[Effects of pressure support ventilation (PSV) or PSV+PEEP on the respiratory function during general anesthesia under spontaneous ventilation].

This study was performed to examine the hypothesis that PSV with PEEP compared to spontaneous breathing with a circle anesthesia system may have beneficial effects on gas exchange and work of breathing during inhalational anesthesia. Nine patients (age; 58 +/- 20 yr) scheduled to receive general anesthesia for orthopedic (n = 3) or ENT (n = 6) surgery were randomly assigned in a triple cross-over manner to breathe with a standard anesthesia circle system, 5 cmH2O PSV, and 5 cm H2O PSV above 5 cmH2O PEEP. General anesthesia was induced with thiamylal (5 mg.kg-1) and succinylcholine (1 mg.kg-1), followed by tracheal intubation. General inhalation anesthesia was maintained with 1% isoflurane and nitrous oxide in 40% oxygen. Patients were permitted to breathe spontaneously. A BiPAP-S Ventilatory Support System was connected to a standard anesthesia machine instead of a reservoir bag to deliver PSV or PSV with PEEP. Respiratory parameters were measured with a C-P 100 Pulmonary Monitor. After breathing for 20 minutes with the assigned mode, measurements and blood gas sampling were performed. Statistical analysis was performed with ANOVA. There were no statistical differences in PaO2 within the three groups (table). PaCO2 was lower during PSV+PEEP, but the difference was not significant. This level of PSV or PSV with PEEP may have little beneficial effects on gas exchange in our study condition. The mean WOBp was smaller in the PSV with PEEP group but the difference was not statistically significant.