Complementary effects of postoperative delirium and frailty on 30-day outcomes in spine surgery

Background context: With an increasingly older population, the number of frail patients requiring surgical management for degenerative spine diseases is rapidly increasing. Older patients are at increased risk of developing postoperative delirium (POD), which increases the odds of postoperative morbidity and mortality in spine surgery patients. Therefore, frail spine surgery patients may be at greater risk of developing POD and subsequent adverse outcomes.

Purpose: To understand the relationship between frailty and POD in spine surgery patients, and the effect of POD on nonfatal and fatal adverse outcomes in frail patients.

Study design/setting: Retrospective cohort study utilizing data from the 2021 American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database.

Patient sample: Patients aged ≥75 years undergoing spine surgery screened for POD, with a total sample size of 4,195 patients.

Outcome measures: Primary outcomes were postoperative delirium (POD), 30-day mortality, and nonfatal adverse outcomes.

Methods: Frailty was measured using the Risk Analysis Index (RAI) with tiered cutoffs indicating increasing frailty. Statistical methods included multivariable logistic regression and mediation analysis to evaluate the relationships between RAI, postoperative delirium, and 30-day mortality.

Results: Out of 4,195 spine surgery patients aged ≥75 years screened for POD, 353 (8.4%) exhibited POD. POD patients had significantly higher RAI scores relative to those without POD (p<.001). Multivariable analysis demonstrated that increasing frailty predicted POD (p<.001). In patients with POD, there were increased odds of mortality and all nonfatal adverse outcomes within 30 days (p<.001). A complementary mediation effect of POD on frailty's contribution to 30-day mortality was observed (p<.001).

Conclusion: POD and increasing preoperative frailty RAI scores were independent predictors of mortality and morbidity in older spine surgery patients. POD has a significant synergistic contribution to the adverse effects of frailty following spine surgery. The RAI may be used to identify frail patients at risk of developing POD to enable optimal surgical candidate selection and provide opportunities for risk mitigation, such as prehabilitation and/or specialized perioperative care teams for frail patients.