CHAPTER 27. Hemodynamic Monitoring
Maureen Mclaughlin
OBJECTIVES
At the conclusion of this chapter, the reader will be able to:
1. Identify surgical patients who may benefit from hemodynamic monitoring based on their risk of oxygen supply and demand imbalance.
2. Define the physiological variables affecting cardiac function and link their interactions.
3. Describe the principles of pressure monitoring and strategies to optimize accuracy.
4. Determine the indications, risks, complications, and perioperative considerations for specific hemodynamic monitoring, including arterial pressure, central venous pressure, and pulmonary artery pressure (PAP).
5. Identify normal waveform configurations for the preceding catheters.
6. List the various ports of the pulmonary artery (PA) catheter, and list their functions.
7. Identify normal and calculated hemodynamic pressures, and link the clinical significance of alterations in surgical patients.
8. Compare and contrast the bolus and continuous cardiac output techniques for thermodilution cardiac output, and determine the significance of altered cardiac output states in surgical patients.
9. Define the function of mixed venous oxygen saturation (Sv o2) and identify causes for variances.
I. GOALS OF HEMODYNAMIC MONITORING
A. Aid in the diagnosis of critically ill patients
B. Evaluate therapies such as vasoactive medications, fluid boluses, mechanical ventilation, etc.
C. Assess and optimize the balance between oxygen supply and demand.
II. INDICATIONS
A. Benefit and patient acuity must outweigh cost and potential for complications.
B. High risk and/or hemodynamically unstable surgical patients
III. PHYSIOLOGICAL VARIABLES AFFECTING CARDIAC FUNCTION
A. Cardiac output (CO)
1. Definition: amount of blood ejected from the ventricles measured in liters per minute
2. CO = Stroke volume (SV) × Heart rate (HR)
3. Influences on CO
a. HR
b. SV
(1) CO definition: amount of blood ejected from the ventricle with each beat
(2) Influences on SV
(a) Preload (right and left)
(i) Definition: amount of end-diastolic stretch on myocardial muscle fibers; determined by volume of blood filling the ventricle at the end of diastole
(ii) Right-sided preload: central venous pressure (CVP) or right atrial pressure (RAP)
(iii) Left-sided preload
[a] Left atrial pressure (LAP)
[b] Pulmonary artery diastolic (PAD) pressure
[c] Pulmonary artery occlusion (wedge) pressure (PAOP)
[d] Pulmonary capillary wedge pressure (PCWP)
(iv) Influences on preload
[a] Any condition that increases blood return to the heart or decreases ejection of blood from the heart. Examples:
[1] Pulmonary hypertension decreases the ability of the right ventricle (RV) to pump, thereby decreasing the ejection of blood from the RV and increasing RV preload.
[2] Fluid infusions increase circulating blood volume, thereby increasing right-sided and left-sided preload.
(b) Afterload (right and left)
(i) Definition: resistance, impedance, or pressure the ventricle must overcome to eject blood
(ii) Affected by:
[a] Volume and viscosity of the blood
[b] Size and thickness of the ventricle
[c] Tone of the vascular beds
(iii) Right-sided afterload: pulmonary vascular resistance
(iv) Left-sided afterload: systemic vascular resistance
(v) Influences on afterload: any condition that increases or decreases the pressure required for the ventricle to eject volume; conditions that would affect afterload include:
[a] Vascular resistance
[b] Valve function
[c] Increased blood viscosity
[d] Examples:
[1] Aortic stenosis would result in a narrowed outflow tract, increasing the pressure required for the left ventricle (LV) to eject blood and therefore increasing left-sided afterload.
[2] Use of a vasodilator would relax the vessel beds and increase the diameter of the vessels, decreasing the pressure required for the ventricles to eject blood and therefore decreasing afterload.
