**2.3. The Swan-Ganz catheter**

The idea of using a cold temperature solution as an indicator, or thermodilution, dates back to the 1950's. At first fine catheter tubes were placed in the pulmonary artery, but this proved very difficult to perform clinically. The idea of using an inflated balloon to float the catheter tip into position was credited to Swan in 1970 and the triple lumen pulmonary artery catheter (PAC) with a thermistor at its tip to Ganz in 1971 [5,6]. Their PAC was produced by the Edwards Laboratory Company. The PAC became the principle method of measuring cardiac output and reached its peak usage by the end of the 1980's with sales worldwide of 1 to 2 million catheters per year. However, doubts about its clinical usefulness arose in the 1980's [7], which were later confirmed by several multicentre clinical trials [8,9]. Since the 1990's there has been a major decline in the use of the PAC catheter [10] as alternative technologies such a TOE have become available. Today, many anaesthetists and critical care doctors are unfamiliar with using PACs. Only a few companies worldwide still manufacture PACs notably Arrow International (Reading, PA, USA) and Edwards Lifesciences (Irvine, CA, USA). More sophis‐ ticated multifunction PACs are now being sold that measure continuous cardiac output using a heated wire and mixed venous oxygen saturation.

Minimally invasive cardiac out monitoring (MICOM) that measured cardiac output continu‐ ously at the bedside started to become available in the 1970's with the emergence of micro‐ processor and computer technology. Today they have become the main focus of clinical monitoring of cardiac output.
