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Preoperative assessment and premedication
All patients scheduled to undergo surgery should be assessed in advance to ensure optimal preparation and perioperative management. This is a standard of care proposed by the Association of Anaesthetists, RCoA and similar bodies worldwide. It is one mechanism by which the standard and quality of care provided by an individual anaesthetist or an anaesthetic department may be measured. Failure to undertake this activity places the patient at increased risk of perioperative morbidity or mortality and exposes the patient to avoidable day of surgery cancellation, which is both inconvenient and distressing.
The principle aims of preoperative assessment are to assess perioperative risk, minimise that risk by producing a tailored and individualised care plan, and educate the patient about the process, choices and expectations of the surgical episode to support informed consent and active participation.
Individualising care may include alteration to the original surgical plan (e.g. arranging for laparoscopic rather than open surgery or reducing the surgical magnitude); medical and social optimisation (potentially involving specialist referral and review); specific preoperative interventions such as enhanced recovery programmes, drug commencement or cessation; and decision on the level of postoperative care required (e.g. ward, High Dependency Unit (HDU) or ICU).
Preoperative assessment is the foundation stone of the emerging discipline of perioperative medicine. Anaesthetists need to develop and maintain knowledge of surgical procedures and pathways and appreciate the necessary anaesthetic management to predict the potential issues and likely progress of an individual patient during the perioperative period. Whilst many units organise elective preoperative assessment within specialist nurse-led clinics, working to local and national guidance and protocols under the oversight of enthusiasts from the anaesthetic department, every anaesthetist needs to remain current in the discipline, as patients requiring urgent surgery may bypass the usual processes.
The process of preoperative assessment
Who, when and where?
All patients listed for surgery should undergo preoperative assessment. The extent of the assessment process may differ depending on the urgency and magnitude of surgery and the intended anaesthetic technique.
A patient may be selected for surgical intervention after a single consultation in surgical clinic; increasingly, decisions regarding major surgery are made at multidisciplinary team meetings, particularly in cancer care, where options of neoadjuvant therapy need consideration. Currently very few multidisciplinary teams include an anaesthetist, though this may change as complex risk–benefit analysis is improved by relevant specialist input to the discussion regarding treatment options. Patients are usually assessed between surgical listing and an intended surgical date, the timing of which is often dictated by non-clinical logistics and can leave limited opportunities for optimisation. Services that are organised on a walk-in (same day as listing) basis can maximise the opportunity for optimisation and minimise journeys to the hospital for the patient.
The core of preassessment is the gathering of relevant administrative and medical information. This can be achieved by patients completing paper or electronic health questionnaires, which are then verified by appropriately trained staff. Questionnaires are particularly useful in patients who are younger or otherwise well and in those undergoing minor or intermediate surgery (e.g. cataract surgery under local anaesthesia). It is preferable that older patients, those with recognised comorbidity and those scheduled for major or complex surgery are assessed by face-to-face interview. This is generally undertaken by trained nurse practitioners with an extended skill set including physical examination and the remit to order specific investigations (both routine screening and other targeted tests). Using local and national protocols, nurse practitioners can make many of the admission arrangements, give general and surgery specific advice and information and refer patients at risk to an anaesthetist responsible for perioperative care for further management.
Hospital admission on the day of surgery is now routine practice. A comprehensive preoperative assessment document (complete with systems review, examination findings, results of screening and specific investigations and specialist instructions where necessary) allows the anaesthetist responsible to concentrate the immediate preoperative discussion on areas of particular relevance, such as discussion of the risks and benefits of regional or general anaesthesia.
History
This should cover all relevant information needed to provide safe anaesthesia and perioperative management of comorbidity (see Chapter 20 ). Both open and direct questioning are necessary to achieve this, and previous hospital and general practice records may require review to verify details.
Presenting condition
The operation, indication and urgency must be clearly understood. Many surgical conditions can have systemic effects that should be sought out, e.g. bowel cancer that can lead to anaemia and malnutrition.
