14.1 Preoperative Assessment & Perioperative Medication Management
Key Takeaways
Preoperative risk stratification utilizes the American Society of Anesthesiologists (ASA) Physical Status Classification (ASA I healthy to ASA V moribund, with the 'E' modifier for emergency procedures) and Cardiopulmonary Exercise Testing (CPET) to evaluate functional physiological reserve.
The preoperative fasting '2-4-6 rule' mandates a minimum fasting interval of 2 hours for clear fluids, 4 hours for breast milk, and 6 hours for light meals, infant formula, and non-human milk prior to elective anaesthesia to prevent pulmonary aspiration.
Cardiovascular medications require targeted perioperative adjustment: ACE inhibitors and ARBs must be withheld 24 hours prior to surgery to prevent refractory intraoperative vasoplegic hypotension, whereas statins and chronic beta-blockers must be maintained (beta-blockers must never be initiated de novo on the day of surgery).
Antithrombotic, endocrine, and steroid therapies demand precise scheduling: warfarin is stopped 5 days preoperatively (target INR <1.5), DOACs 24–48 hours, SGLT2 inhibitors omitted the day before and the day of surgery (risk of euglycaemic DKA), sulfonylureas omitted while fasting, metformin is usually continued unless more than one meal is missed (CPOC 2023), and patients taking 5 mg prednisolone or more for over 4 weeks need hydrocortisone 100 mg IV at induction then 200 mg/24 h to avert adrenal crisis.
Preoperative Assessment & Perioperative Medication Management
Preoperative assessment is a systematic, multidisciplinary clinical process designed to identify comorbid disease, quantify perioperative morbidity and mortality risks, optimize chronic medical therapies, and establish an individualised anaesthetic and surgical care plan. In United Kingdom NHS practice, preoperative assessment clinics (PAC) operate under guidance from the National Institute for Health and Care Excellence (NICE NG180) and the Royal College of Anaesthetists (RCoA).
Preoperative Assessment & Risk Stratification
American Society of Anesthesiologists (ASA) Physical Status Classification
The ASA score is the most widely utilised clinical tool for grading a patient's baseline physiological reserve and overall fitness for anaesthesia and surgery. It correlates directly with perioperative morbidity, intensive care admission rates, and 30-day mortality.
| ASA Grade | Physical Status Definition | Clinical Examples & Disease Characteristics |
|---|---|---|
| ASA I | Normal, healthy patient | Non-smoker, no alcohol misuse, minimal or no systemic physiological abnormality |
| ASA II | Mild systemic disease without substantive functional limitation | Well-controlled hypertension, well-controlled type 2 diabetes mellitus, mild asthma, current smoker, BMI 30–39 kg/m² |
| ASA III | Severe systemic disease with substantive functional limitation | Poorly controlled diabetes mellitus, COPD with limited exercise tolerance, stable angina, prior myocardial infarction (>3 months ago), morbid obesity (BMI ≥40 kg/m²), chronic kidney disease (stage 3) |
| ASA IV | Severe systemic disease that is a constant threat to life | Unstable angina, symptomatic severe aortic stenosis, severe congestive cardiac failure (NYHA class IV), end-stage renal disease not undergoing scheduled dialysis, recent myocardial infarction or stroke (<3 months ago) |
| ASA V | Moribund patient not expected to survive without the operation | Ruptured abdominal aortic aneurysm with profound shock, massive pulmonary embolism with cardiovascular collapse, acute mesenteric ischaemia with multi-organ failure |
| ASA VI | Declared brain-dead patient whose organs are being removed for donor purposes | Certified brainstem death undergoing organ retrieval |
| Modifier 'E' | Emergency operation suffix (added to any class, e.g. ASA IIIE) | Procedure required immediately or within hours where delay would significantly increase the threat to life or limb |
Functional Capacity & Cardiopulmonary Exercise Testing (CPET)
Functional capacity is a critical determinant of operative outcome, traditionally quantified in Metabolic Equivalents of Task (METs). One MET represents the resting basal oxygen consumption of a 70 kg adult (3.5 mL O₂/kg/min). Patients unable to achieve 4 METs of activity (equivalent to climbing two flights of stairs, walking briskly on level ground at 4 mph, or carrying groceries upstairs) face significantly elevated rates of postoperative cardiopulmonary complications.
