External validation of simplified out-of-hospital cardiac arrest and cardiac arrest hospital prognosis scores in a Japanese population: a multicentre retrospective cohort study

Background The novel simplified out-of-hospital cardiac arrest (sOHCA) and simplified cardiac arrest hospital prognosis (sCAHP) scores used for prognostication of hospitalised patients have not been externally validated. Therefore, this study aimed to externally validate the sOHCA and sCAHP scores in a Japanese population. Methods We retrospectively analysed data from a prospectively maintained Japanese database (January 2012 to March 2013). We identified adult patients who had been resuscitated and hospitalised after intrinsic out-of-hospital cardiac arrest (OHCA) (n=2428, age >= 18 years). We validated the sOHCA and sCAHP scores with reference to the original scores in predicting 1-month unfavourable neurological outcomes (cerebral performance categories 3-5) based on the discrimination and calibration measures of area under the receiver operating characteristic curves (AUCs) and a Hosmer-Lemeshow goodness-of-fit test with a calibration plot, respectively. Results In total, 1985/2484 (82%) patients had a 1-month unfavourable neurological outcome. The original OHCA, sOHCA, original cardiac arrest hospital prognosis (CAHP) and sCAHP scores were available for 855/2428 (35%), 1359/2428 (56%), 1130/2428 (47%) and 1834/2428 (76%) patients, respectively. The AUCs of simplified scores did not differ significantly from those of the original scores, whereas the AUC of the sCAHP score was significantly higher than that of the sOHCA score (0.88 vs 0.81, p<0.001). The goodness of fit was poor in the sOHCA score (v=8, chi(2) =19.1 and Hosmer-Lemeshow test: p=0.014) but not in the sCAHP score (v=8, chi(2 )=( )13.5 and Hosmer-Lemeshow test: p=0.10). Conclusion The performances of the original and simplified OHCA and CAHP scores in predicting neurological outcomes in successfully resuscitated OHCA patients were acceptable. With the highest availability, similar discrimination and good calibration, the sCAHP score has promising potential for clinical implementation, although further validation studies to evaluate its clinical acceptance are necessary.