Preoperative assessment and risk: ASA, NICE NG45, comorbidity and VTE

ASA physical status

The American Society of Anesthesiologists classification is the universal shorthand for how unwell a patient is before anaesthesia. It is deliberately simple, correlates with perioperative mortality and anchors the NICE testing tables, but it ignores the operation, its urgency and the team, so it is a description of the patient rather than a prediction for the procedure.

Which tests: NICE NG45

NG45 (Routine preoperative tests for elective surgery) exists to stop reflex ‘bloods and an ECG for everyone’. Tests are matched to the ASA grade and to the grade of surgery: minor (excision of a skin lesion, drainage of a breast abscess), intermediate (primary inguinal hernia repair, varicose vein surgery, tonsillectomy, knee arthroscopy) or major and complex (abdominal hysterectomy, thyroidectomy, joint replacement, colonic resection, lung resection, radical neck dissection). The table below is a simplification; the guideline's own grid has more conditional entries.

Across all grades: measure HbA1c in people with diabetes who have not had one in the last three months, but not in people without diabetes; ask women of childbearing potential whether they might be pregnant and offer a pregnancy test with consent; do not routinely test for sickle cell, send urinalysis, request a chest radiograph or arrange polysomnography; and do not routinely request echocardiography, but consider it, after a resting ECG, when a murmur comes with cardiac symptoms or with signs of heart failure. Clotting is not a screening test — it is for anticoagulated patients and for chronic liver disease.

Functional capacity and cardiac risk

A metabolic equivalent (MET) is resting oxygen consumption, about 3.5 mL/kg/min. Patients who can manage 4 METs — climbing a flight of stairs or a hill, walking briskly on the flat, heavy housework — without symptoms have a low cardiac risk from most surgery; those who cannot, or whose capacity is unknown, need closer assessment. Cardiopulmonary exercise testing quantifies this, and an anaerobic threshold below around 11 mL/kg/min is associated with more complications after major surgery. The Revised Cardiac Risk Index (Lee) is the simplest validated predictor of major cardiac complications and counts six factors:

• High-risk surgery: intraperitoneal, intrathoracic or suprainguinal vascular
• Ischaemic heart disease: previous infarction, positive stress test, angina, nitrate use or pathological Q waves
• History of heart failure
• History of cerebrovascular disease: stroke or transient ischaemic attack
• Insulin-treated diabetes mellitus
• Preoperative serum creatinine above 177 µmol/L (2.0 mg/dL)

Risk rises steeply with the count — under 1% with no factors to over 10% with three or more in the original derivation cohort. Elective surgery is deferred where possible for at least 60 days after a myocardial infarction, and dual antiplatelet therapy after a coronary stent is not interrupted without the cardiologist, which usually means postponing elective surgery for ideally at least six months after a drug-eluting stent. Whole-patient scores complement the cardiac view. P-POSSUM combines 12 physiological and 6 operative variables to predict morbidity and mortality, the Portsmouth modification having corrected POSSUM's over-prediction of death in low-risk patients. The NELA risk calculator, derived from the National Emergency Laparotomy Audit, is used to document predicted mortality before every emergency laparotomy; under the audit's standards a predicted mortality of 5% or more should trigger consultant-delivered surgical and anaesthetic care and postoperative critical care. SORT and the ACS NSQIP calculator are alternatives for elective work. These are planning and conversation tools, and the number is shared with the patient as part of consent.

Airway assessment

Every patient has a predicted airway, documented so that the anaesthetist is not surprised. Mallampati scoring is done with the patient sitting, mouth open, tongue out and without phonation: class I shows the soft palate, fauces, uvula and pillars; class II the soft palate, fauces and uvula; class III the soft palate and the base of the uvula; class IV the hard palate only. Classes III and IV, a thyromental distance under about 6.5 cm, an inter-incisor gap under 3 cm, limited neck extension, a receding mandible, prominent incisors, a large neck circumference and a history of difficult intubation all predict difficult laryngoscopy, which is then graded at the time by the Cormack–Lehane view (1, the whole glottis; 4, no laryngeal structures). Difficult mask ventilation is predicted by a beard, obesity, an edentulous mouth, older age, and snoring or sleep apnoea. Fixed cervical spine disease, previous neck radiotherapy, airway tumours and acute infection (Ludwig's angina, epiglottitis) move the patient into the awake fibreoptic or surgical-airway conversation.

Diabetes

Hyperglycaemia impairs neutrophil function and wound healing and increases infection, so the aim is a controlled patient on the day. Under current UK perioperative diabetes guidance, elective surgery is ideally deferred until HbA1c is below about 69 mmol/mol (8.5%). Patients with diabetes are placed first on the list and their period without food is kept short. If only one meal is missed, most oral agents and basal insulin continue with adjustments: sulphonylureas are omitted on the morning of surgery because they cause hypoglycaemia in the fasted state; metformin is generally continued when the fast is short and renal function normal, and omitted where contrast or a long fast threatens the kidneys; SGLT2 inhibitors are omitted the day before and the day of surgery because of euglycaemic ketoacidosis; long-acting basal insulin continues at a reduced dose and short-acting insulin is omitted with the missed meal. A variable-rate intravenous insulin infusion (VRIII), with a glucose- and potassium-containing fluid running alongside, is indicated when the patient will miss more than one meal, when control is poor, for emergency surgery, and for most patients with type 1 diabetes who are not eating; capillary glucose is checked hourly and kept in the 6–10 mmol/L range, with 4–12 acceptable. Basal insulin is never stopped altogether in type 1 diabetes.

