Prognostic values of blood pH and lactate levels in patients resuscitated from out-of-hospital cardiac arrest

Abstract

Aim: Early prediction of prognosis after out-of-hospital cardiac arrest (OHCA) remains difficult. High blood lactate or low pH levels may be associated with poor prognosis in OHCA patients, but these associations remain controversial. We compared blood lactate and pH levels in OHCA patients transferred to our hospital to measure their prognostic performance.

Methods: We investigated the associations between blood lactate and pH levels on admission and neurological outcomes in 372 OHCA patients who had a return of spontaneous circulation.

Results: Of the 372 OHCA patients, 31 had a favorable neurological outcome. Blood lactate levels were lower in patients with a favorable outcome than in those with an unfavorable outcome, but this difference did not reach statistical significance (82 ± 49 vs. 96 ± 41 mg/dL). However, pH levels were significantly higher in patients with a favorable outcome than in those with an unfavorable outcome (7.26 ± 0.16 vs. 6.93 ± 0.19, P < 0.001). The relative cumulative frequency distribution curve analysis showed the optimal cut-off points of lactate and pH to be approximately 80 mg/dL and 7.05, respectively. Sensitivity and specificity to predict a favorable outcome were 61% and 64% for lactate <80 mg/dL and 84% and 80% for pH >7.05, respectively. Areas under receiver-operating characteristic curves were significantly larger for pH than for lactate levels (P < 0.001). In multivariate analysis, pH >7.05 was an independent predictor for a favorable outcome.

Conclusion: After OHCA, patients with a favorable outcome had lower lactate and higher pH levels than those with an unfavorable outcome, but pH level was a much better predictor for neurological outcome than lactate levels.

Keywords: Blood pH; lactate; out‐of‐hospital cardiac arrest; predictors; prognosis.

Figure 1

Relative cumulative frequency distribution curves for the cut‐off points of blood lactate and pH levels in 372 patients with out‐of hospital cardiac arrest who had a return of spontaneous circulation. The curves indicate that optimal cut‐off points of lactate and pH levels for a favorable neurological outcome were approximately 80 mg/dL and 7.05, respectively. The arrows indicate the optimal cut‐off points of lactate and pH levels. The arrowhead in the lower figure suggests that no patient with a favorable outcome had a pH level <6.95.

Figure 2

Receiver–operating characteristic curves of lactate and pH levels for the comparison of predictive abilities of neurological outcome in 372 patients with out‐of hospital cardiac arrest who had a return of spontaneous circulation. The area under the curve for pH levels was 0.91 (95% confidence interval, 0.87–0.95), which was significantly larger than that for lactate levels (0.62; 95% confidence interval, 0.51–0.74) (P < 0.001).