Atelectasis and pulmonary shunting during induction of general anaesthesia ‐ can they be avoided?

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Abstract
Background: Gas exchange is regularly impaired during general anaesthesia with mechanical ventilation. A major cause of this disorder appears to be atelectasis and consequently pulmonary shunt. After re‐expansion, atelectasis reappears very slowly if 30% oxygen in nitrogen is used, but much faster if 100% oxygen is used. The aim of the present study‐was to evaluate if early formation of atelectasis and pulmonary shunt may be avoided if the lungs are ventilated with 30% oxygen in nitrogen instead of 100% oxygen during the induction of general anaesthesia.Methods: Twenty‐four adult patients with healthy lungs scheduled for elective surgery were investigated. During induction of anaesthesia, the lungs were manually ventilated via a face mask, using either 30% oxygen in nitrogen (group 1, n=12) or 100% oxygen (group 2, n=12). Atelectasis was estimated by computed x‐ray tomography and ventilation‐per‐fusion distribution with the multiple inert gas elimination technique, both awake and during general anaesthesia with mechanical ventilation.Results: No atelectasis was present in the awake subjects. After induction of anaesthesia, the mean amount of atelectasis was minor (0.2±0.4 cm2) in group 1 and considerably greater (8.0±8.2 cm2) in group 2 (PPA/Q mismatch showed no difference between the two groups.Conclusion: During induction of general intravenous anaesthesia in patients with healthy lungs, gas composition plays an important role for atelectasis formation and the establishment of pulmonary shunt. By using a mixture containing 30% oxygen in nitrogen, the early formation of atelectasis and pulmonary shunt may, at least in part, be avoided.