Lucan · Conditions

Perioperative assessment and optimisation

Australian guidance: ANZCA Perioperative Guidelines + eTG Cardiovascular + ACSQHC

1. Definition, scope, and epidemiology

Preoperative assessment is the systematic clinical evaluation of a patient before an elective or emergency surgical or anaesthetic procedure, aimed at quantifying perioperative risk, identifying and optimising modifiable comorbidities, and formulating an anaesthetic and postoperative care plan tailored to that risk. In Australia, this process is typically conducted through a pre-admission clinic for elective surgery, staffed by anaesthetists, nurse practitioners, and increasingly perioperative physicians, and is guided by professional documents from the Australian and New Zealand College of Anaesthetists (ANZCA). The scale of the task is substantial: over 2 million procedures are performed under anaesthesia in Australia each year, and perioperative morbidity and mortality remain a leading source of preventable harm, with cardiac and respiratory complications accounting for the majority of major adverse events. A well-conducted preoperative assessment reduces same-day cancellations, shortens length of stay, and directly reduces the incidence of myocardial infarction, pneumonia, and venous thromboembolism through targeted optimisation and risk-appropriate perioperative planning.

2. Physiological rationale: why surgery and anaesthesia stress each organ system

General anaesthesia and surgical stress perturb homeostasis across multiple organ systems simultaneously, and preoperative assessment exists to anticipate which patients have inadequate physiological reserve to tolerate this perturbation. Induction of general anaesthesia commonly causes a dose-dependent fall in systemic vascular resistance and myocardial contractility, unmasking latent cardiac disease that is well compensated at rest; a patient with critical but asymptomatic coronary stenosis may develop myocardial ischaemia the moment vasodilation and tachycardia increase myocardial oxygen demand while reducing diastolic coronary filling time. The surgical stress response itself, mediated by cortisol, catecholamines, and inflammatory cytokines released in proportion to tissue trauma, increases myocardial oxygen demand, promotes a prothrombotic and hyperglycaemic state, and can precipitate adrenal crisis in patients with unrecognised or under-treated adrenal insufficiency. Positive-pressure ventilation and the recumbent position reduce functional residual capacity and predispose to atelectasis, particularly in patients with pre-existing respiratory disease, reduced respiratory muscle reserve, or a smoking history that has impaired mucociliary clearance. Immobility, venous stasis from pneumoperitoneum or lower-limb positioning, and the procoagulant surgical stress response converge to elevate venous thromboembolism risk in every surgical patient, in proportion to the duration and invasiveness of the procedure. Preoperative assessment is therefore not a single test but a structured attempt to identify, for each organ system, whether baseline reserve is sufficient to absorb this predictable physiological insult, and if not, what can be optimised beforehand or planned for perioperatively.

3. Clinical assessment: ASA classification, functional capacity, and airway assessment

The ASA Physical Status Classification System, maintained by the American Society of Anesthesiologists and adopted throughout ANZCA perioperative practice, is the most widely used global shorthand for a patient's overall burden of systemic disease. ASA I describes a normal healthy patient; ASA II describes mild systemic disease without functional limitation, such as well-controlled hypertension, type 2 diabetes without end-organ complications, or current smoking; ASA III describes severe systemic disease with substantive functional limitation that is not an immediate threat to life, such as diabetes with an end-organ complication like nephropathy or retinopathy, poorly controlled hypertension, or stable angina; ASA IV describes severe systemic disease that is a constant threat to life, such as myocardial infarction within the preceding three months, ongoing cardiac ischaemia, or severe valvular dysfunction; and ASA V describes a moribund patient who is not expected to survive without the operation, such as a patient with a ruptured abdominal aortic aneurysm and haemodynamic instability. ASA VI is reserved for a declared brain-dead patient undergoing organ retrieval for donation, and an "E" suffix denotes emergency surgery and can be appended to any class. ASA class correlates strongly with perioperative mortality and is used for risk communication and resource planning, but it grades disease burden rather than functional reserve, so it must be combined with a specific assessment of functional capacity.

Functional capacity is most efficiently estimated in metabolic equivalents (METs), where 1 MET represents resting oxygen consumption and 4 METs represents the ability to climb a flight of stairs, walk up a hill, or walk on level ground at approximately 6.4 km/h without stopping from dyspnoea, chest pain, or exhaustion. A patient who can achieve 4 METs or more without cardiopulmonary symptoms can generally proceed to surgery without further cardiac investigation regardless of the presence of clinical cardiac risk factors, because self-reported functional capacity at this level predicts adequate perioperative cardiovascular reserve; a patient who cannot reach 4 METs, or whose functional capacity is unknown or unreliable (for example due to musculoskeletal limitation), warrants further risk stratification with tools such as the Revised Cardiac Risk Index before proceeding to intermediate- or high-risk surgery.

