Reliability of the Cerebral Performance Category to classify neurological status among survivors of ventricular fibrillation arrest: a cohort study

BACKGROUND The Cerebral Performance Category (CPC) score is widely used in research and quality assurance to assess neurologic outcome following cardiac arrest. However, little is known about the inter- and intra-reviewer reliability of the CPC. METHODS We undertook an investigation to assess the inter-reviewer and source document reliability of the CPC among a cohort of survivors from out-of-hospital ventricular fibrillation cardiac arrest (n = 131) in a large metropolitan area between November 1, 2003 and December 31, 2005. Subjects with a CPC of 1 or 2 were classified as favorable outcome and those with CPC 3 or greater were classified as unfavorable outcome. One abstractor first used the discharge summary alone to determine the CPC. All 3 abstractors independently reviewed the entire hospital record. Reliability was assessed by determining the proportion of determinations that agreed between abstractors and the respective kappa statistics. We also evaluated the implications for determining survival with favorable neurological outcome when survival to hospital discharge was 20% and 30%. RESULTS When the entire hospital record was used to determine CPC, favorable neurologic outcome (CPC 1 or 2) was recorded in 92% by abstractor 1, 89% by abstractor 2, and 74% by abstractor 3. Agreement was 96% (kappa = 0.78) between abstractors 1 and 2, 84% (kappa = 0.49) between abstractors 2 and 3, 82% (kappa = 0.38) between abstractors 1 and 3. The 3-way kappa was 0.50. Agreement was 90% (kappa = 0.71) between the discharge summary alone and the entire hospital record. If the results from review of the entire record are applied to a circumstance where survival to discharge is 20%, favorable neurologic status would occur in 18.4% for abstractor 1, 17.8% for abstractor 2, and 14.8% for abstractor 3. For survival to hospital discharge of 30%, favorable neurologic status would occur in 27.6% for abstractor 1, 26.7% for abstractor 2, and 22.2% for abstractor 3. CONCLUSIONS In this cohort study of survivors of out-of-hospital ventricular fibrillation cardiac arrest, the use of the CPC to classify favorable versus unfavorable neurological status at hospital discharge produced variable inter- and intra-reviewer agreement. The findings provide useful context to interpret outcome evaluations that report CPC.