Effects of a 1:1 inspiratory to expiratory ratio on respiratory mechanics and oxygenation during one-lung ventilation in the lateral decubitus position

Prolonged inspiratory to expiratory (I:E) ratio ventilation may have both positive and negative effects on respiratory mechanics and oxygenation during one-lung ventilation (OLV), but definitive information is currently lacking. We therefore compared the effects of volume-controlled ventilation with I:E ratios of 1:1 and 1:2 on respiratory mechanics and oxygenation during OLV. Fifty-six patients undergoing thoracoscopic lobectomy were randomly assigned volume-controlled ventilation with an I:E ratio of 1:1 (group 1:1, n=28) or 1:2 (group 1:2, n=28) during OLV. Arterial and central venous blood gas analyses and respiratory variables were recorded 15 minutes into two-lung ventilation, at 30 and 60 minutes during OLV, and 15 minutes after two-lung ventilation was re-initiated. Peak and plateau airway pressures in cmH(2)O [standard deviation] during OLV were significantly lower in group 1:1 than in group 1:2 (P<0.01) (19 [3] and 23 [4]; 16 [3] and 19 [5], respectively). The arterial to end-tidal carbon dioxide tension difference was significantly lower in group 1:1 than in group 1:2 (P<0.01), (0.5 [0.3] and 1.1 [0.5]). There were no significant differences in PaO2 during OLV between the two groups (OLV30, P=0.856; OLV60, P=0.473). In summary, volume-controlled ventilation with an I:E ratio of 1:1 reduced peak and plateau airway pressures improved dynamic compliance and efficiency of alveolar ventilation, but it did not improve arterial oxygenation in a substantial manner. Furthermore, the associated increase in mean airway pressure might have reduced cardiac output, resulting in a lower central venous oxygen saturation.