Functional capacity
Fitness strongly influences perioperative risk and outcome, and even those patients with no comorbidities should be questioned regarding their ability to perform exercise. If limited, the reason for this should be explored, as an undiagnosed cardiorespiratory pathological condition may be present. Questioning should be wide ranging and open. Verbatim description of maximum exercise (e.g. runs 5 km twice a week) or conversion to metabolic equivalents ( Table 19.1 ) should be clearly documented. One metabolic equivalent task (MET) is basal metabolic oxygen consumption at rest (~3.5 ml min −1 kg −1 ). The inability to climb two flights of stairs (~4 METs) is associated with an increased risk of cardiac complications after major surgery. Whilst good exercise capacity is reassuring, many patients are sedentary and often do not describe activity greater than 4 METs. These patients should be considered for further fitness evaluation.
Table 19.1
Metabolic Equivalents of Task (MET)
| Metabolic equivalent | Task |
|---|---|
| 1.5 | Bathing, sitting |
| 2.5 | Dressing, undressing, standing or sitting |
| 3.0 | Standing tasks, light effort (e.g. bartending, store clerk, filing) |
| 3.5 | Scrubbing floors, on hands and knees |
| 4.0 | Walks up two flights of stairs |
| 4.3 | Walking, 3.5 mph, brisk speed, not carrying anything |
| 5.0 | Mowing lawn, walking, power mower, moderate or vigorous effort |
| 7.5 | Carrying groceries upstairs |
| 9.0 | Moving household items upstairs, carrying boxes or furniture |
| 10.0 | Bicycling, 14–15.9 mph, racing or leisure, fast, vigorous effort |
Concurrent medical history
All coexisting medical disease must be identified and the degree of severity, control and stability should be assessed by symptomatology, level of care (general practitioner or specialist) and/or recent investigations. The anaesthetic implications of comorbid conditions are discussed in detail in Chapter 20 . It is essential to establish the presence and severity of cardiorespiratory disease by direct questioning regarding exertional dyspnoea, paroxysmal nocturnal dyspnoea, orthopnoea, angina, palpitations and so on.
A thorough systems enquiry should also be undertaken, with specific questioning for relevant issues that might influence perioperative management (e.g. symptoms such as indigestion and reflux within the gastrointestinal review).
Some conditions require active screening to identify sufferers or those at risk. Most pertinent are the following:
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obstructive sleep apnoea (OSA);
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frailty;
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anaemia; and
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chronic kidney disease
Obstructive sleep apnoea
Obstructive sleep apnoea is highly prevalent in the surgical population, yet often undiagnosed. Patients with OSA have a higher incidence of difficult airway management and perioperative complications, notably respiratory events, delirium and atrial fibrillation. Current recommendations are that patients be considered for continuous postoperative oximetry by using a screening questionnaire progressing, if circumstances allow, to formal diagnosis by sleep studies. Although many questionnaires are in clinical use, the STOP-BANG questionnaire is currently the only tool validated in the surgical population ( Box 19.1 ).
Box 19.1
STOP-BANG questionnaire for obstructive sleep apnoea (OSA)
S: Do you S nore loudly (loud enough to be heard through closed doors or your bed partner elbows you for snoring at night)?
T: Do you often feel T ired, fatigued or sleepy during daytime (such as falling asleep during driving or talking to someone)?
O: Has anyone O bserved you stop breathing or choking or gasping during your sleep?
P: Do you have or are you being treated for high blood P ressure?
B: B MI: >35 kg m 2
A: A ge: >50 years
N: N eck circumference: >40 cm
G: Male G ender
Score 0–2: Low risk of OSA
Score 3–4: Intermediate risk of OSA
Score 5–8: High risk of OSA
As score increases, so does the likelihood of moderate to severe OSA.
Frailty
Frailty is the cumulative loss of physiological reserve across body systems and is common in older people, affecting 10% of those aged older than 65 years, increasing to 25%–50% of those aged older than 85 years. It can be present with or without other comorbidities and renders patients vulnerable to adverse outcomes, even after minor health events. Measurements of the degree of frailty outperform traditional critical care illness severity scores in predicting outcome for older persons in critical care. Frailty can be described by a phenotype model (unintentional weight loss, reduced muscle strength, reduced gait speed, self-reported exhaustion and low energy expenditure) or a cumulative deficits model (symptoms such as poor hearing, low mood, tremor, comorbidity such as dementia and disability). Frailty requires active consideration to be consistently identified. Assessment methods include observation of gait speed around the clinic, timed up-and-go test and the Clinical Frailty Scale. Frailty in the older patient is also discussed in detail in Chapter 31 .
