Interaction between advanced age and ASA physical status on early postoperative mortality after colorectal cancer surgery.

BACKGROUND: It is unknown whether the preoperative anesthesiological risk assessment interacts with patient age in colorectal cancer (CRC) to increase the risk of early postoperative mortality beyond that explained by the independent effects of age and anesthesiological risk assessment.

METHODS: We conducted a nationwide cohort study (2014-2023) of all Danish non-metastatic CRC patients (UICC pathological TNM I-III) aged 70 or more years at time of surgery (n = 15,673). To analyse perioperative risk, we used the American Society of Anesthesiologists (ASA) Physical Status Classification system score. The study cohort was stratified by age at CRC surgery (70-79, 80+) and ASA classification (I, II, III). We estimated mortality rates per 1000 person-days, and calculated interaction contrasts as a measure of the excess mortality rate not explained by the independent effects of age or ASA classification.

RESULTS: 90-day overall survival was lower in patients aged ≥80 years compared with those aged 70-79 years (94.0% vs. 97.9%). Increasing ASA classification was associated with progressively lower survival, with 90-day survival of 98.9% for ASA I, 97.9% for ASA II, and 93.1% for ASA III. Interaction analyses demonstrated that the combined effect of age and ASA classification exceeded their independent effects, with interaction contributing 21% of the mortality rate in ASA II patients aged ≥80 years and 36% in ASA III patients aged ≥80 years.

DISCUSSION: Old CRC patients assessed as ASA III have a high risk of perioperative mortality and may benefit from risk factor reductions or high intensity postoperative monitoring to reduce mortality.