For major elective intracavitary surgery (e.g., oesophagogastrectomy, major colorectal resections, open aortic aneurysm repair), Cardiopulmonary Exercise Testing (CPET) provides an objective, non-invasive assessment of dynamic cardiopulmonary reserve via cycle ergometry:
- Peak Oxygen Uptake (Peak VO₂): An absolute peak VO₂ <15 mL/kg/min indicates diminished physiological reserve.
- Anaerobic Threshold (AT): The point during progressive exercise at which anaerobic metabolism supplements aerobic energy production. An AT <11 mL/kg/min identifies high-risk patients who warrant planned elective postoperative admission to a Level 2 (High Dependency Unit) or Level 3 (Intensive Care Unit) critical care facility.
Baseline Preoperative Investigations (NICE NG180 Guidelines)
Routine, unselective preoperative testing in healthy or mildly ill patients undergoing minor or intermediate elective surgery is clinically unhelpful, wasteful, and actively discouraged by NICE NG180. Investigations must be targeted based on patient comorbidities, age, and surgical invasiveness (minor, intermediate, major/complex):
- Full Blood Count (FBC): Indicated for all patients undergoing major or complex surgery; patients undergoing intermediate surgery with suspected anaemia, chronic renal disease, or cardiopulmonary disease; and any patient with clinical signs or symptoms of anaemia.
- Urea & Electrolytes (U&Es): Indicated for patients undergoing major surgery; any patient receiving medications that alter electrolytes or renal function (e.g., ACE inhibitors, ARBs, diuretics, NSAIDs, digoxin, lithium); patients with chronic kidney disease, diabetes mellitus, or cardiovascular disease.
- Coagulation Screen (PT/INR and APTT): Not routinely indicated. Indicated only in patients with personal or family history of bleeding diatheses, active hepatic impairment, known coagulopathy, malnutrition, or those taking vitamin K antagonists (warfarin) where INR verification is required.
- Group & Save (G&S) vs Crossmatch:
- Group & Save: Determines the patient's ABO and Rhesus (RhD) blood group and screens for atypical red cell antibodies; serum is stored in the blood transfusion laboratory for 24–72 hours. Performed for operations with moderate anticipated blood loss.
- Formal Crossmatch: Physically incubates recipient serum with specific donor blood units to verify immunological compatibility. Reserved strictly for procedures where substantial intraoperative haemorrhage is anticipated (e.g., major vascular repair, revision arthroplasty, radical cystectomy).
- 12-Lead Electrocardiogram (ECG): Indicated for patients with known cardiovascular, renal, or significant respiratory disease; patients aged >65 years undergoing intermediate or major surgery; or patients with cardiovascular symptoms (chest pain, palpitations, unexplained dyspnoea, peripheral oedema).
- Chest Radiograph (CXR): Strictly not routinely indicated. Reserved for patients with acute, new, or unstable cardiorespiratory symptoms or suspected acute lower respiratory tract pathology.
Preoperative Fasting Guidelines: The 2-4-6 Rule
Elective general anaesthesia induces the loss of protective laryngeal airway reflexes and blunts lower oesophageal sphincter tone, placing patients at risk of passive regurgitation and pulmonary aspiration of acidic gastric contents (Mendelson's syndrome). Conversely, prolonged unnecessary fasting induces dehydration, hypovolaemia, insulin resistance, irritability, and starvation ketoacidosis.