Anaesthetic history
Details of previous anaesthetic episodes should be documented. Some sequelae such as sore throat, headache or postoperative nausea may not seem of great significance to the anaesthetist but may be the basis of considerable preoperative anxiety for the patient. The patient may be unaware of anaesthetic problems in the past if they were managed uneventfully, so previous anaesthetic records should be examined if available. More serious problems such as difficult tracheal intubation or other procedures (e.g. insertion of an epidural catheter) should have been documented. Operating theatre booking systems can record alerts regarding a patient, and any flagged adverse event within these systems should be explored. Other serious problems can be suggested by events such as unexpected ICU admission after previous surgery. These episodes should be explored carefully to identify contributing factors that may be re-encountered. Reviewing old notes can be vital to appreciate the course of events, as often patients and relatives can be unsure of the precipitating factors.
Family history
Several hereditary conditions can influence anaesthetic management, such as malignant hyperthermia, cholinesterase abnormalities, porphyria, some haemoglobinopathies and dystrophia myotonica (see Chapter 20 ). Some of these disorders have little relevance or impact in daily life. Their presence can be suggested by the report of immediate family members suffering problems with anaesthetics. Establishing the details of these problems and any referral or investigations made can guide the anaesthetic choice to a suitably safe technique. It is important to remember that a negative family history does not guarantee that there are no familial issues.
Drug history
All current medication must be carefully documented, including over-the-counter preparations. This will help inform understanding of comorbidity – both presence and severity. In addition, many drugs may interact with agents or techniques used during anaesthesia. Anaesthetists must maintain up-to-date knowledge of pharmacological advances as new drugs continue to emerge on the market.
Maintenance of the usual drug regimen, including on the morning of surgery, should be considered the norm, with some notable exceptions ( Table 19.2 ). Consideration must also be given to possible perioperative events that influence subsequent drug administration (e.g. delayed gastric emptying, postoperative ileus) and appropriate plans made to use an alternative route or product with similar action for essential medication.
Table 19.2
Routine medication: relevance to anaesthesia and surgery
| Drug group | Comments |
|---|---|
| Cardiovascular | |
| Antiplatelet agents Aspirin Dipyridamole P2Y12 receptor inhibitors |
Require management in perioperative period to minimise risk of serious surgical bleeding and permit neuraxial techniques. Some peripheral and superficial surgery does not require cessation. Dual antiplatelet therapy of most significance. Do not omit in patients within 6 months of cardiovascular event or stroke without specialist advice, particularly if drug-eluting coronary artery stent(s) inserted as stent thrombosis is catastrophic. Consider delay to surgery if feasible rather than disruption of therapy. Low-dose aspirin (75 mg daily) can be continued perioperatively for most surgeries. Consider reducing higher doses to low dose. Omit dipyridamole 24 h preoperatively. Some P2Y12 receptor inhibitors bind irreversibly and require longer omission for manufacture of functioning platelets – cessation for 3–5 days (ticagrelor) and 5–10 days (clopidogrel) before surgery is recommended. |
| Anticoagulants Warfarin Direct oral anticoagulants (DOACs) Low molecular weight heparin (LMWH) |
Require management in the perioperative period to minimise risk of serious surgical bleeding and permit neuraxial techniques. Some peripheral and superficial surgery does not require cessation (e.g. hand surgery, cataracts). Indication for anticoagulation dictates management strategy. Those at higher risk of thrombotic event (e.g. metallic heart valve) require transition from long-acting oral to alternative shorter-acting agents (bridging anticoagulation). Those at lower risk (e.g. atrial fibrillation with no previous stroke) may be able to omit medication without replacement. Warfarin requires omission for 5 days preoperatively, with INR check 48 h before surgery and administration of vitamin K if inadequate reduction in effect. DOACs (e.g. rivaroxaban, apixaban) require between 2 and 4 days' omission preoperatively (according to renal function). LMWH is often the drug of choice to bridge from oral anticoagulants. Check carefully if the dose prescribed is intended to be therapeutic or prophylactic. Dosing is weight based. The last therapeutic dose of LMWH should be given 24 h before surgery. Fondaparinux requires omission for between 3 and 5 days (according to renal function). |
