Pulmonary extraction of catecholamines in critically ill patients.

Plasma catecholamine concentrations in blood obtained simultaneously from the pulmonary and radial arteries of ten critically ill patients have been measured. The mean mixed venous concentrations of noradrenaline, adrenaline and dopamine were extremely high, noradrenaline 11.3 pmol/ml (SD 11.6), adrenaline 2.7 pmol/ml (SD 3.0) and dopamine 7.1 pmol/ml (SD 12.3). An appreciable drop in the concentrations occurred as the blood passed from the pulmonary artery to the radial artery (mean fall 24.1, 29.7 and 45.8% respectively). Four patients receiving a therapeutic dopamine infusion were also studied and demonstrated similar trends in catecholamine concentrations. The results suggest a substantial pulmonary clearance mechanism for all three catecholamines.