Metabolic effects of Carbon Dioxide (CO2) insufflation during laparoscopic surgery: changes in pH, arterial partial Pressure of Carbon Dioxide (PaCo2) and End Tidal Carbon Dioxide (EtCO2)

Abstract

Background: Acid base alterations occur during laparoscopy with carbon dioxide insufflation. The purpose of this study was to investigate the effects of low tidal volume ventilation on acid base status during pneumoperitonium.

Materials and Methods: 30 patients undergoing laparoscopic surgery under General Anaesthesia were ventilated with tidal volume of 6 ml/kg and respiratory rate of 12 breaths/minute. Arterial blood gas analysis was done before, during and after C0₂ pneumoperitoneum. Arterial haemoglobin oxygen saturation by pulse oximetry (SPO₂) and EtC0₂ were monitored continuously throughout the laparoscopy. Respiratory adjustments were done for EtCO₂ levels above 60mmHg or SPO₂ below 92% or adverse haemodynamic changes.

Results: low tidal volume ventilation during pneumoperitoneum resulted in a significant elevation in PaCO₂ (p<0.001) and a fall of pH (p <0.001), ion bicarbonate (HCO₃^-) (p = 0.011), and base excess (ABE) (p <0.001). A correlation was found between the EtCO₂ and PaCO₂ during pneumoperitoneum. Oxygenation was well maintained during pneumoperitoneum. No ventilatory adjustments were instituted on any of the patients as they maintained EtCO₂ below 60mmHg throughout pneumoperitoneum.

Conclusion: Ventilation with low tidal volume during pneumoperitoneum causes a mixed respiratory and metabolic acidosis. EtCO₂ is still a good non-invasive monitor for estimation of PaCO₂ during low tidal volume ventilation during pneumoperitoneum.