An assessment of preoxygenation techniques using the pulse oximeter.

The effect of preoxygenation with varying inspired oxygen concentration on the arterial oxygen saturation during induction of anaesthesia and intubation was studied using the pulse oximeter. Sixty-five healthy, young adults, (American Society of Anaesthesiologists Class I) undergoing elective surgery were randomly divided into three groups. Group I patients were not preoxygenated. Groups II and III patients were preoxygenated with 50% oxygen and nitrous oxide and 100% oxygen respectively for one minute. All were then induced with thiopentone, paralysed with suxamethonium and orally intubated. During intubation, severe arterial desaturation occurred in those patients who were not preoxygenated (lowest saturation was 81.7 +/- 7.8% occurring 87 +/- 24.5 seconds after suxamethonium injection). This was significantly lower than the other two groups (p < 0.001). No patient had clinical signs of hypoxaemia. Patients who were preoxygenated with either 50% oxygen and nitrous oxide or 100% oxygen showed similar and clinically insignificant desaturation during this period. One minute after intubation and manual ventilation with 100% oxygen, the saturations of all patients returned to preinduction levels.