Both end tidal CO₂ (ETCO₂) and cerebral oxygen saturations (rSO₂) have been studied to determine their ability to monitor the effectiveness of CPR and predict return of spontaneous circulation (ROSC). We compared the accuracy of ETCO₂ and rSO₂ at predicting ROSC in ED patients with out-of-hospital cardiac arrest (OHCA).

We performed a prospective, observational study of adult ED patients presenting in cardiac arrest. We collected demographic and clinical data including age, gender, presenting rhythm, rSO₂, and ETCO₂. We used receiver operating characteristic curves to compare how well rSO₂ and ETCO₂ predicted ROSC.

225 patients presented to the ED with cardiac arrest between 10/11 and 10/14 of which 100 had both rSO₂ and ETCO₂ measurements. Thirty three patients (33%) had sustained ROSC, only 2 survived to discharge. The AUCs for rSO₂ and ETCO₂ were similar (0.69 [95% CI, 0.59–0.80] and 0.77 [95% CI, 0.68–0.86], respectively), however, rSO₂ and ETCO₂ were poorly correlated (0.12, 95% CI, −0.08–0.31). The optimal cutoffs for rSO₂ and ETCO₂ were 50% and 20mm Hg respectively. At these cutoffs, ETCO₂ was more sensitive (100%, 95% CI 87–100 vs. 48%, 31–66) but rSO₂ was more specific (85%, 95% CI, 74–92 vs. 45%, 33–57).

While poorly correlated, rSO₂ and ETCO₂ have similar diagnostic characteristics. ETCO₂ is more sensitive and rSO₂ is more specific at predicting ROSC in OHCA.