performance was optimized thinking patients would have supra-normal metabolic requirements. In 2005, a multi-center randomized controlled trial found no difference in mortality or length of stay in ICU patients who received pulmonary artery catheters, though it did find a 10% incidence of complications related to the procedure. 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. One explanation could be that nurses and physicians are 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). Utility of pulmonary artery catheterization This interpretation of Adolph Ficks' formulation for cardiac output by time/temperature curves is an expedient but limited and invasive model of right heart performance. It remains an exceptional method of monitoring volume overload leading to pulmonary edema in an ICU setting. A feature of the pulmonary artery catheter that has been largely ignored in the clinical setting is its ability to monitor total body oxygen extraction by measuring the mixed venous oxygen saturation. Regardless of the value obtained by measurements of the cardiac output, the mixed venous oxygen saturation is an accurate parameter of total body blood flow and therefore cardiac output. The assumption that a low mixed venous oxygen saturation (normal = 60% except for the coronary sinus where it approximates 40% reflecting the high metabolic rate of the myocardium) represents less than adequate oxygen delivery is consistent with physiological and metabolic observations. High oxygen extraction is associated with low cardiac output and decreased mixed venous oxygen saturation. Except during hypothermia and in severe sepsis, low mixed venous oxygen saturations are indication of inadequate hemodynamics. The ability of the pulmonary artery catheter to sample mixed venous blood is of great utility to manage low cardiac output states. Non-invasive echocardiography and pulse-wave cardiac output monitoring are concordant with (and much safer) if not better than invasive methods defining right and left heart performance. The emergence of MRSA and similar hospital based catheter infections now clearly limits the utility of this type of invasive cardiac ICU intervention. Notes References Further reading