve between the mask and the reservoir bag, which prevents the patient’s exhaled gas from entering the reservoir bag.
(4) One-way valves are located on either one or both exhalation ports of the mask to prevent room air entrainment. If only one exhalation port is covered with a one-way valve, FiO2 decreases because more room air can enter the mask. In this case, the mask is considered a low-flow mask; however, if both exhalation ports are covered by one-way valves, no air entrainment can occur, FiO2 increases, and the mask is considered a high-flow device. Most commonly, only one exhalation port is covered by a one-way valve. Most manufacturers provide only one valve for the exhalation ports.
(5) Ensure that the reservoir bag does not kink or cut off flow, especially if both exhalation ports have one-way valves, because no room air would be available to the patient. (For this reason, one valve is commonly left off.)
h. Low-flow O2 devices are adequate O2 delivery systems only when the patient meets the following criteria:
(3) Consistent VT of 300 to 700 mL (not fluctuating between 300 and 700 mL but consistent [e.g., a VT of 450 mL or 600 mL])
(4) The percentage of O2 delivered by a low-flow device is variable, depending on the patient’s VT, respiratory rate, inspiratory time, and ventilatory pattern.
Exam Note2. High-flow O2 delivery devices provide all of the inspiratory flow required by the patient at relatively accurate and consistent O2 percentages. Increasing the flow rate on high-flow devices will not increase FiO2
The entrainment port must be prevented from becoming occluded (e.g., by the patient’s hand or bedsheet) because this decreases the amount of air entrainment and thus increases the delivered O2 percentage.| O2 Percentage | Air/O2 Entrainment Ratio |
|---|---|
| 24% | 25 : 1 |
| 28% | 10 : 1 |
| 30% | 8 : 1 |
| 35% | 5 : 1 |
| 40% | 3 : 1 |
| 45% | 2 : 1 |
| 50% | 1 : 7 : 1 |
| 60% | 1 : 1 |
| These ratios may be calculated by the following formula:
|
|
*Use 21 with percentages less than 40%.
EXAMPLE:
Calculate the air/O2 ratio for 40% O2.
| 20 | 60 | |
| 40 | ||
| 100 | 20 |
1. Draw a tic-tac-toe box and place 20 or 21 (depending on the percentage you are calculating) in the upper left corner.
3. Place the percentage you are calculating in the middle box of the middle row (in this example, use 40).
Exam Note
EXAMPLE:
A Venturi mask is set on 24% O2 with a flow of 4 L/min.
Sum of the ratio of parts multiplied by flow:
Exam Note
To determine a patient’s inspiratory flow, use the following equation:
The flow will be in L/s, so multiply by 60 to change to L/min.
(1) This mask delivers 21% to 100% O2 (depending on nebulizer setting) at flow rates of 8 to 15 L/min.
(2) If the nebulizer is set on 100%, the device probably would not meet the patient’s inspiratory flow demands. Room air would enter the mask through the exhalation ports during inspiration, decreasing FiO2. In this case, two flowmeters must be used to provide adequate flow.
(3) A 50-mL piece of reservoir tubing should be attached to the end of the T-piece (opposite from where the aerosol tubing from the nebulizer is attached). This prevents air from entering the T-piece during inspiration, and if the reservoir falls off, FiO2 may decrease.
(3) Not an ideal O2 delivery device because of the leakage and reduced O2 delivery when the tent is opened for patient care.
(4) A fire hazard exists if electrical devices or friction toys, which may spark, are left in the tent.
(1) This cannula provides high-flow therapy (HFT) by the use of a thermally controlled humidification system. These devices provide close to 100% body humidity to infant, pediatric, and adult patients. Flows of up to 8 L/min are used on infants and up to 40 L/min on adults and provide an oxygen percentage of up to 80%. These flows are capable of meeting the patient’s inspiratory flow demands and are therefore considered high-flow devices.
(2) Because the gas is delivered at body temperature and almost fully saturated, high flows are tolerable and even comfortable for the patient to breathe.
(3) Studies indicate that the high flow reduces anatomic dead space by washing out CO2 from the nasopharynx. This increases alveolar PO2 levels and results in increased PaO2 and saturation levels.
(4) Another advantage is that oxygen through a cannula is better tolerated than oxygen through a mask. Communication is more difficult with a mask, and some patients experience claustrophobia, which results in poor patient compliance. Masks also limit the ability to eat and drink.
1. High-flow O2 devices set on 60% or higher may deliver a total flow rate of less than 25 to 30 L/min, thereby not meeting the patient’s inspiratory flow demands and essentially acting as a low-flow device with the patient breathing in room air to make up the difference. When this happens, it means the O2 percentage setting on the nebulizer is no longer accurate, and the patient is receiving less delivered O2 than the setting suggests.
