Association of pain–opioid exposure trajectories after ultrasound-guided suprainguinal fascia iliaca compartment block with postoperative hypoactive delirium in older patients undergoing hip fracture surgery: a single-centre retrospective cohort study

Pain and opioid requirements vary after fascia iliaca compartment block. This study examined their joint trajectories and associations with postoperative hypoactive delirium in older patients with hip fracture. This single-centre retrospective cohort included 328 patients aged ≥ 65 years who received an ultrasound-guided suprainguinal fascia iliaca compartment block. Resting pain at nominal 0.5-, 2-, 6-, and 12-hour assessments and oral morphine equivalent (OME) exposure rates during the first 12 h were used to define the trajectories. The first postoperative delirium episode recorded within 7 days after surgery was classified using the Confusion Assessment. Method (CAM) and Richmond Agitation-Sedation Scale (RASS). Adjusted cause-specific Cox models incorporated 100 pseudo-class draws; other delirium subtypes, discharge before any delirium, and death before any delirium were treated as competing events. Four trajectories were identified: low pain-low opioid exposure, decreasing pain-moderate opioid exposure, persistent moderate pain-low opioid exposure, and persistent high pain-high opioid exposure. Any delirium occurred in 99 patients (30.2%), and hypoactive delirium occurred in 72 patients (22.0% of the full cohort); the corresponding proportions across the four trajectory groups were 8.3%, 17.4%, 32.4%, and 50.0%. Relative to the low pain-low opioid exposure group, adjusted cause-specific hazard ratios were 1.97 (95% confidence interval [CI], 0.82–4.73), 3.10 (1.27–7.59), and 4.93 (1.84–13.24). Associations for both persistent-pain trajectories remained in separate sensitivity analyses excluding patients with preoperative CAM positivity and additionally adjusting for OME during the remaining preoperative period and time-updated postoperative OME. Overall trajectory tests were nonsignificant after extended baseline adjustment (P = 0.254) and in the 48-hour landmark analysis (P = 0.218). Persistent-pain trajectories were associated with a higher cause-specific hazard of hypoactive delirium, although estimates depended on the adjustment set and the population analysed. Their incremental prognostic value and clinical utility require prospective validation. Not applicable.