Author: Alba Badell
Date of first publication: 22.07.2024
The authors' point? Targeting EtCO2 levels of 35–45 mmHg seems reasonable during prehospital care as lower levels are associated with a significant increase in 30-day mortality.
What is the association between prehospital end-tidal carbon dioxide (EtCO2) levels and mortality in patients with suspected severe traumatic brain injury (TBI)?
BRAIN-PROTECT is a multicenter prospective observational study focusing on the prehospital treatment of patients with severe TBI in the Netherlands.
The study included four Dutch physician-staffed helicopter emergency medical services (HEMS) and nine trauma centers. From February 2012 to December 2017, data was collected from patients with suspected severe TBI treated by participating HEMS services.
| Primary | All-cause mortality at 30 days |
| Secondary | Functional neurologic outcome at discharge assessed using the Glasgow Outcome Scale (GOS) |
| Inclusion criteria | Suspected severe TBI rather than confirmed TBI Prehospital GCS score of 8 or lower Transferral to one of the nine participating trauma centers after prehospital care |
| Exclusion criteria | Transferral to a non-participating trauma center (no follow-up data) Prehospital traumatic cardiopulmonary resuscitation No prehospital advanced airway management |
After advanced airway management, patients were usually mechanically ventilated or manually ventilated with a self-inflating bag, depending on the availability of a mechanical ventilator in the ambulance, the distance to the hospital, and the preference of the treating physician.
The following measurements and parameters were utilized in various analyses, including logistic regression, Cox proportional hazards regression, and subgroup analyses, to investigate associations between prehospital EtCO2 levels and outcomes such as 30-day mortality and survival time up to 1 year after trauma.
| Prehospital EtCO2 level | Recorded at three timepoints: 1. After HEMS arrival 2. After initial stabilization and airway management 3. Before arriving at the emergency department Only values from the second and third timepoints were considered as most patients did not undergo advanced airway management before HEMS arrival. |
| Vital parameters | Systolic blood pressure Heart rate Oxygen saturation (measured at the same time as EtCO2) |
| Injury severity | Injury severity score First GCS score |
| Additional analyses | First, second, lowest, and highest EtCO2 values per patient EtCO2 categorized into: 1. Hypocapnia (< 35 mmHg) 2. Normocapnia (35–44 mmHg) 3. Hypercapnia (≥ 45 mmHg) |
| Subgroup analyses | Confirmed TBI: head abbreviated injury score (HAIS) ≥ 3 Isolated TBI: HAIS ≥ 3, all other AIS ≤ 2 Symptoms of intracerebral herniation: Abnormal pupils, signs of elevated intracranial pressure on initial CT scan |
| Patients included | 1776 out of 2589 patients with suspected severe traumatic brain injury |
| Patient characteristics | Majority male Median age: 45 years [23, 65] Initial GCS: 4 |
| Outcome at 30 days | 66.8% of patients alive 40.6% recovered with moderate or good recovery at discharge (GOS 4–5) |
| EtCO2 measurements | Total of 2649 measurements available Moderate correlation between measurements at two time points Weak correlation between last EtCO2 measurement and first in-hospital PaCO2 |
| Ventilation after airway management | Most patients mechanically ventilated (61.4%) 35.4% manually ventilated with a self-inflating bag |
| Association between EtCO2 and mortality | L-shaped association observed Marked increase in mortality with EtCO2 levels below 35 mmHg No evident increase in mortality for high EtCO2 level |
| Hypocapnia vs. normocapnia | Hypocapnia is associated with approximately 90% increased odds of mortality (OR 1.89) compared to normocapnia (p < 0.001) |
| Hypercapnia vs. normocapnia | No significant association between hypercapnia and mortality was observed (p = 0.212) |
| Subgroup analyses | EtCO2 values < 35 mmHg associated with increased mortality in patients with confirmed TBI and isolated TBI Consistent results found in survival analyses and after multiple imputation |
At discharge, 40.6% of the patients who survived the initial injury had a functional neurologic outcome categorized as moderate or good recovery (GOS score of 4 or 5).
Hamilton Medical ventilators offer a range of features to support effective monitoring of end-tidal CO2, such as the ventilation mode INTELLiVENT-ASV and time-based or volumetric capnography. With these tools, healthcare professionals can measure and maintain EtCO2 levels within the recommended range of 35–45 mmHg for patients with severe traumatic brain injury (TBI).
The incorporation of time-based and volumetric capnography allows for continuous and accurate monitoring of EtCO2 levels, ensuring precise ventilation management. Being able to observe SBCO2 (single breath of CO2) helps identify ventilation/perfusion changes, lung heterogeneity, etc.
In addition, INTELLiVENT-ASV offers an automated solution that optimizes ventilation parameters by continuously adjusting them breath by breath. EtCO2 is thus kept within the target range, minimizing the risk of hypo- or hypercapnia while promoting better patient outcomes as concluded in this paper.
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