Preoperative Functional Capacity Assessment Using MET Thresholds

MET Threshold and Peri‑operative Risk Stratification

• Achieving ≥ 4 metabolic equivalents (METs) without symptoms obviates the need for pre‑operative echocardiography or any other non‑invasive cardiac testing before non‑cardiac surgery. American College of Cardiology/AHA guideline (Class IIa). 1
• A functional capacity of 4 METs serves as the pivotal dividing line between “poor” and “adequate” capacity for peri‑operative risk assessment. American College of Cardiology/AHA guideline (Class I). 2
• Patients who cannot climb ≈ 2 flights of stairs or walk ≈ 4 city blocks are classified as having < 4 METs, a status that markedly raises peri‑operative cardiac risk. American College of Cardiology/AHA guideline (Class I). 3
• The incidence of serious peri‑operative complications declines progressively as the number of stair flights a patient can climb increases (trend P < 0.01). American College of Cardiology/AHA evidence (Level B). 3

Activity MET Values (Illustrative Examples)

All activity classifications are derived from *American College of Cardiology* data. 4

Guideline Recommendations by Functional Capacity

Class I – Proceed to Surgery Without Additional Testing

• Patients with < 4 METs or unknown functional capacity and no clinical risk factors may proceed directly to the planned operation without cardiac testing. ACC/AHA Class I recommendation. 5

Class IIa – Probably Proceed Without Testing

• Patients with ≥ 4 METs and no symptoms should probably proceed to surgery without further cardiac evaluation. ACC/AHA Class IIa recommendation. 5
• Non‑invasive cardiac testing may be considered in patients who have clinical risk factors if the results are expected to change peri‑operative management. ACC/AHA Class IIa. 1

Clinical Risk Factors (Trigger for Consideration of Testing)

• Ischemic heart disease, prior or compensated heart failure, diabetes mellitus, renal insufficiency, and cerebrovascular disease. ACC/AHA guideline (Class IIa). 1

Class IIb – Testing May Be Considered in Select Scenarios

• For patients with ≥ 1–2 clinical risk factors and poor functional capacity (< 4 METs) who are scheduled for intermediate‑risk or vascular surgery, non‑invasive stress testing may be performed if it is likely to influence management decisions. ACC/AHA Class IIb. 2
• Liver transplant candidates who cannot achieve 4 METs or who possess at least one intermediate‑risk factor should undergo further cardiac evaluation. Guideline from the American Association for the Study of Liver Diseases (adapted). 6

Factors Influencing MET Estimates

• Predicted MET values for activities are modulated by an individual’s conditioning level, genetic background, age, and body weight. American College of Cardiology analysis (Level B). 3

Special Populations & Assessment Limitations

• In patients with lower‑extremity arterial disease undergoing vascular procedures, stair‑climbing may be infeasible; alternative risk‑stratification methods should be employed. European Society of Cardiology recommendation (Class IIb). 7

Metabolic Equivalent (MET) of Stair Climbing in Cardiovascular Risk Assessment

MET Value and Functional‑Capacity Threshold

• Climbing one flight of stairs expends roughly 4 METs, representing a moderate‑intensity activity and serving as the key threshold for evaluating functional capacity in cardiovascular risk stratification. [8][9]10
• One flight of stairs is the minimum activity level at 4 METs that separates poor from moderate functional capacity. 11

Perioperative Risk Assessment

• Patients who cannot climb two flights of stairs (or walk four blocks) are classified as having poor functional capacity (<4 METs), which markedly raises peri‑operative cardiac risk. [8][9]10
• The risk of serious peri‑operative complications decreases as the number of flights climbed increases (P < 0.01). [8][9]10

Guideline Benchmark and Clinical Application

• Clinical guidelines adopt a 4‑MET benchmark as a practical tool for peri‑operative risk stratification. [8][9][10][11]
• The benchmark assumes the combined activity of climbing + descending stairs, reflecting how functional capacity is normally assessed. [8][9]10
• Activities below 4 METs (e.g., slow ballroom dancing, golfing with a cart, walking 2–3 mph) are considered low‑intensity. [8][9][10][11]
• Activities at or above 4 METs (e.g., stair climbing, walking 4 mph on level ground, moderate cycling, heavy housework) are classified as moderate‑intensity. [8][9][10][11]

Factors Influencing Predicted MET Level

• The estimated MET value for stair climbing is modulated by conditioning level, genetic factors, age, and body weight. [8][9]10

Sex‑Specific Differences

• Women generally exhibit 1–2 METs lower absolute intensity for the same stair‑climbing activity compared with men. 12

Duke Activity Status Index (DASI) Weighting

• The Duke Activity Status Index assigns 5.5 weight points to climbing one flight of stairs, reflecting its moderate‑to‑vigorous intensity classification. 11