Body mass index and risk of post-induction hypotension in older adults undergoing non-cardiac surgery: a retrospective cohort study.

backgroundPost-induction hypotension (PIH) is a frequent complication among older adults undergoing general anaesthesia, associated with organ hypoperfusion and increased perioperative risk. The role of body mass index (BMI), a routinely assessed and potentially modifiable risk factor, in the development of PIH remains unclear in geriatric populations.

methodsWe conducted a retrospective cohort study of patients aged ≥ 60 years who underwent elective non-cardiac surgery under general anaesthesia between 2013 and 2022 at a tertiary hospital. Preoperative BMI was analysed both as a continuous and categorical variable. The primary outcome was PIH, defined as a systolic blood pressure < 90 mmHg or > 30% reduction from baseline during the post-induction period. Secondary outcomes included ICU admission, hospital length of stay, and in-hospital mortality. Non-linear associations were explored using restricted cubic spline models and segmented linear regression.

resultsA total of 70,487 patients were included in the final analysis, and PIH occurred in 73.3% of patients. A U-shaped association was observed between BMI and PIH, with the lowest risk between 24.2 and 29.7 kg/m². Patients below this range had significantly higher odds of PIH (OR 1.13; 95% CI 1.09-1.17), ICU admission (OR 1.31; 95% CI 1.24-1.39), and longer hospitalisation (IRR 1.08; 95% CI 1.06-1.10). Subgroup analyses showed significant interaction effects by sex, age, and hypertension. Sensitivity analyses excluding PIH as a covariate yielded consistent findings for secondary outcomes.

conclusionsBMI demonstrates a non-linear relationship with PIH and related outcomes. Both underweight and obese older adults are at increased risk. BMI should be integrated into preoperative risk stratification, and maintaining BMI within a moderate range may help reduce peri-induction haemodynamic instability.