Pulmonary artery catheter

In medicine pulmonary artery catheterisation 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.

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Indications

General indications are

• Management of complicated myocardial infarction
  • Hypovolemia vs cardiogenic shock
  • Ventricular septal rupture (VSR) vs acute mitral regurgitation
  • Severe left ventricular failure
  • Right ventricular infarction
  • Unstable angina
  • Refractory ventricular tachycardia
• Assessment of respiratory distress
  • Cardiogenic vs non-cardiogenic pulmonary oedema
  • Primary vs secondary pulmonary hypertension
• Assessment of type of shock
• Assessment of therapy
  • Afterload reduction
  • Vasopressors
  • Beta blockers
  • Intra-aortic balloon counter-pulsation
• Assessment of fluid requirement in critically ill patients
  • Haemorrhage
  • Sepsis
  • Acute renal failure
  • Burns
• Management of postoperative open heart surgical patients
• Assessment of valvular heart disease
• Assessment of cardiac tamponade/constriction

Procedure

The catheter is introduced through a large vein—often the internal jugular, subclavian, or femoral veins. From this entry site, it is threaded, often with the aid of fluoroscopy, through the right atrium of the heart, the right ventricle, and subsequently into the pulmonary artery.

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 End Diastolic Ventricular 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 mls 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.

Complications

The procedure is not without risk, and complications can be life threatening. It can lead to arrhythmias, rupture of the pulmonary artery, thrombosis, infection, pneumothorax, bleeding, and other problems.

Controversy

The benefit of the use of this type of catheter has been controversial. Therefore many clinicians minimize its use.

Evidence of benefit

Several studies in the 1980s seemed to show a benefit of the increase in physiological information. Many reports showing benefit of the PA catheter are from anaesthetic, and Intensive Care settings. In these settings cardiovascular performance was optimized thinking patients would have supra-normal metabolic requirements.

Evidence of harm or lack of benefit

Contrary to earlier studies there is growing evidence the use of a PA catheter (PAC) does not necessarily lead to improved outcome. For example, see [1]. The following explanations have been advanced. One explanation could be that nurses and physicians were insufficiently knowledgeable to adequately interpret the PA catheter measurements. Also, the benefits might be reduced by the complications from the use of the PAC. Furthermore, using information from the PAC might result in a more aggressive therapy causing the detrimental effect. Or, it could give rise to more harmful therapies (i.e. achieving supra-normal values could be associated with increased mortality).

References

• Swan HJ, Ganz W, Forrester J, Marcus H, Diamond G, Chonette D. Catheterization of the heart in man with use of a flow-directed balloon-tipped catheter. N Engl J Med 1970;283:447-51. PMID 5434111.
• Intensive Care Medicine by Irwin and Rippe
• The ICU Book by Marino
• Procedures and Techniques in Intensive Care Medicine by Irwin and Rippe