2. To ensure adequate flow rates on a device set on 60% or higher, use two flowmeters connected in line together.
3. To ensure adequate flow rates, set the flowmeter to a rate that delivers a total flow of at least 40 L/min.
4. A restriction, such as kinked aerosol tubing or water in the tubing, causes back pressure into the nebulizer, decreasing the amount of air entrainment and therefore increasing the percentage of O2.
5. Increasing the flow on a high-flow device does not increase the delivered FiO2. It only increases the total flow.
1. These devices use 50-psig gas sources to mix or blend O2 and compressed air proportionately to deliver 21% to 100% O2 at flow rates of 2 to 100 L/min.
2. A blender consists of pressure-regulating valves that regulate O2 and air inlet pressure, a mixture control (precision metering device), and an audible alarm system, which sounds if there is a drop in inlet pressure.
3. Blenders provide a stable FiO2 as long as the outlet flow exceeds the patient’s inspiratory flow demands.
4. When using a blender/nebulizer to provide oxygen, make sure the nebulizer is set on 100%. As the gas from the blender enters the nebulizer, room air will be entrained, which dilutes the blender mixture to a lower percentage if the nebulizer is set to anything but 100%.
CRT Exam Content Matrix: IB9k, IB10k
RRT Exam Content Matrix: IB10l
A. Alveolar PO2 is calculated by the following formula:
(47 mm Hg is the level of water vapor pressure at body temperature)
B. This value is often compared with PaO2 to determine the P(A−a)O2 gradient, which refers to the difference between alveolar O2 tension and arterial O2 tension. The normal gradient on room air is 4 to 12 mm Hg.
Exam Note
A patient using a 40% air entrainment mask has the following arterial blood gas (ABG) levels:
What is this patient’s A−a gradient? (PB = 747 mm Hg)
CRT Exam Content Matrix: IIIF2e1-2
RRT Exam Content Matrix: IB9k, IB10k, IIA8, IIIF2c1-2
1. Helium is the second lightest gas and therefore, when combined with O2, decreases the total density of the gas. This allows the gas to pass through obstructions more easily.
4. Running these gas mixtures through an O2 flowmeter gives inaccurate readings because the gas is lighter than pure O2. A correction factor may be used to make the reading accurate.
a. For an 80 : 20 mixture of helium and O2, multiply the flowmeter reading by 1.8 to determine the correct flow rate. To deliver a specific flow, divide the flow rate by 1.8.
b. For a 70 : 30 mixture of helium and O2, multiply the flowmeter reading by 1.6. Divide by 1.6 to obtain a specific flow rate. (See example above and substitute 1.6 for 1.8.)
5. Helium and O2 mixtures must be delivered in a tightly closed system, such as a non-rebreathing mask, ET tube, or tracheostomy tube, to prevent this lighter gas from leaking out.
7. Extreme caution must be used when mixing heliox from a helium cylinder and an O2 cylinder. Inaccurate flow readings may result in the patient receiving less than 21% O2. A premixed helium/O2 cylinder is recommended.
1. Inhaled nitric oxide (NO) is a selective pulmonary vasodilator that improves blood flow to ventilated alveoli, which results in decreased intrapulmonary shunting and improved arterial oxygenation.
2. It is indicated in term or near-term neonates of more than 34 weeks’ gestation who have evidence of persistent pulmonary hypertension of the newborn (PPHN).
3. Although ARDS is characterized by pulmonary hypertension and hypoxemia, studies have demonstrated only short-term improvement with NO inhalation. Inhaled NO may be beneficial in improving refractory hypoxemia in ARDS patients after chest trauma.
4. The normal starting dose is 20 parts per million (ppm). The dose is then weaned to the lowest effective dose and continued until the neonate’s condition has improved.
6. Patients must be weaned from NO to prevent rebound effects during withdrawal. The recommend guidelines include
d. Before discontinuing NO, increase the patient’s FiO2 and be prepared to provide hemodynamic support if necessary.
B. Hyperbaric oxygen (HBO) therapy is the delivery of O2 at greater than atmospheric pressure and is accomplished by placing the patient in a hyperbaric chamber.
E. The chambers are usually pressurized to 3 atm, or 3 times atmospheric pressure, as the patient breathes 100% O2.
F. This increased pressure likewise increases the amount of O2 in the blood and body tissues. While breathing room air at 1 atm, the patient has a PaO2 of about 100 mm Hg with about 0.3 vol% O2 dissolved in the plasma; however, while breathing 100% O2 at 3 atm, the patient has a PaO2 of about 1800 mm Hg with 6.2 vol% O2 dissolved in the plasma.
