METs and DASI: How Functional Capacity Shapes Perioperative Risk Assessment
Functional capacity is not just a number. It reflects how much physiologic stress the cardiovascular system can tolerate — and it is one of the most important filters in perioperative cardiac evaluation.
Key points
- Functional capacity is one of the most important elements of perioperative cardiac assessment — it reflects cardiovascular reserve, not just mobility.
- 4 METs is the key perioperative threshold — patients below it may warrant further evaluation, not automatic surgical cancellation.
- Self-reported walking ability frequently overestimates functional capacity — ask specifically about hills, stairs, and behavioral avoidance.
- DASI (Duke Activity Status Index) outperformed subjective METs estimation in the METS Trial (Lancet 2018) for predicting postoperative cardiac outcomes.
When to use this page
When functional capacity is unclear or self-reported walking seems unreliable. When deciding whether DASI would be more useful than a subjective estimate. When you want to understand how FC integrates with RCRI and BNP in the Navigator.
Why functional capacity matters
Key point
Functional capacity is not just about whether the patient can walk. It is a practical estimate of cardiovascular reserve — how much physiologic stress the heart can tolerate before becoming overwhelmed. This makes it one of the most important inputs in perioperative cardiac risk assessment.
Metabolic equivalents (METs) express activity intensity relative to resting oxygen consumption (3.5 mL/kg/min = 1 MET). A patient who can comfortably perform activities at or above 4 METs demonstrates that the cardiovascular system can sustain meaningful physiologic demand. A patient who cannot may be at higher risk for adverse events when the surgical stress response imposes a similar or greater load.
Why 4 METs became the key threshold
Key point
4 METs corresponds roughly to the activities of daily life that require sustained cardiovascular effort. It is not a hard cutoff — it is a perioperative signal. Patients below 4 METs may benefit from further evaluation; patients clearly above it generally do not require additional cardiac workup.
The following activities correspond to approximately 4 METs:
- Climbing one flight of stairs without stopping
- Brisk walking on flat ground (approximately 6 km/h)
- Walking up a gentle incline
- Carrying groceries while walking
Inability to perform these activities — or behavioral avoidance of them — may indicate FC below 4 METs. Importantly, FC below 4 METs is not a reason to cancel surgery. It is a signal to consider BNP measurement, RCRI confirmation, and possible further evaluation before proceeding.
Why self-reported activity often fails
Key point
Patients frequently overestimate their own functional capacity. Open-ended questions about activity — 'Do you exercise?' or 'Are you active?' — tend to yield optimistic answers that do not reflect actual cardiovascular reserve.
The METS Trial (Lancet 2018) demonstrated that clinician-estimated METs based on patient history had poor predictive value for postoperative cardiac complications. Subjective impressions — 'this patient seems active' — are particularly unreliable when the patient has adapted their behavior to avoid symptoms.
Walking is not the same as adequate functional capacity
One of the most common errors in perioperative assessment is equating walking with adequate FC. The presence of behavioral adaptation is the key finding to look for:
- Avoiding hills by taking a longer route
- Stopping partway up a single flight of stairs
- No longer carrying bags while walking
- Unable to cross the street quickly
- Feeling more fatigued after routine outings than before
These patterns reveal that the patient is managing symptoms by reducing demand — not that they have maintained capacity. A patient who 'walks every day' but avoids all inclines and stops on every staircase may have FC well below 4 METs.
What DASI adds
Key point
DASI (Duke Activity Status Index) is a 12-item structured questionnaire that quantifies functional capacity and calculates an estimated METs value. Because the questions are standardized, it reduces variability between assessors and reduces the influence of open-ended self-report.
DASI covers a range of activities from basic self-care to vigorous exercise, each weighted by metabolic demand. The patient indicates which activities they can perform without stopping, and the responses are used to calculate an estimated METs score. This provides a more reproducible and objective estimate than asking 'can you climb stairs?'
Evidence from the METS Trial
The METS Trial (Lancet 2018) enrolled over 1400 patients across multiple centers and directly compared DASI, clinician-estimated METs, and NT-proBNP for predicting 30-day postoperative death or myocardial injury. Key findings:
- DASI predicted postoperative cardiac outcomes significantly better than clinician-estimated METs
- Clinician METs estimation (subjective) showed poor discriminative ability
- NT-proBNP also predicted outcomes independently of functional capacity measures
- Neither DASI nor NT-proBNP was definitively superior to the other — both contributed information
The METS Trial is the primary reason current guidelines and perioperative tools favor structured functional capacity assessment over subjective impression. It is also the reason functional capacity and BNP are evaluated as complementary — not competing — inputs.
How functional capacity changes perioperative decision-making
Key point
METs assessment is not used to decide whether surgery proceeds. It is used to determine whether further evaluation is needed before surgery.
- FC ≥4 METs → additional cardiac workup is generally not required
- FC <4 METs → consider BNP measurement and further evaluation
- FC unknown or unreliable → use DASI to quantify before deciding
Practical questions to ask at the bedside
Specific, activity-based questions are more informative than open-ended ones:
- Can you climb one flight of stairs without stopping?
- Do you get short of breath walking up a gentle hill?
- Can you carry shopping bags while walking?
- Can you walk quickly to cross the street before the light changes?
- Do you need to stop and rest during activities you used to find easy?
Notice that these questions probe for limitation and avoidance, not just capability. A patient who answers 'yes, I walk every day' to a general question may answer 'no' to one or more of these specific items.
Basis for this approach
ACC/AHA 2014 Guideline on Perioperative Cardiovascular Evaluation (functional capacity assessment section) / METS Trial, Lancet 2018 (DASI vs subjective METs in predicting postoperative cardiac outcomes) / JCS 2022 Guidelines on Perioperative Cardiovascular Evaluation for Non-cardiac Surgery
Continue learning
Dyspnea on Stairs: Is Functional Capacity Really Adequate?
Patients often report that they are 'active' or 'walking regularly.' That does not mean they have adequate functional capacity. This case teaches how to move from symptom to functional limitation to perioperative decision.
Elevated BNP Before Surgery: A Signal, Not a Diagnosis
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A Prior PCI Is Not the Whole Story: Assessing Coronary Disease Before Surgery
When a patient has a history of PCI, the first question is not about antiplatelet therapy. The first question is whether coronary artery disease remains stable today.
Apply this in practice
Enter FC, RCRI, and BNP into the Navigator to see the integrated risk assessment
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