Pressure support ventilation versus continuous positive airway pressure with the laryngeal mask airway - A randomized crossover study of anesthetizedadult patients

Background: The authors tested the hypothesis that pressure support ventila tion (PSV) provides more effective gas exchange than does unassisted ventil ation with continuous positive ait-way pressure (CPAP) in anesthetized adul t patients treated using the laryngeal mask airway. Methods: Forty patients were randomized to two equal-sized crossover groups , and data were collected before surgery. In group 1, patients underwent CP AP, PSV, and CPAP in sequence. In group 2, patients underwent PSV, CPAP, an d PSV in sequence. PSV comprised positive end expiratory pressure set at 5 cm H2O and inspiratory pressure support set at 5 cm H2O above positive end expiratory pressure. CPAP was set at 5 cm H2O. Each ventilatory mode was ma intained for 10 min. The following data were recorded every minute for the last 5 min of each ventilatory mode and the average reading taken: end tida l carbon dioxide, oxygen saturation, expired tidal volume, leak fraction, r espiratory rate, noninvasive mean arterial pressure, and heart rate. Results: In both groups, PSV showed lower end tidal carbon dioxide (P < 0.0 01), higher oxygen saturation, (P < 0.001), and higher expired tidal volume (P < 0.001) compared with CPAP. In both groups, PSV had similar leak fract ion, respiratory rate, mean arterial pressure, and heart rate compared with CPAP, In group 1, measurements for CPAP were similar before and after PSV, In group 2, measurements for PSV were similar before and after CPAP. Conclusion: The authors concluded that PSV provides more effective gas exch ange than does unassisted ventilation with CPAP during LMA anesthesia while preserving leak fraction and hemodynamic homeostasis.