SYSTEMIC EFFECTS OF NITROUS OXIDE WHEN USED WITH HALOTHANE AND OXYGEN ANAESTHESIA AT NORMAL BODY TEMPERATURE

Abstract

SUMMARY Observations made during thirty-five routine operations, using 0.5–2.0 per cent halothane in a 70–80 per cent mixture of nitrous oxide with oxygen, indicate that addition of nitrous oxide to halothane and oxygen may be associated with decrease in blood pressure, heart rate, tidal volume and muscle tone, and increase in respiratory rate; reversal of these changes may be obtained by withdrawal of nitrous oxide. In three of five observations the rise in respiratory rate was inadequate to compensate for the fall in tidal volume, and minute volume fell by 16–37 per cent. In patients with chronic respiratory disease, a fall in minute volume of this order might result in serious arterial oxygen desaturation, particularly when oxygen constitutes 25 per cent or less of the inspired gas. When halothane, which also depresses ventilation, is used together with high concentrations of nitrous oxide, this might result in serious respiratory depression.