How do you assess and manage surgical risk in relation to a patient's functional capacity?

Functional Capacity Assessment for Surgical Risk

Functional capacity assessment using the 4 MET threshold is the cornerstone of perioperative risk stratification—patients who can achieve ≥4 METs can proceed to surgery without further cardiac testing, while those with <4 METs require additional evaluation based on clinical risk factors and surgery type. 1

The 4 MET Threshold: Clinical Decision Point

The ability to perform activities requiring 4 METs or more identifies patients at low perioperative cardiac risk who can proceed directly to surgery without additional testing. 1, 2

Activities Below 4 METs (Poor Functional Capacity):

• Walking at 2-3 mph on level ground 1, 2
• Light housework, self-care activities 1, 2
• Slow ballroom dancing, golfing with a cart 1, 2
• Playing a musical instrument 1, 2

Activities At or Above 4 METs (Adequate Functional Capacity):

• Climbing one flight of stairs or walking up a hill 1, 2
• Walking on level ground at 4 mph 1, 2
• Heavy housework, yard work 1, 2
• Running a short distance, strenuous sports 1, 2

Structured Assessment Approach

Two-Question Screen (European Society of Cardiology):

Ask every patient these two standardized questions: 1, 2

• Can you walk 4 blocks without stopping? 1, 2
• Can you climb 2 flights of stairs without stopping? 1, 2

Inability to perform either activity identifies poor functional capacity (<4 METs) and significantly increased risk of perioperative myocardial ischemia. 1, 2

Duke Activity Status Index (DASI):

The DASI provides superior predictive value compared to unstructured clinical assessment for identifying patients at risk of death or MI within 30 days of surgery. 1, 2 A DASI score ≤34 indicates poor functional capacity. 1

Risk-Stratified Management Algorithm

Excellent Functional Capacity (>10 METs):

Patients with excellent functional capacity can proceed directly to surgery regardless of clinical risk factors—further testing is not beneficial. 1 The prognosis is excellent even in the presence of stable coronary disease. 1

Good to Moderate Functional Capacity (4-10 METs):

Patients with adequate functional capacity (≥4 METs) who are asymptomatic can proceed to surgery without further cardiovascular testing, as management is rarely changed by additional testing. 1, 2 This applies even to patients with intermediate cardiac risk factors. 1

Poor or Unknown Functional Capacity (<4 METs):

Management depends on the number of clinical risk factors and surgery-specific risk: 1

• 0 clinical risk factors: Proceed to surgery 1
• 1-2 clinical risk factors: Either proceed with beta-blockade or consider stress testing if it will change management 1
• ≥3 clinical risk factors undergoing vascular surgery: Consider noninvasive stress testing if it will change management 1
• ≥3 clinical risk factors undergoing intermediate-risk surgery: Insufficient data—either proceed with beta-blockade or test if it will change management 1

Advanced Testing When Indicated

Cardiopulmonary Exercise Testing (CPET):

CPET may be considered for high-risk patients undergoing elevated-risk procedures with reduced functional capacity when additional physiological data are needed to inform perioperative care. 1 An anaerobic threshold <10 mL O2/kg/min predicts perioperative cardiovascular complications and postoperative death. 1

CPET provides the gold-standard objective measure of functional capacity and can diagnose the etiology of exercise intolerance (cardiac versus pulmonary). 1 However, most studies are retrospective and single-center with variable predictive precision. 1

Pharmacological Stress Testing:

For patients at elevated risk with poor functional capacity (<4 METs), dobutamine stress echocardiography or myocardial perfusion imaging is reasonable if it will change management. 1 Routine screening with noninvasive stress testing is not useful for low-risk surgery. 1

Critical Caveats

Poor functional capacity has stronger prognostic value for thoracic surgery compared to other non-cardiac surgeries, reflecting the importance of pulmonary function. 2 Patients with intermediate cardiac risk factors but reasonable functional capacity (able to comfortably walk up one flight of stairs) should not be regarded as at greater than average risk and do not need further cardiac testing. 1

Unstructured patient interviews about functional capacity do not predict outcomes—only structured interviews with validated questionnaires or standardized questions about physical activities have predictive value. 3

Routine preoperative evaluation of left ventricular function is not recommended. 1 Testing should be reserved for patients with dyspnea of unknown origin or worsening heart failure symptoms. 1