Association between intraoperative blood pressure and postoperative delirium in elderly hip fracture patients

Background: One possible area of intervention to prevent postoperative delirium (PD) is intraoperative blood pressure management. However, the relationship between intraoperative blood pressure and PD is unclear. A secondary analysis of a RCT study examining the PD risk over the range of absolute intraoperative mean arterial blood pressure (MAP) readings and the corresponding relative changes from preoperative baseline level was performed to determine the role of MAP on PD. Methods: Nonparametric locally weighted quadratic polynomial smoothing (LOESS) regression explored the pattern of PD risk at postoperative day 2 as a function of mean surgery MAP (msMAP) and percent change of msMAP from baseline in 103 elderly hip fracture patients. Segment-linear logistic regression models were then constructed to determine the odds ratios (OR) of PD over the observed range of these msMAP measures, adjusting for potential confounds. Results: Twenty-three patients (22%) developed PD on day 2. LOESS regression revealed a j-shaped association between absolute levels of msMAP and PD risk. When msMAP was ≥ 80 mmHg, higher msMAP imparted greater PD risk (OR = 2.28 per 10 mmHg msMAP increase; 95% CI: 1.11-4.70), while higher msMAP was associated with lower PD risk (OR = 0.19 per 10 mmHg increase; CI: 0.05-0.76) if msMAP was <80 mmHg. There was no statistically significant relationship between PD risk and average percent change from baseline in these msMAP measures. Conclusion: In elderly hip fracture patients, both very high and very low levels of msMAP were associated with significantly increased risk of PD.