Airway assessment aims to predict difficult mask ventilation, difficult laryngoscopy, and difficult intubation before they are encountered unexpectedly under anaesthesia. The Mallampati classification is performed with the patient sitting upright, mouth open maximally, and tongue protruded without phonation: class I visualises the soft palate, uvula, fauces, and pillars; class II visualises the soft palate, uvula, and fauces with the pillars obscured; class III visualises only the soft palate and the base of the uvula; and class IV visualises only the hard palate. Class III and IV airways carry a substantially increased risk of difficult laryngoscopy. Thyromental distance, measured from the thyroid cartilage notch to the tip of the mandible with the neck fully extended, is a further independent predictor, with a distance below approximately 6 to 6.5 cm suggesting a difficult airway due to reduced mandibular space for laryngoscopic visualisation. Additional predictors of a difficult airway include reduced mouth opening (an interincisor gap below three finger-breadths), limited neck extension or cervical spine mobility, retrognathia or micrognathia, a short thick neck or elevated body mass index, obstructive sleep apnoea, poor dentition or prominent incisors, and a documented history of previous difficult intubation, which is the single most reliable predictor when available and should always be sought specifically in the preoperative history.

4. Cardiac and respiratory risk stratification

The Revised Cardiac Risk Index (RCRI), derived by Lee and colleagues, remains the most widely used bedside tool for estimating the risk of a major perioperative cardiac complication before non-cardiac surgery. It assigns one point each for six factors: high-risk surgery (intraperitoneal, intrathoracic, or suprainguinal vascular surgery), a history of ischaemic heart disease, a history of congestive heart failure, a history of cerebrovascular disease, insulin-treated diabetes mellitus, and a preoperative serum creatinine above 177 micromol/L. The risk of a major cardiac complication rises from approximately 0.4 percent with zero risk factors to approximately 1 percent with one factor, 2.4 percent with two factors, and 5.4 percent or higher with three or more factors, and a rising score prompts consideration of further investigation (such as resting echocardiography or non-invasive cardiac stress testing) or specialist cardiology input before proceeding, particularly when functional capacity is also reduced.

Certain cardiac conditions are classified as "active" and mandate cardiology evaluation and, wherever possible, delay of elective non-cardiac surgery until they are optimised: unstable coronary syndromes (unstable or severe angina, recent myocardial infarction), decompensated heart failure, significant arrhythmias (high-grade atrioventricular block, symptomatic bradyarrhythmias, or uncontrolled supraventricular or ventricular arrhythmias), and severe symptomatic valvular disease such as severe aortic stenosis. Where possible, elective non-cardiac surgery should be delayed for a minimum of 60 days (approximately two months) following myocardial infarction, because the risk of perioperative reinfarction is highest in the first 30 days and remains meaningfully elevated until around 60 days, after which it approaches baseline. Patients with a recent coronary stent require particular caution because of the risk of perioperative stent thrombosis if antiplatelet therapy is interrupted prematurely: elective surgery should be delayed at least 4 to 6 weeks after a bare metal stent, and at least 6 months (ideally 12 months) after a drug-eluting stent, wherever the clinical urgency of surgery allows; aspirin is generally continued through the perioperative period where possible, and it is the P2Y12 inhibitor component of dual antiplatelet therapy that is more often withheld once the minimum window has passed, always in consultation with the treating cardiologist.

Respiratory optimisation focuses on identifying and controlling reversible airway disease before surgery: uncontrolled asthma or COPD should be optimised with inhaled therapy and, where indicated, a short course of oral corticosteroids in the days before surgery, and active respiratory tract infection should prompt deferral of elective surgery until it has resolved. Smoking cessation at least 4 weeks before elective surgery measurably reduces postoperative pulmonary complications and improves wound healing, with the benefit increasing the longer the period of abstinence, but even brief cessation in the 12 to 24 hours before surgery reduces circulating carboxyhaemoglobin and nicotine, improving tissue oxygen delivery and reducing perioperative cardiovascular stress; patients should therefore always be encouraged and assisted to quit at any point before surgery, rather than told that a short interval is not worthwhile.

