Patterns of care and outcomes following external ventricular drain placement: Insights from the England HES administrative data set.

Objectives: To evaluate the outcomes of patients undergoing external ventricular drain (EVD) insertion in England, focusing on the timing of EVD relative to index neurosurgical procedures, and to assess the implications for benchmarking and performance monitoring between neurosurgical centres. Methods: We conducted a retrospective cohort study using Hospital Episode Statistics. Adult patients (≥16 years) undergoing EVD insertion between April 2013 and March 2020. Outcomes included 90-day mortality, length of stay (LOS), and emergency readmission within 30 days. Multivariable logistic regression was used for mortality and readmission, with adjustment for age, admission method, comorbidity (RCS Charlson index), and neurosurgical clinical category. A quantile regression model was performed with LOS as the outcome. Results: The cohort comprised 10,239 patients. Crude 90-day mortality was 26.7 % overall, highest in the EVD-only group (43.2 %) and lowest when EVD was performed with an index procedure (19.7 %). Mortality rose with age, comorbidity, emergency admission, and was highest in Oncology, Vascular, and General & Trauma categories. The final risk-adjustment model showed good discrimination (AUC 0.71) and reduced apparent inter-unit variation in mortality. Conclusions: Our findings demonstrate that treating all EVD insertions as a single cohort obscures clinically meaningful differences in patient trajectories and leads to misleading comparisons of outcomes. Although the absence of detailed severity markers in administrative data means that conclusions about quality of care must be interpreted cautiously, this study illustrates how carefully constructed, clinically meaningful cohorts can transform the interpretation of common neurosurgical procedures.