Associations of intraoperative end-tidal carbon dioxide concentrations with postoperative outcomes: is mechanical power next?

In an important patient-level analysis of two randomised controlled trials published in the British Journal of Anaesthesia, hypocapnia, as reflected by low end-tidal carbon dioxide (ETCO2) during surgery was associated with worse outcomes than normocapnia, with higher rates of postoperative pulmonary complications (PPCs). The results can be used by anaesthesiologists in the operating theatre to reduce the occurrence of PPCs by carefully determining ventilatory settings to avoid overventilation in patients, and by considering cardiopulmonary interactions. This involves reducing tidal volume and respiratory rate as far as possible while aiming for a normal-to-high ETCO2 (optimal cutoff to be determined). Previous trials assessing mechanical ventilation settings in the operating room have produced conflicting results. The answer might lie in the objective of ETCO2 monitoring, as a surrogate of partial pressure of carbon dioxide (PaCO2), which is strongly associated with mechanical power through ventilatory settings.