I. HBO treatments, or “dives” (as they are often called), usually require 90 min at 2 to 3 atm, two to four times a day.
CRT Exam Content Matrix: IIA2,4, IIC2, IIIE10
RRT Exam Content Matrix: IIA10, IIC2
3. The analyzer reading is affected by water, positive pressure, high altitude, a torn membrane, or lack of electrolyte gel.
1. A battery polarizes the electrodes to allow O2 reduction to occur, which gives off electron flow.
3. The analyzer reading is affected by water, positive pressure, high altitude, a torn membrane, or lack of electrolyte gel.
4. Electrodes last longer on the galvanic cell analyzer, but the polarographic analyzer has a quicker response time.
Other specialty gas analyzers may be used in the hospital setting. Helium and CO analyzers are seen in pulmonary function laboratories. Although much could be said about how these analyzers function, the most important aspect to remember for the examination is that these analyzers read zero when calibrated to room air.VII. OXYGEN SATURATION MONITORING (PULSE OXIMETRY)
CRT Exam Content Matrix: IA7e, IB9c, o, IB10c, o, r, IC7, IIA20, IIIA1b5, IIIE3b, IIIE4d
RRT Exam Content Matrix: IA7e, IB9c, p, IB10c, q, IC8, IIIA1b5
1. Pulse oximeters are devices that measure SaO2 by the principle of spectrophotometry. This is also referred to as “SpO2.”
2. Light from the probe is directed through a capillary bed to be absorbed in different amounts, depending on the amount of O2 bound to Hb. The result is displayed on the monitor as a percentage of saturation.
3. The probe is noninvasive and may be attached to the finger, toe, or ear of adults and the ankle or foot of infants.
4. Pulse oximeters seem to be accurate, although some studies show they may be less accurate when used for “spot checks” rather than for continuous monitoring.
5. Pulse oximeters may be used during overnight sleep studies (polysomnogram) to detect oxygen saturation trends for several hours. Pulse oximeters can be useful in many sleep disorders, but they should not be used exclusively to diagnose sleep-related disorders. More comprehensive sleep studies should be done. (See Chapter 12 on disorders of the respiratory system.)
2. CO poisoning. A pulse oximeter is not capable of determining what substance is being carried by hemoglobin. Therefore, a reading of 100% saturation doesnt reflect 100% oxygen saturation, but may actually be 60% oxygen and 40% CO. An oximeter should never be used on patients with suspected CO exposure since the reading may reflect an inaccurately high value.
7. Nail polish, especially blue, green, brown, and black colors, may cause lower oximetry readings. Polish should be removed or the oximeter should be placed on the earlobe instead of the fingers.
8. Ambient light sources, such as direct sunlight, phototherapy, and fluorescent lights, affect the accuracy of the pulse reading. Wrapping the sensor site with a towel or gauze to block the light can eliminate this problem.
VIII. CO-OXIMETRY (HEMOXIMETRY)
CRT Exam Content Matrix: IB10j, IIA24, IIC2, IIIE3c, IIIE4b
RRT Exam Content Matrix: IB9j, IB10j, IIA10, IIC2, IIIE3b
A. This procedure requires arterial blood to be obtained. The oximeter, part of the blood gas analyzer, is able to measure the amount of Hb, HbO2, and HbCO in blood.
B. This procedure uses the principle of spectrophotometry to measure the blood level of CO bound to Hb (HbCO).
2. HbCO as high as 10% may be seen in heavy smokers, but higher levels are measured in patients who have inhaled large amounts of car fumes or smoke.
Transcutaneous oxygen monitoring is covered in Chapter 13 on neonatal and pediatric respiratory care.
POSTCHAPTER STUDY QUESTIONS
1. List the air/O2 ratios for 60% O2, 40% O2, 35% O2, 30% O2, and 24% O2.
2. Give four examples of high-flow O2 delivery devices.
3. What is the primary benefit of using a reservoir cannula?
4. Calculate total O2 content, given the following ABG test results:
5. What is the total flow delivered by an aerosol mask on 60% O2, running at 12 L/min?
6. List the three ventilatory criteria that should be met by patients receiving O2 from a low-flow device.
7. An 80 : 20 mixture of helium/O2 running through an O2 flowmeter at 6 L/min is delivering how much flow to the patient?
8. Calculate how long an “E” cylinder with 1900 psig will run at 5 L/min.
9. Give examples of three low-flow O2 delivery devices.
10. List five conditions that affect the accuracy of pulse oximeters.
11. List five indications for the use of hyperbaric O2 therapy.
12. How does water in the aerosol tubing of a mask affect the delivered FiO2?
13. The physician orders O2 therapy for a patient with a VT of 400 mL and an inspiratory time of 0.5 s. What flow must the mask deliver to meet this patient’s inspiratory flow demands?
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