SN6 SHORT NOTE 5M

Describe Functional Capacity & METs in detail.

General Surgery · Final Professional

Definition

Functional capacity — a patient’s ability to perform physical activity — is a valuable, simple predictor of perioperative (especially cardiac) risk. It is expressed in metabolic equivalents (METs), where 1 met is the oxygen consumption at rest (~3.5 mL/kg/min). The more a patient can do, the greater their cardiorespiratory reserve.

METs	Activity
1 met	Eating, dressing, using the toilet
4 METs	Climbing a flight of stairs, walking on level ground briskly
> 10 METs	Strenuous sport (swimming, running)

Clinical Use

A functional capacity of ≥ 4 METs (e.g. Able to climb a flight of stairs without stopping) suggests adequate reserve and is reassuring before non-cardiac surgery, often allowing surgery to proceed without further cardiac testing. Patients unable to reach 4 METs, or whose capacity is unknown/limited by non-cardiac factors, may need further evaluation before major surgery.

CLINICAL PEARL

A practical rule of thumb: a patient who can climb a flight of stairs (≥ 4 METs) without stopping usually has enough reserve for most surgery — poor or unknown functional capacity is a flag for closer assessment.

Objective Measurement

When the history of functional capacity is unclear or the surgery is major, more objective assessment can be used, the most sophisticated being cardiopulmonary exercise testing (CPET), which measures oxygen uptake during graded exercise and yields values such as the anaerobic threshold that predict the ability to meet the increased oxygen demand of the perioperative period. Simpler surrogates such as the ability to climb stairs remain useful at the bedside, but CPET provides a quantified estimate of reserve that helps guide the level of postoperative care in high-risk major surgery.

CLINICAL PEARL

Let the stairs be your bedside test: a patient who can climb a flight without stopping has roughly 4 METs of reserve and usually tolerates surgery well, whereas poor or unknown capacity is the signal to look harder before a major operation.

DANGER / REMEMBER

Beware the patient whose functional capacity is unknown or limited by non-cardiac factors (arthritis, claudication, general debility): their inability to climb stairs may mask, rather than exclude, cardiac disease, so poor or indeterminate capacity before major surgery is a prompt for objective assessment rather than false reassurance.

Climbing two flights of stairs is roughly 4 METs.

KEY POINT

Key points TO remember

Functional capacity predicts perioperative (cardiac) risk; measured in METs (1 met = resting O₂ use).
4 METs = climbing a flight of stairs / brisk level walking.
≥ 4 METs is reassuring — often allows surgery without further cardiac testing.
Poor/unknown capacity flags the need for further evaluation before major surgery.

EXAM TIP

Sources: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.

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