In medicine pulmonary artery catheterization (PAC) is the insertion of a catheter into a pulmonary artery. Its purpose is diagnostic; it is used to detect heart failure or sepsis, monitor therapy, and evaluate the effects of drugs. The pulmonary artery catheter allows direct, simultaneous measurement of pressures in the right atrium, right ventricle, pulmonary artery, and the filling pressure ("wedge" pressure) of the left atrium.
The pulmonary artery catheter is frequently referred to as a Swan-Ganz catheter, in honor of its inventors Jeremy Swan and William Ganz, from Cedars-Sinai Medical Center. The idea for this catheter (as later revealed by Dr. Swan) came about from the observation of sail boats on the water.
The standard pulmonary artery catheter has two lumens (Swan-Ganz) and is equipped with an inflatable balloon at the tip, which facilitates its placement into the pulmonary artery through the flow of blood. The balloon, when inflated, causes the catheter to "wedge" in a small pulmonary blood vessel. So wedged, the catheter can provide a measurement of the pressure in the left atrium of the heart, termed Left Ventricular End Diastolic Pressure or LVEDP.
Modern catheters have multiple lumens (multiple tubes) five or six are common and have openings along the length to allow administration of inotropes and other drugs directly into the atrium. The other major change is the addition of a small themistor (temp probe) about 3 cms behind the tip. Either cold fluid under 10 Celsius or room temperature (not as accurate) is injected into an opening in the Right atrium, typically 10 ml of saline (0.9% NaCL).
As this cooler fluid passes the tip thermistor, a very brief drop in the blood temperature is recorded. By attaching both the injector site and the ventricular thermistor to a small computer, the thermodilution curve can be plotted. If details about the patients body mass index (size); core temp, Systolic, diastolic, central venous pressure CVP (measured from the atrium by the third lumen simultaneously) and pulmonary artery pressure are input, a comprehensive flow vs pressure map can be calculated. In crude terms, this measurement compares left and right cardiac activity and calculates pre-load and after load flow and pressures which theoretically if stabilised or adjusted with drugs to either constrict/dilate the vessels i.e. raise/lower the pressure of blood flow to the lungs in order to maximise oxygen for delivery to the body tissues. The true art remains with the consultant physician or intensivist in the balancing fluid load, which is why the ability to record results is not a guarantee of patient survivability, so much so the catheter which is usually yellow has been nicknamed "The kiss of the yellow snake".
Drugs to achieve these changes can be delivered into the Atrium via the fourth lumen, usually dedicated to medication. Common drugs used are various inotropes, nor-adrenaline or even atropine. A further set of calculations can be made by measuring the arterial blood and central venous (from the 3rd lumen) and inputting these figures into a spreadsheet or the Cardiac output computer, if so equipped, and plotting an Oxygen Delivery profile.
One further (expensive) development in recent years has been the invention of a catheter with a fibre-optic based probe which is extended and lodged into the ventricle wall providing instant readings of SvO2 or oxygen saturation of the ventricle tissues. This technique has a finite life as the sensor becomes coated with protein and it can irritate the ventricle via the contact area.
Recent variations in design are the incorporation of a heating coil on the catheter (30cms from the tip, residing in the atrium area) which eliminates the cold fluid bolus, a major factor in human technique variation.
Various other techniques have largely relegated the PA catheter to history, eg the lithium dilution technique; the external bio-resistance monitor or the very simple and reliable technique of oesophageal doppler measurements of the descending aorta.