ACID-BASE CHANGES IN ARTERIAL BLOOD ASSOCIATED WITH SPONTANEOUS AND CONTROLLED VENTILATION DURING ANAESTHESIA

Arterial pH, Pco2 and whole blood standard bicarbonate were measured in surgical patients before, during, and after spontaneous or controlled pulmonary ventilation with nitrous oxide, oxygen and halothane. Relative increases in arterial Pco were accompanied by significant reductions in standard bicarbonate, indicative of a non-respiratory acid aemia. This effect may be attributable in part to differences between the log Pco2 equilibration lines for blood and for the whole organism. Small reductions in standard bicarbonate occurred over several hours of pulmonary overventilation in neurosurgical patients during induced hypothermia, and in the early postoperative period.