Why We Do It & the ASA Physical Status
"The purpose of the preoperative evaluation is not simply to 'clear' a patient for surgery. It is to characterise the patient's medical condition, estimate perioperative risk, optimise that condition where time allows, formulate an anaesthetic plan, and β through information and rapport β reduce the patient's anxiety. A good preoperative visit is the single most cost-effective intervention the anaesthetist makes: it prevents cancellations, avoids unnecessary tests, and turns surprises in theatre into decisions made in the clinic."
Miller's Anesthesia, 9th Ed. Preoperative Evaluation. Elsevier; 2020.The PAC answers three questions
- Is the patient in the best achievable condition for this surgery?
- Is there anything that can be optimised in the time available? (and is the risk of delay worth the gain)
- What is the safest anaesthetic plan β technique, airway, monitoring, post-op disposition (ward / HDU / ICU)?
Add "E" for emergency surgery (e.g. ASA III E). ASA-PS predicts perioperative morbidity/mortality but is subjective and does not account for surgery type, age or airway β it is a communication shorthand, not a full risk score.
Ask what the patient can actually do. Climbing two flights of stairs or brisk walking uphill β β₯4 METs and predicts they will tolerate most surgery. Poor (<4 METs) or indeterminate capacity in a patient facing intermediate/high-risk surgery is what should trigger further cardiac thought β not a resting ECG in an asymptomatic person.
Metabolic equivalents (METs) β grading functional capacity
1 MET = 3.5 mL Oβ/kg/min (resting oxygen uptake). 4 METs is the clinical threshold for proceeding without further cardiac testing.
| Capacity | Can the patient⦠|
|---|---|
| 1 MET | Look after themselves β eat, dress, use the toilet; walk indoors around the house |
| 2β3 METs | Walk a block or two on level ground (3β5 km/h) |
| 4 METs β threshold | Climb a flight of stairs / walk up a hill; do light housework (dusting, washing dishes) |
| 4β10 METs | Moderate work (scrubbing floors, moving furniture); golf, bowling, doubles tennis |
| >10 METs | Strenuous sport β swimming, singles tennis, football |
A 12-item self-administered questionnaire of daily activities (each carries a weight, e.g. self-care 2.75, climbing stairs 5.5, running 8, strenuous sport 7.5). It removes the subjectivity of "how many stairs" and estimates METs directly:
Estimated METs = (0.43 Γ DASI score + 9.6) Γ· 3.5
NYHA functional class (heart-failure patients)
| Class | Limitation |
|---|---|
| I | No limitation β ordinary activity causes no symptoms |
| II | Slight limitation β comfortable at rest; ordinary activity β fatigue/dyspnoea/palpitations |
| III | Marked limitation β comfortable at rest; less-than-ordinary activity β symptoms |
| IV | Symptoms at rest; any activity increases discomfort |
The Focused History, Examination & Airway Assessment
"No investigation replaces a careful history and a look at the airway. The airway examination in particular is the one part of the preoperative assessment that only the anaesthetist can do and that no consultant referral will provide. A history of a previous difficult intubation is the strongest single predictor of a difficult airway β ask for it, and read the old anaesthetic chart."
Barash β Clinical Anesthesia, 9th Ed; Morgan & Mikhail's Clinical Anesthesiology, 6th Ed.Focused history β what actually changes the plan
- Presenting surgical problem + urgency (elective / urgent / emergency, and full-stomach status).
- Comorbidities β cardiac (angina, MI, failure, valves, CIED), respiratory (asthma/COPD, OSA), diabetes, renal, hepatic, neuro (epilepsy, stroke, raised ICP), thyroid.
- Previous anaesthesia β difficult airway, PONV, awareness, prolonged block; family history of malignant hyperthermia or suxamethonium apnoea (pseudocholinesterase deficiency).
- Drugs & allergies β anticoagulants/antiplatelets, insulin, steroids, GLP-1 agonists, SGLT2 inhibitors; latex/antibiotic/anaesthetic allergy (and what actually happened).
- Social β smoking, alcohol/recreational drugs, exercise tolerance (METs), pregnancy/LMP.
- Fasting status and whether an interpreter or attendant is needed.
- LEMON (difficult laryngoscopy/intubation): Look externally Β· Evaluate 3-3-2 (3 fingers mouth opening, 3 fingers hyoidβchin, 2 fingers floor-of-mouthβthyroid) Β· Mallampati Β· Obstruction/Obesity Β· Neck mobility.
- MOANS (difficult mask ventilation): Mask seal (beard) Β· Obesity/Obstruction Β· Age >55 Β· No teeth Β· Stiff lungs/Snoring (OSA).
