End-tidal to arterial carbon dioxide gradient is associated with increased mortality in patients with traumatic brain injury: a retrospective observational study

Abstract

Early definitive airway protection and normoventilation are key principles in the treatment of severe traumatic brain injury. These are currently guided by end tidal CO2 as a proxy for PaCO2. We assessed whether the difference between end tidal CO2 and PaCO2 at hospital admission is associated with in-hospital mortality. We conducted a retrospective observational cohort study of consecutive patients with traumatic brain injury who were intubated and transported by Helicopter Emergency Medical Services to a Level 1 trauma center between January 2014 and December 2019. We assessed the association between the CO2 gap—defined as the difference between end tidal CO2 and PaCO2—and in-hospital mortality using multivariate logistic regression models. 105 patients were included in this study. The mean ± SD CO2 gap at admission was 1.64 ± 1.09 kPa and significantly greater in non-survivors than survivors (2.26 ± 1.30 kPa vs. 1.42 ± 0.92 kPa, p < .001). The correlation between EtCO2 and PaCO2 at admission was low (Pearson's r = .287). The mean CO2 gap after 24 h was only 0.64 ± 0.82 kPa, and no longer significantly different between non-survivors and survivors. The multivariate logistic regression model showed that the CO2 gap was independently associated with increased mortality in this cohort and associated with a 2.7-fold increased mortality for every 1 kPa increase in the CO2 gap (OR 2.692, 95% CI 1.293 to 5.646, p = .009). This study demonstrates that the difference between EtCO2 and PaCO2 is significantly associated with in-hospital mortality in patients with traumatic brain injury. EtCO2 was significantly lower than PaCO2, making it an unreliable proxy for PaCO2 when aiming for normocapnic ventilation. The CO2 gap can lead to iatrogenic hypoventilation when normocapnic ventilation is aimed and might thereby increase in-hospital mortality.

Airway management in a Helicopter Emergency Medical Service (HEMS): a retrospective observational study of 365 out-of-hospital intubations

“…Injuries due to trauma seem to be the predominant reason for providing advanced airway management in many HEMS services around the globe [ 15 , 16 ]. Early definitive airway protection as well as normoventilation plays a key role in the recent literature on traumatic brain injury (TBI) [ 16 , 17 ]. This is in accordance with our data showing that TBI was the predominant indication for RSI among all indications.…”

American Association for the Surgery of Trauma/American College of Surgeons Committee on Trauma: Clinical protocol for damage-control resuscitation for the adult trauma patient

“…14 In one study, prehospital EtCO 2 was a better predictor of mortality than SBP or SI, 14 and in another, initial EtCO 2 effectively predicted poor outcome including when controlling for mechanism and ISS. 15 These associations have been confirmed in traumatic brain injury (TBI), 16 and for nonintubated, non-full trauma activation patients. 17 The physiologic underpinnings of EtCO 2 utility have been confirmed by correlating EtCO 2 in the emergently intubated trauma patient with noninvasive measures of cardiac output, 18 showing that the PaCO 2 -EtCO 2 difference is closely associated with outcome.…”

Management of traumatic brain injury: a narrative review of current evidence

“…A systematic review examined the association between ventilation strategies during the initial post-injury and resuscitation phase in patients with TBI [54]. Normocapnia (the definition of which varied between the six studies) was associated with a lower mortality, although neurological outcomes were not assessed, and some studies measured endtidal carbon dioxide which may not be reflective of PaCO 2 [55]. However, this suggests that pre-hospital emergency services that can undertake advanced airway interventions (such as tracheal intubation) may improve outcomes for patients with TBI, which is in line with the findings from retrospective analyses of UK trauma registries [56,57].…”