Pre-operative Assessment

Purpose and structure

Pre-operative assessment exists to reduce avoidable harm, and it does so in four ways: by identifying patients whose risk is higher than the operation warrants, by optimising the modifiable elements of that risk, by planning the anaesthetic, the level of postoperative care and the discharge, and by informing the patient well enough for their consent to be meaningful.

It is not a form-filling exercise, and the commonest failures are practical ones - an operation cancelled on the morning because a warfarin was not stopped, a diabetic patient starved from midnight and operated on last, an anaemic patient transfused in theatre who could have been given iron four weeks earlier.

Elective patients are usually seen in a pre-assessment clinic two to six weeks before surgery, which is deliberate: it leaves enough time for iron infusion, smoking cessation, glycaemic optimisation and cardiology review. Emergency patients get the same assessment compressed into hours, with the emphasis shifting from optimisation to accurate risk documentation and the right level of postoperative care.

History and examination

Key history

• The surgical problem and its urgency, and whether the operation is still the right one
• Cardiovascular - angina, previous myocardial infarction or revascularisation, heart failure, valve disease, arrhythmia, hypertension, and exercise tolerance in concrete terms
• Respiratory - asthma, COPD, obstructive sleep apnoea, recent respiratory tract infection, smoking history in pack-years
• Renal, hepatic and endocrine - chronic kidney disease, liver disease, diabetes and its control, thyroid disease, adrenal insufficiency and long-term steroid use
• Neurological - stroke or TIA, epilepsy, cognitive impairment, and neuromuscular disease
• Previous anaesthetics - any problems, postoperative nausea and vomiting, difficulty with intubation, awareness, or a prolonged recovery
• Family history of anaesthetic problems - malignant hyperthermia and suxamethonium (pseudocholinesterase) apnoea are both inherited and must be asked about specifically
• Allergies, including latex and chlorhexidine, with the nature of each reaction
• Full drug history including over-the-counter medicines, herbal remedies and recreational drugs
• Alcohol intake, smoking status and body mass index
• Pregnancy - offer a test to any person of childbearing potential, and document the discussion
• Social circumstances - who is at home, stairs, and the discharge plan, which should be made before admission rather than after

Functional capacity

Exercise tolerance is one of the strongest predictors of perioperative outcome and costs nothing to assess. It is expressed in metabolic equivalents (METs), where 1 MET is resting oxygen consumption.

Inability to achieve 4 METs, or an inability to assess it because of arthritis or claudication, is what prompts further investigation such as echocardiography or cardiopulmonary exercise testing. Note that the evidence base for subjective assessment is imperfect: the METS study found that a clinician's subjective estimate of functional capacity was poorly predictive, whereas measured peak oxygen consumption and the Duke Activity Status Index performed better.¹

Airway assessment

• Mallampati score - the patient sits, opens the mouth and protrudes the tongue without phonating. Class I shows the soft palate, fauces, uvula and pillars; class IV shows only the hard palate. Higher classes predict difficult laryngoscopy, though the test used alone is unreliable.
• Mouth opening - an interincisor distance of less than about 3 cm predicts difficulty
• Thyromental distance - less than 6.5 cm suggests a difficult airway
• Neck movement - flexion and extension, and particularly any cervical spine disease, rheumatoid arthritis or previous fusion
• Dentition - loose teeth, crowns, caps and dentures, documented before anaesthesia because dental damage is a common claim
• Other features - obesity, a short thick neck, a large tongue, beard, previous neck radiotherapy or surgery, and any history of difficult intubation

Grading risk

The suffix E is added for emergency surgery, which independently increases risk substantially. Other tools in common UK use include the Revised Cardiac Risk Index for cardiac risk, P-POSSUM and the NELA risk calculator for emergency laparotomy, and the Surgical Outcome Risk Tool (SORT). Documented risk assessment before emergency laparotomy is one of the process measures associated with the fall in NELA mortality.

Investigations

NICE NG45 replaced routine batteries of tests with selective testing based on ASA grade and the grade of surgery. Ordering an unnecessary test is not harmless: it generates incidental abnormalities, delays and anxiety.²

• FBC - for ASA 2 and above having intermediate surgery, and for all patients having major surgery. Anaemia found here should be investigated and treated, not simply noted.
• U&Es and creatinine - where there is risk of acute kidney injury, in ASA 2 and above having intermediate or major surgery, and in anyone on drugs affecting renal function
• ECG - for ASA 3 and above, for anyone with cardiovascular, renal or diabetic disease having intermediate or major surgery, and for all patients over a locally agreed age having major surgery
• Clotting screen - only where there is a history of bleeding disorder, liver disease or anticoagulation. Not routine.
• HbA1c - in all patients with diabetes who have not had one measured within three months
• Group and save, or crossmatch, according to the expected blood loss and local maximum surgical blood ordering schedule
• Pregnancy test - offered to anyone of childbearing potential, on the day of surgery
• Sickle cell test - where the patient's ancestry places them at risk and their status is unknown
• Echocardiography, lung function tests and cardiopulmonary exercise testing - only where the history or examination raises a specific question, not as a screen
• Chest radiograph - not recommended routinely, even before major surgery

Managing the drug chart

This is where most preventable cancellations arise, and it is a favourite of written papers.

