Pulmonary Artery Swan Ganz Catheter

This is Dr. Cal Shipley with a review of the Swan-Ganz pulmonary artery catheter: placement, structure, and function.

Role of Pulmonary Artery Swan Ganz Catheter

The placement of a Swan-Ganz pulmonary artery catheter can aid in the diagnosis and treatment of many potentially life-threatening cardiovascular and pulmonary conditions, including shock, pulmonary edema, heart failure, congenital heart disease, and pulmonary hypertension to name a few.

Cardiomyopathy

One of the cardiac conditions in which a pulmonary artery catheter can be enormously helpful is cardiomyopathy, characterized by marked enlargement of the cardiac chambers with impairment of chamber contraction and pumping action.

Pulmonary Artery Catheter Placement

The focus of this presentation is going to be on the placement of the pulmonary catheter and how it works.

The pulmonary arterial system carries deoxygenated blood from the right ventricle into the lungs for reoxygenation. From the right ventricle, the blood enters the main pulmonary artery.

The catheter may be advanced to the heart through the inferior vena cava, in which case the insertion is started in the right inguinal region, accessing the femoral vein, or through the superior vena cava via the right subclavian or right internal jugular vein in the neck region.

For the purposes of this demonstration, I’m going to show the catheter entering the right atrium from the superior vena cava.

Initially, the catheter is advanced until it is positioned just outside the right atrium. Typically fluoroscopy is used to assess the position of the catheter during insertion. When insertion is performed at the bedside, ultrasound and echocardiography may be used to assess catheter position.

Floating the Catheter

A latex balloon is inflated at the tip of the catheter. Inflating the balloon is also known as floating the catheter, as it causes the catheter tip to move with the flow of blood through the right atrium and ventricle and into the pulmonary artery.

As the catheter is advanced, the flow of blood against the balloon helps to guide the tip through the right atrium and ventricle and across the tricuspid and pulmonary valves into the pulmonary artery. The catheter is then advanced into the right atrium and through the tricuspid valve until it contacts the wall of the right ventricle. The ventricular wall acts as a base which allows the catheter to make a U-turn to pass to and through the pulmonary valve and into the main pulmonary artery.

The catheter is then advanced into a primary branch of the left pulmonary artery. Now that the catheter has been fully inserted, let’s take a look at its structure and how it works.

Pulmonary Artery Catheter Structure and Function

Quad Lumen Design

Although there are variations, most modern Swan-Ganz catheters contain four lumens (tubes) housed within the main catheter sheath. The blue lumen connects to a port, which is simply an opening in the main catheter sheath, which is located 30 centimeters from the tip of the catheter. The blue lumen is connected to an external transducer, which can record central venous pressure and right atrial pressures. The blue lumen can also be used to infuse medications and fluids.

The white lumen is connected to a port which is 31 centimeters from the tip of the catheter and so its port is also located within the right atrium. The white lumen is used for infusions of either fluids or medications.

The red lumen runs to the tip of the catheter and connects to the balloon and allows for inflation and deflation. Here is the catheter balloon in a deflated state. A small syringe is attached to the external connector of the red lumen and is used to inject air into the lumen with the inflation of the balloon. This process is simply reversed to deflate the balloon and inflation or deflation may be repeated as needed.

The fourth lumen in the Swan-Ganz pulmonary artery catheter is yellow. This lumen is connected to a port which is positioned at the tip of the catheter just beyond the balloon. The yellow port is connected to a pressure transducer. When the catheter balloon is deflated, the yellow port measures pulmonary artery pressure. When the balloon is inflated, blood flow from the pulmonary artery is obstructed and the pressure measured by the yellow port is equivalent to the left atrial pressure. The term applied to this measurement is the pulmonary wedge pressure, or sometimes the pulmonary capillary wedge pressure. The pulmonary wedge pressure is helpful in assessing not only the left atrial function but also mitral valve and left ventricular function.

Here is a summary of the functions of the four lumens contained within the Swan-Ganz pulmonary artery catheter.

Thermodilution and Cardiac Output Measurement

There is one other parameter of cardiovascular function that the Swan-Ganz pulmonary artery catheter can measure. That is cardiac output. It achieves this with a really fascinating piece of technology called thermodilution. The key to the thermodilution technique is a device known as a thermistor. A thermistor, short for resistance thermometer is a device whose resistance varies with temperature. The thermistor in a thermodilution capable Swan-Ganz catheter is located about four centimeters from the catheter tip.

Thermistor Bead

The thermistor “bead”, as it is termed, lies within the main catheter sheath and is attached by wires to an external connector.

Thermodilution Technique

The thermodilution technique works as follows. A known volume of saline at a known temperature (which is below body temperature) is injected into the right atrium via one of the infusion ports. This temporarily cools the blood flowing into the pulmonary artery, briefly changing the resistance in the thermistor bead. A computer attached to the thermistor’s external connector translates the resistance of the thermistor bead into a temperature.

The computer then takes the temperature of the saline initially injected and the temperature change at the thermistor caused by the saline as it circulates from the right atrium into the pulmonary artery, and takes into consideration the volume of saline injected, to calculate the cardiac output.

To try to get at the essence of what’s happening here, the greater the cardiac output, the faster the injected saline passes over the thermistor, and the shorter the duration of the temperature change measured at the thermistor.

When cardiac output is reduced, the saline moves more slowly across the thermistor and the measured temperature change is of longer duration.

Thermal Filament

A more recent development in the thermodilution technique has been an addition to the pulmonary artery catheter of a thermal filament.

The thermal filament is an exposed and very thin metallic sheath. A brief electrical current is applied to the filament from an external source causing it to heat up. This in turn results in warming of the blood running over the filament.

The warmed blood alters the resistance in the thermistor bead and the externally connected computer processes the data to calculate the cardiac output.

Please check the links on this page to learn much more about the thermodilution technique as well as other aspects of Swan-Ganz pulmonary artery catheter use.

Cal Shipley, M.D. copyright 2020