The Association of Anaesthetists and European Society of Anaesthesiology and Intensive Care (ESAIC) endorse the evidence-based 2-4-6 fasting protocol for elective procedures in adults (children differ slightly; see the note below):
| Intake Category | Minimum Fasting Period | Permissible Items & Clinical Caveats |
|---|---|---|
| Clear Fluids | 2 Hours | Water, pulp-free clear fruit juice, clear tea or black coffee (without milk). Chewing gum and boiled sweets are permitted up to 2 hours pre-op. |
| Breast Milk | 4 Hours | Exclusively breast milk in infants (digests faster than formula due to lower curd/protein content). |
| Light Meal / Formula / Cow's Milk | 6 Hours | Tea/coffee with added milk, infant formula milk, non-human animal milk, and light solids (e.g., plain toast with jam, clear broth, plain crackers). |
| Heavy / Fatty Solids | 8 Hours | Meals containing fried foods, fatty meats, cheese, or high-lipid content (substantially delays gastric emptying). |
Note
Children: UK paediatric anaesthesia societies (2018) and the ESAIC paediatric guideline (2022) encourage clear fluids until 1 hour before anaesthesia, breast milk until 3 hours, and formula or other milk and light food until 4–6 hours, to reduce the harms of prolonged fasting. The 8-hour rule for heavy, fatty meals comes from American guidance.
Important
Emergency Surgery & The 'Full Stomach' Rule: In emergency surgery (e.g., perforated viscus, acute peritonitis, major trauma, acute bowel obstruction), normal physiological gastric emptying is delayed or halted by severe pain, trauma, sympathetic activation, and opioid analgesia. All emergency surgical patients must be regarded as having a full stomach regardless of the time elapsed since their last oral intake. Airway management demands a Rapid Sequence Induction (RSI) with pre-oxygenation, a predetermined rapid-onset hypnotic agent, cricoid pressure (Sellick's manoeuvre), and a rapid-onset neuromuscular blocking drug (suxamethonium or high-dose rocuronium).
Perioperative Medication Management
Managing long-term pharmacotherapy requires balancing the risk of perioperative withdrawal exacerbations against the danger of adverse pharmacological interactions with anaesthetic agents and surgical bleeding.
Comprehensive Perioperative Medication Guide
| Drug Class & Generic Names | Perioperative Action | Clinical Rationale & UK Guidelines |
|---|---|---|
| ACE Inhibitors & ARBs (Ramipril, Lisinopril, Losartan, Candesartan) | STOP 24 hours prior to elective surgery | General and regional anaesthesia depress sympathetic vascular tone. Concurrent inhibition of the renin-angiotensin-aldosterone system (RAAS) causes severe, refractory intraoperative vasoplegic hypotension unresponsive to standard ephedrine or phenylephrine. Restart postoperatively once euvolaemic and eating. |
| Beta-Blockers (Bisoprolol, Atenolol, Metoprolol) | CONTINUE as normal on the morning of surgery | Abrupt withdrawal triggers severe rebound sympathetic hyperactivity, tachycardia, hypertension, and perioperative myocardial infarction. Critical rule: Do not initiate beta-blockers de novo on the morning of surgery (POISE trial: increases stroke and overall mortality). |
| Statins (Atorvastatin, Simvastatin) | CONTINUE as normal | Statins stabilise vascular endothelial plaques, blunt systemic inflammation, and reduce 30-day perioperative cardiovascular events. Take regular evening dose. |
| Calcium Channel Blockers (Amlodipine, Diltiazem) | CONTINUE as normal | Maintains blood pressure control and prevents coronary vasospasm. |
| Warfarin | STOP 5 days prior to elective surgery | Target INR for surgery is <1.5. Check INR on the day before surgery. Bridging therapy with therapeutic subcutaneous Low Molecular Weight Heparin (LMWH) is not routinely indicated and is restricted strictly to patients at very high risk of thromboembolism (e.g., mechanical mitral valve prosthesis, AF with prior stroke/CHADS-VASc ≥6, VTE within preceding 3 months). Stop LMWH 24h prior to surgery. |
