Reducing tidal volume does not affect oxygenation in ASA I-II patients during anesthesia

The aim of this study was to evaluate the need of high tidal volumes for me chanical ventilation during general anesthesia. We studied the effects of different tidal volumes (T1 baseline- 9.7 ml/kg, T2- 8.8 ml/kg, T3- 7.8 ml/kg and T4- 6.9 ml/kg) and minute ventilation on a rterial blood gases, airway pressures and arterial to end-tidal PCO2 differ ence in 69 adult ASA physical status I and II patients (Group A). Arterial oxygenation was also evaluated in 33 patients (Group B) in which the order of tidal volume steps was reversed. In Group A there were no significant changes in arterial oxygen tension, ox ygen saturation and arterial to end-tidal PCO2 difference during tidal volu me reduction. Comparison of T1-T2, T2-T3 and T3-T4 showed significant diffe rences in arterial carbon dioxide tension (29.7 +/- 4.7 mmHg, 31.7 +/- 5.3 mmHg, 33.5 +/- 5.6 mmHg, 34.6 +/- 5.6 mmHg) (p < 0.001, p < 0.001 and p < 0 .05, respectively), end-tidal PCO2 (p < 0.001, p < 0.001 and p < 0.01, resp ectively), peak (26.3 +/- 6.4 cmH(2)O, 23.5 +/- 5.7 cmH(2)O, 20.8 +/- 4.9 c mH(2)O, 18.5 +/- 4.6 cmH(2)O) (p < 0.001 for all comparisons), plateau (p < 0.001 for all comparisons) and mean (p < 0.001,p < 0.001 and p < 0.05, res pectively) airway pressures. Arterial pH showed a significant difference be tween T1-T2 (p < 0.001). There were no significant changes in arterial oxygen tension and oxygen sat uration in Group B. Comparison of those parameters between equal tidal volu me steps in Groups A and B did not show a significant difference. In conclu sion, we suggest that lower tidal volumes of 7 or 8 ml/kg lead to more favo rable arterial carbon dioxide tension, pH and airway pressure values withou t having any detrimental effects on arterial oxygenation or on the efficacy of ventilation during general anesthesia.