Local policy and specialist advice override any general table, particularly for mechanical heart valves, recent stents and complex immunosuppression.

Fasting, thromboprophylaxis and consent

Fasting

• Six hours for solid food, sweets, milk and formula feeds
• Four hours for breast milk
• Two hours for clear fluids - water, black tea or coffee, and clear carbohydrate drinks
• Encourage clear fluids up to two hours before, rather than starving from midnight. Prolonged fasting causes dehydration, hypoglycaemia, headache, irritability and, in older patients, delirium and acute kidney injury, and it does not reduce aspiration risk.
• Preoperative carbohydrate loading is a component of enhanced recovery programmes and reduces insulin resistance and postoperative nausea

Venous thromboembolism assessment

Every patient must have a documented VTE risk assessment weighing thrombosis risk against bleeding risk, in line with NICE NG89.³ Mechanical prophylaxis with anti-embolism stockings or intermittent pneumatic compression is combined with pharmacological prophylaxis, usually low molecular weight heparin, where the balance favours it. Anti-embolism stockings are contraindicated in peripheral arterial disease, so check pulses and the ABPI.

Consent

Consent must be taken by someone capable of performing the procedure or specifically trained to take consent for it, and it should be taken well before the day of surgery wherever possible so the patient has time to consider it.

• Explain the diagnosis, the proposed procedure and its intended benefit
• Discuss material risks. Since Montgomery v Lanarkshire Health Board (2015), the legal test is what a reasonable person in the patient's position would consider significant, or what this particular patient would consider significant - not what a body of reasonable doctors would disclose.⁴
• Discuss the alternatives, including doing nothing, and their respective risks
• Check understanding, invite questions, and provide written information
• Assess capacity where there is any doubt, and follow the Mental Capacity Act framework with a best interests decision and an IMCA where required
• Document the discussion, including the specific risks named and the questions asked

In theatre

The WHO Surgical Safety Checklist has three parts: Sign in before induction of anaesthesia, Time out before the skin incision, and Sign out before the patient leaves theatre. It confirms identity, site, procedure, consent, allergies, airway risk, blood loss, antibiotic prophylaxis, imaging availability and instrument counts, and its introduction was associated with significant reductions in surgical mortality and complications.

Optimisation

The weeks before an elective operation are the only time some of these can be changed, and this is the part of pre-assessment that actually alters outcome.

• Smoking cessation - benefits begin within 24 to 48 hours as carboxyhaemoglobin falls, but reductions in pulmonary and wound complications require at least four to eight weeks of abstinence. Offer nicotine replacement and referral to a cessation service.
• Alcohol reduction for at least four weeks, and planning for withdrawal in dependent patients
• Anaemia - identify, investigate and correct with iron
• Diabetes - aim for an HbA1c below about 69 mmol/mol before elective surgery, and place the patient first on the list
• Blood pressure - severe uncontrolled hypertension may warrant postponement, but modest elevation on the day is common and usually reflects anxiety
• Nutrition - screen with MUST, and provide supplementation or dietetic input where malnourished, since this affects wound healing and infection risk
• Prehabilitation - structured exercise, nutritional and psychological preparation before major surgery, which improves functional capacity and reduces complications
• Frailty assessment in older patients, with comprehensive geriatric assessment and a realistic discussion about whether the operation is the right treatment at all

Red flags

Outcomes

Good pre-assessment reduces day-of-surgery cancellations, shortens length of stay, and reduces complications. The interventions with the clearest evidence behind them are unglamorous: correcting anaemia, stopping smoking, optimising diabetes, avoiding prolonged fasting, documented VTE risk assessment, appropriate antibiotic prophylaxis and the surgical safety checklist.

The other function of pre-assessment is more difficult and is often skipped. For a frail, comorbid patient facing major surgery, an honest discussion about the likely outcome - including the possibility that the operation will result in survival with substantially reduced independence - is part of the assessment. Documenting the patient's own priorities, and any decision about escalation and resuscitation, before they are anaesthetised is far better than trying to reconstruct them in intensive care at two in the morning.

The practical summary is that pre-operative assessment is where the outcome of an operation is largely determined, and that the most useful things a junior clinician can do are to take an accurate drug history, ask about exercise tolerance in concrete terms, check the haemoglobin early, and make sure the person who will operate has had a real conversation with the person being operated on.