| Direct Oral Anticoagulants (DOACs) (Apixaban, Rivaroxaban, Edoxaban, Dabigatran) | STOP 24–48 hours prior to elective surgery | For low-bleeding-risk surgery: omit 24 hours prior (last dose 2 days before). For high-bleeding-risk surgery or neuraxial blockade: omit 48 hours prior. For dabigatran in renal impairment (CrCl 30–50 mL/min), omit 48–72 hours prior. Routine bridging with LMWH is never indicated for DOACs due to predictable rapid offset. |
| Aspirin | CONTINUE for most surgeries | For secondary prevention in ischaemic heart disease or cerebrovascular disease, aspirin 75 mg is continued throughout the perioperative period. Exceptions (STOP 7 days prior): Operations where even minimal bleeding carries catastrophic consequences in enclosed spaces: intracranial neurosurgery, posterior chamber ophthalmic surgery, and spinal canal surgery. |
| P2Y12 Inhibitors (Clopidogrel, Prasugrel, Ticagrelor) | STOP 7 days prior to elective surgery | Irreversible platelet inhibition persists for the lifespan of the platelet (7–10 days). If the patient has a recent coronary drug-eluting stent (<6–12 months), elective surgery must be deferred to prevent fatal in-stent thrombosis; if urgent surgery is required, multidisciplinary cardiology review is mandatory. |
| Metformin | Usually CONTINUE (CPOC 2023) | If taken once or twice daily it can be continued when only one meal will be missed (omit the lunchtime dose if taken three times daily). Omit it if more than one meal will be missed, if eGFR is below 60 mL/min/1.73m², or if IV contrast is planned, because of the risk of lactic acidosis with hypoperfusion or AKI; restart once eating and renal function is stable. |
| SGLT2 Inhibitors (Empagliflozin, Dapagliflozin, Canagliflozin) | OMIT the day before and the day of surgery (CPOC 2023); restart when eating and drinking normally | SGLT2 inhibitors promote glucosuria. Under perioperative physiological stress, fasting, and dehydration, they precipitate euglycaemic Diabetic Ketoacidosis (euDKA)—a life-threatening high-anion-gap ketoacidosis occurring despite normal or near-normal blood glucose (<14 mmol/L). |
| Sulfonylureas (Gliclazide, Glimepiride) | OMIT morning dose while fasting | Omitting the morning dose prevents profound intraoperative hypoglycaemia while the patient is nil-by-mouth. |
| Basal Long-Acting Insulin (Glargine, Degludec, Detemir) | REDUCE dose by 20% on evening before / morning of surgery | Reducing baseline basal insulin by 20% provides essential background ketoacidosis suppression while mitigating fasting hypoglycaemia risk. |
| Variable-Rate Intravenous Insulin Infusion (VRIII) | Initiate if missing >1 meal or poorly controlled diabetes | Indicated for type 1 or 2 diabetics who will miss more than one meal, those undergoing major surgery, or HbA1c >69 mmol/mol (8.5%). Run concurrently with intravenous substrate infusion (5% glucose + 0.45% NaCl with 0.15%–0.3% KCl) to prevent ketosis and hypokalaemia. |
| Long-Term Systemic Corticosteroids (prednisolone 5 mg/day or more, or equivalent, for more than 4 weeks) | CONTINUE usual dose + stress-dose IV hydrocortisone | Chronic exogenous corticosteroid administration induces hypothalamic-pituitary-adrenal (HPA) axis suppression. Under operative stress, patients cannot mount an endogenous cortisol surge, precipitating a fatal Addisonian crisis (shock, refractory vasoplegia, hypoglycaemia). For major surgery the Association of Anaesthetists (2020) advises IV hydrocortisone 100 mg at induction, then 200 mg per 24 hours by infusion (or 50 mg IV/IM 6-hourly) while nil by mouth, followed by double the usual oral dose for 48 hours (up to a week after major surgery). |
| Combined Oral Contraceptive (COCP) & HRT | STOP 4 weeks prior to major elective surgery | Estrogen-containing medications significantly elevate the risk of deep vein thrombosis and pulmonary embolism. Discontinue 4 weeks before major elective surgery or operations requiring prolonged lower limb immobilisation; convert to a progestogen-only pill (POP) or barrier contraception. Resume 2 weeks postoperatively once fully mobile. |
Section Summary
- Preoperative assessment identifies physiological vulnerability using the ASA classification and CPET metrics (AT <11 mL/kg/min indicates high perioperative risk).