- Predictors of difficult SGA β RODS; difficult cricothyrotomy β SHORT (Surgery/Scar, Haematoma, Obesity, Radiation, Tumour).
Bedside airway tests β thresholds & significance
No single test predicts a difficult airway reliably β combine several. The figures below are the ones asked in vivas.
| Test | How to do it | Reassuring | Concerning β difficult |
|---|---|---|---|
| Modified Mallampati | Sitting, head neutral, mouth wide open, tongue maximally out, no phonation | Class I (soft palate, fauces, uvula, pillars) / Class II (uvula tip hidden) | Class III (only soft palate) / IV (only hard palate) |
| Inter-incisor gap (mouth opening) | Maximal mouth opening between incisors | >5 cm / admits 3 fingers | <3 cm β difficult laryngoscopy; <2 cm β difficult LMA |
| Thyromental distance (TMD) | Thyroid notch β tip of chin, neck fully extended | >6.5 cm | 6β6.5 cm difficult but possible; <6 cm may be impossible |
| Hyomental distance | Hyoid bone β mentum | >6 cm (Grade I) | 4β6 cm (II); <4 cm (III) β impossible laryngoscopy/intubation |
| Upper-lip-bite test | Ask patient to bite the upper lip with the lower incisors | Class I β bite above the vermilion line | Class II (below vermilion); Class III β cannot reach lip |
| Mandibular protrusion (ULBT variant) | Advance lower incisors in front of the upper incisors | Class A β lower teeth protrude beyond upper | Class B / C β difficult laryngoscopy |
| Neck / atlanto-occipital movement | Chin-to-chest (flexion) & look at the ceiling without raising brows (extension) | Full flexion + extension | β₯β loss of AO extension β difficult rigid laryngoscopy |
| 3-3-2 rule | Patient's own fingers | 3 (mouth opening) Β· 3 (hyoidβchin) Β· 2 (thyroid notchβfloor of mouth) | Any value smaller than above |
Systemic examination
- Vitals & general β BP both arms if relevant, SpOβ, weight/BMI, pallor, cyanosis, oedema, hydration.
- CVS β heart sounds, murmurs, JVP, peripheral pulses, signs of failure.
- RS β air entry, added sounds, wheeze; SpOβ on air.
- Spine & back β landmarks, deformity, local sepsis if regional/neuraxial planned; peripheral neurology if a block is planned.
- IV access β anticipate difficulty; site for lines.
Co-Existing Disease β System by System
"The goal of the preoperative visit in the patient with co-existing disease is to ensure the disease is treated as well as it reasonably can be before an elective operation, and to decide which chronic therapies are continued, modified, or stopped. Cancelling a case rarely improves outcome unless the delay is used to make a specific, achievable change β a controlled blood sugar, a treated infection, a rate-controlled AF, an optimised inhaler regimen."
Stoelting's Anesthesia and Co-Existing Disease, 8th Ed. Elsevier; 2022.- IHD / stents: liaise with cardiology before any elective surgery and do not stop dual antiplatelet therapy without their input β balance the risk of stent thrombosis against surgical bleeding.
- Hypertension: proceed if BP <180/110; very high pressures on the day are usually anxiety/white-coat β continue most agents (see Β§5).
- Heart failure: decompensated failure is high-risk β echo and optimise first. Know the CIED (pacemaker/ICD) type and the reprogramming/magnet plan for diathermy.
- Asthma / COPD: operate when optimised and infection-free; continue inhalers; a course of steroids/nebulisers for an exacerbation is worth the delay.
- Smoking cessation: helps most when stopped >4β8 weeks before surgery; even 24β48 h lowers carboxyhaemoglobin and improves oxygen delivery.
- OSA: screen with the STOP-BANG questionnaire (below); a high score means plan opioid-sparing analgesia and enhanced post-operative monitoring.
| STOP-BANG questionnaire for OSA β score 1 point for each "yes" | |
|---|---|
| S β Snoring | Do you snore loudly (louder than talking, or audible through a closed door)? |
| T β Tiredness | Do you often feel tired, fatigued or sleepy during the daytime? |
| O β Observed apnoea | Has anyone observed you stop breathing, choke or gasp during sleep? |
| P β Pressure | Do you have, or are you being treated for, high blood pressure? |
| B β BMI | Is your BMI greater than 35 kg/mΒ²? |
| A β Age | Are you older than 50 years? |
| N β Neck | Is your neck circumference greater than 40 cm (β16 inches)? |
| G β Gender | Are you male? |
Interpretation: 0β2 = low risk Β· 3β4 = intermediate risk Β· β₯5 = high risk of moderate-to-severe obstructive sleep apnoea.