(c) Contractility
(i) Definition: inherent ability of myocardial muscle fibers to shorten and contract regardless of preload or afterload
(ii) Indirectly assessed through a calculated stroke work index
c. Atrioventricular (AV) synchrony
(1) Definition: coordinated contraction pattern between atria and ventricles
(2) Influences on AV synchrony
(a) Ischemia
(b) Infarction
(c) Conduction deficits
(d) Dysrhythmia
(3) Loss of synchrony
(a) Decreases CO
(b) Decreases blood pressure (BP)
(c) Decreases SV
(d) Increases LAP
IV. HEMODYNAMIC EVALUATION OF CARDIAC FUNCTION
A. Hemodynamic normal values (Table 27-1)
| Pressure | Value | Range |
|---|---|---|
| Right atrial pressure (RAP) | Mean | 2-6 mm Hg |
| Central venous pressure (CVP) | Mean | 3-8 cm H 2O |
| Right ventricular pressure (RVP) |
Systolic
Diastolic
|
15-30 mm Hg
0-8 mm Hg
|
| Pulmonary artery pressure (PAP) |
Systolic
Diastolic
Mean
|
15-30 mm Hg
5-15 mm Hg
10-20 mm Hg
|
| Left atrial pressure (LAP) | Mean | 8-12 mm Hg |
| Pulmonary artery occlusion pressure (PAOP) | Mean | 8-12 mm Hg |
| Pulmonary capillary wedge pressure (PCWP) | Mean | 8-12 mm Hg |
| Left ventricular end-diastolic pressure (LVEDP) | Mean | 4-12 mm Hg |
B. Hemodynamic calculations (Table 27-2)
| BP, Blood pressure; BSA, body surface area; CI, cardiac index; CO, cardiac output; CVP, central venous pressure; EDV, end-diastolic volume; HR, heart rate; MAP, mean arterial pressure; MPAP, mean pulmonary artery pressure; PAOP, pulmonary artery occlusion pressure; RAP, right atrial pressure; SI, stroke index; SV, stroke volume. | ||
| Pressure | Formula | Value |
|---|---|---|
| Mean arterial pressure | Systole + (2 × Diastole) / 3 | 70-105 mm Hg |
| Cardiac output | HR × SV | 4-8 L/min |
| Cardiac index | CO/BSA | 2.5-4.0 L/min/m 2 |
| Stroke volume | (CO/HR) × 1000 | 60-100 mL |
| Stroke index |
SV/BSA
or
CI/HR
|
30-65 mL/beat/m 2 |
| Left ventricular stroke work index | [1.36 × SI × (MAP − PAOP)] / 100 | 45-65 g-m/beat/m 2 |
| Right ventricular stroke work index | [1.36 × SI × (MPAP − RAP)] / 100 | 5-12 g-m/beat/m 2 |
| Systemic vascular resistance |
[(MAP − RAP) × 80] / CO
or
[(MAP − CVP) × 80] / CO
|
900-1400 dynes/sec/cm −5 |
| Pulmonary vascular resistance | {[RAP − (PAOP × MPAP)] × 80} / CO | <250 dynes/sec/cm −5 |
| Ejection fraction | (SV/EDV) × 100 | 55%-75% (left ventricle) |
V. LIMITATIONS OF HEMODYNAMIC MONITORING
A. Presumptions and assumptions
1. Major presumption: Pressure = Volume
a. RAP = Right ventricular end-diastolic volume = RV preload
b. PA diastolic pressure = LAP = PCWP = Left ventricular end-diastolic volume = LV preload
2. Reality
a. Relationship between pressure and volume is curvilinear.
b. Influenced by compliance or ease of distensibility of the ventricle
VI. PRINCIPLES OF PRESSURE MONITORING
A. Uses a fluid-filled tubing system with a pressure transducer
B. Mechanical impulse transmitted from tip of catheter through the fluid to the transducer chip
1. Impulse converted from a mechanical signal to an electronic signal
2. Signal sent to the monitor through the transducer cable to be displayed as an electronic waveform on the monitor screen
C. Optimizing accuracy of pressures
1. Remove bubbles from tubing when priming.
2. Use a continuous flush system with 300 mm Hg pressure to infusion bag.
3. Eliminate tubing extensions if possible (use only nondistensible extension tubing).
4. Level and zero transducer when indicated.
a. Position patient in 0° to 45° supine position (position of tolerance).
b. Place air and fluid interface at the phlebostatic axis (fourth intercostal space, midchest) and open to air while activating the zero function on your bedside monitor (Figure 27-1).
 |
| FIGURE 27-1 ▪
Phlebostatic axis is an approximation of right atrium and is used for leveling air interface port of pressure monitoring system.
