Endotracheal intubation, but not laryngeal mask airway insertion, produces reversible bronchoconstriction

Background: Tracheal intubation frequently results in an increase in respiratory system resistance that can be reversed by inhaled bronchodilators. The authors hypothesized that insertion of a laryngeal mask airway would be less likely to result in reversible bronchoconstriction than would insertion of an endotracheal tube. Methods: Fifty-two (45 men, 7 women) patients were randomized to receive a 7.5-mm (women) or 8-mm (men) endotracheal tube or a No. 4 (women) or No. 5 (men) laryngeal mask airway. Anesthesia was induced with 2 mu g/kg fentanyl and 5 mg/kg thiopental, and airway placement was facilitated with 1 mg/kg succinylcholine. When a seal to more than 20 cm water was verified, respiratory system resistance was measured immediately after airway placement. Inhalation anesthesia was begun with isoflurane to achieve an end-tidal concentration of 1% for 10 min. Respiratory system resistance was measured again during identical conditions. Results: Among patients receiving laryngeal mask airways, the initial respiratory system resistance was significantly less than among patients with endotracheal tubes (9.2 +/- 3.3 cm water . l(-1) . s(-1) [mean +/-SD] compared with 13.4 +/- 9.6 cm water . l(-1) s(-1); P < 0.05). After 10 min of isoflurane, the resistance decreased to 8.6 +/- 3.6 cm water . l(-1) . s(-1) in the endotracheal tube group but remained unchanged at 9.1 +/- 3.3 cm water . l(-1) . s(-1) in the laryngeal mask airway group. The decrease in respiratory system resistance in the endotracheal tube group of 4.7 +/- 7 cm water . l(-1) . s(-1) was highly significant compared with the lack of change in the laryngeal mask airway group (P < 0.01). Conclusions: Resistance decreased rapidly only in patients with endotracheal tubes after they received isoflurane, a potent bronchodilator, suggesting that reversible bronchoconstriction was present in patients with endotracheal tubes but not in those with laryngeal mask airways. A laryngeal mask airway is a better choice of airway to minimize airway reaction.