[Effect of mechanical ventilation with different tidal volumes on the respiratory function during general anesthesia]

To determine the effect of mechanical ventilation with different tidal volumes on the respiratory function during general anesthesia and to seek optimum way and parameters of mechanical ventilation during general anesthesia.

Forty ASA I-II patients scheduled for elective craniotomies in the supine position were included in this study. According to latin square design, the patients were randomly divided into 4 groups. Every group has its own tidal volume sequence. Each patient used 4 tidal volumes in turn. Every tidal volume maintained 30 minutes. The rate of mechanical ventilation was 15. But ECG, blood pressure, heart rate, SPO2, ETCO2, airway pressure, lung compliance, and blood gas analysis were continuously monitored.

A-aDO2, P(a-ET)CO2, P(PEAK), P(MEAN), P(PLAT), C(DYN), and C(STAT) significantly increased as the tidal volume increased (P<0.05). But ETCO2 and PaCO2 decreased as the tidal volume increased (P<0.05). PaO2, SPO2, MAP and HR had no significant difference between the 4 tidal volume groups(P>0.05).

The optimum tidal volume of mechanical ventilation is not 4 mL/kg at the rate of 15 respiratory rate during general anesthesia in the supine position because of a high arterial carbon dioxide tension. Yet 6-8 mL/kg is better for neurosurgical anesthesia. Increasing the tidal volume alone may not improve the respiratory function impairment during general anesthesia.