(Adapted from Dresden DG: Core curriculum for perianesthesia nursing practice, ed 4, Philadelphia, 1999, Saunders.)
|
c. Transducer must be leveled and zeroed to atmospheric pressure initially and whenever the tubing is disconnected or changed.
(1) Standards of care for the leveling and zeroing of pressure lines vary per institution.
(2) Common practice is to level and zero the transducer:
(a) At change of shift
(b) After a change in patient’s position
(c) Whenever there is a significant change in filling pressures
d. Allow 5 minutes after position changes before measuring pressures.
e. Maintain as much consistency in patient’s position as possible for measurement.
5. Square wave test: evaluates dynamic response of pressure monitoring system (Figure 27-2)
a. Perform by:
(1) Activate the fast flush device for 1 to 2 seconds.
(2) Immediately evaluate configuration on the monitor.
(3) Waveform will be replaced with a square wave.
b. Analyze waveform.
(1) Optimally damped waveform
(a) One to two oscillations
(b) No peaks >1 mm apart
(c) Straight vertical downstroke back to baseline
(2) Overly damped system
(a) Slurred upstroke with downstroke
(b) No oscillations after the square wave
(c) Treat
(i) Check for occlusion.
(ii) Ensure nonpliable tubing being used.
(iii) Make sure all components securely connected.
(3) Underdamped
(a) Numerous oscillations above and below baseline after activation of flush
(b) Overestimation of systolic pressure
(c) Underestimation of diastolic pressure
(d) Treatment
(i) Restrict catheter and tubing length to 4 feet.
(ii) Remove all air bubbles.
 |
| FIGURE 27-2 ▪
Square wave test using the fast-flush valve. A, Normal test and accurate waveform. B, Overdamped. C, Underdamped.
(From Dennison RD: Pass CCRN!, ed 3, St Louis, 2007, Mosby.)
|
VII. DIRECT INTRA-ARTERIAL PRESSURE MONITORING (ARTERIAL LINE)
A. Allows for continuous observation of the patient’s systemic BP with calculation of the mean arterial pressure
B. Provides more accuracy than use of a sphygmomanometer during low CO states
C. Under optimal conditions, an indirect BP, such as an auscultated BP or one obtained via an automated BP cuff, will underestimate the systolic pressure and overestimate the diastolic pressure by about 5 mm Hg.
D. Indications
1. Cardiopulmonary bypass
2. Procedures with potential for wide variation in BP intraoperatively or postoperatively, such as:
a. Carotid endarterectomy
b. Aortic aneurysm resection
c. Craniotomies
3. Need for strict BP control
4. Multiple arterial blood gases or laboratory tests
5. Titration of vasoactive medications (particularly those with an extremely short half-life, e.g., nitroprusside)
E. Placement
1. Site needs to be accessible and easily compressible in case of bleeding.
2. Radial artery (most common)
a. Allen test should be performed before insertion to assess for collateral ulnar flow.
(1) Procedure
(a) Compress both ulnar and radial arteries on one extremity while the patient repeatedly makes a tight fist to squeeze blood out of the hand.
(b) Release compression of the ulnar artery to observe for reperfusion indicated by a blush of color.
(c) Color should return within 5 to 10 seconds or radial artery should not be cannulated.
(d) Test can be repeated on radial artery for evidence of brisk perfusion.
3. Femoral
a. Most commonly seen with patients undergoing cardiac catheterization laboratory procedures
4. Other sites may include axillary, brachial, or pedal artery (uncommon).
F. Arterial pressure waveform; two components (Figure 27-3)
1. Anacrotic limb: a sharp uprise in the tracing that reflects the outflow of blood from the ventricle and into the arterial system
2. Dicrotic limb: descending of the pressure tracing that reflects the decrease in pressure during diastole. Beginning of diastole is seen as a small notch on the descending limb of the tracing caused by the closing of the aortic valve and is commonly called the dicrotic notch.
 |
| FIGURE 27-3 ▪
Arterial pressure waveform.
(From Headley JM: Invasive hemodynamic monitoring: Physiological principles and clinical applications, Irvine, CA, 1996, Edwards Lifesciences.)
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G. Risks and complications
1. Vascular compromise (e.g., thrombus, spasm)
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