Arterial desaturation during induction with and without preoxygenation: evaluation of four techniques

The incidence and degree of hypoxaemia during induction of balanced anaesthesia and endotracheal intubation were studied prospectively in 80 healthy adults undergoing elective surgery randomly divided into four equal groups of 20. Group 1 was preoxygenated for three minutes. The other three groups were not preoxygenated. Groups 1 and 2 were ventilated with 100% oxygen, while Groups 3 and 4 were ventilated with 50% and 33% oxygen respectively. Anaesthesia was induced with thiopentone 3-5 mg/kg and endotracheal intubation was done after ventilating for one minute with the chosen gas. Arterial desaturation was measured by pulse oximetry. In Groups 1-3 there was a significant increase and in Group 4 a significant decrease in saturation from the preinduction value. The arterial oxygen saturation was similar in Groups 1 and 2. Two patients in Group 3 and four in Group 4 had hypoxaemia. This incidence was not statistically significant. We conclude that ventilation with 100% oxygen for one minute prior to intubation and preoxygenation for three minutes are equally effective in preventing hypoxaemia during induction.