Preoperative Assessment

PERIOPERATIVE CARE

© 2003 The Medicine Publishing Company Ltd319ANAESTHESIA AND INTENSIVE CARE MEDICINE

The preoperative evaluation of patients is an essential compo-nent of their subsequent successful management. Its importance is often underestimated and it can be time consuming. In addition to assessing the patient’s physical health, the preoperative visit is the first contact between patient and anaesthetist so it is important for establishing the patient’s confidence. The aims of assessment are summarized in Figure 1. The main objective is to avoid any unanticipated problems during the patient’s subsequent management. Anticipation of potential difficulties allows a suitable plan to be made and avoids crisis management. In patients with challenging problems it is essential to involve senior anaesthetists and surgeons at an early stage and, if possible, to work at elective times. Specific demands imposed by the surgery must be considered, such as the expected blood loss or the risk of nausea and vomiting. The various anaesthetic and analgesic techniques can be discussed and the pre operative medication rationalized. Postoperative treatment in high depen-dency or intensive care units can be planned and electivecases deferred until such beds are available. In emergency sur-gery, the time for evaluation is limited, as is the opportunity to optimize the patient’s medical condition or organize special investigations.

History and examination

Co-existing medical conditions: a system-based enquiry is gen-erally used to identify the disease processes that may influence anaesthesia. Most hospitals provide a pre-assessment questionnaire for patients to fill in before the anaesthetist’s visit. This highlights areas that require more detailed enquiry and examination. The aim is to optimize the patient’s physical condition before the

procedure. With all co-existing medical conditions it is important to determine their severity and the extent to which the patient is compromised by them. This allows some assessment of risk and helps to predict the chance of perioperative problems. It is also important to assess any systemic effects of the presenting pathology, for example, dehydration or electrolyte imbalance with gastric obstruction, or anaemia associated with bowel tumours. It is impossible to give an exhaustive list of all the medical disorders impacting on the practice of anaesthesia, but Figure 2 lists some that are common or important.

Hypertension: poorly controlled blood pressure is associated with lability under anaesthesia and increased perioperative cardiac morbidity. The usual cut-off for concern is a diastolic pressure greater than 110 mm Hg; however, blood pressure increases lin-early with age and levels must be interpreted accordingly. Genuine raised pressure is suggested by elevated readings on more than one occasion, raised levels recorded out of hospital, and clinical evidence of sustained hypertension, particularly left ventricular hypertrophy.

Upper respiratory tract infections: anaesthetists often have to decide whether to proceed with or cancel surgery if the patient, especially a child, has had a recent upper respiratory tract infection. Complications are related to the presence of secretions, mucous plugging of the bronchi and increased airway reactivity, which may persist for up to 6 weeks. The risks of perioperative airway problems are increased when there is a history of prematurity, asthma, a young age (under 5 years), exposure to smoking or the need to intubate the trachea. However, if all children with mild upper respiratory tract infections had their surgery cancelled,half the patients would be sent home in winter. If a child is obviously ill, with fever, a productive cough and wheeze, theirsurgery should probably be cancelled. For most others, with mild symptoms, the risks are minimal and complications easilymanaged.

Previous general anaesthesia: it is especially helpful to see old anaesthetic records. Even if there have been no apparent problems, the patient’s past experience forms the basis of their expectations, fears and preferences.

Preoperative AssessmentRuth Spencer

Andrew K McIndoe

Ruth Spencer is a Clinical Fellow in Paediatric Intensive Care at the Bristol

Children’s Hospital. She graduated from Bristol University and initially

trained in general medicine as an SHO and registrar. She has completed

the Bristol Specialist Registrar rotation in anaesthetics.

Andrew K McIndoe is Consultant Anaesthetist and Senior Clinical Lecturer

in the Sir Humphry Davy Department of Anaesthesia, Bristol Royal

Infi rmary. He is also the Director of Research and Education at the Bristol

Medical Simulation Centre where he has developed a specifi c interest in

human factors and crisis management.

