Background: Pneumoperitoneum (PP) by CO2-inflation may result in acid-base alterations such ashypercarbia and respiratory acidosis. We studied in an animal preparation the effect of abdominal inflation by carbon dioxide (CO2) and air on gas exchange during PP.
Methods: 27 anesthetized pigs were allocated to 3 groups. PP was maintained either with 1/ CO2 or 2/ air or 3/ CO2 during intravenous natriumprusside infusion (SNP) (n=9 in each group). In 3 pigs in each group, SPECT was used for analysis of ventilation and perfusion distributions, in another 6 pigs MIGET was used for assessing V/Q matching. MIGET, SPECT and central haemodynamics and pulmonary gas exchange were recorded during anaesthesia and after 60 minutes of PP.
Results: CO2-PP but not Air-PP caused a shift of blood flow away from collapsed to aerated regions. SNP-PP shifted blood flow towards atelectatic areas of the lung. V/Q analysis by MIGET showed a decrease in shunt during CO2-PP (6±1% compared to baseline 9±2%, p<0.001) but an increase during SNP-PP (16±2%, p< 0.001) and no changes during Air-PP (10±2%). PaO2 increased from 266±21 to 305±20 mmHg (baseline to CO2-PP/p<0.01) and decreased to 240±24 mmHg during Air-PP and to 200±22 mmHg during SNP-PP. Arterial carbon dioxide (PCO2) increased only during CO2 and SNP- PP.
Conclusion: CO2-PP enhanced the shift of blood flow towards better ventilated areas of the lung compared to Air-PP. Moreover, SNP worsened the ventilation-perfusion match even more and blunted the effects previously seen with CO2. CO2 should therefore be the mediator of enhanced HPV during PP.