- Diabetes: assess control (HbA1c), aim for a capillary glucose of ~6β10 mmol/L on the day, and place the patient first on the list; manage agents per Β§5.
- Thyroid: render the patient euthyroid before elective surgery; continue anti-thyroid or replacement therapy on the day.
- Steroids / adrenal: continue chronic corticosteroids and give a perioperative stress dose for significant surgery (Β§5).
- Know the eGFR and dialysis schedule (dialyse the day before, not immediately before surgery); correct electrolytes β especially potassium.
- Adjust the choice and dose of renally-excreted drugs and avoid nephrotoxins.
- Anaemia: investigate and treat (iron Β± erythropoietin) before elective surgery β a modifiable, independent risk factor that reduces transfusion.
- Assess severity (ChildβPugh / MELD) and correct any coagulopathy; anticipate altered drug handling.
- Identify and manage the complications β ascites, encephalopathy, varices and hypoalbuminaemia β before an elective case.
Evidence-Based Guidelines
β’ Clear fluids β 2 hours (water, black tea/coffee, pulp-free juice, carbohydrate drinks; encourage clears up to 2h)
β’ Breast milk β 4 hours
β’ Infant formula / light meal (toast) β 6 hours
β’ Fatty/fried food, meat, full meal β 8 hours
GLP-1 receptor agonists (semaglutide etc.): delay gastric emptying β the ASA 2023 consensus advises holding the dose on the day of surgery (daily preparations) or the week of surgery (weekly preparations); if not held or GI symptoms are present, treat as a full stomach (consider gastric ultrasound / RSI).
| Class | Example | Action |
|---|---|---|
| Hβ-receptor antagonist | Ranitidine, famotidine | β gastric acid secretion β lower volume & higher pH (needs time to work) |
| Proton-pump inhibitor | Omeprazole, pantoprazole | Suppress acid by blocking the parietal-cell proton pump |
| Non-particulate antacid | Sodium citrate 0.3 M | Immediate neutralisation of existing acid β first choice in obstetrics |
| Prokinetic | Metoclopramide (dopamine antagonist) | Speeds gastric emptying & raises lower-oesophageal-sphincter tone |
| RCRI predictor β 1 point each |
|---|
| High-risk surgery β intraperitoneal, intrathoracic or suprainguinal vascular |
| Ischaemic heart disease |
| History of congestive heart failure |
| History of cerebrovascular disease (stroke / TIA) |
| Insulin-treated diabetes mellitus |
| Serum creatinine >177 Β΅mol/L (2 mg/dL) |
| RCRI score | Estimated risk of MACE |
|---|---|
| 0 | ~0.4% |
| 1 | ~0.9% |
| 2 | ~6.6% (elevated) |
| β₯3 | ~11% |
| Surgical risk (30-day MACE) | Examples |
|---|---|
| High (>5%) | Emergency major operations (esp. in the elderly); aortic & major vascular; peripheral vascular; anticipated prolonged surgery with large fluid shifts and/or blood loss |
| Intermediate (<5%) | Carotid endarterectomy; head & neck; intraperitoneal & intrathoracic; orthopaedic; prostate |
| Low (<1%) | Endoscopic procedures; superficial procedures; cataract; breast; ambulatory / day-case surgery |
β’ FBC β if ASA III/IV, or major surgery, or symptoms of anaemia.
β’ U&E / renal β if at risk of AKI, on relevant drugs (ACEi/diuretic), ASA III/IV, or major surgery.
β’ ECG β cardiovascular/renal disease, ASA III+, or major surgery (not routine by age alone).
β’ HbA1c β known/suspected diabetes; Ξ²-hCG β where pregnancy is possible (ask & document); sickle test where relevant; group & save/crossmatch per expected blood loss.
Coagulation only for liver disease, anticoagulants or bleeding history β not "routine".
