Effects of adding small amounts of oxygen to a carbon dioxide–pneumoperitoneum of increasing pressure in rabbit ventilation models

Objective To evaluate the metabolic consequences of the addition of oxygen to the CO2 -pneumoperitoneum. Design Prospective randomized study in rabbits. After 30 minutes of ventilation pneumoperitoneum was maintained for 90 minutes with pure CO2 or CO2 with 2% or 6% of oxygen. The intraperitoneal pressure was increased from 10 to 15 and 20 mm Hg every 30 minutes. Ventilation rate was either fixed or a progressive hyperventilation. End points were changes in arterial blood gases (P co2 , P o2 ), pH, acid-base balance (actual base excess [ABE], standard bicarbonate [SBC], standard base excess [SBE], hydrogen carbonate [HCO3− ], concentration of total carbon dioxide [T co2 ]); oxygen and oximetry (oxyhemoglobin [O2 Hb], oxygen saturation [S o2 ], reduced hemoglobin [RHb], total oxygen concentration [T o2 ], and oxygen tension at half saturation assessing hemoglobin oxygen affinity [p50]); and lactate concentrations assayed every 15 minutes. Setting University research center. Animals Twenty-four adult female New Zealand white rabbits. Intervention(s) Anesthesia, mechanical ventilation, and pneumoperitoneum. Result(s) The effects of CO2 -pneumoperitoneum on all end points increased with the elevated intraperitoneal pressure and were more pronounced when ventilation was fixed. Changes were less when 2% or 6% of oxygen had been added to the CO2 -pneumoperitoneum. With use of logistic regression, the addition of oxygen, intraperitoneal pressure, and ventilation were found to be independent variables affecting P co2 , pH, ABE, SBE, HCO3− , O2 Hb, S o2 , p50, and end-tidal CO2. Conclusion(s) The metabolic consequences of the combined effect of increased intraperitoneal pressure and CO2 -pneumoperitoneum were less when 2% to 6% of oxygen was added or when animals were hyperventilated. We suggest that metabolic and mesothelial hypoxemia caused by CO2 absorption can be reduced by adding small amounts of oxygen and by hyperventilation.