- Unselective routine investigations are avoided under NICE NG180; FBC, U&Es, and ECG are targeted based on comorbidities and surgical magnitude.
- The 2-4-6 fasting rule minimizes pulmonary aspiration risk (clear fluids up to 2 hours, breast milk 4 hours, solids/formula 6 hours), while emergency cases are treated as having a full stomach requiring rapid sequence induction.
- ACE inhibitors and ARBs are stopped 24 hours prior to prevent intraoperative vasoplegic hypotension, while chronic beta-blockers and statins are continued.
- Warfarin is discontinued 5 days pre-op (INR <1.5); DOACs 24–48 hours; SGLT2 inhibitors 48 hours (to prevent euglycaemic DKA); and long-term steroid users require perioperative stress-dose IV hydrocortisone.
A 64-year-old man with essential hypertension, type 2 diabetes mellitus, and osteoarthritis is scheduled for an elective total hip replacement under general anaesthesia tomorrow morning. His regular medications comprise ramipril 10 mg once daily, amlodipine 5 mg once daily, atorvastatin 20 mg once daily, and metformin 500 mg twice daily. His blood pressure in the pre-assessment clinic is 134/78 mmHg, heart rate is 68 bpm, and serum creatinine is 82 micromol/L. What is the most appropriate instruction regarding his ramipril prior to tomorrow's surgery?
Switch ramipril to an equivalent dose of candesartan on the morning of surgery
Double the ramipril dose this evening to avoid rebound intraoperative hypertension
Continue ramipril as normal with a sip of water on the morning of surgery
Omit ramipril on the morning of surgery (stop 24 hours prior to anaesthetic induction)
A 58-year-old woman with type 2 diabetes mellitus is admitted to the surgical admissions lounge at 07:00 for an elective laparoscopic cholecystectomy scheduled for 09:30. Her regular medications include empagliflozin 10 mg once daily, gliclazide 80 mg twice daily, and metformin 1 g twice daily. She was told at pre-assessment to omit empagliflozin the day before and the day of surgery, and she took her last dose 2 days ago; she has fasted from midnight. Her capillary blood glucose is 7.4 mmol/L, blood ketones are 0.3 mmol/L, and she feels well. What is the most appropriate perioperative instruction regarding her SGLT2 inhibitor therapy?
Administer empagliflozin now with a small sip of water before transfer to theatre
Switch empagliflozin to subcutaneous exenatide immediately prior to anaesthetic induction
Keep withholding empagliflozin today and restart it only when she is eating and drinking normally
Increase the empagliflozin dose to 25 mg to counteract surgical stress-induced hyperglycaemia
A 52-year-old woman with severe rheumatoid arthritis is admitted for an elective total abdominal hysterectomy and bilateral salpingo-oophorectomy. She has been taking oral prednisolone 15 mg once daily for the past 9 months, alongside methotrexate 15 mg weekly. Her blood pressure is 122/76 mmHg and heart rate is 72 bpm. What is the most appropriate management regarding her corticosteroid regimen for this major surgical procedure?
Administer intravenous hydrocortisone at anaesthetic induction followed by continued IV doses for 24–48 hours
Administer her regular oral prednisolone 15 mg on the morning of surgery with no additional steroids
Administer oral fludrocortisone 100 micrograms single dose at induction without hydrocortisone
Stop prednisolone completely 48 hours prior to surgery to minimize postoperative wound infection risk
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