The effect of type of anaesthetic on delirium after surgery for acute hip fracture: An instrumental variable analysis to assess causation

Jan 6, 2025Anaesthesia and intensive care

How Different Types of Anesthesia May Affect Delirium After Emergency Hip Fracture Surgery

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Abstract

Of 35,252 patients, 40.6% who received general anaesthesia developed delirium compared to 35.7% who received spinal or regional anaesthesia.

General anaesthesia was used in 72.9% of the patients undergoing hip fracture surgery.
Patients receiving general anaesthesia had an odds ratio (OR) of 1.23 for developing delirium compared to those receiving spinal or regional anaesthesia.
After controlling for known confounders, the odds of delirium with general anaesthesia increased slightly (OR 1.14).
Instrumental variable analysis indicated no statistically significant difference in delirium rates between the anaesthesia groups (OR 1.03).
A weak association was observed between general anaesthesia and postoperative delirium, but no causal link was established.

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Delirium is the most common in-hospital complication affecting older adults with acute hip fractures. Current evidence demonstrates inconsistent associations between anaesthetic type for acute hip fracture surgery and postoperative delirium. Using the Australian and New Zealand Hip Fracture Registry database, we conducted a retrospective cohort study of patients aged 50 years and over who underwent acute hip fracture surgery between 2015 and 2020. The incidence of delirium in patients who received general anaesthesia alone or combined with a regional technique, versus those who received spinal or regional anaesthesia was assessed. Multivariable multilevel logistic regression was used to test associations between anaesthetic type and delirium controlling for known confounders. Finally, given hospital variation in preference for anaesthetic type, an instrumental variable analysis was performed to include the effect of both known and unknown confounding. Of 35,252 patients, 25,682 (72.9%) patients received general anaesthesia, and 9570 (27.2%) patients received spinal or regional anaesthesia for their hip fracture surgery. A higher proportion of patients who received general anaesthesia developed delirium than those who received spinal or regional anaesthesia (40.6% vs. 35.7%, odds ratio (OR) 1.23, 95% confidence intervals (CI) 1.18 to 1.30, < 0.0001). After adjusting for known confounders, general anaesthesia patients were at slightly increased odds of developing delirium (OR 1.14, 95% CI 1.04 to 1.25, = 0.0052). However, the instrumental variable analysis found no statistically significant difference between groups (OR 1.03, 95% CI 0.99 to 1.07, = 0.141). Therefore, while a weak association was found between general anaesthesia exposure and postoperative delirium, an instrumental variable analysis to compensate for unmeasured confounding showed no causal association between general anaesthesia and postoperative delirium. P P P

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The effect of type of anaesthetic on delirium after surgery for acute hip fracture: An instrumental variable analysis to assess causation

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