Days alive and out of hospital after burr-hole drainage for chronic subdural haematoma: a national cohort study using Hospital Episode Statistics in England

OBJECTIVES: The objective of this study was to investigate the utility of the days alive and out of hospital (DAOH) metric within a cohort of patients undergoing burr-hole drainage of a chronic subdural haematoma (CSDH). We evaluate the validity of the DAOH metric in a national CSDH cohort and examine how the DAOH metric compares to its constituent outcomes (mortality and hospital bed days) at an organisational level. METHODS: Retrospective cohort study using Hospital Episode Statistics data linked to the national death registry to identify patients who underwent burr-hole drainage of CSDH in English National Health Service neurosurgical units between 1 April 2013 and 31 March 2020. Construct validity was assessed by measuring the patterns of DAOH across categories of known perioperative risk factors. Variation between units in the risk-adjusted values for DAOH, postoperative mortality and days in hospital was explored using funnel plots. Linear regression and logistic regression were used to derive the risk-adjusted rates. RESULTS: Overall, 16 450 patients who underwent at least one burr-hole drainage of CSDH were identified during the time period. The median 30-day DAOH was 16 (IQR, 0-24); the median for the 90-day DAOH was 74 (42-84), and was better at measuring the complete stay associated with the index admission. Worse 90-day DAOH values were associated with older age, increasing comorbidities and greater frailty. Risk-adjusted 90-day DAOH values for neurosurgical units varied more markedly than for its constituent outcomes. CONCLUSIONS: The 90-day DAOH looks to be a valid outcome metric for patients undergoing burr-hole drainage for CSDH that is feasible to derive using national hospital data. Future work should explore how to estimate a minimally important clinical difference for DAOH and evaluate its utility as an outcome measure.