Summary This paper evaluates the effectiveness of nasopharyngeal oxygen insufflation following preoxygenation using the four deep breath technique within 30 s, on the onset of haemoglobin desaturation during the subsequent apnoea. Thirty ASA I or II patients were randomly allocated to one of two groups. In the study group (n = 15), pre-oxygenation was followed by insufflation of oxygen at a flow of 5 l.min )1 via a nasopharyngeal catheter commenced at the onset of apnoea. In the control group, pre-oxygenation was not followed by nasopharyngeal oxygen insufflation (n = 15). In the control group, S p O 2 fell to 95% within a mean (SD) apnoea time of 3.65 (1.15) min, whereas in the study group, S p O 2 was maintained in all patients at 100% throughout the 6 min of apnoea, at which point apnoea was terminated and positive pressure ventilation commenced. We conclude that nasopharyngeal oxygen insufflation following pre-oxygenation using the four deep breath technique can delay the onset of haemoglobin desaturation for a significant period of time during the subsequent apnoea. Increasing ambient O 2 fraction from 0.9 to 1.0 more than doubled the time before haemoglobin desaturation fell to 50% and extended the period of apnoea to a greater extent than when the ambient O 2 fraction was increased from 0.21 to 0.9. During brainstem death testing, only one study has compared the effects of 100% oxygen and air as alternative ambient gases on P a O 2 ; patients who had been pre-oxygenated with 100% O 2 developed little or no hypoxaemia when compared to those receiving ai