Aims of preoperative assessment

• History and examination

• Optimizing the patient’s medical condition

• Prescribing preoperative drugs

• Planning the anaesthetic technique

• Discussing methods of analgesia

• Deciding the number and seniority of staff who will be needed

• Establishing a rapport with the patient

• Supplying information to the patient and answering questions

• Planning postoperative care

1

spencer.indd 319 15/09/03, 10:42:48

PERIOPERATIVE CARE


Family history: it is important to detect rare, inherited conditions (e.g. malignant hyperpyrexia, suxamethonium apnoea) that do not manifest as problems in everyday life but have serious conse-quences under anaesthesia.

Allergies: consider drug sensitivities, latex allergy or food products known to have cross-over reactions with anaesthetic drugs.

Smoking is associated with an increase in adverse perioperative events. Patients should be told that stopping smoking, even for 12 hours before surgery, could reverse some of the detrimental effects.

Alcohol and drug abuse: in addition to their deleterious effects on health, the effect of sudden withdrawal during a hospital admis-sion should be addressed.

Dental examination: damage to teeth is one of the most common causes of litigation against anaesthetists. The condition of the teeth

should be well documented before surgery and the patient must be warned that loose teeth, caps and crowns can be accidentally dislodged.

Airway assessment will almost certainly not have been carried out by anyone else, even when a thorough physical examination has been conducted. Many ways of assessing the airway have been described, all of which are unreliable in predicting difficulty. The most reliable predictor of difficulties is a history of airway problems during previous anaesthesia.

Starvation policy: the patient needs to know for what period of time they must abstain from food and fluids. It is helpful to specify the latest time at which fluids can be taken, in order to avoid unnecessarily long periods of starvation. In adults, 6 hours starvation from solids is usual, but most anaesthetists would allow clear fluids until 4 hours before surgery. Postoperative analgesia: the proposed method of pain control

Diseases that may affect anaesthesia

Cardiovascular system• Hypertension and its control

• Angina (stable or unstable)

• Myocardial infarction (how recent? effect on function?)

• Cardiac failure

• Dysrhythmias and heart block

• Valvular heart disease

• Peripheral vascular disease

• Cardiomyopathies

Respiratory system• Asthma

• Chronic obstructive pulmonary disease

• Recent upper respiratory tract infection

• Emphysema

• Bronchiectasis

• Smoking

• Lung fibrosis

• Tuberculosis

• Sleep apnoea or snoring

Gastrointestinal system• Obesity

• Hiatus hernia or gastro-oesophageal reflux

• History of nausea and vomiting

• Gastric obstruction

• Jaundice (past or present)

Endocrine and metabolic conditions• Diabetes mellitus

• Thyroid disorders

• Pregnancy

• Cushing’s or Addison’s disease

• Long-term corticosteroid medication

• Porphyria

• Acromegaly

Renal disease• Acute renal failure

• Chronic renal failure ± dialysis

• Renal calculi

CNS• Epilepsy

• Previous transient ischaemic attacks or strokes

• Head injury

• Neuropathies

• Pre-existing nerve palsies or paraesthesia

• Multiple sclerosis

• Myasthenia gravis

Musculoskeletal and connective tissue disorders• Rheumatoid arthritis

• Vasculitides (e.g. systemic lupus erythematosus, polyarteritis

nodosa)

• Malignant hyperpyrexia

• Dystrophia myotonica

• Myopathies

Haematological conditions• Anaemia

• Immunodeficiency

• Clotting abnormalities

• History of thromboembolism

• Haemoglobinopathies (sickle cell disease, thalassaemia)

2

spencer.indd 320 15/09/03, 10:42:50

PERIOPERATIVE CARE


must be discussed. The risks and benefits of epidural or spinal anaesthesia can be explained, as can other regional blocks. Itmust be made clear to patients whether procedures will takeplace while they are awake or asleep and that general anaesthesia can be offered if regional anaesthesia is inadequate. Explaining how to use patient-controlled analgesia is also essential pre-operatively.

Investigations

The need for investigations should be determined by the history and examination, the patient’s age, the medication they are taking, and the planned procedure. Preoperative assessment is not an opportunity for routine screening. Investigations should be tailored to individual patients and targeted according to the underlying pathology. They should be restricted to those that will alter man-agement or detect a condition, the risk of which can be reduced. However, while most people agree that a blanket approach to ordering routine tests on healthy individuals is neither beneficial nor cost effective, it is more difficult to know where the balance lies in older patients or those with underlying medical disorders. Many hospitals have protocols for investigations guided by the age of the patient and the nature of the surgery but evidence as to how far these tests alter anaesthetic management or patient outcome is lacking. It should also be remembered that 5% of healthy individuals have a result that falls outside the laboratory’s normal range.

