The flow-directed pulmonary artery catheter (ie, Swan-Ganz catheter) permits the clinician to measure pressures and sample blood from the right atrium, right ventricle, and pulmonary artery [1,2]. It can also estimate the left atrial pressure by measuring the pulmonary artery wedge pressure (also called the pulmonary capillary wedge pressure or pulmonary artery occlusion pressure). This involves inflating a balloon at the tip of the catheter, allowing the balloon to occlude a branch of the pulmonary artery, and then measuring the pressure during occlusion.
Pulmonary artery catheterization can be used for a variety of clinical purposes. It can differentiate among the types of shock, identify etiologies of respiratory and cardiac failure, and diagnose and manage a range of conditions in critically ill patients (table 1). In addition, inspection of the pressure waveforms can detect cardiac tamponade, cardiac constriction, restrictive cardiomyopathy, mitral valvular regurgitation, tricuspid valvular regurgitation, intracardiac shunts (eg, atrial or ventricular septal defects), mechanical events related to the atria and ventricles, and intravascular volume status.
The interpretation of pulmonary artery catheter pressure tracings is described here. The effect of invasive hemodynamic monitoring on clinical outcomes is discussed separately, as are the insertion technique, indications, and complications. (See "Insertion of pulmonary artery catheters" and "Pulmonary artery catheterization: Indications and complications".)
ZEROING AND REFERENCING
The pulmonary artery catheter must be appropriately zeroed and referenced to obtain accurate diagnostic information. Zeroing and referencing are done in one step, but they represent two separate processes:
- Zeroing involves opening the system to the air to establish atmospheric pressure as zero.
- Referencing (or leveling) is accomplished by placing the air-fluid interface of the catheter or transducer at a specific point to negate the effects of the weight of the catheter tubing and fluid column . This point is usually the intersection of a frontal plane passing midway between the anterior and posterior surface of the chest and a transverse plane lying at the junction of the 4th intercostal space and the sternal margin (figure 1). It is important to note that this "phlebostatic level" changes with differences in the position of the patient (figure 2) [3,4].