Extent, nature and consequences of adverse events: results of a retrospective casenote review in a large NHS hospital

Objectives: To estimate the extent, nature and consequences of adverse events in a large National Health Service ( NHS) hospital, and to evaluate the reliability of a two- stage casenote review method in identifying adverse events. Design: A two- stage structured retrospective patient casenote review. Setting: A large NHS hospital in England. Population: A random sample of 1006 hospital admissions between January and May 2004: surgery ( n = 311), general medicine ( n = 251), elderly ( n = 184), orthopaedics ( n = 131), urology ( n = 61) and three other specialties ( n = 68). Main outcome measures: Proportion of admissions with adverse events, the proportion of preventable adverse events, and the types and consequences of adverse events. Results: 8.7% ( n = 87) of the 1006 admissions had at least one adverse event ( 95% Cl 7.0% to 10.4%), of which 31% ( n = 27) were preventable. 15% of adverse events led to impairment or disability which lasted more than 6 months and another 10% contributed to patient death. Adverse events led to a mean increased length of stay of 8 days ( 95% Cl 6.5 to 9). The sensitivity of the screening criteria in identifying adverse events was 92% ( 95% Cl 87% to 96%) and the specificity was 62% ( 95% Cl 53% to 71%). Inter- rater reliability for determination of adverse events was good ( k = 0.64), but for the assessment of preventability it was only moderate ( k = 0.44). Conclusion: This study confirms that adverse events are common, serious and potentially preventable source of harm to patients in NHS hospitals. The accuracy and reliability of a structured two- stage casenote review in identifying adverse events in the UK was confirmed.