The Use of Capnometry in Prehospital Intubation and Association with 30-Day Mortality: A Nationwide Registry Study

Capnometry is the gold standard for confirming endotracheal tube placement, yet the implementation in prehospital airway management remains inconsistent. This study aimed to investigate the use of capnometry during prehospital endotracheal intubation in Denmark, and to evaluate the association between capnometry use and 30-day mortality.

We conducted an observational study design with a nationwide retrospective registry-based cohort of prehospital endotracheal intubations in Denmark using data from January 1, 2016, to December 31, 2021. Data were obtained from the Danish Prehospital Medical Record system and linked to the Danish Civil Registration System for mortality outcomes. Capnometry use was defined as at least one recorded end-tidal carbon dioxide (EtCO₂) value >0. The primary outcome was capnometry use. Secondary outcomes included 30-day mortality and EtCO₂ values categorized as eucapnic (4.0-6.0 kPa), hypocapnic (<4.0 kPa), hypercapnic (>6.0 kPa). Associations with mortality were assessed using multivariable logistic regression adjusted for age, sex, symptom category, cardiopulmonary resuscitation, and time of day.

A total of 8,720 intubations in 8,625 patients were identified, and only the first intubation per patient was included. Capnometry was used in 6,926 of 8,625 cases (80.3%) and increased from 75.4% in 2016 to 82.6% in 2021 (IRR 1.014, 95% CI 1.0004-1.0284; p = 0.04). Thirty-day mortality was 62.6%. Capnometry use was more frequent among survivors (87% vs. 76%, p < 0.001) and was independently associated with lower mortality (adjusted OR 0.52, 95% CI 0.46-0.60). Unadjusted 30-day mortality was higher for patients without capnometry use (74.8% vs. 59.6%; 1,270/1,699 vs. 4,131/6,926; p < 0.001). Abnormal EtCO₂ values were common: hypocapnic in 38.3%, hypercapnic in 19.0%, both in 22.6%, and only 10.1% had values within the normal range. Mortality was highest in patients with recorded hypocapnic values (70.4%; adjusted OR 2.67, 95% CI 2.20-3.24) and lowest in those with normal values (36.7%).

Capnometry use during prehospital intubation increased over time but remained incomplete and was independently associated with lower 30-day mortality. Abnormal EtCO₂ values were frequent and associated with worse outcomes, particularly low EtCO₂ values. These findings support adherence to current recommendations for routine EtCO₂ monitoring in prehospital airway management.