The ventilatory responses to CO2 without hypoxia, to hypoxia at constant PACo2 and to CO2 combined with hypoxia were measured in duplicate with an interval of 20 min. between the two sets of measurements. The PAC0O threshold during the second set differed in only random fashion from that during the first set; so did the CO2 sensitivity in the absence of hypoxia. The CO2 sensitivity during hypoxia, however, was significantly greater during the second set of measurements. The relevance of these results to the investigation of drugs which affect respiration is discussed.IN studies of the analeptic drugs ethamivan and prethcamide [Anderton et al., 1962; Anderton and Harris, 1963 b] the ventilatory response to changes in alveolar CO2 tension (Pco2) was measured before and during administration of the drug. Both drugs were shown to stimulate breathing, as compared with the effect of merely repeating the ventilatory measurements without giving any drug. Subsequent experiments were carried out, using ethamivan, to study the ventilatory response to hypoxia at constant alveolar Pco, and these appeared to show that the drug also increases the response to hypoxia. When control experiments were done, however, it was found that repeating the measurements, without giving the drug, resulted in an increased hypoxic response of about the same magnitude as when ethamivan was given. We therefore decided to undertake further control experiments and the results of these and the previous ones are now presented. METHODSGas mixtures were supplied to the subjects, and ventilation and alveolar gas tensions measured, by methods and under conditions previously described [Cunningham et at., 1957;Anderton et al., 1962;. The subjects were all young, healthy volunteers, mostly male medical students; two nurses were the only females studied. All ventilatory measurements were made in the steady state of ventilation and alveolar Pco2. Each experiment consisted of a duplicate set of observations (periods 1 and 2) separated by an interval of 20 mi. during which the mouthpiece was removed and the subject breathed room air. The total duration of the experiment was practically the same for each subject in any one programme, and the order and duration of administration of gas mixtures were standardized as far as was compatible with the attainment of steady states. The experimental programmes were of three kinds:1. Response to Hypoxia at Constant PACO (six subjects).-Four subjects were studied at low PA (1-2 mm. Hg above resting) and two at a higher PACO (6-8 mm. Hg above resting). The first group was first given a mixture containing 02 at 43

We have compared gastric aspirate pH and volume at induction of anaesthesia in 222 patients who had received either omeprazole or ranitidine before elective operations. Omeprazole was given orally either as 40 mg on the evening before and 40 mg on the morning of surgery or as 80 mg on the morning of surgery. Ranitidine 150 mg was given orally on the evening before surgery and 2 h before anaesthesia. Treatment success was defined as aspirate pH > or = 2.5 and volume < 25 ml at induction of anaesthesia. Treatment was successful in 84% (95% confidence interval (CI) 73-91%) of patients in the omeprazole 40 + 40 mg group, 84% (95% CI 73-91%) in the ranitidine group and 73% (95% CI 61-83%) in the omeprazole 80 mg group. There were no statistically significant differences between the groups. Twelve patients in the omeprazole 80 mg group had gastric pH < 2.5 and four had volume > 25 ml. Only three patients had a gastric pH < 2.5 in the omeprazole 40 + 40 mg group and none had volume > 25 ml, which compared well with the ranitidine group. Omeprazole, given as 40 mg in the evening and 40 mg on the morning of operation, has a potential role for use in patients at risk for aspiration during general anaesthesia.

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