| Angiotensin-converting enzyme inhibitors | Hypotensive effects may be potentiated by anaesthetic agents. Consider omitting 24–36 h preoperatively. |
| Angiotensin II receptor blockers | May be associated with severe intraoperative hypotension. Omit 24 h preoperatively. |
| Beta-blockers | Can cause exaggerated hypotension and mask compensatory tachycardia. Acute withdrawal may result in angina, ventricular extrasystoles or precipitate myocardial infarction. Do not omit and ensure ongoing dosing throughout the perioperative period. |
| Calcium channel blockers Verapamil |
Interacts with volatile anaesthetic agents leading to bradyarrhythmias and decreased cardiac output. Do not omit. |
| Diltiazem Nifedipine |
Interacts with volatile anaesthetic agents to cause hypotension. Acute withdrawal may exacerbate angina. Do not omit. |
| Other antihypertensives Clonidine Guanethidine Methyldopa Reserpine |
Hypotension seen with all anaesthetic agents, requiring extreme care with dosage and administration. Acute withdrawal of long-term treatment may result in a hypertensive crisis. Do not omit. |
| Digoxin | Toxicity enhanced by hypokalaemia and suxamethonium. Beware of bradyarrhythmias. Do not omit. |
| Diuretics | Preparations often taken at variable times for convenience by patients. Omission acceptable. |
| Central nervous system | |
| Anticonvulsants | Sudden withdrawal may produce rebound convulsive activity. Do not omit. |
| Benzodiazepines | Additive effect with many CNS-depressant drugs. Do not omit. |
| Monoamine oxidase inhibitors (MAOIs) | Severe hypertensive response to pressor agents as a result of inhibition of metabolism of indirectly acting sympathomimetics. Treatment of regional anaesthetic-induced hypotension may be difficult. Consider withdrawal 2–3 weeks before surgery and use of alternative medication. |
| Tricyclic antidepressants | Potentiation of indirectly acting sympathomimetics can precipitate hypertensive crisis. Abrupt withdrawal should be avoided because of risk of cholinergic symptoms. Do not omit. |
| Phenothiazines, butyrophenones | Interact with other hypotensive agents. Do not omit. |
| Lithium | Renal excretion with narrow therapeutic window. Consider omission 24 h before major surgery and monitoring with dose adjustment postoperatively after major surgery and those with acute kidney injury. |
| l -dopa | Multiple drug interactions. Ensure regular administration throughout perioperative period; note short half-life requires stringent dosing intervals. Do not omit. |
| Diabetic medication | |
| Insulin | Dose reduction required for insulins of all duration, except extended release (weekly dosing) preparations. Close monitoring required; avoid variable-rate insulin infusion where possible. Do not omit. |
| Oral hypoglycaemic agents | Meglitinides (e.g. repaglinide) and sulphonylureas (e.g. gliclazide) require omission because of risk of hypoglycaemia. Sodium-glucose cotransporter-2 (SGLT2) inhibitors (e.g. dapagliflozin) require omission because of risk of ketoacidosis. Acarbose, dipeptidyl peptidase-4 (DPP-4) inhibitors (e.g. sitagliptin), glucagon-like peptide-1 (GLP-1) analogues (e.g. liraglutide) and pioglitazone can be taken whilst fasting. Metformin can be taken whilst fasting (except in those with chronic kidney disease stage ≥3 or those expected to receive a dose of contrast media). |
| Immune modulation and suppression | |
| Oral preparations (e.g. azathioprine, leflunomide, hydroxychloroquine, methotrexate, tacrolimus) |
Whilst infective risks may be increased, these drugs should be continued in the perioperative period. Methotrexate can cause leucopenia, and a full blood count should be checked preoperatively. Omit if significant leucopenia and consider omission in patients with renal impairment. |
| Biological disease-modifying agents (e.g. infliximab, etanercept, adalimumab, rituximab) | Continuation or omission dependent on the likelihood of relapse or loss of disease control vs. the infective risks of the procedure proposed. May require specialist advice. Cessation is variable, between 1 and 12 weeks before surgery, and restart only after wounds healed and dry. |
| Steroids | Potential adrenocortical suppression. Additional steroid cover may be required for the perioperative period. |
| Oral contraceptive pill | Increased risk of thromboembolic complications with oestrogen-containing formulations. Discuss stopping 4 weeks before elective surgery, with substitution of alternative reliable contraception. If continued, ensure adequate thromboembolic prophylaxis. |
INR, international normalised ratio.
