![]() ![]() Tidal volume was set to 6 ml/kg, and I : E ratio was adjusted at the onset of pneumoperitoneum. One hundred patients undergoing gynaecologic laparoscopic surgery were randomly assigned to one of four groups: conventional inspiratory-to-expiratory (I : E) ratio (Group 1 : 2), I : E ratio of 1 : 1 (Group 1 : 1), 2 : 1 (Group 2 : 1), or 1 : 2 with external positive end-expiratory pressure (PEEP) of 5 cmH2 O (Group 1 : 2 PEEP). We supposed that prolonged inspiratory time can improve gas exchange at lower airway pressure. Haldane effect magnified the shunt component of VD/VTCO2 but reduced the influence of midrange VA/Q heterogeneity.Laparoscopic surgery performed with a patient in the Trendelenburg position is known to have adverse effects on pulmonary gas exchange and respiratory mechanics. The increase in VD/VTCO2 that occurred with higher PEEP levels was due to increased ventilation to high VA/Q regions and a larger anatomic dead space. The decrease in VD/VTCO2 at 5 or 10 cmH2O PEEP was due to reductions in shunt and midrange VA/Q heterogeneity. It decreased with 5 or 10 cmH2O PEEP but increased progressively at higher PEEP levels. PEEP of 5, 10, 15, and 20 cmH2O was applied in random sequence. We used the multiple inert gas elimination technique to assess the effect of positive end-expiratory pressure (PEEP) on each of these components of VD/VTCO2 in 14 pentobarbital-anesthetized dogs with increased permeability edema induced by infused oleic acid. In acute increased-permeability edema, the Bohr physiological dead space (VD/VTCO2) can be influenced by changes in anatomic dead space, ventilation-perfusion (VA/Q) heterogeneity, shunt, and the Haldane effect. ![]()
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