01Core principlesThe concepts and mechanisms needed to understand the subject.
Preoperative assessment is a decision process rather than a checklist of tests. It asks whether the proposed operation remains appropriate, what preventable harm can be reduced, what anaesthetic and postoperative resources are needed, and whether the patient understands the likely course. The surgical indication and harm from delay must be considered alongside anaesthetic risk; discovering disease does not automatically justify postponement.
Risk has several layers. Procedure-specific hazards include haemorrhage, fluid shifts, pain, immobility and the need for organ support. Patient-specific hazards arise from cardiovascular, respiratory, renal, endocrine, haematological and neurological disease, frailty and limited reserve. Social support, cognition, medicines and prior anaesthetic experience alter practical safety. A validated prediction tool can calibrate discussion and resource planning, but performance depends on the population and outcome it was built to predict.
Testing is useful when a result is plausible, timely and capable of changing action. NICE NG45 links routine preoperative tests to ASA class, operation magnitude and comorbidity. Symptoms still trigger diagnostic pathways outside the routine table. Conversely, indiscriminate panels create false positives, repeat work and delay without reducing risk. Every requested result needs a reviewer and a pre-agreed response.
Optimisation begins early enough to matter. Treating iron deficiency, improving nutrition, stopping smoking, moderating alcohol, planning diabetes care, reviewing frailty and preparing postoperative support can reduce avoidable problems. Shared decision making converts these findings into choices: proceed as planned, modify the procedure or anaesthetic, arrange additional support, or defer when the benefit of optimisation outweighs the cost of delay.
Key points
- Define the procedure, indication, urgency, expected physiological stress, bleeding risk and likely recovery burden before interpreting any patient factor or score.
- Use a validated risk tool to supplement clinical assessment, then explain absolute outcomes and alternatives; a score does not decide consent, operability or postoperative destination by itself.
- Select tests from the operation grade, ASA status, comorbidity and a clear management question. Do not order routine chest radiography, urine dipstick or coagulation tests for an otherwise well adult without an indication.
- Identify modifiable hazards early: anaemia and iron deficiency, smoking, harmful alcohol use, malnutrition, poor glucose control, frailty, deconditioning and an unsafe medicine plan need time and ownership.
- Record previous anaesthetic problems, allergies, airway and dental features, reflux or aspiration risk, VTE history, organ function, functional capacity, cognition, support and discharge barriers.
- Finish with a visible plan: what is optimised, what risk remains, which medicines change, whether blood is acceptable, required monitoring or critical care, and who will review an abnormal result.
02Mechanisms and patternsImportant relationships and how to distinguish them.
Clarify what is planned, whether it is curative or symptom-relieving, likely duration, position, blood loss, postoperative pain, immobility and the clinical consequence of deferral.
Ask what activity produces symptoms, whether the person can climb stairs, recent decline, falls, frailty, nutrition and independence; change over time often matters more than a single label.
Elicit chest pain, syncope, breathlessness, orthopnoea, oedema, wheeze, exacerbations, sleep apnoea and smoking, then examine pulse, pressure, heart, lungs, oxygenation and volume status.
Inspect mouth opening, dentition, neck movement and relevant anatomy, and obtain prior charts for difficult ventilation or intubation, allergies, anaphylaxis, awareness or malignant hyperthermia.
Reconcile prescribed, non-prescribed and injected drugs with last doses and indications, focusing on anticoagulants, antiplatelets, diabetes drugs, steroids, antihypertensives and interactions.
Treat new chest pain, resting hypoxaemia, sepsis, acute kidney injury, active bleeding or metabolic decompensation as an urgent clinical finding and escalate before continuing routine elective preparation.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Targeted history, examination and observations - Why
- Establish active disease, functional change, airway factors and baseline physiology before choosing tests.
- Interpretation and limitations
- A new symptom or abnormal observation triggers focused diagnostic assessment; a normal generic blood panel cannot exclude an unstable clinical syndrome.
- 02
Full blood count with red-cell indices - Why
- Detect anaemia, abnormal indices, thrombocytopenia or other cytopenia when operation grade or disease makes the result relevant.
- Interpretation and limitations
- Before major surgery, anaemia should be identified early and its cause investigated. Iron studies and other haematinics follow the pattern; transfusion is not routine treatment for uncomplicated deficiency.
- 03
Kidney function and electrolytes - Why
- Quantify renal reserve and detect electrolyte disturbance where comorbidity, medicine exposure or operation magnitude makes this actionable.
- Interpretation and limitations
- Interpret trends with volume status and medicines. Renal impairment changes fluid, analgesic, anticoagulant and diabetes-drug planning and may require a disease-specific pathway.
- 04
Electrocardiogram - Why
- Document rhythm or cardiovascular abnormalities in the ASA, age, comorbidity and surgery categories identified by the routine-test table.
