Measurement of cardiac output.

Float catheterisation of the pulmonary artery was described in The Lancet by Dr R D Bradley (as he then was) in 1964 at a time when invasive circulatory monitoring was almost non-existent outside cardiac surgical units, and ‘intensive care’ was a term barely in use. Cardiac catheterisation was laboratory based and required radiological control: management of acute circulatory crises relied on clinical assessment alone. Dr Bradley recognised the diagnostic and therapeutic value which might accrue from knowledge of central circulatory variables, and used the flow of the circulation itself to direct a fine nylon tube (ID 0.5mm) through the heart and into the pulmonary artery. The catheter was introduced through a short nylon cannula inserted most often in an antecubital vein using the Seldinger technique. A similar cannula in the brachial artery provided not only far more reliable measurement of low arterial pressure than can be achieved with a sphygmomanometer but also permitted display of the arterial waveform, itself of value in interpreting circulatory dynamics.