Jameel Ahmed, MD and George Philippides, MD

1. What is a Swan-Ganz catheter?

    A Swan-Ganz catheter is a relatively soft, flexible catheter with an inflatable balloon at its tip that is used in right heart catheterization. The balloon-tip allows the catheter to “float” with the flow of blood from the great veins through the right heart chambers and into the pulmonary artery, before “wedging” in a distal branch of the pulmonary artery.

2. How is a Swan-Ganz catheter constructed?

    The basic Swan-Ganz catheter in current clinical use has four lumens. One is connected to the distal port of the catheter, allowing for measurement of the pulmonary artery pressure when the balloon is deflated, and the pulmonary artery wedge pressure (PAWP) when the balloon is inflated. The second lumen is attached to a temperature-sensing thermocouple 5 cm proximal to the catheter tip and is used for measurement of cardiac output (CO) by thermodilution. The third lumen is connected to a port 15 cm proximal to the catheter tip, allowing for measurement of pressure in the right atrium and for infusion of drugs or fluids into the central circulation. The fourth lumen is used to inflate the balloon with air when initially floating the catheter into position and later to reinflate the balloon for intermittent measurement of PAWP. Many catheters contain an additional proximal port for infusion of fluids and drugs. Some catheters have an additional lumen through which a temporary pacing electrode can be passed into the apex of the right ventricle for internal cardiac pacing.

3. What information can be gained from a Swan-Ganz catheter?

    Direct measurements obtained from the catheter include vascular pressures and oxygen saturations within the cardiac chambers, cardiac output, and systemic venous oxygen saturation (Svo₂). These hemodynamic measurements can be used to calculate other hemodynamic parameters, such as systemic vascular resistance and pulmonary vascular resistance.

4. How is a Swan-Ganz catheter inserted?

    At the bedside, venous access is usually obtained by introducing an 8.5 French sheath into the internal jugular or subclavian vein using the Seldinger technique. The right internal jugular or left subclavian veins are preferred sites as the natural curve of the catheter will allow easier flotation into the pulmonary artery. Less commonly, the antecubital or femoral veins are used.

    Next, a 7.5 French Swan-Ganz catheter is passed through the introducer sheath and advanced approximately 15 cm to exit the sheath into the central vein. The balloon is then inflated with 1.5 mL of air, and the catheter is advanced slowly, allowing the balloon to float through the right atrium, right ventricle, and pulmonary artery, and finally achieving a wedge position in a distal branch of the pulmonary artery that is smaller in diameter than the balloon itself. The wedge position is usually achieved when the catheter has advanced a total of 35 to 55 cm, depending on which central vein is cannulated.

5. Describe the normal pressure waveforms along the path of an advancing Swan-Ganz catheter.

    The a wave is produced by atrial contraction and follows the electrical P wave of an electrocardiogram (ECG). The x descent reflects atrial relaxation. The c wave is produced at the beginning of ventricular systole as the closed tricuspid valve bulges into the right atrium. The x′ descent is thought to be the result of the descent of the atrioventricular ring during ventricular contraction as well as continued atrial relaxation. The v wave is caused by venous filling of the atrium during ventricular systole, when the tricuspid valve is closed. This should correspond with the electrical T wave. However, at the bedside, due to a lag in pressure transmission, the a wave will align with the QRS complex and the v wave will follow the T wave. Finally, the y descent is produced by rapid atrial emptying, when the tricuspid valve opens at the onset of diastole (Fig. 12-1).

6. How is the location of the catheter determined?

    At the bedside, continuous monitoring of pressure tracings from the distal port and simultaneous ECG tracings allow the operator to determine the catheter’s position and to detect any arrhythmias caused by the catheter, as it passes through the right ventricle. Fluoroscopy can be used in the cardiac catheterization lab to guide placement. The use of fluoroscopy should especially be considered if a Swan-Ganz catheter is placed via the femoral or brachial veins or in patients with dilated right ventricles.

7. How do we know that the catheter is in the true wedge position?

    There are three ways to confirm that the catheter is in the wedge position (Figures 12-1 and 12-2). At the bedside, an atrial tracing (reflecting left atrial pressure) will be seen when the catheter is in the wedge position. Secondly, if the catheter is withdrawn from the wedge position, the mean arterial pressure should be observed to rise from the wedge pressure (reflecting a physiologic gradient between the mean pulmonary artery and mean wedge pressure). Gentle aspiration of blood from the distal port should reveal high-oxygenated blood if the catheter is truly wedged. Additionally, in the catheterization lab, fluoroscopy can be used to determine that the catheter is in a distal pulmonary arteriole, immobile in the wedge position.

8. What does the PAWP signify?

    When the catheter is in the wedge position (Fig. 12-3, B), proximal blood flow is occluded and a static column of blood is created between the catheter tip and the distal cardiac chambers. With the balloon shielding the catheter tip from the pressure in the pulmonary artery proximally, the pressure transducer measures pressure distally in the pulmonary arterioles. This pressure closely approximates left atrial pressure. When the mitral valve is open at end diastole, left ventricular (LV) end diastolic pressure is measured (Fig. 12-3, C), assuming that there is no obstruction between the catheter tip and the LV (i.e., mitral stenosis). The PAWP can be used to approximate LV preload.

9. How is cardiac output determined?

    Cardiac output can be determined either by the measured thermodilution method or the calculated Fick method.

    With thermodilution, 5 to 10 mL of normal saline is injected rapidly via the proximal port into the right atrium. The injectate mixes completely with blood and causes a drop in temperature that is measured continuously by a thermocouple near the catheter tip. The area under the curve is calculated and is inversely related to cardiac output (Fig. 12-4). This method of measurement is not reliable in patients with low cardiac output or significant tricuspid regurgitation. In a low cardiac output state, blood is rewarmed by the walls of the cardiac chambers and surrounding tissue, resulting in an overestimation of cardiac output.

    Alternatively, the Fick method can be used to calculate cardiac output.