Preoperative assessment and medicines

Preoperative Risk Stratification & Postoperative Surgical Complications

Perioperative medicine bridges preoperative risk stratification and active postoperative vigilance, aiming to minimize surgical morbidity and accelerate recovery. Structured multidisciplinary evaluation in the preoperative clinic, adherence to pharmacology withholding guidelines, and systematic evaluation of postoperative complications are fundamental components of patient safety in Australian surgical practice.

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Preoperative Risk Stratification & Functional Capacity

Preoperative assessment seeks to detect undiagnosed chronic illnesses, optimize pre-existing medical conditions, quantify perioperative cardiopulmonary risk, and plan post-surgical monitoring (ward vs high-dependency or intensive care unit).

Functional Capacity: Metabolic Equivalents (METs)

Cardiopulmonary exercise tolerance is an exceptionally strong predictor of postoperative outcome. Functional capacity is quantified in Metabolic Equivalents of Task (METs), where $1\text{ MET}$ represents the basal oxygen consumption of an adult at rest ($3.5\text{ mL }O_2\text{/kg/min}$):

• $\ge 4\text{ METs}$ (Adequate Functional Capacity): The patient can climb two flights of stairs without stopping, walk up a moderate hill, carry a bag of groceries ($> 10\text{ kg}$), or perform heavy household work. Patients with $\ge 4\text{ METs}$ have low rates of major adverse cardiac events, and can generally proceed to elective surgery without advanced cardiac stress imaging.
• $< 4\text{ METs}$ (Poor Functional Capacity): The patient cannot walk four blocks or climb two flights of stairs without stopping. Poor functional capacity indicates diminished cardiopulmonary reserve and mandates formal cardiovascular risk stratification.

The Revised Cardiac Risk Index (RCRI / Lee's Criteria)

The RCRI is the standard validated tool for predicting major adverse cardiac events (MACE: myocardial infarction, pulmonary oedema, complete heart block, or cardiac arrest) following non-cardiac surgery. It incorporates six independent clinical variables (each assigned 1 point):

1. High-risk surgical procedure: Intraperitoneal, intrathoracic, or suprainguinal vascular surgery.
2. History of ischemic heart disease: Previous myocardial infarction, positive stress test, active angina, or pathological Q waves on ECG.
3. History of congestive heart failure: Current or prior signs, elevated BNP, or history of pulmonary oedema.
4. History of cerebrovascular disease: Prior stroke or transient ischemic attack.
5. Preoperative insulin therapy for diabetes mellitus.
6. Preoperative renal impairment: Serum creatinine $> 177\text{ }\mu\text{mol/L}$ ($> 2.0\text{ mg/dL}$).

MACE Risk Stratification:

• Class I ($0\text{ points}$): $0.4\%$ cardiac risk.
• Class II ($1\text{ point}$): $0.9\%$ cardiac risk.
• Class III ($2\text{ points}$): $6.6\%$ cardiac risk.
• Class IV ($\ge 3\text{ points}$): $> 11\%$ cardiac risk; requires multidisciplinary anaesthetic and cardiology review, optimization, and post-op telemetry/ICU placement.

Pulmonary Risk & Smoking Cessation

Risk factors for postoperative pulmonary complications (atelectasis, pneumonia, prolonged mechanical ventilation) include advanced age ($> 65$ years), COPD, obstructive sleep apnoea (STOP-Bang score), and current smoking. Smoking cessation $\ge 4\text{ to }8\text{ weeks}$ prior to surgery improves tracheobronchial ciliary clearance and reduces sputum volume; quitting even $24\text{ to }48\text{ hours}$ before surgery significantly eliminates carbon monoxide and restores tissue oxygen delivery.

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Perioperative Medication Management Guidelines

Managing chronic medications requires balancing the risks of intraoperative physiological instability against the rebound exacerbation of chronic diseases.

Antihypertensives & Cardiovascular Drugs

• ACE inhibitors/ARBs: The anaesthetic plan depends on indication, haemodynamics and procedure. Omitting a dose may reduce hypotension when used for hypertension; HFrEF and other indications require individual assessment rather than a universal stop rule.
• Beta-Blockers (e.g., metoprolol, atenolol, bisoprolol): Continue without interruption throughout the perioperative period. Abrupt cessation provokes rebound sympathetic hyperactivity, tachycardia, severe hypertension, and acute myocardial ischaemia. However, acute initiation of high-dose beta-blockade on the day of surgery is dangerous and increases perioperative stroke and mortality.
• Statins & Calcium Channel Blockers: Continue throughout the perioperative period.

Diabetes Medications

• SGLT2 medicines: Australian guidance for major surgery or procedures involving bowel preparation generally omits the drug for two days before and on the procedure day (three days total). Minor procedures differ. Check ketones in an unwell or fasting patient, even with normal glucose, and restart only when clinically safe and eating normally.
• Metformin: Manage according to fasting, kidney function and contrast-associated AKI risk. Every contrast study does not require an automatic 48-hour interruption; use the radiology/diabetes protocol and reassess renal function where indicated.
• Sulfonylureas (e.g., gliclazide): Withhold on the morning of surgery while fasting to avoid intraoperative hypoglycaemia.
• GLP1/GIP medicines: The 2025 Australian multisociety recommendation is to continue therapy, use a 24-hour clear-fluid diet before the procedure followed by standard fasting, and assess aspiration mitigation when this has not occurred. Coordinate with anaesthesia and local protocols; a routine weekly-dose seven-day hold imported from earlier overseas guidance is not the current Australian default.
• Insulin: Reduce the basal insulin dose by $20\%\text{ to }30\%$ on the evening before or morning of surgery; withhold short-acting bolus insulin while fasting. For major surgeries or prolonged fasting, transition to a Variable Rate Intravenous Insulin Infusion (VRIII) with $5\%$ dextrose and potassium.

Anticoagulants & Antiplatelets

• Aspirin: Continue for secondary prevention (e.g., prior coronary stents, ischemic stroke) in most operations; withhold 7 days prior only for high-bleeding-risk operations (intracranial, spinal, or posterior eye surgery).
• Antiplatelets: Balance bleeding with stent thrombosis risk and consult cardiology for recent PCI. If interruption is appropriate, the interval differs between ticagrelor, clopidogrel and prasugrel; never substitute one blanket five-day rule.
• Direct Oral Anticoagulants (DOACs: apixaban, rivaroxaban, dabigatran): Withhold 24 to 48 hours prior for low/moderate bleeding risk procedures, and 48 to 72 hours (or longer if renal clearance is impaired) for high bleeding risk procedures. Routine heparin bridging is not indicated for DOACs.
• Warfarin: Withhold 5 days prior, targeting an INR $< 1.5$. Bridging with therapeutic low-molecular-weight heparin (LMWH) is reserved strictly for high-thromboembolic-risk patients (mechanical mitral valves, recent stroke $< 3\text{ months}$, recent VTE $< 3\text{ months}$).

Corticosteroids

Steroid exposure can suppress adrenal reserve, but the risk depends on dose, duration, recency and the patient. Continue necessary baseline treatment and plan supplemental cover according to surgical stress and the relevant endocrine/anaesthetic pathway. Every person who took steroids in the preceding year does not automatically need the same high-dose regimen.

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Primary references (checked 7 October 2026): Australian 2025 GLP1/GIP perioperative recommendations.