IMPORTANCE: Major postoperative complications and delirium contribute independently to adverse outcomes and high resource use in patients who undergo major surgery; however, their interrelationship is not well examined.

OBJECTIVE: To evaluate the association of major postoperative complications and delirium, alone and combined, with adverse outcomes after surgery.

DESIGN, SETTING, AND PARTICIPANTS: Prospective cohort study in 2 large academic medical centers of 566 patients who were 70 years or older without recognized dementia or a history of delirium and underwent elective major orthopedic, vascular, or abdominal surgical procedures with a minimum 3-day hospitalization between June 18, 2010, and August 8, 2013. Data analysis took place from December 13, 2013, through May 1, 2015.

MAIN OUTCOMES AND MEASURES: Major postoperative complications, defined as life-altering or life-threatening events (Accordion Severity grade 2 or higher), were identified by expert-panel adjudication. Delirium was measured daily with the Confusion Assessment Method and a validated medical record review method. The following 4 subgroups were analyzed: (1) no complications or delirium; (2) complications only; (3) delirium only; and (4) complications and delirium. Adverse outcomes included a length of stay (LOS) of more than 5 days, institutional discharge, and rehospitalization within 30 days of discharge.

RESULTS: In the 566 participants, the mean (SD) age was 76.7 (5.2) years, 236 (41.7%) were male, and 523 (92.4%) were white. Forty-seven patients (8.3%) developed major complications and 135 (23.9%) developed delirium. Compared with no complications or delirium as the reference group, major complications only contributed to prolonged LOS only (relative risk [RR], 2.8; 95% CI, 1.9-4.0); by contrast, delirium only significantly increased all adverse outcomes, including prolonged LOS (RR, 1.9; 95% CI, 1.4-2.7), institutional discharge (RR, 1.5; 95% CI, 1.3-1.7), and 30-day readmission (RR, 2.3; 95% CI, 1.4-3.7). The subgroup with complications and delirium had the highest rates of all adverse outcomes, including prolonged LOS (RR, 3.4; 95% CI, 2.3-4.8), institutional discharge (RR, 1.8; 95% CI, 1.4-2.5), and 30-day readmission (RR, 3.0; 95% CI, 1.3-6.8). Delirium exerted the highest attributable risk at the population level (5.8%; 95% CI, 4.7-6.8) compared with all other adverse events (prolonged LOS, institutional discharge, or readmission).

CONCLUSIONS AND RELEVANCE: Major postoperative complications and delirium are separately associated with adverse events and demonstrate a combined effect. Delirium occurs more frequently and has a greater effect at the population level than other major complications.