5. Fasting rules and consent

The ANZCA guideline on pre-procedure fasting sets minimum fasting intervals for adults and children without risk factors for delayed gastric emptying, commonly remembered as the "2-4-6" rule: clear fluids are permitted up to 2 hours before anaesthesia, breast milk is permitted up to 4 hours before, and solid food, infant formula, and other non-human milk are permitted up to 6 hours before. These intervals balance the risk of pulmonary aspiration of gastric contents at induction, which rises with residual gastric volume and acidity, against the harms of prolonged unnecessary fasting, which include patient discomfort, dehydration, hypoglycaemia in young children, and increased perioperative insulin resistance. The older practice of fasting all patients from midnight regardless of the scheduled time of surgery is no longer recommended, because it offers no additional safety margin over the tiered rule while causing avoidable dehydration and distress, particularly in children and older patients. Patients with risk factors for delayed gastric emptying, including diabetic gastroparesis, symptomatic gastro-oesophageal reflux, bowel obstruction, pregnancy, or emergency surgery with an unknown last meal time, are managed as though they have a full stomach regardless of the stated fasting interval, with a rapid sequence induction technique used to minimise aspiration risk.

Valid consent to a surgical or anaesthetic procedure requires four elements under Australian law: it must be voluntary, free from coercion or undue influence from family, staff, or circumstance; it must be given by a person with capacity, meaning the ability to understand, retain, weigh, and communicate a decision about the relevant information; it must be adequately informed, covering the nature and purpose of the procedure, its material risks, the expected benefits, and reasonable alternatives including the option of no treatment; and it must be specific to the procedure actually being performed. The Australian standard for what constitutes a material risk requiring disclosure was established in the High Court decision Rogers v Whitaker, which defines a material risk as one that a reasonable person in the patient's position would be likely to attach significance to, or one that the particular patient would be likely to attach significance to if the treating doctor is or should reasonably be aware of this, replacing the earlier paternalistic standard of what a reasonable body of medical opinion would choose to disclose. Consent for a specific procedure should generally be obtained by a clinician capable of performing that procedure or of explaining it in comparable detail, and should be revisited whenever the clinical circumstances or the planned procedure change materially from what was originally discussed.

6. Perioperative medication management

Chronic medication review is one of the highest-yield components of preoperative assessment, because several common drug classes require deliberate continuation, cessation, or dose adjustment to avoid preventable perioperative harm. Warfarin is generally stopped 4 to 5 days before elective surgery with moderate or high bleeding risk to allow the INR to fall below 1.5, and can usually be restarted on the evening of surgery at the patient's usual maintenance dose; bridging with therapeutic-dose low molecular weight heparin is reserved for patients at genuinely high thromboembolic risk, such as those with a mechanical heart valve, and is no longer routinely used for most patients with non-valvular atrial fibrillation given the lack of demonstrated benefit and the added bleeding risk. Direct oral anticoagulants are ceased for a period determined jointly by the bleeding risk of the surgery and the patient's renal function: apixaban and rivaroxaban are stopped 1 day before low-to-moderate bleeding risk surgery and 2 days before high bleeding risk surgery, largely irrespective of renal function down to their respective lower creatinine clearance limits, whereas dabigatran, which is approximately 80 percent renally cleared, requires a longer interval in renal impairment, stopped 1 day before low-to-moderate risk surgery (2 days if creatinine clearance is 30 to 50 mL/min) and 2 days before high bleeding risk surgery (4 days if creatinine clearance is 30 to 50 mL/min); urgent surgery or a creatinine clearance below 30 mL/min on any DOAC warrants specialist haematology or anaesthetic advice regarding residual anticoagulant effect and, where necessary, targeted reversal (idarucizumab for dabigatran, andexanet alfa for apixaban or rivaroxaban where available).

