Pre Operative Medical Evaluation

Introduction to Pre-Operative Assessment for MCCQE1

The goal of the pre-operative medical evaluation is not merely to “clear” a patient for surgery, but to risk stratify and optimize the patient’s medical conditions to minimize perioperative morbidity and mortality.

For MCCQE1 preparation, understanding the role of the Medical Consultant is crucial. This topic integrates several CanMEDS roles:

Medical Expert: Applying clinical knowledge to assess risk.
Collaborator: Communicating risk to the surgeon and anesthesiologist.
Health Advocate: Ensuring patient safety and appropriate resource utilization (Choosing Wisely Canada).

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Canadian Context: In Canada, pre-operative testing is heavily influenced by Choosing Wisely Canada recommendations to reduce unnecessary testing. The Canadian Cardiovascular Society (CCS) guidelines are the gold standard for cardiac risk assessment in this domain.

Clinical Approach: The History and Physical

A structured approach is essential for the MCCQE1 Clinical Decision Making (CDM) and MCQ components.

Step 1: Focused History

The history determines the extent of the workup. Key components include:

Surgical Risk: Is the surgery low risk (e.g., cataract, breast) or high risk (e.g., vascular, thoracic)?
Functional Capacity: Can the patient perform < 4 METs (Metabolic Equivalents)?
- Example: Can they climb two flights of stairs or walk up a hill without stopping due to dyspnea or angina?
Cardiovascular Hx: CAD, CHF, arrhythmias, valvular disease, pacemakers.
Respiratory Hx: COPD, Asthma, OSA (Snoring, Tiredness, Observed apnea, Pressure - STOP-Bang).
Bleeding Hx: Personal or family history of coagulopathy.
Medications: Specifically anticoagulants, antiplatelets, insulin, and corticosteroids.

Step 2: Physical Examination

Focus on systems that affect anesthesia and surgical outcomes:

Airway: Mallampati score, mouth opening, thyromental distance, neck mobility.
Cardiac: Murmurs (specifically Aortic Stenosis), signs of CHF (JVP, edema).
Respiratory: Wheezing, crackles, prolonged expiration.

Step 3: Risk Stratification

Utilize validated scores to quantify risk.

Risk Stratification Tools

1. ASA Physical Status Classification

The American Society of Anesthesiologists (ASA) classification is a global standard used in Canadian hospitals.

ASA Class	Definition	Examples
ASA I	A normal healthy patient	Non-smoking, no alcohol misuse
ASA II	Mild systemic disease	Controlled HTN, Controlled DM, Smoker, BMI > 30
ASA III	Severe systemic disease (limits activity)	Poorly controlled DM/HTN, COPD, BMI > 40, Active hepatitis
ASA IV	Severe systemic disease that is a constant threat to life	Recent MI (< 3 months), CVA, TIA, Sepsis
ASA V	Moribund patient not expected to survive without surgery	Ruptured aneurysm, massive trauma
ASA VI	Brain-dead organ donor
E	Emergency modifier	Added to any class (e.g., ASA IIE)

2. Revised Cardiac Risk Index (RCRI)

The RCRI is widely used in Canada to estimate the risk of major cardiac complications.

RCRI Risk Factors (1 point each)

High-risk surgery (Intraperitoneal, intrathoracic, suprainguinal vascular)
History of Ischemic Heart Disease (MI, positive stress test, angina, nitrate use)
History of Congestive Heart Failure
History of Cerebrovascular Disease (Stroke or TIA)
Pre-operative treatment with Insulin (IDDM)
Pre-operative Creatinine > 177 µmol/L (> 2.0 mg/dL)

Interpretation:

0 predictors: ~0.4% risk
1 predictor: ~1% risk
2 predictors: ~2.4% risk
≥3 predictors: ~5.4% risk

Pre-Operative Testing: Choosing Wisely Canada

Routine testing for healthy patients undergoing low-risk surgery is not recommended. Testing should be guided by history and physical exam.

ECG Guidelines

When to order an ECG:

Known coronary artery disease or structural heart disease.
Arrhythmia symptoms.
Asymptomatic patients with RCRI ≥ 1 (Canadian Cardiovascular Society recommendation).
Note: Routine ECG is not indicated for asymptomatic patients undergoing low-risk surgery.

The Canadian “BNP” Guideline

A unique aspect of Canadian practice (CCS Guidelines) is the use of BNP (Brain Natriuretic Peptide) or NT-proBNP.

CCS Recommendation: Measure BNP or NT-proBNP before noncardiac surgery in patients who are:

65 years of age or older

45-64 years of age with significant cardiovascular disease or RCRI score ≥ 1

Elevated BNP is a strong independent predictor of perioperative cardiac death and MI.

Medication Management

Managing perioperative medications is a high-yield topic for the MCCQE1.

Cardiovascular Medications

Medication Class	Recommendation	Rationale
Beta-Blockers	CONTINUE	Do not stop abruptly (rebound hypertension/tachycardia). Note: Do not start acutely pre-op solely for surgery (POISE trial).
ACE Inhibitors / ARBs	HOLD (usually)	Hold on the morning of surgery to prevent refractory hypotension upon induction. Restart when euvolemic.
Diuretics	HOLD	Hold morning of surgery to prevent hypovolemia/electrolyte disturbance.
Statins	CONTINUE	Plaque stabilization.
Calcium Channel Blockers	CONTINUE	Maintenance of rate/BP control.

