Prehospital Normoventilation in Critically Ill Anaesthetised Patients Cannot Be Reliably Monitored by Capnography—A Retrospective Observational Study

Background End‐tidal carbon dioxide capnography (EtCO 2 ) is widely used to guide intubated patients' ventilation. Current guidelines for prehospital advanced airway management assume a gradient of approximately 0.67 kPa between EtCO 2 and arterial carbon dioxide partial pressure (PaCO 2 ). However, concerns have been raised about the accuracy of capnography. We aimed to assess the agreement between EtCO 2 and PaCO 2 in different patient groups to see if EtCO 2 could be accurate enough to guide ventilation during prehospital care. Methods We carried out a retrospective study of all anaesthetised and intubated patients with a measured PaCO 2 by a single helicopter emergency medical services unit from 1 January 2014 to 31 December 2021. The patients were divided into five different patient groups based on clinical diagnosis: out‐of‐hospital cardiac arrest, trauma, intoxication, neurological conditions (including stroke) and other. The agreement between EtCO 2 and PaCO 2 in each group was assessed with Bland–Altman analysis. In addition, the percentage of patients with a higher PaCO 2 –EtCO 2 gradient than 0.67 kPa was calculated. Results In Bland–Altman analysis, the overall bias was 1.7 kPa (standard deviation = 1.6) with limits of agreement of −1.4 to 4.8 kPa. Out of 670, the PaCO 2 –EtCO 2 gradient was higher than 0.67 kPa in 530 (79.1% [75.9–82.0]) patients. 186/221 (84.2% [78.8–88.4]) in out‐of‐hospital cardiac arrest patients, 85/104 (81.7% [73.2–88.0]) in trauma patients, 146/197 (74.1% [67.6–97.7]) in neurological patients, 75/99 (75.8% [66.5–83.1]) in intoxicated patients and 38/49 (77.6% [64.1–87.0]) in other patients. The results are presented as n/nn (% [95% confidence interval]). Conclusions Our results show that for critically ill patients intubated in the prehospital setting, capnography is not accurate in guiding ventilation. Editorial Comment Capnography may be used to assess ventilation effect in intubated patients. In an intubated helicopter ambulance mixed‐diagnosis cohort end‐tidal carbon dioxide levers were assessed, compared to pCO 2 results from a point of care blood gas analysis device. The proportion of larger gaps between these two values in this mixed cohort is presented.