Antiplatelet management after coronary stenting follows the timing principles outlined in Section 4: aspirin is usually continued perioperatively, while the P2Y12 inhibitor is withheld only once the minimum post-stent interval has passed and only after discussion with cardiology, given the competing risks of perioperative bleeding against acute stent thrombosis. Among diabetes medications, metformin is generally continued up to and including the day of surgery for most procedures but should be withheld if postoperative renal impairment, hypoperfusion, or iodinated contrast administration is anticipated, given the risk of lactic acidosis with accumulation in renal impairment. Sodium-glucose co-transporter-2 inhibitors (SGLT2i), including dapagliflozin, empagliflozin, and ertugliflozin, carry a specific and clinically important perioperative risk: euglycaemic diabetic ketoacidosis, in which significant ketoacidosis develops despite a near-normal or only mildly elevated blood glucose, so a reassuring glucose reading does not exclude the diagnosis and blood (not urine) ketone testing is required whenever it is suspected. Per the Australian Diabetes Society, Australian Diabetes Educators Association, ANZCA, and New Zealand Society for the Study of Diabetes joint alert, SGLT2i should be omitted for at least 3 days before surgery requiring one or more nights of hospital admission (the 2 days immediately before the procedure plus the day of the procedure itself), or for the day of the procedure alone before a day-stay procedure not requiring bowel preparation, restarting once the patient has resumed normal oral intake.

Beta-blocker therapy taken chronically for hypertension, ischaemic heart disease, or arrhythmia should be continued without interruption through the perioperative period, because abrupt cessation risks rebound tachycardia, hypertension, and myocardial ischaemia; conversely, new beta-blocker therapy should not be initiated purely for perioperative cardioprotection in the days immediately before surgery, since trial evidence has shown this practice increases perioperative stroke and mortality despite modestly reducing myocardial infarction. ACE inhibitors and angiotensin receptor blockers are generally withheld on the morning of surgery, with the final dose taken the evening before, because their combination with the vasodilatory effects of general anaesthesia can produce refractory intraoperative hypotension resistant to standard vasopressor therapy. Patients on long-term corticosteroid therapy, or with primary or secondary adrenal insufficiency, require perioperative glucocorticoid stress dosing to prevent adrenal crisis: per eTG Endocrinology, a procedure requiring general anaesthetic, sedation, or fasting warrants hydrocortisone 100 mg intravenously at induction, followed by 50 mg intravenously 6-hourly until oral intake is tolerated, after which the usual maintenance dose is resumed, typically tapering over 2 to 3 days for a patient recovering well; minor procedures not requiring general anaesthetic can instead be covered with a simple doubling of the usual oral dose on the morning of the procedure.

7. VTE prophylaxis and preoperative investigations

Venous thromboembolism risk assessment is required for every surgical patient and weighs individual risk factors, which include age 60 years or older, obesity, active cancer, prior VTE, known thrombophilia, recent trauma or surgery, and anticipated immobility, against the type and duration of the planned procedure and the patient's bleeding risk. For major general surgery, including abdominal, gynaecological, cardiac, thoracic, or vascular procedures, the standard regimen per eTG is low molecular weight heparin or unfractionated heparin, continued for up to 1 week or until the patient is fully mobile, combined with mechanical prophylaxis such as graduated compression stockings or intermittent pneumatic compression until fully mobile; pharmacological prophylaxis should not commence in the first 6 hours after surgery because of increased bleeding risk, and is typically started 6 to 12 hours postoperatively once the surgeon confirms the bleeding risk is acceptably low. Total hip and knee replacement, hip fracture surgery, and major cancer surgery carry distinct, longer prophylaxis regimens of up to 28 to 35 days given their disproportionately high and prolonged VTE risk, while mechanical prophylaxis alone is preferred over pharmacological agents when even minor bleeding would be catastrophic, such as after neurosurgery or ophthalmic surgery.

Preoperative investigations should be targeted rather than routine: unselected "shotgun" testing, such as a full blood count, electrolytes, coagulation studies, ECG, and chest radiograph applied indiscriminately to every patient regardless of risk, does not improve outcomes in healthy patients undergoing low-risk surgery, rarely changes perioperative management, and generates false-positive results that can trigger unnecessary further investigation and delay or cancellation of surgery. Consistent with Choosing Wisely Australia recommendations, investigations should instead be guided by findings on history and examination, the patient's specific comorbidities, the medications they take (for example, renal function and electrolytes for a patient on an ACE inhibitor, diuretic, or DOAC), and the invasiveness of the planned procedure (for example, a group and hold or cross-match for surgery with meaningful anticipated blood loss). A healthy, asymptomatic patient undergoing low-risk day-case surgery requires no routine investigations beyond a thorough history and examination; conversely, a patient with reduced functional capacity, an elevated RCRI score, or a high-risk procedure warrants a more extensive and specifically targeted preoperative work-up, potentially including resting ECG, transthoracic echocardiography, or non-invasive cardiac stress testing, as guided by the specific risk factors identified.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.