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Multicenter Study
. 2023 May;49(5):491-504.
doi: 10.1007/s00134-023-07012-z. Epub 2023 Apr 19.

Association between prehospital end-tidal carbon dioxide levels and mortality in patients with suspected severe traumatic brain injury

Sebastiaan M Bossers  1 , Floor Mansvelder  2 , Stephan A Loer  2 , Christa Boer  2 , Frank W Bloemers  3 , Esther M M Van Lieshout  4 , Dennis Den Hartog  4 , Nico Hoogerwerf  5   6 , Joukje van der Naalt  7 , Anthony R Absalom  8 , Lothar A Schwarte  2   9 , Jos W R Twisk  10 , Patrick Schober  2   9 ; BRAIN-PROTECT Collaborators
Collaborators, Affiliations
Multicenter Study

Association between prehospital end-tidal carbon dioxide levels and mortality in patients with suspected severe traumatic brain injury

Sebastiaan M Bossers et al. Intensive Care Med. 2023 May.

Abstract

Purpose: Severe traumatic brain injury is a leading cause of mortality and morbidity, and these patients are frequently intubated in the prehospital setting. Cerebral perfusion and intracranial pressure are influenced by the arterial partial pressure of CO2 and derangements might induce further brain damage. We investigated which lower and upper limits of prehospital end-tidal CO2 levels are associated with increased mortality in patients with severe traumatic brain injury.

Methods: The BRAIN-PROTECT study is an observational multicenter study. Patients with severe traumatic brain injury, treated by Dutch Helicopter Emergency Medical Services between February 2012 and December 2017, were included. Follow-up continued for 1 year after inclusion. End-tidal CO2 levels were measured during prehospital care and their association with 30-day mortality was analyzed with multivariable logistic regression.

Results: A total of 1776 patients were eligible for analysis. An L-shaped association between end-tidal CO2 levels and 30-day mortality was observed (p = 0.01), with a sharp increase in mortality with values below 35 mmHg. End-tidal CO2 values between 35 and 45 mmHg were associated with better survival rates compared to < 35 mmHg. No association between hypercapnia and mortality was observed. The odds ratio for the association between hypocapnia (< 35 mmHg) and mortality was 1.89 (95% CI 1.53-2.34, p < 0.001) and for hypercapnia (≥ 45 mmHg) 0.83 (0.62-1.11, p = 0.212).

Conclusion: A safe zone of 35-45 mmHg for end-tidal CO2 guidance seems reasonable during prehospital care. Particularly, end-tidal partial pressures of less than 35 mmHg were associated with a significantly increased mortality.

Keywords: Carbon dioxide; Critical care; Endotracheal intubation; Traumatic brain injury; Ventilation.

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Conflict of interest statement

SMB reported receiving grants from Achmea Healthcare Foundation during the conduct of the study. ARA reported receiving grants and personal fees from Becton Dickson and The Medicines Company; grants from Draeger; sponsor-initiated and funded phase 1 research from Rigel; and personal fees from PAION, Janssen Pharma, Ever Pharma, and Philips outside the submitted work. PS reported receiving grants from Dutch Brain Foundation and Achmea Healthcare Foundation during the conduct of the study. No other disclosures were reported.

Figures

Fig. 1
Fig. 1
Patient flow diagram
Fig. 2
Fig. 2
Prehospital ETCO2 values and predicted mortality—unadjusted analysis. Association between prehospital end-tidal CO2 values (regression model based on 2505 ETCO2 values observed after advanced airway management at two time points in 1342 patients; see text for details) and predicted 30-day mortality. This analysis does not adjust for confounders but does adjust for the time point of the end-tidal CO2 measurement. The figure can be interpreted as the expected probability of mortality given the first recorded ETCO2 value during prehospital ventilation. The curve for the second measurement time point is virtually identical (not shown)
Fig. 3
Fig. 3
Prehospital ETCO2 values and predicted mortality—multivariable analysis. Prehospital end-tidal CO2 values measured after advanced airway management versus predicted 30-day mortality, after multivariable correction. The multivariable model is based on 1504 ETCO2 measurements in 836 patients and included the time point of the end-tidal CO2 measurement, age (spline variable), sex, ASA score, systolic blood pressure (spline variable), heart rate (spline variable), oxygen saturation (spline variable), Injury Severity Score (spline variable), first Glasgow Coma Scale score, HEMS service involved in the treatment, and distance between incident scene and trauma hospital (spline variable). As the plotted curve depends on the levels or values of all covariates in the model, this figure is just an example in which covariates were fixed at their mode (categorical variables) or mean (continuous variables) to obtain an estimate for the “average” patient, namely male gender, age 45 years, ISS 27, systolic blood pressure 131 mmHg, heart rate 95 beats per minute, ASA I, GCS 3, distance to hospital 28.6 km, and treated by the HEMS service that contributed most patients to the dataset. Moreover, as the time point of ETCO2 measurement was also included in the model, the figure shows the expected adjusted probability of mortality given the first recorded ETCO2 value after airway management. The curve for the second measurement time point is virtually identical (not shown)
Fig. 4
Fig. 4
Kaplan–Meier plots of the estimated survival function (up to 1 year after the trauma) per ETCO2 category based on values measured after advanced airway management at two time points (time point 1 is the first recorded ETCO2 value after advanced airway management; time point 2 is before arrival at the emergency department); see text for details
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Comment in

References

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