[Effects of preoxygenation methods on the course of PaO2 and PaCO2 in anesthetic post-induction apnea]

This study compares two preoxygenation techniques by blood gases measurements during induction of anaesthesia. After hospital ethics committee approval, 17 adult surgical patients, ASA I, all free of cardiac or lung disease were randomly assigned to two groups. Before preoxygenation, venous and radial artery canulations were performed. The patients were not premedicated and rested supine. Oxygen was given using a Mapleson A system with a 10 l.min-1 flow. In group I, 9 patients breathed 100 per cent O2 with a normal pattern. In group II, 8 patients took four deep breaths of 100 per cent O2 within 30 seconds. After this, the mask was removed and anaesthesia was induced with thiopental (5 mg.kg-1), phenoperidine (0.04 mg.kg-1) and vecuronium (0.1 mg.kg-1). After intubation, patients remained apnoeic until SpO2 decreased to 90%. Samples for arterial blood gas measurements were obtained before preoxygenation and then every minute. The two groups were similar in age (26.8 +/- 8.1 vs 29.2 +/- 9.0 years) and weight. The group I had significantly higher PaO2 immediately after preoxygenation (397 +/- 49 vs 293 +/- 86 mmHg) and the time for SaO2 to decrease to 95% was significantly shorter in group II (3 +/- 1 vs 1.87 +/- 0.99 min). PaCO2 was not different after preoxygenation in group II. In summary, healthy and young patients receive better protection against hypoxia with normal breathing of 100% for 4 minutes.