• Knowledge of the anatomy and physiology of the cardiovascular system is necessary.

• Knowledge of the anatomy and physiology of the vasculature and adjacent structures is needed.

• Understanding of the pathophysiologic changes that occur in heart disease and affect flow dynamics is necessary.

• Understanding of aseptic technique is needed.

• Understanding of the hemodynamic effects of vasoactive medications is needed.

• Understanding of the principles involved in hemodynamic monitoring is necessary.

• Knowledge of invasive cardiac output monitoring is needed.

• Knowledge of arterial waveform interpretation is needed.

• Knowledge of definitions and norms for cardiac output, cardiac index, systemic vascular resistance, stroke volume, stroke index, preload, afterload, and contractility and stroke volume variation is necessary.

• Arterial pressure represents the forcible ejection of blood from the left ventricle into the aorta and out into the arterial system. During ventricular systole, blood is ejected into the aorta, generating a pressure wave. Because of the intermittent pumping action of the heart, this arterial pressure wave is generated in a pulsatile manner (see Fig. 62-1). The ascending limb of the aortic pressure wave (anacrotic limb) represents an increase in pressure because of left ventricular ejection. The peak of this ejection is the peak systolic pressure, which is normally 100 to 140 mm Hg in adults. After reaching this peak, the ventricular pressure declines to a level below aortic pressure and the aortic valve closes, marking the end of ventricular systole. The closure of the aortic valve produces a small rebound wave that creates a notch known as the dicrotic notch. The descending limb of the curve (diastolic downslope) represents diastole and is characterized by a long declining pressure wave, during which the aortic wall recoils and propels blood into the arterial network. The diastolic pressure is measured as the lowest point of the diastolic downslope and is normally 60 to 80 mm Hg.

• The difference between the systolic and diastolic pressures is called the pulse pressure, with a normal value of 40 mm Hg.⁹

• Arterial pressure is determined by the relationship between blood flow through the vessels (cardiac output), the compliance of the aorta and larger vessels and the resistance of the more peripheral vessel walls (systemic vascular resistance). The arterial pressure is therefore affected by any factors that change either cardiac output, compliance or systemic vascular resistance.

• The average arterial pressure during a cardiac cycle is called the mean arterial pressure (MAP). It is not the average of the systolic plus the diastolic pressures, because at normal heart rates, systole accounts for 1/3 of the cardiac cycle and diastole accounts for 2/3 of the cardiac cycle. The MAP is calculated automatically by most patient monitoring systems; however, it can be calculated roughly by using the following formula:

• MAP represents the driving force (perfusion pressure) for blood flow through the cardiovascular system. MAP is at its highest point in the aorta. As blood travels through the circulatory system, systolic pressure increases and diastolic pressure decreases, with an overall decline in the MAP (see Fig. 62-2).

• Arterial pressure-based cardiac output (APCO) is obtained from an arterial catheter.3,5,11

• APCO technology measures the rate of flow (cardiac output).

• Stroke volume and heart rate are key determinants of cardiac output.

• Although systemic vascular resistance affects cardiac output, the location of that effect is global and not limited by location of that measurement because cardiac output is flow per minute throughout the body. Manufacturers of the arterial pressure-based cardiac output systems have factored in variance for both radial artery catheters and femoral artery catheters.³

• Invasive arterial catheter and insertion kit

• Specialized sterile transducer and sensor kit (manufacturer-specific)

• Intravenous (IV) pole and cartridge holder (manufacturer-specific)

• Pressure transducer system, including flush solution recommended according to institution standard, a pressure bag or device, pressure tubing with transducer, and flush device