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A new technique for recording and analysing continuous measurements of oxygen saturation (SpO2) by pulse oximeter during haemodialysis was used to compare changes in SpO2 in eight patients during two 4 h periods of dialysis using a cuprophane membrane, once using an acetate dialysate, and once using bicarbonate. The computer-derived patterns of SpO2 show whether hypoxaemia was caused mainly by extrapulmonary abnormalities (ventilatory control) or intrapulmonary abnormalities (V/Q distribution). The patterns of oxygen saturation were analysed for (i) stability, (ii) the lower median 20th centile of SpO2, and (iii) time below a SpO2 of 90%. Not all patients had reduced oxygenation during acetate dialysis. Three of eight patients had a stable pattern with acetate dialysis and six of eight were stable with bicarbonate. Five of eight patients had a lower SpO2 with acetate but one patient had a lower SpO2 with bicarbonate. Four patients had prolonged, clinically significant periods of oxygen desaturation with SpO2 less than 90%; two of these had particularly prolonged periods during acetate (62 min and 12 min), but one patient showed a longer period during bicarbonate than acetate dialysis (7 min). In two patients the SpO2 declined to less than 84%. The patterns of SpO2 suggested that the decrease in oxygen saturation was due more to extrapulmonary abnormalities causing an instability in ventilatory control rather than to venous admixture. It is recommended that pulse oximetry is used to identify patients at risk of hypoxaemia, to monitor these patients during haemodialysis, and to administer oxygen to those whose SpO2 falls below 90%, particularly if they have anaemia or cardiovascular disease.

Forty patients undergoing middle ear surgery were allocated randomly to receive propofol induction and maintenance, or thiopentone induction and enflurane maintenance for anaesthesia. Both groups also received fentanyl, alcuronium, nitrous oxide and oxygen. If this did not reduce systolic arterial pressure to 70 mm Hg, labetalol, glyceryl trinitrate (GTN), or both, was administered. Fifteen control patients had enflurane anaesthesia without hypotension. Pre- and postoperative psychometric tests were performed in all groups. The propofol group received significantly more labetalol (P = 0.014) and GTN (P = 0.004) than the enflurane group. There was a greater increase in reaction times after operation in the study groups (P < 0.05) compared with controls. There was no difference between the propofol and enflurane groups in control of arterial pressure, recovery from anaesthesia or psychometric testing.

SummaryTwenty patients, scheduled for minor gynaecological surgery, were studied. Anaesthesia was induced with propofol and maintained with oxygen, nitrous oxide and enjlurane. Patients were randomly allocated to two groups: group 1 were given alfentanilO.2 mg; group 2 were given morphine 5 mg. The rate of gastric emptying was measured indirectly by the paracetamol absorption technique. The results showed that morphine caused greater delay in gastric emptying compared with alfentanil ( p c 0.05). The observed effect on gastric emptying rate may potentially affect the risk of peri-operative regurgitation and aspiration. This study provides further evidence that in short day-case procedures, when oral medication may be required postoperatively, alfentanil may be preferable to morphine as an intra-operative opioid.