Exercise tolerance is an important indicator of cardiac health and provides valuable information regarding a patient's cardiopulmonary reserve and perioperative risk. Functional capacity reflects the ability of the cardiovascular, pulmonary, and musculoskeletal systems to meet increased metabolic demands. Numerous studies have demonstrated that impaired exercise tolerance is associated with higher rates of postoperative cardiac complications, prolonged hospitalization, disability, and mortality. As a result, current perioperative guidelines continue to emphasize the assessment of exercise tolerance during the preoperative evaluation for at-risk patients as a key step in risk stratification.
Traditionally, exercise tolerance has been estimated using metabolic equivalents (METs), with 1 MET representing resting oxygen consumption of approximately 3.5 mL/kg/min. A threshold of 4 METs has historically been used to distinguish adequate from poor functional capacity. Activities requiring approximately 4 METs include climbing a flight of stairs, walking uphill, or performing moderate household work. Patients unable to perform these activities may have increased perioperative cardiovascular risk and may warrant additional evaluation.
Historically, anesthesiologists and surgeons relied on subjective questioning to estimate exercise capacity. However, evidence suggests that using only this metric correlates poorly with objective measures of fitness and postoperative outcomes. Studies comparing physician estimates with validated assessment tools have demonstrated significant variability and limited predictive accuracy. Consequently, structured assessments have become increasingly preferred in modern perioperative practice.
The Duke Activity Status Index (DASI) is one tool for preoperative functional assessment. This validated 12-item questionnaire evaluates a patient's ability to perform activities of daily living and recreational tasks. DASI scores correlate with peak oxygen consumption and have been shown to predict postoperative complications, disability-free survival, and mortality. The 2024 American Heart Association/American College of Cardiology perioperative guideline specifically recommends structured assessment tools such as DASI when evaluating patients undergoing elevated-risk noncardiac surgery.
For patients with uncertain or poor functional capacity, objective testing may provide additional information. Cardiopulmonary exercise testing (CPET) is considered the gold standard for measuring exercise tolerance. CPET directly evaluates oxygen uptake, carbon dioxide production, and ventilatory efficiency during graded exercise. Parameters such as peak oxygen consumption (VO₂ peak) and anaerobic threshold have demonstrated associations with postoperative outcomes. Although CPET provides comprehensive physiologic data, its cost, specialized equipment requirements, and limited availability restrict its routine use.
Alternative objective assessments include the 6-minute walk test and incremental shuttle walk test. These tests are less resource-intensive than CPET and can provide useful information regarding functional capacity. However, their predictive performance varies across surgical populations, and they have not consistently demonstrated superiority over validated questionnaires such as DASI.
In contemporary practice, evaluation of exercise tolerance should be viewed as part of a comprehensive preoperative assessment rather than a standalone screening tool. Functional capacity data should be integrated with surgical risk, comorbidities, frailty, and validated risk prediction models. A structured approach using DASI, supplemented by objective testing when indicated, can help identify patients at increased perioperative risk and guide shared decision-making regarding surgery and preoperative optimization.