Previous research found that after surviving cardiac arrest initially, the arterio-alveolar carbon dioxide gradient (ΔCO2) predicted in-hospital death. For a study, researchers assessed ΔCO2 as a predictor for a favorable neurological outcome in their sample since early outcome predictors were critically needed.

From their resuscitation database, they retrospectively examined all patients ≥18 years who experienced non-traumatic in- and outpatient cardiac arrest in 2018. Excluded patients were those without advanced airway management, with inadequate data, or without spontaneous circulation returning. From the patient’s records, the initial arterial pCO2 upon admission and the etCO2 in mmHg at the time of blood sample were noted. Then, they estimated the CO2 (pCO2 – etCO2). With separation at the median, CO2 was dichotomized into low and high groups for baseline analysis. The main goal was to achieve a good neurological result on day 30, as measured by Cerebral Performance Category 1-2. The secondary objective was survival for 30 days.

A total of 128 patients out of 302 that were screened were still qualified for analysis. Both 30-day survivors (12.5 mmHg vs. 20.0 mmHg, P=0.001) and 30-day survivors with favorable neurological outcomes (12.2 mmHg vs. 18.8 mmHg, P=0.009) had reduced ΔCO2 levels. A cardiac etiology of arrest was less frequently detected in individuals with elevated ΔCO2. They had lower pO2 levels but greater levels of pCO2 and blood lactate, which led to lower blood pH and HCO3levels upon admission. They also had higher body mass index, longer resuscitation times, larger doses of epinephrine, and lower pO2 levels. ΔCO2 was linked to a 30-day neurological outcome in a crude binary logistic regression analysis (OR=1.041 per mmHg of ΔCO2, 95% CI 1.008-1.074, P=0.014). After being adjusted for age, sex observed arrest, and shocking initial rhythm, this connection remained. However, ΔCO2 lost its relationship when the length of resuscitation or the total dose of epinephrine was included in the model.

After successful resuscitation, ΔCO2 at admission was linked to a 30-day survival rate and a positive neurological prognosis. However, rather than serving as a standalone outcome predictor, a greater ΔCO2 may serve as a proxy for poor resuscitation settings.