It is advised that some drugs be discontinued several weeks before surgery if feasible (e.g. oestrogen-containing oral contraceptive pill, long-acting monoamine oxidase inhibitors) because of the potential severity of perioperative complications. The pros and cons of these decisions should be considered carefully as severe consequences (unintended pregnancy, relapse of severe depression) may result.
Patients can present for surgery with an illicit drug habit. Abuse of opioids and cocaine is not uncommon, and there is significant information available about potential perioperative problems related to acute or chronic toxicity. The same is not true for the increasing number of designer drugs, nor is much published regarding anabolic steroid use and other image-enhancing drugs. Route of administration should be sought when discussing illicit drug use because of the transmission of bloodborne viruses with s.c. or i.v. injection.
There are potential interactions from herbal remedies used during the perioperative period:
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Garlic, ginseng and gingko: increased bleeding
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St John's wort: induces cytochrome P4503A4 and cytochrome 2C9
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Valerian: modulates γ-aminobutyric acid (GABA) pathways
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Traditional Chinese herbal medicines: variety of adverse effects, including hypertension and delayed emergence
The clinical importance of these interactions is not clear. Current guidance is that patients should be asked explicitly about their use and, if possible, should discontinue them 2 weeks before surgery. There is no evidence to postpone surgery purely because patients are taking herbal remedies.
History of allergy
A history of allergy to specific substances must be sought, whether drug, food or adhesives, and the exact nature of the symptoms and signs should be elicited and documented to distinguish true allergy from other predictable adverse reactions (see Chapter 26 ).
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Latex allergy is becoming increasingly common; it requires latex-free equipment and a theatre with a full air change to be used for surgery. Logistically this is often achieved by placing the latex-allergic patient first on the morning list.
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A small number of patients describe an allergic reaction to previous anaesthetic exposure. A careful history and examination of the relevant medical notes should clarify the details of the problem, together with the documentation of any postoperative investigations.
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Reported allergy to local anaesthetics is usually a manifestation of anxiety or a response to peak concentrations of local anaesthetic or adrenaline. There are a small number of individuals who are allergic to sulphites, which are commonly found in local anaesthetic preparations (and other drugs).
Smoking history
Long-term deleterious effects of smoking include peripheral vascular disease, coronary artery disease, many cancers and chronic obstructive pulmonary disease (COPD). There are several potential mechanisms by which cigarette smoking can contribute to an adverse perioperative outcome:
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The cardiovascular effects of smoking (tachycardia and hypertension) are caused by the action of nicotine on the sympathetic nervous system.
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Smoking causes an increase in coronary vascular resistance; cessation of smoking improves the symptoms of angina.
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Cigarette smoke contains carbon monoxide, which converts haemoglobin to carboxyhaemoglobin (COHb).
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In heavy smokers this may result in a reduction in available oxygen by up to 25%.
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As the half-life of COHb is short, abstinence for 12 h leads to an increase in arterial oxygen content.
-
-
The effect of smoking on the respiratory tract leads to a sixfold increase in postoperative respiratory morbidity.
It appears sensible to advise all patients to cease cigarette smoking for at least 12 h before surgery, and if seen with sufficient lead time, be abstinent for 6 weeks to reduce bronchoconstriction and mucus secretion. The preoperative period can be considered an opportunity for health education; preoperative assessment clinics should be able to refer patients freely to smoking cessation services.