Laboratory investigationsFull blood count: haemoglobin levels vary widely in the surgical population. The haemoglobin level should be checked if the his-tory or examination suggests anaemia or if significant blood loss is expected during the operation. It is also important if the oxygen- carrying capacity of the blood will be impaired by other factors(e.g. lung disease). Healthy individuals undergoing minor surgery do not generally require a full blood count because mild, chronic anaemia is well tolerated under anaesthesia. Unexpectedly low white cell counts and platelet counts occur in less than 1% of those for whom the history did not suggest a problem, but many anaes-thetists prefer to see a platelet count before performing regional anaesthesia. Polycythaemia rubra vera (haemoglobin > 16–17 g/dl)is associated with an increased risk of cardiac complications, bleeding and thromboembolic events.

Clotting screen: in the absence of a history of bleeding diatheses, anticoagulant drugs or excessive alcohol intake, the chance of the clotting screen being abnormal is less than 1%. In terms of drug effects, an assessment of platelet function rather than count may be more important because aspirin and non-steroidal anti-inflammatory drugs are widely used. Newer drugs affectingplatelet aggregation (e.g. clopidogrel) are associated withincreased bleeding. Thromboelastography is the only test that measures the whole dynamic process of clot formation, strength and stability.

Sickle cell tests should be carried out in all patients belonging to an ethnic group at risk (see Anaesthesia and Intensive CareMedicine 2:4: 145). The presence of sickle cells affects the conduct of anaesthesia and precludes the use of surgical tourniquets.

Electrolyte abnormalities are common in surgical patients and should be checked before major surgery. Hypokalaemia is a minor risk factor for cardiac complications and common in those taking diuretics or who have suffered diarrhoea and vomiting. The pres-ence of mild renal impairment is also common and influences the choice of drugs, such as antibiotics and analgesics, in favour of those that are not nephrotoxic. Despite a large number of published guidelines, the age limit above which routine biochemical testing should be carried out is unclear. Some studies recommend testing for all patients over 40 years, while others suggest over 70 years is appropriate. The likelihood of abnormal blood glucose levels increases with age and is associated with higher perioperative risks. It should be checked in the obese, those taking corticosteroid treatment and those with a positive family history.

Cross-matching depends on the starting haemoglobin level, the anticipated losses and the speed with which blood can be obtained. Most hospitals have a cross-matching schedule for each operation, designed to minimize this increasingly expensive procedure.

Tests of respiratory functionPulmonary function tests may be appropriate in assessing patients with chronic obstructive airways disease, lung fibrosis, asthma or significant musculoskeletal abnormalities. They are also help-ful before thoracic surgery to determine whether the patient has sufficient respiratory reserve to tolerate lung resection. The usual tests are the peak expiratory flow rate and the spirometry tests (forced expiratory volume in 1 second and forced vital capacity). Other tests of lung function include flow-volume loops and carbon monoxide transfer factor. Before major surgery, a preoperative blood gas measurement is useful to determine the patient’s usual baseline levels of oxygen and carbon dioxide.

RadiologyChest: preoperative radiology should be reserved for those with a history of significant cardiac or respiratory disease. Up to 70% of patients in whom cardiomegaly is present radiologically, have an ejection fraction of under 50%. Many will have had radiographs taken recently and unnecessary repeats should be avoided.

Cervical spine: cervical spine instability is indicated by a distance of over 5 mm between the anterior arch of C1 and the odontoid peg in flexion. Cervical spine involvement in rheumatoid arthritis is present radiologically in up to 85% of those with established disease. This suggests that all rheumatoid patients should undergo radiology but an alternative is to assume a degree of instability in anyone with established rheumatoid arthritis and manage appropriately.

Thoracic inlet: views of the thoracic inlet are sometimes ordered to investigate tracheal compression or deviation, but CT scanning is a better guide.