Anticoagulation and Antiplatelets

Aspirin: generally CONTINUED for patients with stents or high cardiovascular risk, unless surgery involves closed space (neurosurgery, posterior eye, spinal).
Clopidogrel/Ticagrelor: Generally STOP 5-7 days prior (unless high risk of stent thrombosis; requires specialist consult).
Warfarin: Stop 5 days prior. Check INR pre-op (Target < 1.5). Bridge with LMWH/Heparin if high thromboembolic risk (e.g., mechanical mitral valve).
DOACs (e.g., Apixaban, Rivaroxaban): Stop 2-3 days prior (depending on renal function and bleeding risk of surgery). No bridging required usually.

Diabetes Management

Oral Hypoglycemics: Hold on the morning of surgery.
- Metformin: Hold day of surgery (risk of lactic acidosis if renal injury occurs).
- SGLT2 Inhibitors (e.g., Empagliflozin): Hold 3 days prior (Risk of euglycemic DKA).
Insulin:
- Long-acting (Lantus/Levemir): Give 50-80% of dose the night before/morning of.
- Short-acting: Hold while NPO. Use sliding scale.

Airway Assessment: The “LEMON” Law

For anesthesia questions on the MCCQE1, remember the LEMON mnemonic for difficult airway prediction:

Look externally (facial trauma, large tongue, beard).
Evaluate 3-3-2 rule:
- Mouth opening > 3 fingers.
- Hyoid-mental distance > 3 fingers.
- Thyroid-to-mouth floor > 2 fingers.
Mallampati Score (Class I-IV).
Obstruction (stridor, foreign body).
Neck mobility (limited extension).

Canadian Guidelines Summary

🇨🇦 Key Canadian Guidelines for MCCQE1

CCS (2017): Emphasis on BNP measurement for risk stratification.
Choosing Wisely Canada: Avoid baseline labs, ECGs, and CXRs in healthy patients for low-risk surgery.
Diabetes Canada: Specific protocols for perioperative glycemic control (Target 5.0 - 10.0 mmol/L).
Thrombosis Canada: Excellent resource for bridging protocols (often referenced in clinical practice).

Key Points to Remember for MCCQE1

Functional Capacity is King: A patient with poor functional capacity (< 4 METs) often requires non-invasive stress testing if the results will change management.
SGLT2 Inhibitors: Stop them 3 days pre-op (unique and high-yield safety point).
Beta-Blockers: Continue if already on them; do not start them acutely pre-op.
Smoking Cessation: Ideally 4-8 weeks pre-op to reduce pulmonary complications. Short-term cessation (< 24h) helps with carboxyhemoglobin levels but not mucus clearance.
Emergency Surgery: Risk stratification should not delay life-saving surgery. Optimize rapidly and proceed.

Sample Question

Case Presentation

A 72-year-old male presents for a pre-operative evaluation prior to an elective total hip arthroplasty. He has a history of hypertension, type 2 diabetes mellitus, and osteoarthritis. He denies any chest pain or shortness of breath. He is able to walk 2 blocks but stops due to hip pain, not dyspnea. His medications include Ramipril, Metformin, Empagliflozin, and Atorvastatin.

Vitals: BP 135/82 mmHg, HR 76 bpm, BMI 29 kg/m². Physical Exam: Unremarkable cardiac and respiratory exam. Labs: Creatinine 95 µmol/L, HbA1c 7.2%.

Which one of the following is the most appropriate management of his medications prior to surgery?

A. Continue all medications including the morning of surgery
B. Hold Ramipril, Metformin, and Empagliflozin on the morning of surgery
C. Hold Empagliflozin 3 days prior, hold Ramipril and Metformin on the morning of surgery
D. Stop Atorvastatin 7 days prior to surgery
E. Start a Beta-blocker to reduce perioperative cardiac risk

Explanation

The correct answer is:

C. Hold Empagliflozin 3 days prior, hold Ramipril and Metformin on the morning of surgery

Detailed Explanation:

Empagliflozin (SGLT2 Inhibitor): FDA and Canadian guidelines recommend holding SGLT2 inhibitors at least 3 days (some guidelines say 3-4 days) prior to surgery to reduce the risk of euglycemic diabetic ketoacidosis (DKA). This is a critical safety point.
Ramipril (ACE Inhibitor): Generally held on the morning of surgery to prevent refractory hypotension under anesthesia, especially in major orthopedic surgery.
Metformin: Held on the day of surgery due to the theoretical risk of lactic acidosis if renal perfusion is compromised intraoperatively.
Atorvastatin: Statins should be continued perioperatively as they have plaque-stabilizing effects.
Beta-blockers: Should not be started acutely prior to surgery (POISE trial) as it increases the risk of stroke and hypotension, although it prevents non-fatal MI. They should only be continued if the patient is already taking them.

Why other options are incorrect:

A: Taking ACEi and SGLT2i morning of surgery poses significant risks (hypotension and DKA respectively).
B: Holding Empagliflozin only on the morning of surgery is insufficient to clear the drug and mitigate DKA risk.
D: Statins should be continued.
E: Initiating beta-blockers acutely is contraindicated.

References

Canadian Cardiovascular Society. (2017). CCS Guidelines on Perioperative Cardiac Risk Assessment and Management for Patients Who Undergo Noncardiac Surgery. https://www.onlinecjc.ca
Choosing Wisely Canada. Pre-operative Tests. https://choosingwiselycanada.org/pre-operative-tests/
Diabetes Canada. Clinical Practice Guidelines: In-Hospital Management of Diabetes.
Thrombosis Canada. Peri-operative Management of Anticoagulants. https://thrombosiscanada.ca
Fleisher, L. A., et al. (2014). ACC/AHA Guideline on Perioperative Cardiovascular Evaluation and Management of Patients Undergoing Noncardiac Surgery. Journal of the American College of Cardiology.