What to Continue, Modify or Stop
| Drug / Class | Peri-op instruction | Why |
|---|---|---|
| Beta-blockers | Continue (incl. morning of surgery) | Abrupt withdrawal β rebound ischaemia/tachycardia; don't start de novo on the day (POISE β stroke/hypotension) |
| Statins | Continue | Plaque stabilisation; continued through the perioperative period |
| ACE inhibitors / ARBs | Consider omitting morning dose (esp. if taken for HTN) | Refractory intra-op hypotension; continue if for heart failure β individualise |
| Aspirin | Continue for secondary prevention/stents (surgeon-dependent); stop 5β7 d only if bleeding risk > thrombotic | Balance stent thrombosis vs surgical bleeding |
| Clopidogrel / P2Y12 | Stop 5β7 days pre-op β only after cardiology input for stents | Bleeding vs stent thrombosis; timing driven by stent age |
| Warfarin | Stop 5 days pre-op, check INR <1.5; bridge with LMWH only if high thrombotic risk | Most patients (incl. AF) do not need bridging (BRIDGE trial) |
| DOACs | Stop 24β48 h (up to 72 h if high bleed risk / renal impairment); no routine bridging | Predictable pharmacokinetics; timing by drug + eGFR + bleeding risk |
| Metformin | Continue up to day of surgery in most; omit on the day for major surgery / contrast / renal impairment | Small lactic-acidosis risk only with AKI/hypoperfusion |
| SGLT2 inhibitors (βgliflozins) | Stop 3β4 days before surgery | Euglycaemic diabetic ketoacidosis risk |
| GLP-1 agonists (βglutides) | Hold day-of (daily) / week-of (weekly); full-stomach precautions | Delayed gastric emptying β aspiration (ASA 2023) |
| Insulin | Long-acting: 60β80% of usual dose the night before/morning; withhold short-acting while fasting; VRIII for major/poorly controlled | Avoid hypoglycaemia while starved; maintain control |
| Corticosteroids (chronic) | Continue + peri-op stress dose for significant surgery | Suppressed HPA axis β adrenal crisis |
| Diuretics | Omit on the day of surgery β except a thiazide taken for hypertension (continue) | Hypovolaemia/hypotension & electrolyte shifts on induction |
| NSAIDs | Stop 48 h before surgery (COX-2 selective may be continued unless bone-healing concern) | Platelet effect / bleeding, renal impairment |
| Sildenafil & PDE-5 inhibitors | Stop 24 h before surgery | Refractory hypotension with anaesthetic vasodilators |
| OCP / HRT | Consider stopping 4 weeks before major/lower-limb surgery (VTE risk) β balance vs pregnancy risk | Oestrogen is prothrombotic |
| Herbal / OTC | Stop the "G"s ~1β2 weeks before (Garlic, Ginkgo, Ginseng, etc.) | Bleeding, drug interactions, sedation |
Beta-blockers, statins, most antihypertensives (except ACEi/ARB β individualise), inhalers, antiepileptics, anti-parkinsonian, thyroid, immunosuppressants, most psychiatric drugs, and chronic steroids. Give with a sip of water. When in doubt, the harm is usually in stopping chronic therapy, not continuing it.
The PAC Workflow
History & records
- Surgical problem + urgency + fasting/full-stomach status
- Comorbidities, previous anaesthesia, family h/o (MH, scoline apnoea), drugs, allergies
- Functional capacity (METs), smoking/alcohol, pregnancy; read the old anaesthetic chart
Examination β airway first
- Mallampati, mouth opening, TMD, 3-3-2, neck movement, dentition (LEMON/MOANS)
- CVS, RS, spine/back if regional planned, IV access
- Assign ASA physical status (Β± E)
Targeted investigations
- Order by ASA grade Γ surgical grade (NICE NG45) β not a routine battery
- Cardiac work-up only if it will change management (poor METs + higher-risk surgery)
Optimise & instruct
- Optimise comorbidities where time allows (glucose, inhalers, rate control, anaemia)
- Medication plan (continue/stop/bridge β Β§5); fasting instructions (ASA 2023)
- Only cancel if delay buys a specific, achievable improvement
Plan, consent & premedicate
- Technique, airway device, lines/monitoring, analgesia, PONV & VTE prophylaxis
- Post-op destination (ward / HDU / ICU); informed consent (Montgomery)
- Anxiolysis/premedication and aspiration prophylaxis where indicated
Common Mistakes in the PAC
Age-based or blanket investigations in a well ASA I patient for minor surgery add cost, delay and false-positive chases without improving outcome. Test by comorbidity and surgical grade (NICE NG45).
The airway assessment is the one thing only the anaesthetist can do. A previous difficult intubation is the strongest predictor β always ask and read the old chart. Document Mallampati, mouth opening, TMD, neck movement and dentition.
Beta-blockers, statins, inhalers, antiepileptics and steroids should continue. Rebound ischaemia (beta-blocker withdrawal) and adrenal crisis (steroid omission) are avoidable harms.
GLP-1 agonists delay gastric emptying (aspiration risk β hold and treat as full stomach if not held). SGLT2 inhibitors cause euglycaemic DKA β stop 3β4 days before. Both are now very common and easy to overlook.
Prolonged starvation causes dehydration, hypoglycaemia and misery with no benefit. Encourage clear fluids up to 2 hours before surgery (ASA 2023).