- Interpretation and limitations
- A new arrhythmia, ischaemic feature or conduction abnormality requires clinical correlation; an ECG is not a universal screening test for low-risk healthy adults.
- 05
HbA1c and perioperative glucose data - Why
- Assess recent glycaemic control in known diabetes and support a safe fasting, medicine and monitoring plan.
- Interpretation and limitations
- Use a result from the preceding three months when available. A high value informs optimisation and shared timing rather than acting as an isolated universal cancellation rule.
- 06
Validated perioperative risk estimate - Why
- Supplement clinical judgment with an outcome-specific estimate that can guide discussion and resources.
- Interpretation and limitations
- State the outcome and time horizon, recognise calibration limits, and combine the result with surgical benefit, frailty, functional reserve and patient priorities.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked case: planned major surgeryReduced exercise tolerance before colectomyAn adult booked for elective major abdominal surgery reports a recent fall in walking distance and has anaemia on referral blood tests.+
- 1Confirm the cancer or symptom indication and acceptable timing with the surgeon, then characterise breathlessness, chest symptoms, bleeding, nutrition, weight loss, functional decline and the expected operative stress.
- 2Examine cardiorespiratory and volume status, reconcile medicines and prior anaesthetic records, and request only investigations that answer the suspected anaemia, cardiac, respiratory or renal questions.
- 3Use an outcome-appropriate validated tool to frame risk, but treat the new functional decline and anaemia as clinical problems requiring explanation rather than accepting a low numerical estimate.
- 4Investigate anaemia early, treat iron deficiency through the relevant oral or IV route, address nutrition and smoking, and agree whether benefit from optimisation outweighs delay.
- 5Document the shared decision, medicine instructions, transfusion preferences, postoperative monitoring and escalation plan, and name the clinician who will close each abnormal result.
02Routine elective testingHealthy adult having minor surgeryHistory, examination and observations reveal no active disease and the proposed procedure has low physiological stress.+
- 1Classify ASA status and operation grade accurately and use the NG45 table instead of ordering a habitual panel.
- 2Do not routinely add chest radiography, urine testing or coagulation studies without symptoms, comorbidity, medicine exposure or a procedure-specific reason.
- 3Give fasting and medicine instructions, confirm transport and recovery support, and provide a route for reporting a new illness before surgery.
03Raised blood pressureHypertension found in preassessmentAn adult attending planned non-obstetric, non-endocrine surgery has no documented acceptable primary-care reading in the previous year.+
- 1Repeat blood pressure with correct cuff, rest and technique, check symptoms of accelerated hypertension and seek recent clinic or home readings.
- 2If clinic pressure is below 180/120 mmHg, hypertension alone need not prohibit surgery; communicate long-term follow-up. At or above that threshold, postpone planned surgery and arrange assessment unless urgency changes the balance.
- 3Screen selected older, diabetic or symptomatic patients for postural fall and manage subsequent targets against standing pressure where a significant drop is present.
05Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- Track whether every investigation result has been reviewed, interpreted in context and converted into a documented action or explicit no-action decision.
- Reassess symptoms, functional status, weight, nutrition, haemoglobin and glycaemic control after optimisation when those changes affect timing or postoperative resources.
- Confirm the final medication plan with exact last and restart doses rather than relying on generic instructions such as stop tablets or take usual medicines.
- Check on admission for interval infection, cardiorespiratory deterioration, new medicines, recent hospital attendance, changed consent or failure to follow fasting and withholding instructions.
- Communicate predicted risk, transfusion preferences, airway information, allergies and escalation or critical-care decisions at each handover.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Risk tools supplement
A score improves consistency only when its population and outcome fit; it cannot capture every active symptom, technical hazard, patient value or consequence of delay.
Tests need consequences
Before requesting a test, decide which plausible result would change treatment, anaesthetic technique, surgical timing, monitoring or postoperative destination and who will act on it.
ASA describes burden
ASA physical status supports communication of systemic disease burden but does not include operation magnitude and should not be presented as a complete predicted probability.
Optimisation has a clock
Oral iron, smoking cessation, exercise and nutrition require time; start near the decision to operate and balance achievable benefit against disease progression or prolonged disability.
Blood pressure context
The planned-surgery threshold addresses immediate perioperative safety and differs from community diagnostic and treatment thresholds, which still require follow-up.
07Common pitfallsFrequent interpretation and management errors.
- 01
Using a normal routine panel to dismiss new chest pain, dyspnoea, infection or functional decline.
- 02
Ordering every available test without identifying how an abnormal result would change management.
- 03
Treating a validated score as permission to proceed or cancel without surgical benefit and patient priorities.
- 04
Applying the planned adult blood-pressure threshold to emergency, obstetric, paediatric or endocrine surgery.
- 05
Giving vague medication instructions that omit drug name, indication, last dose and restart conditions.
- 06
Discovering anaemia shortly before major surgery because screening did not occur early in the pathway.