Ventilation–perfusion distributions and gas exchange during carbon dioxide-pneumoperitoneum in a porcine model

Abstract

BackgroundCarbon dioxide (CO2)-pneumoperitoneum (PP) of 12 mm Hg increases arterial oxygenation, but it also promotes collapse of dependent lung regions. This seeming paradox prompted the present animal study on the effects of PP on ventilation–perfusion distribution (V/Q) and gas exchange. MethodsFourteen anaesthetized pigs were studied. In seven pigs, single photon emission computed tomography (SPECT) was used for spatial analysis of ventilation and perfusion distributions, and in another seven pigs, multiple inert gas elimination technique (MIGET) was used for detailed analysis of V/Q matching. SPECT/MIGET and central haemodynamics and pulmonary gas exchange were recorded during anaesthesia before and 60 min after induction of PP. ResultsSPECT during PP showed no or only poorly ventilated regions in the dependent lung compared with the ventilation distribution during anaesthesia before PP. PP was accompanied by redistribution of blood flow away from the non- or poorly ventilated regions. V/Q analysis by MIGET showed decreased shunt from 9 (sd 2) to 7 (2)% after induction of PP (P<0.05). No regions of low V/Q were seen either before or during PP. Almost no regions of high V/Q developed during PP (1% of total ventilation). Pao2 increased from 33 (1.2) to 35.7 (3.2) kPa (P<0.01) and arterial to end-tidal Pco2 gradient (Pae′co2) increased from 0.3 (0.1) to 0.6 (0.2) kPa (P<0.05). ConclusionsPerfusion was redistributed away from dorsal, collapsed lung regions when PP was established. This resulted in a better V/Q match. A possible mechanism is enhanced hypoxic pulmonary vasoconstriction.