Tests of cardiac function12-lead ECG: the main purpose of preoperative ECGs is to identify high-risk patients who have silent ischaemia, previous myocardial infarcts or undetected arrhythmias. There is a clear association between a recent myocardial infarction and perioperative mortal-ity. Surgery within 3 weeks of a myocardial infarction carries a 25% mortality, reduced to 10% at 3 months and 5% at 6 months.

spencer.indd 321 15/09/03, 10:42:50

PERIOPERATIVE CARE


Abnormalities of the ECG rise with age and ASA (American Society of Anesthesiology) status. ECGs should be carried out in patients over 50 years, smokers, the obese, diabetics, those with raised cholesterol, and those with a strong family history of ischaemic heart disease. Although ischaemia on a resting ECG indicates marked cardiac disease, it is not a sensitive test. The ECG is normal in 50% of those with known coronary artery disease and the predictive power of preoperative ECGs for postoperative complications is weak. Dynamic tests of exercise tolerance and functional assessment are more useful for determining the extent of cardiac disease and predicting how the heart will cope with the stresses imposed by anaesthesia and surgery.

Exercise testing can predict potential cardiac problems. One study on vascular patients showed that those who could achieve 85% of their maximum predicted heart rate had only a 6% chance of cardiac complications, compared with a 24% rate in those who could not. In many patients, especially those with peripheral vas-cular disease, exercise testing cannot be performed because their exercise tolerance is limited by factors other than their heart.

Echocardiography is a non-invasive, easily available test, which allows a dynamic view of cardiac performance, including left ventricular function. It is especially useful in the assessment of murmurs and cardiac failure. Stress echocardiography using dobutamine can be used to demonstrate cardiac reserve in those who cannot exercise.

Dipyridamole/thallium scanning relies on thallium being taken up by the myocardium in proportion to its perfusion, so that underperfused areas appear as ‘cold spots.’ Dipyridamole then induces coronary artery vasodilatation and allows thallium to be redistributed to previously hypoperfused areas. The presence of areas with reversible underperfusion strongly correlates with perioperative myocardial ischaemia.

Angiography remains the gold standard of coronary artery assess-ment. In addition to defining the anatomy, it allows therapeutic interventions such as stents or angioplasty. However, it is invasive and has an associated morbidity and mortality.

Assessing risk

Assessing risk allows the doctor and patient to balance the ben-efits of surgery against the risks incurred during the perioperative period. Many large studies have attempted to quantify risk fac-tors. The most important influences are the pre-morbid condition of the patient, and the extent and urgency of the surgery. Some perioperative scoring systems predict general, nonspecific adverse outcomes while others predict more specific morbidities such as a difficult airway or the chance of cardiac complications.

ASA statusThe ASA classification (Figure 3), introduced in 1963, relates to the patient’s general health and whether the surgery is an elective or an emergency procedure. Although widely used, it is nonspecific and a poor predictor of outcome when used alone. It does not take into account the severity of the presenting pathology nor does it

American Society of Anesthesiologists (ASA) classification of physical status

• ASA 1 A normal healthy patient

• ASA 2 A patient with mild systemic disease

• ASA 3 A patient with severe systemic disease

that limits activity

• ASA 4 A patient with incapacitating disease

that is a constant threat to life

• ASA 5 A moribund patient not expected to

survive 24 hours with or without an

operation

• E Appended to any grade in the event of

emergency surgery

3

identify factors that could be treated preoperatively to improve the outcome.

Cardiac riskCardiac disease is the main cause of postoperative death. Trying to assess the patient’s risk is vital in determining how and when to proceed with surgery and whether any interventions might improve outcome. Historically, a number of cardiac risk indices have attempted to stratify patients preoperatively. The American

Clinical predictors for cardiac complications

Major

• Recent myocardial infarction (within 1 month)

• Unstable angina

• Decompensated cardiac failure

• Severe valvular disease

• Serious arrhythmias

Intermediate

• Mild angina

• Prior myocardial infarction by history or ECG

• Previous cardiac failure

• Diabetes

• Renal insufficiency

Minor• Advanced age

• Uncontrolled hypertension

• Rhythm other than sinus

• History of stroke

• Abnormal ECG (e.g. left bundle branch block)

4

spencer.indd 322 15/09/03, 10:42:50

PERIOPERATIVE CARE


College of Cardiologists along with the American Heart Association produce guidelines, most recently updated in 2002. They attempt to assess risk without subjecting the patient to unnecessary investiga-tions. Cardiac problems are considered as major, intermediate or minor clinical predictors of complications (Figure 4). Subsequent management also depends on the patient's exercise tolerance and the nature of the surgery. High-risk surgery includes operations associated with large fluid shifts or blood loss, vascular procedures and emergency operations. Major predictors justify the cancellation of elective surgery. If surgery is essential, dynamic tests of cardiac function (e.g. stress testing, echocardiography) should be carried out.