Isolated white-coat hypertension <180/110 is not a reason to cancel. Cancel only when the delay will be used to achieve a specific, worthwhile optimisation.
Most patients on warfarin (including AF) do not need LMWH bridging (BRIDGE trial β more bleeding, no thrombotic benefit). Reserve bridging for genuinely high thrombotic risk (mechanical mitral valve, recent VTE/stroke).
Exam Pearls
Q: What are the objectives of the pre-anaesthetic check-up?
Assess and characterise the patient's condition, estimate perioperative risk, optimise co-existing disease, formulate the anaesthetic plan, obtain informed consent, and reduce anxiety β while avoiding unnecessary tests and cancellations.
Q: Define the ASA physical status classes.
I normal healthy; II mild systemic disease; III severe systemic disease (functional limitation); IV severe disease that is a constant threat to life; V moribund, not expected to survive without surgery; VI brain-dead organ donor. Add "E" for emergency. It is subjective and ignores surgery type, age and airway.
Q: State the ASA 2023 fasting times.
Clear fluids 2 h, breast milk 4 h, formula/light meal 6 h, fatty/fried/full meal 8 h. GLP-1 agonists: hold on the day (daily) or the week (weekly) and treat as full stomach if not held.
Q: What is the Revised Cardiac Risk Index?
Six equally-weighted predictors: high-risk surgery, ischaemic heart disease, heart failure, cerebrovascular disease, insulin-treated diabetes, creatinine >2 mg/dL. Increasing points β increasing risk of major cardiac events.
Q: How do you assess the airway pre-operatively?
History of difficulty + LEMON: Look externally, Evaluate 3-3-2, Mallampati, Obstruction/Obesity, Neck mobility; plus mouth opening, thyromental distance, dentition and upper-lip-bite test. MOANS predicts difficult mask ventilation.
Q: How much does functional capacity matter, and how is it measured?
Greatly β β₯4 METs (two flights of stairs, brisk uphill walk) predicts tolerance of most surgery. Poor/unknown capacity before higher-risk surgery is what triggers further cardiac assessment (ACC/AHA 2024), not routine testing.
Q: Which drugs do you stop, and when, before surgery?
SGLT2 inhibitors 3β4 days; clopidogrel 5β7 days; warfarin 5 days (INR <1.5); DOACs 24β72 h by drug/eGFR/bleed risk; GLP-1 agonists on the day/week; the herbal "G"s 1β2 weeks. Continue beta-blockers, statins, inhalers, antiepileptics and steroids.
Q: STOP-BANG β what is it?
An OSA screen: Snoring, Tiredness, Observed apnoea, high Pressure (BP), BMI >35, Age >50, Neck >40 cm, male Gender. β₯3 = intermediateβhigh risk β opioid-sparing plan and enhanced post-op monitoring.
References
- Gropper MA, et al. (eds). Miller's Anesthesia, 9th Edition. Preoperative Evaluation. Philadelphia, PA: Elsevier; 2020.
- Barash PG, Cullen BF, Stoelting RK, et al. (eds). Clinical Anesthesia, 9th Edition. Preoperative Assessment & the Airway. Wolters Kluwer; 2023.
- Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail's Clinical Anesthesiology, 6th Edition. Preoperative Evaluation & Airway Management. McGraw-Hill; 2018.
- Hines RL, Marschall KE (eds). Stoelting's Anesthesia and Co-Existing Disease, 8th Edition. Elsevier; 2022.
- American Society of Anesthesiologists. ASA Physical Status Classification System (last approved/amended 2020).
- ASA Task Force on Preoperative Fasting. Practice Guidelines for Preoperative Fasting β 2023 update, and 2023 consensus on GLP-1 receptor agonists. Anesthesiology.
- Thompson A, et al. (ACC/AHA). 2024 Guideline for Perioperative Cardiovascular Management for Noncardiac Surgery. Circulation / J Am Coll Cardiol. 2024.
- Lee TH, Marcantonio ER, Mangione CM, et al. Derivation and prospective validation of the Revised Cardiac Risk Index (RCRI). Circulation. 1999;100:1043β1049.
- National Institute for Health and Care Excellence. Routine preoperative tests for elective surgery (NG45). NICE; 2016.
- Douketis JD, Spyropoulos AC, Kaatz S, et al. (BRIDGE). Perioperative Bridging Anticoagulation in Patients with Atrial Fibrillation. N Engl J Med. 2015;373:823β833.
- POISE Study Group. Effects of extended-release metoprolol succinate in patients undergoing non-cardiac surgery (POISE trial). Lancet. 2008;371:1839β1847.