E-cigarettes are used by many smokers alongside cigarettes in an attempt to reduce consumption. These deliver an aerosol containing nicotine, propylene glycol and various flavours, without smoke, tar or carbon monoxide. There is concern regarding the wide variety of chemicals and metals found in vapour; however, it would appear advantageous to advise smokers using both cigarettes and e-cigarettes to switch entirely to e-cigarettes in the preoperative period if they are unwilling to stop smoking entirely. As nicotine is a sympathomimetic, ceasing e-cigarette smoking for some hours before surgery should be advocated.
Alcohol history
Patients may present with acute intoxication, sequelae of chronic consumption (liver disease and cirrhosis) or other non-specific features of secondary organ damage such as cardiomyopathy, pancreatitis and gastritis. Obtaining a clear history of consumption can be difficult. Where patients admit to regular daily consumption, careful questioning regarding dependence and features of risk should be undertaken. The Alcohol Use Dependence Identification Test (AUDIT) developed by the WHO for use in primary care can also be used in the preoperative assessment clinic.
Social circumstances
Suitability for day-case surgery should be established in the clinic; it is a requirement that the patient is escorted home and stays in the presence of a responsible adult in a suitable environment for the first 24 h after anaesthesia. Some patients can be identified as requiring occupational therapy or physiotherapy assessment preoperatively to allow smooth discharge planning.
Physical examination
Examination should complement the clinical history and systems enquiry, and all patients should have basic clinical observations, including recording of height and weight and an airway assessment (see Chapter 23 ). Detailed physical examination of a patient who is fit and well is arguably unnecessary, but it is a simple and safe method to confirm or refute the expectations of the history. Examination can provide information in case morbidity arises postoperatively e.g. foot drop after poor positioning during anaesthesia and surgery. Occasionally, occult morbidity of particular interest (e.g. aortic stenosis) can be revealed. Features of particular relevance are presented in Table 19.3 .
Table 19.3
Features of clinical examination particularly relevant to the anaesthetist
| System | Features of interest |
|---|---|
| General | Nutritional state, fluid balance Skin and mucous membranes (anaemia, perfusion, jaundice) Temperature Evidence of frailty (slow to undress, weak grip, reduced muscle mass) |
| CVS | Peripheral pulse (rate, rhythm, volume) Arterial blood pressure Heart sounds Carotid bruits Dependent oedema |
| RS | Central or peripheral cyanosis Oxygen saturations on air, sitting and supine Respiratory rate and observation for dyspnoea Auscultation of lung fields |
| Airway | Specific airway assessment tests Dentition |
| CNS | Any dysfunction of special senses Cranial/peripheral motor and sensory nerves |
Investigations
Before ordering investigations, these questions should be considered:
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Will this investigation yield information not already apparent from clinical assessment?
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Will the results of the investigation give additional information on diagnosis or prognosis relevant to the planned surgery?
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Will the results of the investigation alter the perioperative preparation and management of the patient and meaningfully reduce perioperative risk?
The number of routine investigations should be minimised by using stringent protocols. The UK National Institute for Health and Care Excellence (NICE) has produced comprehensive guidance on routine testing (NG45), considering both patient and surgical factors. The advice regarding routine testing presented here is based upon this ( Table 19.4 ).