Intermediate predictors warrant careful assessment of functional capacity. If the patient’s exercise tolerance is good and the surgery of low risk, it can proceed with careful monitoring. However, if they have poor exercise tolerance or need a high-risk operation, tests of dynamic function are helpful. Those with dipyridamole/thallium scans showing areas of underperfusion have a 30% chance of cardiac complications compared with 3% of those who have a normal test.

Minor predictors are markers of cardiac disease that have not been shown independently to increase perioperative risk. Patients do not require further cardiac investigations unless their functional capacity is poor.

Consent

In the UK, patients are always asked to sign a consent form for surgery. Consent for anaesthesia is implicit rather than requiring a second, specific form. It is essential that the anaesthetist explains the full process and discusses areas about which the patient may be concerned or about which there is some choice. The most obvious decision is whether the patient will be awake or asleep, and those for whom an awake procedure is planned will need careful reassurance. It is helpful to tell patients where they will wake up and what monitoring or therapeutic devices (e.g. urinary catheters, arterial lines, nasogastric tubes) will have been sited. The use of rectal analgesia must also be discussed. It is important to explain the risks and benefits of various proce-dures, especially epidural analgesia. It can be difficult to know exactly how many possible problems should be explained, but it is the duty of doctors to warn of any ‘material risk’ to the patient. This is defined as one to which a reasonable person would attach significanceand is considered according to the gravity of the risk, thefrequency with which it occurs and the risks of any alternative techniques. The Association of Anaesthetists of Great Britain and Ireland (AAGBI) has produced a working party document advising on all aspects of consent. It covers difficult areas such as participation in research studies, the training of medical students on anaesthetized patients and advance directives. It considers who can consent if an adult patient is deemed mentally incompetent and the valid-ity of consent obtained when a patient is in extreme distress and pain (e.g. in obstetrics). It also advises about restricted consent, for example if a patient agrees to surgery, but refuses to have a blood transfusion.

Medication

Rationalizing the patient’s usual medication: many patients presenting for surgery are taking regular medication that could interact with anaesthetic drugs. It is important to decide whether drugs are to be continued or stopped and whether the dose or route should be changed. Patients taking warfarin may need to be transferred to heparin in time for the international normalized ratio (INR) to reduce to acceptable operative levels. A history of prolonged or high-dose corticosteroid treatment requires periopera-tive supplementation. Oral hypoglycaemics should stop on the day of surgery. Short-acting insulin sliding scales should be started in good time for those on maintenance insulin or when prolonged fasting is necessary. Oral contraceptives and hormone replacement treatment can be continued, but for major surgery, antithrombotic measures should be considered.

Premedication: many anaesthetists prescribe sedative medication to allay anxiety and reduce stress-induced physiological changes. This is usually achieved with benzodiazepines though they have wide inter-patient variability. Anti-emetic and analgesic medication is often also prescribed.

Prophylactic measures: medication may be started preoperatively to reduce some of the risks of anaesthesia and surgery. Those at risk of acid aspiration may be given histamine H2-antagonists, proton-pump inhibitors or sodium citrate. The chances of thrombo-embolism can be reduced with subcutaneous heparin. Antibiotics are often prescribed on induction and must be used if prophylaxis for endocarditis is required. There is also strong evidence that the use of perioperative β-blockade improves the outcome for those with cardiac disease.

FURTHER READINGAssociation of Anaesthetists of Great Britain and Ireland. Information

and consent for anaesthesia. London: AAGBI, 1999.

β-blockers and reduction of cardiac events in non-cardiac surgery. J Am

Med Assoc 2002; 287: 1445–7.

General Medical Council. Seeking patient's consent: the ethical

considerations. www.gmc-uk.org/standards/consent.htmNational Institute for Clinical Excellence. CG3 – Preoperative testing,

the use of routine preoperative tests for elective surgery. 2003.

www.nice.org.uk

spencer.indd 323 15/09/03, 10:42:51

Documents

Preoperative Assessment