Left and right ventricular function is frequently abnormal or discordant; therefore, the relationship of CVP to cardiac function and to intravascular volume is not maintained. When this occurs, measurement of pulmonary artery occlusion pressure can be used to accurately assess volume status and cardiovascular function. The use of a pulmonary artery catheter allows detection of changes in cardiovascular function with more sensitivity and rapidity than clinical observation.
The balloon-tipped pulmonary artery catheter (Swan-Ganz catheter) can measure pulmonary artery and pulmonary artery occlusion pressures (210). The catheter can measure cardiac output, be used to perform intracavitary electrocardiography, and provide temporary cardiac pacing. The standard pulmonary artery occlusion catheter is a 7-French, radiopaque, ﬂexible, polyvinyl chloride, 4-lumen catheter with a 1.5-mL latex balloon at its distal tip. Most often, a right internal jugular cannulation is used for placement of the catheter, because this site provides the most direct access into the right atrium and has fewer complications when compared with a subclavian route of placement. After the catheter is placed into the right atrium, the balloon is inﬂated, and the catheter is pulled by blood ﬂow through the right ventricle into the pulmonary artery. The position of the catheter can be identified and followed by the various pressure waveforms generated by the right atrium, right ventricle, and pulmonary artery. As the catheter passes through increasingly smaller branches of the pulmonary artery, the inﬂated balloon eventually occludes the pulmonary artery.
The distal lumen of the catheter, which is beyond the balloon, measures left atrial pressure (LAP) and, in the absence of mitral valvular disease, LAP approximates LVEDP. Pulmonary–capillary wedge pressure (PCWP) equals the LAP, which equals LVEDP and is normal at 8 to 12 mm Hg. Because the standard pulmonary artery catheter has an incorporated thermistor, thermodilution studies can be performed to determine cardiac output. This thermodilution method is performed by injecting cold 5% dextrose in water through the proximal port of the catheter, which cools the blood entering the right atrium. The change in temperature measured at the more distal thermistor (4 cm from the catheter tip) generates a curve proportional to cardiac output. Knowledge of the cardiac output is helpful in establishing cardiovascular diagnoses. For example, a patient with hypotension, low-to-normal wedge pressure, and a cardiac output of 3 L per minute is most likely hypovolemic. The same patient with a cardiac output of 8 L per minute is probably septic with resultant low systemic vascular resistance.
Pulmonary artery catheters are associated with a small but significant complication rate. The complications can be grouped into those occurring during venous cannulation or insertion, during maintenance and use, and those related to interpretation of hemodynamic data (210). The most common problems encountered during venous access are cannulation of the carotid or subclavian artery and introduction of a pneumothorax. Problems resulting from the catheter itself include dysrhythmias, sepsis, and disruption of the pulmonary artery. Pulmonary artery catheters (PAC) should be placed under the supervision of experienced personnel in a setting in which complications can be rapidly diagnosed and treated. Accessory equipment such as resuscitation equipment and an external pacing device must be immediately available. Ultrasound and ﬂuoroscopic equipment if available may aid in PAC placement (211).