Table 19.4
Guidelines for preoperative investigations
| Pregnancy tests | Discuss on day of surgery with women of childbearing age. Test with patient consent. Develop and adhere to local protocols for checking pregnancy status. |
| Urine tests | Do not routinely offer urine dipstick tests. Consider microscopy and culture of midstream urine sample where presence of UTI would influence decision to operate. Perform microscopy and culture of midstream urine sample in patients symptomatic of UTI. |
| Full blood count | Do not routinely offer test to any patient for minor surgery. Do not routinely offer test to ASA 1 or 2 patients for intermediate surgery. Consider in ASA 3 or 4 patients with cardiovascular or renal comorbidity if any symptoms not recently investigated, for intermediate surgery. Perform test in all patients for major or complex surgery. Various groups will also require an FBC depending on clinical presentation, including: patients with a surgical pathological condition that causes bleeding or with clinical evidence of anaemia; those undergoing treatment for anaemia without recent check of therapeutic efficacy; patients with a history of long-term immunosuppressive medication use, current neoadjuvant chemotherapy use, or taking some antiepileptic medications; those with recognised blood or bone marrow disorders; patients with a positive bleeding history or known bleeding disorder; those with alcohol dependency or anorexia nervosa; and patients who would refuse blood transfusion. |
| Urea, creatinine and electrolytes | Do not routinely offer test to ASA 1 or 2 patients for minor surgery. Consider in ASA 3 or 4 patients for minor surgery at risk of AKI. Do not routinely offer test to ASA 1 patients for intermediate surgery. Consider in ASA 2 patients for intermediate surgery at risk of AKI. Perform test in ASA 3 or 4 patients for intermediate surgery. Consider in ASA 1 patients for major or complex surgery at risk of AKI. Perform test in ASA 2, 3 or 4 patients for major or complex surgery. Consider in patients who have hypertension and those taking medication that can cause renal impairment (e.g. diuretics, ACE inhibitors, ARA, aminoglycoside antibiotics). Consider measuring venous bicarbonate in those with STOP-BANG score ≥5 (≥28 mmol L –1 is a sensitive indicator of hypoventilation with ensuing hypercarbia). Patients at risk of AKI include: those undergoing emergency surgery, particularly in the context of sepsis or hypovolaemia, or intraperitoneal surgery; patients with CKD (eGFR <60 ml min –1 1.73 m –2 ), heart failure, diabetes or liver disease; patients aged older than 65 years; and patients prescribed drugs with nephrotoxic potential in the perioperative period. |
| Liver function tests | Do not routinely offer. Consider before hepatobiliary surgery and in patients with liver disease, previous hepatitis, high alcohol intake, jaundice, unexplained bleeding or bruising, morbid obesity, anorexia, malnutrition or HIV. |
| Haemostasis | Do not routinely offer test to any patient for minor surgery. Do not routinely offer test to ASA 1 or 2 patients for intermediate or major or complex surgery. Consider in ASA 3 or 4 patients with chronic liver disease for intermediate or major surgery. Consider in patients who score positively on a structured bleeding questionnaire and those with significant malabsorption. Note: Patients taking direct acting oral anticoagulants will have abnormal coagulation tests that do not reflect the degree of anticoagulation. To assess the regression of these agents after cessation and before surgery requires specific assays such as anti-Xa; specialist haematological advice should be sought. |
| HbA1c | Do not routinely offer test to patients without a history of diabetes. Those referred for surgery with a history of diabetes should have their most recent HbA1c result included in the surgical referral. Offer HbA1c testing to patients with diabetes having surgery if they have not been tested in the previous 3 months. Consider random glucose and HbA1c testing in obese patients and other groups at high risk, particularly patients with symptoms suggestive of occult diabetes such as recurrent soft tissue infections, fatigue, polydipsia and polyuria. |
| Sickle-cell disease or sickle-cell trait tests | Do not routinely offer test. Consider testing in context of family history. |
| Chest radiograph | Do not routinely offer test. Consider only if acute symptoms of infection or failure. |
| Other radiographs | Consider cervical spine radiographs in selected patients where there is a possibility of vertebral instability (e.g. those with rheumatoid arthritis). |
| ECG | Do not routinely offer test to ASA 1 or 2 patients for minor surgery. Consider in ASA 3 or 4 patients for minor surgery if no ECG result available from prior 12 months. Do not routinely offer test to ASA 1 patients for intermediate surgery. Consider in ASA 2 patients for intermediate surgery with cardiovascular or renal comorbidity or diabetes. Perform in ASA 3 or 4 patients for intermediate surgery. Consider for ASA 1 patients for major or complex surgery aged older than 65 if no ECG result available from prior 12 months. Perform in ASA 2, 3 and 4 patients for major or complex surgery. Perform before referral for echocardiography. Perform if new stage of hypertension (stage 2/3) is diagnosed. Consider where assessment suggests or reveals conditions that can lead to cardiomyopathy (e.g. high alcohol intake, illicit steroid use, illicit cocaine use, anorexia nervosa) or if high risk for OSA. |
| Resting echocardiography | Do not routinely offer test. Consider if patient has a heart murmur and any cardiac symptom (e.g. breathlessness, presyncope, syncope or chest pain). Consider if patient has signs or symptoms of heart failure. |
| Lung function tests (spirometry and blood gas analysis) | Do not routinely offer test to any patient for minor surgery. Do not routinely offer test to ASA 1 or 2 patients for intermediate or major surgery. Consider seeking advice of senior anaesthetist for patients who are ASA 3 or 4 because of known or suspected respiratory disease for intermediate or major surgery. |
ACE, Angiotensin-converting enzyme; AKI, acute kidney injury; ARA, angiotensinogen receptor antagonists; ASA, American Society of Anesthesiologists; CKD, chronic kidney disease; eGFR, estimated glomerular filtration rate; FBC, full blood count; HbA1c, glycated haemoglobin; HIV, human immunodeficiency virus; OSA, obstructive sleep apnoea; UTI, urinary tract infection.
