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KEY CONCEPTS
The tip of the central venous pressure catheter should not be allowed to migrate into the heart chambers.
Although the pulmonary artery (PA) catheter can be used to guide goal-directed hemodynamic therapy to ensure organ perfusion in shock states, other less invasive methods to determine hemodynamic performance are available, including transpulmonary thermodilution cardiac output (CO) measurements, pulse contour analyses of the arterial pressure waveform, and methods based on bioimpedance measurements across the chest.
Relative contraindications to PA catheterization include left bundle-branch block (because of the concern about complete heart block) and conditions associated with a greatly increased risk of arrhythmias.
Pulmonary artery pressure should be continuously monitored to detect an overwedged position indicative of catheter migration.
Accurate measurements of CO depend on rapid and smooth injection, precisely known injectant temperature and volume, correct entry of the calibration factors for the specific type of PA catheter into the CO computer, and avoidance of measurements during electrocautery.
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Vigilant perioperative monitoring of the cardiovascular system is one of the primary duties of anesthesia providers. The American Society of Anesthesiologists has established standards for basic anesthesia monitoring, which includes continuous monitoring of oxygenation, ventilation, circulation, and temperature throughout the anesthetic. This chapter focuses on the specific monitoring devices and techniques used to monitor cardiac function and circulation in healthy and nonhealthy patients alike.
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ARTERIAL BLOOD PRESSURE
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The rhythmic contraction of the left ventricle, ejecting blood into the arterial tree, results in pulsatile arterial pressures. The peak left ventricular end-systolic pressure (in the absence of aortic valve stenosis) approximates the systolic arterial blood pressure (SBP); the lowest arterial pressure during diastolic relaxation is the diastolic blood pressure (DBP). Pulse pressure is the difference between the systolic and diastolic pressures. The time-weighted average of arterial pressures during a pulse cycle is the mean arterial pressure (MAP). MAP can be estimated by application of the following formula:
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Arterial blood pressure varies depending upon where within the vasculature the pressure is measured. As a pulse moves peripherally through the arterial tree, wave reflection distorts the pressure waveform, leading to an exaggeration of systolic and pulse pressures (Figure 5–1). For example, radial artery systolic pressure is usually greater than aortic systolic pressure because of its more distal location. In contrast, radial artery systolic pressures often underestimate more “central” pressures immediately following hypothermic cardiopulmonary bypass because of changes in hand vascular resistance. Vasodilating drugs may accentuate this discrepancy. The level of the sampling site relative to the heart affects the measurement of blood pressure because of the effect of gravity (Figure 5–2). In patients with severe peripheral vascular disease, there may be significant differences in blood pressure measurements among the extremities. The greater value should be used in these patients.
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