MD Anaesthesiology – Model Answer

Q1. What is METs? Recent guidelines for assessment of functional capacity in a patient with coronary stents in-situ, and role of cardiac biomarkers [2+4+4]

A. What is METs? (2 marks)

• 1 MET = resting oxygen consumption of an average 40-year-old, 70-kg adult = 3.5 mL O₂/kg/min
• Functional capacity is graded as multiples of this baseline (e.g., walking on level ground ≈ 2-3 METs; climbing 2 flights of stairs or heavy housework ≈ 4-5 METs; strenuous sports, e.g., swimming, singles tennis ≈ >10 METs)
• ≥4 METs is the clinically critical cut-off - patients who can achieve this without symptoms (angina, dyspnea) have a low risk of perioperative cardiac events and generally do not need further cardiac testing before intermediate/high-risk noncardiac surgery
• Poor functional capacity (<4 METs) has a bidirectional relationship with cardiopulmonary disease and independently predicts perioperative mortality, cardiac and pulmonary complications (Mulholland & Greenfield's Surgery, p. 250; Sabiston Textbook of Surgery)

B. Recent guidelines for assessment of functional capacity (with coronary stents in-situ) (4 marks)

• Functional capacity assessment must be interpreted alongside stent-specific timing rules, because in these patients the decision is not only "fit vs unfit for surgery" but also "safe timing after PCI":
  • Balloon angioplasty alone → delay elective NCS ≥14 days
  • Bare-metal stent (BMS) → delay ≥30 days (up to 3 months per newer data)
  • Drug-eluting stent (DES) for chronic coronary disease → delay ≥6 months (ideally 12 months)
  • DES for acute coronary syndrome → delay ≥12 months; complex DES (bifurcation, long/multivessel) may also warrant 12 months
  • If surgery cannot be delayed, a multidisciplinary discussion (anesthesiologist, cardiologist, surgeon) is mandatory to weigh stent thrombosis risk (from interrupting DAPT) against surgical bleeding risk (from continuing DAPT); aspirin is usually continued perioperatively when possible, with only the P2Y12 inhibitor (clopidogrel/ticagrelor/prasugrel) interrupted for the shortest safe interval.
• Good functional capacity (≥4 METs / DASI ≥34) in a stented patient supports proceeding without additional noninvasive cardiac testing, provided the PCI-to-surgery interval and antiplatelet plan are appropriate. Poor functional capacity in this population should prompt biomarker testing and/or cardiology referral rather than routine revascularization (prophylactic PCI/CABG has not been shown to improve perioperative outcomes in patients with stable CAD).

C. Role of cardiac biomarkers in this patient (4 marks)

• Known cardiovascular disease (including prior coronary stent)
• Age >65 years
• Age 45-64 years with symptoms/signs suggestive of CVD
• Patients with elevated risk undergoing elevated-risk noncardiac surgery, especially those with poor or unknown functional capacity

1. Preoperative: If natriuretic peptide/troponin is normal, the patient is classified low-risk and no further cardiac testing is needed even with borderline functional capacity. If elevated, a multidisciplinary team should discuss further cardiac evaluation (e.g., stress testing, cardiology input) before proceeding, since elevated baseline biomarkers combined with a stent history raise concern for silent ischemia, in-stent restenosis, or reduced cardiac reserve.
2. Postoperative: Troponin surveillance is recommended in high-risk patients (including those with coronary stents) to detect myocardial injury after noncardiac surgery (MINS), which is often asymptomatic but carries significant 30-day mortality risk. A rise in postoperative troponin above baseline should trigger cardiology consultation, ECG, and evaluation for perioperative MI versus other causes of injury (e.g., stent thrombosis).
3. Biomarkers thus complement, not replace, functional capacity assessment - a patient with a coronary stent, poor exercise tolerance, and elevated NT-proBNP/troponin represents the highest-risk group warranting the most cautious perioperative plan (staged surgery, invasive monitoring, ICU-level postoperative care), whereas normal biomarkers with good functional capacity allow safe progression to surgery once the stent-appropriate waiting period has elapsed.

Exam tip - structure your answer as:

1. Define MET with the numeric value (2 marks - quick, precise)
2. Guidelines: subjective vs structured/validated tools (DASI, MET-REPAIR) → 2024 AHA/ACC algorithm → stent-timing table → DAPT/multidisciplinary decision (4 marks)
3. Biomarkers: indications → NT-proBNP vs troponin → pre-op decision node → post-op MINS surveillance (4 marks)