To date, several scores that predict the prognosis of patients with cardiac arrest have been published; however, no study has used the same patient group to verify the accuracy of each score at one time. The present study was the first to simultaneously validate various cardiac arrest prognostic scores. All prognostic scores that were evaluated in the present study had a sufficiently high predictive ability. Among them, the NULL-PLEASE score could be easily calculated in various OHCA patients, including those without bystander witnesses. Furthermore, the NULL-PLEASE score had a high predictive ability for good and poor neurological outcome in patients with bystander-witnessed OHCA.
Previous studies have revealed various factors, such as older age, cardiac arrest occurring at home, initial rhythm other than ventricular tachycardia/ventricular fibrillation, longer duration of no flow, longer duration of low flow, treatment with adrenaline (epinephrine), pupillary response, and a serum lactate level, as prognostic factors for OHCA patients [16–20]. Despite the prognosis scores proposed using these predictors [4–9], prognostication of OHCA patients remains challenging, and no single risk-assessment tool has been recommended for the prognostic classification of OHCA patients. Although various prognostic scores have been reported, the target patients were different in each instance [4–9]. For example, the targets for the NULL-PLEASE score were all OHCA patients, whereas those for the OHCA and CAHP scores were restricted to bystander-witnessed OHCA patients [4, 6]. Furthermore, the targets of CAST and rCAST scores were restricted to OHCA patients in whom therapeutic hypothermia was induced [10, 11]. However, where possible, we were able to evaluate the prognostic scores in various OHCA patient subgroups, regardless of the original targets.
The prognostic scores require various variables for their calculation. Although no-flow time is required in OHCA and CAHP scores, the variable cannot be obtained in OHCA patients without bystander witnesses [4, 6]. Therefore, OHCA and CAHP scores could not be calculated in OHCA patients without bystander witnesses [4, 6]. In addition, some scores require information that may be difficult to obtain, such as medical history, neurological findings, and findings of brain computed tomography [5, 7, 9, 10]. For these reasons, score calculation is often complicated and/or impossible. In the present study, the OHCA score was the simplest, whereas the CAST score was the most troublesome.
We examined the accuracy of the aforementioned predictive scores across all OHCA patients and various subgroups. As a result, large differences were not observed among these predictive scores. However, the NULL-PLEASE score had a high, comprehensive predictive ability in all OHCA patients and various subgroups. Furthermore, it had a high predictive ability for good and poor neurological outcome in patients with bystander-witnessed OHCA. Moreover, the NULL-PLEASE score can apply to various OHCA patients because all the variables required to calculate it can be easily collected in clinical settings. Therefore, the NULL-PLEASE score is a useful predictive score in various clinical settings.
Originally, the CAST and rCAST scores were targeted at OHCA patients in whom therapeutic hypothermia was induced [10, 11]. In clinical settings, OHCA patients who have regained consciousness or are strongly predicted to have a poor prognosis tend to be excluded from therapeutic hypothermia. Therefore, the characteristics of OHCA patients who undergo therapeutic hypothermia tend to be restrictive. Furthermore, in OHCA patients who underwent therapeutic hypothermia, the prior probability for good or poor neurological outcome was completely different from that in all OHCA patients. In the present study, although CAST and rCAST scores had high predictive ability in OHCA patients who underwent therapeutic hypothermia, CAST and rCAST scores did not in other OHCA patients. These results were likely to be affected by the differences in the aforementioned prior probability.
Although CAST and rCAST scores can be calculated online (http://www.castscore.sakura.ne.jp/), other predictive scores cannot. Furthermore, almost all variables required to calculate predictive scores were the same. Therefore, we created a website to conveniently calculate and compare multiple prognostic scores for OHCA patients (https://hokudai-qq.com/score). Comparing different scores simultaneously and selecting the appropriate score for patients with cardiac arrest will be helpful in clinical settings.
This study was conducted retrospectively in a single institution, and the number of target patients was small. In addition, there was potential for selection bias and confounding due to unknown or unmeasured variables.