What is a Swan-Ganz catheter?

A Swan-Ganz catheter is a relatively soft, flexible right heart catheter with an inflatable balloon at its tip. This balloon allows the catheter to float with the flow of blood from the great veins, through the right heart chambers, and into the pulmonary artery.

How is a Swan-Ganz catheter constructed?

Most catheters in clinical use in intensive care units have four lumens. One is connected to the end hole of the catheter, allowing for measurement of pressure in the pulmonary artery. The second lumen is attached to a temperature-sensing thermocouple 5 cm from the catheter’s tip, allowing for measurement of cardiac output. A third lumen is connected to a port 15 cm back from the tip of the catheter, allowing for measurement of pressure in the right atrium or for infusion of drugs or fluid into the central circulation. The last lumen is used to fill the balloon with air and to deflate it after insertion is completed. In addition, some catheters contain an additional port for infusion of drugs or fluid, fiberoptics for continuous monitoring of pulmonary oxygen saturation, or a lumen through which a temporary pacing electrode can be passed into the apex of the right ventricle.

How is the Swan-Ganz catheter inserted?

Most commonly, a catheter known as a sheath is inserted into the subclavian or internal jugular vein. The Swan-Ganz catheter is passed through this sheath into the central vein. The balloon is inflated, and the catheter advanced. It follows blood flow through the right atrium and ventricle, and into the pulmonary artery. Its position is monitored by watching the pressure recorded from the distal port. The catheter is advanced until a wedge tracing is obtained; the balloon is then deflated. This generally occurs when the catheter has been advanced a total of about 55 cm. In some circumstances, it may be preferable to insert the catheter via the femoral vein or a peripheral vein in the antecubital fossa.

What information can be gained from the Swan-Ganz catheter?

Basically two main types of data are obtained from the catheter: cardiac output and left ventricular preload.

Cardiac output is measured by injecting saline colder than the blood through the proximal port of the lumen into the right atrium, and the temperature of the blood in the pulmonary artery is measured continuously by a temperature sensor (actually, a thermocouple) positioned 5 cm back from the tip of the catheter. The brief dip in the blood’s temperature with time is related to cardiac output by a somewhat complicated formula, which, luckily, is calculated by computer.

Left ventricular preload is estimated by measuring the pulmonary capillary wedge pressure (PCW), also known as the pulmonary artery wedge pressure (PAW). The wedge pressure is obtained by inflating the balloon while the catheter is positioned in the left or right main pulmonary artery. Blood flow carries the catheter distally, until the diameter of the branch of the pulmonary artery is smaller than the diameter of the balloon. The catheter tip becomes stuck or wedged. The tip of the catheter is now shielded from the pressure in the pulmonary artery, and records pressure in the pulmonary arterioles. It turns out that this pressure closely approximates left atrial pressure, which in turn is a good measure of left ventricular preload.

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