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Atelectasis and pulmonary shunting during induction of general anaesthesia ‐ can they be avoided?
Author(s) -
Rothen H. U.,
Sporre B.,
Engberg G.,
Wegenius G.,
Reber A.,
Hedenstierna G.
Publication year - 1996
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1996.tb04483.x
Subject(s) - atelectasis , medicine , anesthesia , general anaesthesia , pulmonary shunt , ventilation (architecture) , mechanical ventilation , inhalation , lung , hemodynamics , mechanical engineering , engineering
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 cm 2 ) in group 1 and considerably greater (8.0±8.2 cm 2 ) in group 2 ( P <0.001). The pulmonary shunt was 0.3±0.7% of cardiac output in the awake subjects. This value increased to 2.1±3.8% in group 1 and to 6.5±5.2% in group 2 ( P <0.05). The indices of V A /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.