Anticoagulants, antiplatelets and steroids

Warfarin

Stopped about five days before surgery; the INR is checked on the day and most procedures proceed when it is below 1.5. Bridging with therapeutic LMWH is for high thrombotic risk only — a mechanical mitral valve, venous thromboembolism within the previous three months, or atrial fibrillation with a previous stroke — because bridging increases bleeding without benefit in lower-risk patients. For urgent surgery, warfarin is reversed with intravenous vitamin K plus prothrombin complex concentrate; vitamin K alone takes six to twelve hours to act.

Direct oral anticoagulants

Apixaban, rivaroxaban, edoxaban and dabigatran are omitted for typically 24–48 hours before surgery, longer with renal impairment (dabigatran, which is renally cleared, needs the longest) and for high-bleeding-risk or neuraxial procedures. No bridging is needed. Specific reversal agents exist (idarucizumab for dabigatran; andexanet alfa for apixaban and rivaroxaban in some settings), and prothrombin complex concentrate is used where they are not available.

Antiplatelets

Aspirin is usually continued through surgery unless the bleeding risk is unacceptable — intracranial, spinal, posterior-chamber eye and some urological surgery. Clopidogrel, prasugrel and ticagrelor are stopped around five to seven days before elective surgery after discussion, and are never stopped in the months after a coronary stent without cardiology advice. Platelet transfusion is the reversal strategy for life-threatening bleeding.

Corticosteroids

Patients on long-term steroids — conventionally more than about 5 mg of prednisolone a day for three weeks or more, or any dose with Cushingoid features — have a suppressed hypothalamic–pituitary–adrenal axis and cannot mount the cortisol surge that surgery demands; the result is refractory hypotension, hyponatraemia and hypoglycaemia. The usual dose is continued and supplemented with intravenous hydrocortisone at induction and for a period scaled to the magnitude of surgery, then weaned back to baseline. The same applies to Addison's disease.

Venous thromboembolism: NICE NG89

Every patient admitted to hospital is assessed for the risk of venous thromboembolism and of bleeding, with a validated tool such as the Department of Health one, on admission and again whenever the clinical picture changes. Surgical risk factors include a general anaesthetic with total surgical time over 90 minutes (60 minutes if the pelvis or lower limb is involved), an acute surgical admission with an inflammatory or intra-abdominal condition, and an expected significant reduction in mobility, alongside the patient factors: active cancer or cancer treatment, age over 60, dehydration, known thrombophilia, obesity, significant comorbidity, hormone replacement or oestrogen-containing contraception, varicose veins with phlebitis, pregnancy and the puerperium, and previous or family history of VTE. Bleeding risk factors include active bleeding, acquired or inherited bleeding disorders, concurrent anticoagulation, a lumbar puncture, epidural or spinal expected within the next 12 hours or performed in the previous four, acute stroke, uncontrolled hypertension and thrombocytopenia.

Prophylaxis has two arms. Mechanical: anti-embolism stockings — contraindicated in peripheral arterial disease, peripheral neuropathy, severe leg oedema, dermatitis and legs that cannot be fitted — or intermittent pneumatic compression, which is preferred after stroke. Pharmacological: low-molecular-weight heparin for most surgical patients, started once haemostasis is secure (the joint-replacement recommendations specify 6–12 hours after surgery), with unfractionated heparin where renal function is severely impaired and fondaparinux as an alternative, and continued for a minimum of seven days or until mobility is no longer significantly reduced. Extended prophylaxis for 28 days is given after major abdominal or pelvic surgery for cancer, and after elective hip replacement and hip fracture surgery, with a shorter course after knee replacement. Oestrogen-containing contraception and HRT are considered for stopping four weeks before elective surgery. A VTE that develops on prophylaxis prompts a check that the regimen was weight-appropriate and that it was actually given.

Fasting, consent and the checklist

Standard preoperative fasting is six hours for solid food, formula milk and milk-containing drinks, four hours for breast milk in infants, and two hours for clear fluids — water, dilute squash, and tea or coffee without milk — which should be encouraged up to that point to reduce dehydration and nausea; enhanced-recovery pathways add a carbohydrate drink up to two hours before. Gastric emptying is delayed by opioids, pain, trauma, pregnancy, diabetes and bowel obstruction, which is why an emergency patient is treated as having a full stomach whatever the clock says.

Consent is a process, not a signature. Since Montgomery v Lanarkshire (2015) the surgeon must take reasonable care to ensure the patient is aware of any material risk — one to which a reasonable person in the patient's position would attach significance, or which the surgeon knows this particular patient would — and of reasonable alternatives including no treatment, in a dialogue rather than a disclosure. The Mental Capacity Act 2005 presumes capacity, which requires the patient to understand, retain and weigh the information and to communicate a decision; a patient who lacks it is treated in their best interests, and no one can consent on behalf of another adult except an attorney or deputy with the relevant powers. Consent should be taken by someone who can perform the procedure or has been trained to advise on it, ideally well before the day. The WHO Surgical Safety Checklist adds three pauses — sign in before induction, time out before the knife, sign out before the patient leaves theatre — within the Five Steps to Safer Surgery of team brief and debrief, codified in England as the National Safety Standards for Invasive Procedures (NatSSIPs).