By reviewing recent investigations undertaken in the community or surgical clinic, unnecessary blood sampling and expense can be avoided, particularly where there has been no change in symptoms in a patient with chronic disease.
All tests ordered in the preassessment clinic should be reviewed and serious abnormalities acted upon promptly. This may involve direct communication with the patient, primary care specialists, waiting list coordinator and/or admitting team.
Cardiorespiratory investigations
Routine investigations should be minimised, and patients with known stable cardiorespiratory disease do not require repeated investigation where recent results are available. However, preoperative assessment often uncovers functional incapacity or unstable cardiorespiratory disease. In these situations, basic investigations should be arranged to decide the most likely pathological condition, direct onward referral and provide a baseline. The perioperative management of patients with significant cardiorespiratory disease is discussed in Chapter 20 .
Plasma biomarkers
Biomarkers are biochemical substances that can be assayed from plasma samples, and abnormal concentrations may be associated with certain disease states. Concentrations of B-type natriuretic peptide (BNP), a hormone secreted by cardiac cells in response to stretching of the myocardium, are raised in patients with heart failure, resulting in increased sodium excretion and decreased systemic vascular resistance and correlate with the degree of severity of the disease. A raised BNP concentration is associated with a higher risk of adverse cardiac events and mortality after surgery, and normal concentrations are negative predictors of complications. Cardiac troponin is a marker of myocardial damage, and an elevated preoperative value confers a twofold to threefold increase in the risk of postoperative mortality in major non-cardiac surgery.
ECG
A 12-lead ECG is of greatest value in the assessment of rhythm and should be performed in patients with persistent tachycardia or an irregular pulse. However, it has a low sensitivity for the detection of pathological cardiac conditions and can appear essentially normal in the face of a wide variety of conditions, including clinically significant coronary artery disease, valvular heart disease and even the presence of an internal defibrillator. The indications for a preoperative ECG are shown in Table 19.4 .
Resting transthoracic echocardiography
Echocardiography is the investigation of choice for valvular heart disease and can be required in the evaluation of patients with newly detected heart murmurs (see Table 19.4 ). Murmurs are common; where there is an absence of cardiac symptoms, the murmur is unlikely to represent significant valve disease. An echocardiogram should only be requested when the patient is symptomatic or has an undiagnosed heart murmur but whose function is so limited that they do not increase cardiac output (CO) sufficiently to reveal symptoms. Those with diagnosed heart murmurs or replacement valves may also require echocardiography before surgery when they have developed symptoms or if they are approaching or have exceeded a planned surveillance interval.
It is important to remember that an echocardiogram is performed at rest, at a singular point in time, and thus does not inform the anaesthetist of how the heart may respond to increased demands. Patients with severe left ventricular impairment on a recent echocardiogram can demonstrate normal oxygen delivery on subsequent functional testing. Similarly, normal left ventricular function in terms of ejection fraction on resting echocardiogram does not necessarily mean that the risk of cardiac complications is low, as a significant proportion of patients with heart failure have a preserved ejection fraction. These patients may have diastolic dysfunction and have an increased postoperative risk of adverse cardiac events.
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