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 (HES) data linked to the national death registry to identify patients who underwent burr-hole drainage of CSDH in English NHS neurosurgical units between 1st April 2013 and 31st 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 (interquartile range [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.