Pulmonary artery catheter
A pulmonary artery catheter (PAC), also known as a Swan-Ganz catheter or right heart catheter, is a balloon-tipped catheter that is inserted into a pulmonary artery in a procedure known as pulmonary artery catheterization or right heart catheterization.[1][2] Pulmonary artery catheterization is a useful measure of the overall function of the heart particularly in those with complications from heart failure, heart attack, arrythmias or pulmonary embolism. It is also a good measure for those needing intravenous fluid therapy, for instance post heart surgery, shock, and severe burns.[2] The procedure can also be used to measure pressures in the heart chambers.
The pulmonary artery catheter allows direct, simultaneous measurement of pressures in the right atrium, right ventricle, pulmonary artery, and the filling pressure (pulmonary 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.[3]
General indications are:
No study has definitively demonstrated improved outcome in critically ill patients managed with PA catheters.[4][5] Given that the PA catheter is a monitoring tool and not a therapy in and of itself this is not entirely surprising. Justification for its continued use rests on a large body of clinical experience, disadvantages of other cardiac output monitoring systems, its ability to accurately measure pulmonary artery pressure, and the potential to use the catheter as a direct conduit for drug administration into the pulmonary artery.
Procedure[edit]
The catheter is introduced through a large vein—often the internal jugular, subclavian, or femoral veins. Ease of placement for a pulmonary artery catheter from easiest to difficult is: right internal jugular > left subclavian > left internal jugular > right subclavian.[5] From this entry site, it is threaded through the right atrium of the heart, the right ventricle, and subsequently into the pulmonary artery. The passage of the catheter may be monitored by dynamic pressure readings from the catheter tip or with the aid of fluoroscopy.
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 an indirect measurement of the pressure in the left atrium of the heart, showing a mean pressure, in addition to a, x, v, and y waves which have implications for status of the left atria and the mitral valve. Left ventricular end diastolic pressure (LVedp) is measured using a different procedure, with a catheter that has directly crossed the aortic valve and is well positioned in the left ventricle. LV edp reflects fluid status of the individual in addition to heart health. See also pulmonary wedge pressure and ventricular pressure.
Technical developments[edit]
Thermal dilution[edit]
The idea for a sail or balloon tip modification of Ronald Bradley's simple portex tubing method came about from Swan's observation from the Laguna Beach CA shore of sail boats on the water on a relatively calm day. Boats with conventional slot sails were still; one with a spinnaker was able to make reasonable headway. The concept of using thermodilution to measure cardiac output was originally the idea of Arnost Fronek.[6] As a former colleague of Fronek, Ganz added the thermistor modification after Swan showed him the initial balloon design, which was fabricated by Edwards Laboratories, which had previously contracted with Swan as a consultant.
After Swan developed the initial balloon tip, Ganz used Fronek's idea and added a small thermistor (temperature probe) about 3 cm behind the tip. 10 ml of saline (0.9% NaCl) under 10 °C or room temperature (not as accurate) is injected into an opening in the right atrium. As this cooler fluid passes the tip thermistor, a very brief drop in the blood temperature is recorded. A recent variation in design is the incorporation of a heating coil on the catheter (30 cm from the tip, residing in the atrium area) which eliminates the cold fluid bolus, a major factor in human technique variation.
By attaching both the injector site and the ventricular thermistor to a small computer, the thermodilution curve can be plotted. If details about the patient's 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 preload and afterload flow and pressures which, theoretically, can be stabilized or adjusted with drugs to either constrict or dilate the vessels (to raise or lower, respectively, the pressure of blood flowing to the lungs), in order to maximize oxygen for delivery to the body tissues.
The ability to record results is not a guarantee of patient survivability.
Pharmacotherapy lumina[edit]
Modern catheters have multiple lumina — five or six are common — and have openings along the length to allow administration of inotropes and other drugs directly into the atrium. 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, norepinephrine or even atropine. A further set of calculations can be made by measuring the arterial blood and central venous (from the third lumen) and inputting these figures into a spreadsheet or the cardiac output computer, if so equipped, and plotting an oxygen delivery profile.
SvO2 measurement[edit]
One further development in recent years has been the invention of a catheter with a fiber-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.
Alternatives[edit]
Various other techniques have largely relegated the PA catheter to history, e.g. the lithium dilution technique; the external bio-resistance monitor, pulse contour analysis or the very simple and reliable technique of esophogeal doppler measurements of the descending aorta.
Complications[edit]
The procedure is not without risk, and complications can be life-threatening. It can lead to arrhythmias, pseudoaneurysm formation or rupture of the pulmonary artery, thrombosis, infection, pneumothorax, bleeding, and other problems.[7]