Variability of haemoglobin concentration during anaesthesia. A statistical investigation of three anaesthetic methods.

Changes in haemoglobin concentration and systolic blood pressure were measured for fifty-six patients receiving three different methods of anaesthesia. One group received anaesthesia comprising a relaxant with nitrous oxide and oxygen and controlled respiration: no significant changes occurred. A second group received halothane inhaled spontaneously with oxygen: significant decreases in mean (integral) operative blood pressure and Hb concentration were observed. A third group had lumbar epidural block, spontaneous respiration and halothane inhalation. There was a statistically significant fall in blood pressure and Hb concentration. The fall in Hb concentration correlated significantly with the blood pressure decrease occurring some 5 minutes before. The possible sources of an increase in plasma volume during anaesthesia accompanied by peripheral vasodilatation are discussed.