Ventilatory adequacy and respiratory mechanics with laryngeal mask versus tracheal intubation during positive pressure ventilation.

The ventilatory adequacy and respiratory mechanics during positive pressure ventilation (PPV) via the laryngeal mask airway (LMA) are compared with the respiratory mechanics via the tracheal tube (TT). Thirty patients undergoing breast surgery were studied. After induction of anesthesia and muscle relaxation an LMA was inserted. Data were collected every 5 min for a 15 min period and included inspired (VTinsp) and expired (VTexp) tidal volumes, I:E ratio, peak airway pressure (Ppeak), plateau pressure (Pplat), total dynamic compliance (C), and the percentage of VT exhaled passively in the first second of expiration (V1.0%). Then the trachea was intubated and measurements were repeated as previously. Gas leak was calculated as the fraction (VTinsp- VTexp)/Vtinsp. VTinsp and VTexp did not differ significantly between the LMA or TT anesthesia at any time (P = 0.9318, P = 0.7071 for VTinsp and VTexp respectively), neither the Ppeak (P = 0.1382). Significant differences were found for Pplat (P = 0.000) and C (P = 0.0001). Individual comparisons showed a significant difference between the LMA Pplat at 5 min when compared with all the Pplat mean values recorded with the LMA or the TT (P < 0.05-0.01). The C mean value with the LMA at 5 min was significantly lower when compared with all the C mean values via the TT anesthesia (P < 0.05-0.01). Significant differences were found among the V1.0% measurements (P = 0.030) but not between individual comparisons. Leak was similar with the LMA or TT airway management. It is concluded that, in patients with normal airway pressure and compliance, PPV using the LMA is comparatively effective with the use of TT.