The effect of introducing fibreoptic bronchoscopes on gas flow in laryngeal masks and tracheal tubes

The laryngeal mask airway, reinforced laryngeal mask airway and tracheal tube were studied to determine (1) flow resistance during simulated inspiration and (2) the maximum size of fibreoptic scope which can be passes down to the lumen at clinically useful ventilatory settings. In addition, the flow resistance imposed by the mast aperature bars was quantified. the laryngeal mask airway can accommodate a larger fibrescope than the corresponding sizes oof reinforced laryngeal mask airway or tracheal tube. Mean (range) flow resistance was 2.3(1.7-3.5) times higher with the reinforced laryngeal mask airway compared to the laryngeal mask airway, 2.1 (1.2-4.2) times higher with the tracheal tube compared with the laryngeal mask airway and 1.2 (0.7-1.8) times lower with the tracheal compared with the reinforced laryngeal mask airway. Removal of the mask aperture bars resulted in a mean decrease in flow resistance of 3.6%. Our data have shown that the laryngeal mask airway can accommodate a larger fibrescope than either laryngeal mask airway or tracheal tube at clinically useful ventilatory setting and that the current recommendations for maximum size of fibrescope should be revised.