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From Other Journals April 2009

If ‘some is good’, then is ‘more even better’? The present study examines whether an additional 4 min of preoxygenation before intubation is beneficial. Patients were recruited from one of five intensive care units – surgical, cardiac, medical, trauma and coronary care – in a single level one trauma centre in the USA. In general, they were patients requiring mechanical ventilation following failure of non-invasive methods; only one patient was intubated for airway protection. Arterial blood gas samples were taken at time 0 (T-0), when the intubating anaesthetist arrived at the bedside. Preoxygenation then commenced using a bag-valve-mask circuit. Arterial blood gases were repeated at 4 (T-4), 6 (T-6) and 8 (T-8) min. Sedation and endotracheal intubation were then performed. A total of 57 patients were recruited, that is, intubated by the main author over a 7 month period. The mean PaO2 was 62 mmHg, which rose to 84 mmHg at 4 min. There were further small rises at 6 (to 88 mmHg) and 8 min (to 93 mmHg). From T-4 to T-8, only 10 patients increased their PaO2 by more than 10%, and 14 patients had a fall in PaO2. The improvement in PaO2 from T-0 to T-4 was statistically significant; however, the increase from T-4 to T-8 was not. The study did not examine any cardiovascular changes during the pre-oxygenation period, nor did it record any adverse events (such as patients becoming obtunded, and at increased risk of aspiration). Regardless, on the basis of the present study, there is a clear benefit to a period of pre-oxygenation, but prolonged pre-oxygenation beyond 4 min is not recommended as it is not beneficial and in some cases the PaO2 might actually fall. (Mort TC. Crit Care Med 2009; 37: 68–71)