Figure 40.1. West Lung Zones. PA catheter should be placed in Zone 3 where both arterial and venous pressures are greater than alveolar pressures.

    If truly a reflection of LAP, this information gives the clinician an idea of the left ventricular end-diastolic pressure (LVEDP) and in turn the left ventricular end-diastolic volume (LVEDV). This information can be used to assess cardiac filling and cardiac function. It also allows the calculation of pulmonary vascular resistance. Additionally, a PA catheter can be used to calculate cardiac output and systemic vascular resistance.

PULMONARY ARTERY CATHETER PLACEMENT

A pulmonary artery catheter, when placed in the ICU, is inserted through a cordis in one of the large veins of the neck or chest. Internal jugular and subclavian veins on either the left or right are acceptable locations for access, but the PA catheter is more easily positioned when the right internal jugular or the left subclavian vein is used. These vessels provide a straighter path to the right atrium and afford a higher likelihood of the catheter successfully passing through the central vein to the right atrium and beyond.

    After a cordis is placed under sterile conditions, the patient is generally redraped for placement of the PA catheter. At times, clinicians will reglove for the procedure, as sterility is essential. The catheter is inserted and advanced 20 cm so that it is clear of the cordis. At this time, the balloon at the tip of the catheter (see Figure 40.2) is inflated with 1–1.5 cc of air, which allows the catheter to “float” in the bloodstream. The catheter is then advanced, being guided by the appearance of varying waveforms, through the central vein to the right atrium, through the tricuspid valve, into the right ventricle (RV), and eventually into the right pulmonary artery. At this point, the clinician slowly advances the catheter until it “wedges” in a more distal pulmonary artery, resulting in occlusion of flow. This position is determined by distance advanced and waveform appearance. These waveforms are the focus of the following section.

    At times it can be difficult to place a PA catheter. As already mentioned, placement via the left internal jugular or right subclavian approach can be challenging because of the more acute turns the catheter must take. If a patient has significant tricuspid regurgitation, it can be difficult to advance from the right atrium to the right ventricle. Similarly, if a patient has a dilated right ventricle it is sometimes difficult to navigate out of the ventricle and advance into the pulmonary artery. In these circumstances, PA catheter placement can be aided by fluoroscopic guidance.

    In addition to the risks associated with placement and use of a central venous catheter (e.g., bleeding, infection, pneumothorax), PA catheter placement and maintenance have multiple potential complications. While floating a PA line, particularly while traversing the right ventricle, there is a risk of inducing ventricular tachycardia from contact with the conduction system of the heart. Similarly, it is possible to induce a right bundle branch block during placement, a life-threatening complication in a patient with an underlying left bundle branch block at baseline. During pulmonary artery occlusion, there is a small risk of pulmonary infarction and less commonly pulmonary artery rupture. Finally, over time, a pulmonary artery catheter can become knotted in the right ventricle. This complication generally requires surgical intervention. Because of rare but potentially life-threatening complications, PA catheter placement should be done with care and after thoughtful decision making about the value of the data provided.

WAVEFORM ANALYSIS

RIGHT ATRIAL PRESSURE

The initial pressure that is seen when a PA catheter is inserted is that of the central vein (CVP). This is usually apparent after the catheter is advanced 20 cm and is clear of the cordis. The CVP is an approximation of the right atrial pressure (RAP), and the waveform in the central vein and the right atrium look the same.

    The RAP waveform can demonstrate three distinct deflections, although the fidelity of a PA catheter tracing in the ICU is often not good enough to distinguish each. The first upward deflection is the a–wave and is a reflection of atrial contraction. This is followed by the x descent as pressures fall with atrial relaxation. The second upward deflection, termed the c–wave, which is often not discernible, is a small rise associated with closure of the tricuspid valve. The final upward deflection, the v–wave, is associated with passive filling of the atrium and occurs at the time of ventricular contraction. This is followed by the y descent as the tricuspid valve opens and blood flows into the ventricle.

    In order to interpret the CVP or RAP tracing, a synchronous electrocardiogram (EKG) is used. As mechanical activity in the heart follows slightly on electrical activity, the EKG changes will precede the pressure tracing changes. Accordingly, the CVP a-wave will follow the P wave on the EKG, and the v-wave will follow the T wave, as shown in Figure 40.3. The measurement of the CVP or RAP is by convention taken as the mean of the a-wave. As valvular pathology can result in large v-waves, the maximal deflection of the tracing is not used. Normal values for CVP range from 2 to 8 mm Hg, although there is considerable variability.

RIGHT VENTRICULAR PRESSURE

There is a dramatic change in the waveform as the catheter moves from the right atrium to the right ventricle, as demonstrated in Figure 40.4. This will happen when the catheter is advanced 25–30 cm, varying based on site of vascular access and patient anatomy. As shown, there is a rapid rise in pressure as the right ventricle contracts and then a rapid fall as the right ventricle relaxes. Right ventricular pressures are reported with a systolic, diastolic, and mean value. Normal values are in the range of 15–25 mm Hg systolic and 4–10 mm Hg diastolic. This tracing should only be seen during the floating of the PA line, as the catheter tip should not remain in the right ventricle, where there is a greater risk of inducing arrhythmias, and none of the catheter measurement ports will remain in the RV if the catheter is appropriately positioned.

PULMONARY ARTERY PRESSURE

Close attention must be paid as the PA catheter is advanced from the right ventricle into the pulmonary artery, usually 5–10 cm after the RV tracing is seen. The waveform will have three distinct changes in appearance after this transition. While the systolic pressure will remain essentially constant (15–25 mm Hg), the diastolic pressure will rise in the pulmonary artery (normal range 8–15 mm Hg). The waveform will have a dicrotic notch (see Figure 40.5), which is a reflection of pulmonic valve closure. Finally, the diastolic portion of the curve will now be downsloping, as pressures fall during diastole with runoff into the pulmonary vascular bed between cardiac contractions.

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