Development and validation of risk factors prediction model for hypoxemia in the PACU patients after major abdominal surgery: a retrospective study.

Anthropometric measures such as body mass index (BMI), waist circumference (WC) are widely used in clinical, community, and research settings because they are low-cost, non-invasive indicators of chronic disease risk (e.g., coronary heart disease, dyslipidemia, type II diabetes, high blood pressure) and mortality (). Five commonly used indices are BMI, WC, weight-adjusted waist index (WWI), waist-to-height ratio (WHtR), and waist-to-height^0.5 (WHT.5R) (, , ). Despite frequent criticism for failing to discern between lean and fat mass, BMI remains a standard tool in both practice and clinical guidelines (). However, WC is a better predictor of metabolic risk than BMI because it reflects abdominal adiposity (). A newer metric, the WWI, measures WC relative to body weight (, ). To account for body size differences, WHtR was introduced as a screening tool for central adiposity, while WHT.5R further adjusts this relationship to account for potential height-related bias (). Previous studies have examined the associations between BMI, WC, and WC-related indices and mortality risk among older adults (, ). Although the “obesity paradox” has been observed in older populations (), both increases and decreases in BMI have been associated with higher mortality risk (). Weight change is also recognized as a phenotypic marker of frailty and is a predictor of mortality risk in both middle-aged and older adults (). However, findings regarding WC change and mortality remain inconsistent, with studies reporting null, inverse, or positive associations depending on the population and methodology (). Most epidemiologic studies rely on single-time-point measurements of body size, which may not capture the dynamic physiological changes that occur with aging. Yet fat distribution can shift with age even at a stable weight (). These longitudinal changes may reflect underlying processes such as sarcopenia, fat redistribution, or disease progression (, ). Focusing on annual percentage change (APC) in anthropometric indices may capture prognostic information and trends that static measures miss. Weight loss and gain in older adults have both been associated with increased mortality risk, though findings remain inconsistent across different populations and measurement approaches () In particular, relatively few studies have examined dynamic changes across multiple anthropometric indices simultaneously ().