Pain and Opioid Trajectories After Hip Fracture Nerve Block Linked to Higher Delirium Risk in Older Patients

Older patients recovering from hip fracture surgery who remained in severe pain while receiving high opioid doses faced the greatest risk of a particularly elusive postoperative complication: hypoactive delirium, a state in which patients become withdrawn, sluggish, and hard to recognize as delirious. That is the central finding of a single-centre retrospective cohort study published in BMC Anesthesiology, which tracked joint pain and opioid exposure patterns in 328 patients aged 65 years or older after an ultrasound-guided suprainguinal fascia iliaca compartment block.

The research team, led by Wei Zheng, Fayong Qu, Xin Tian, and Kaili Yi, set out to examine how pain and opioid requirements vary together after the block and whether their combined trajectories relate to postoperative hypoactive delirium. Rather than treating pain intensity and opioid use as separate snapshots, the investigators modeled them jointly, using resting pain measured at nominal 0.5-, 2-, 6-, and 12-hour assessments together with oral morphine equivalent exposure rates during the first 12 hours after surgery to define each patient’s trajectory.

Four distinct trajectories emerged from the analysis. One group showed low pain with low opioid exposure. A second experienced decreasing pain alongside moderate opioid exposure. A third endured persistent moderate pain despite low opioid exposure, and a fourth suffered persistent high pain combined with high opioid exposure. This grouping matters because delirium risk was far from evenly distributed across the four patterns.

Overall, any delirium occurred in 99 patients, or 30.2 percent of the cohort, and hypoactive delirium occurred in 72 patients, representing 22.0 percent of the full cohort. The corresponding proportions across the four trajectory groups were 8.3 percent, 17.4 percent, 32.4 percent, and 50.0 percent, climbing steadily from the low pain-low opioid group to the persistent high pain-high opioid group. Hypoactive delirium is notoriously easy to miss because affected patients appear quiet rather than agitated, making systematic screening with validated tools essential.

To classify the first postoperative delirium episode recorded within 7 days after surgery, the researchers used the Confusion Assessment Method together with the Richmond Agitation-Sedation Scale. The statistical approach was deliberately cautious. Adjusted cause-specific Cox models incorporated 100 pseudo-class draws to account for uncertainty in trajectory assignment, and other delirium subtypes, discharge before any delirium, and death before any delirium were treated as competing events, preventing these occurrences from being miscounted as freedom from delirium.

Compared with patients in the low pain-low opioid exposure group, the adjusted cause-specific hazard ratios for hypoactive delirium were 1.97 for the decreasing pain-moderate opioid group, with a 95 percent confidence interval of 0.82 to 4.73; 3.10 for the persistent moderate pain-low opioid group, at 1.27 to 7.59; and 4.93 for the persistent high pain-high opioid group, at 1.84 to 13.24. Only the two persistent-pain trajectories showed confidence intervals excluding the null value, suggesting that sustained pain, rather than opioid exposure alone, drove much of the association.

The association held up under several robustness checks. Separate sensitivity analyses excluded patients with preoperative CAM positivity and additionally adjusted for oral morphine equivalents during the remaining preoperative period and for time-updated postoperative opioid exposure, and the associations for both persistent-pain trajectories remained. However, the picture was not uniformly stable. Overall trajectory tests were nonsignificant after extended baseline adjustment, with a P value of 0.254, and in the 48-hour landmark analysis, with a P value of 0.218.

The authors themselves flagged this fragility in their conclusions, noting that persistent-pain trajectories were associated with a higher cause-specific hazard of hypoactive delirium although the estimates depended on the adjustment set and the population analysed. They concluded that the incremental prognostic value and clinical utility of these trajectories require prospective validation. In other words, the findings are hypothesis-generating rather than practice-changing, and the retrospective single-centre design limits how confidently they can be generalized.

For clinicians caring for the growing population of older adults with hip fractures, the study offers a mechanistically plausible signal: unrelieved pain in the crucial first half-day after a regional block may mark patients at elevated risk of a delirium subtype that often goes undetected. Whether actively monitoring joint pain-opioid trajectories after a suprainguinal fascia iliaca compartment block can meaningfully improve risk prediction, and whether intervening on persistent pain would lower delirium incidence, are questions that only prospective studies can answer.

Subject of Research: Pain and opioid exposure trajectories after a suprainguinal fascia iliaca compartment block and their association with postoperative hypoactive delirium in older hip fracture surgery patients.

Article Title: 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

Article References: Zheng, W., Qu, F., Tian, X., & Yi, K. (2026). 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. BMC Anesthesiology. https://doi.org/10.1186/s12871-026-04399-2

Image Credits: AI Generated

DOI: 10.1186/s12871-026-04399-2

Keywords: hip fracture surgery, fascia iliaca compartment block, postoperative delirium, hypoactive delirium, opioid exposure, pain trajectories, older patients, retrospective cohort study, cause-specific Cox model, ultrasound-guided regional anesthesia, Confusion Assessment Method, morphine equivalent dose