Preoperative Assessment and Premedication

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Preoperative Assessment and Premedication

All patients scheduled to undergo surgery should be assessed in advance with a view to planning optimal preparation and perioperative management. This is a standard of care of the Association of Anaesthetists of Great Britain and Ireland, 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.

The overall aims of preoperative assessment should include the following:

To enable the most appropriate treatment for the patient, taking into consideration the patient’s current health, the nature of the proposed surgery and anaesthetic technique, and the skills and expertise of the anaesthetist.

To confirm that the surgery proposed is realistic and allow assessment of the likely benefit to the patient and the possible risks involved.

To anticipate potential problems and ensure that adequate facilities and appropriately trained staff are available to provide satisfactory perioperative care.

To ensure that the patient is prepared correctly for the operation and allow time for further investigations and specialist referral to improve any existing factors which may increase the risk of an adverse outcome.

To provide appropriate information to the patient, and obtain informed consent for surgery and the planned anaesthetic technique.

To prescribe premedication and/or other specific prophylactic measures if required.

To ensure that proper documentation is made of the assessment process.

It is implicit that the anaesthetist has sufficient knowledge and experience of both the proposed surgery and necessary anaesthetic management to predict the potential progress of an individual patient during the perioperative period. Appropriate skills must be achieved and maintained by an ongoing commitment to education, both individually and within the profession overall. There are organizational issues to be considered within any hospital in order that preoperative assessment and preparation of patients can be accomplished successfully. Increasingly, this makes use of a nurse-led assessment process combined with gaining an anaesthetic opinion when appropriate, guided and supported by the use of evidence-based protocols.

THE PROCESS OF PREOPERATIVE ASSESSMENT

Who, When and Where?

The decision regarding the need for an operation is normally made by an experienced surgeon on the basis of the patient’s presenting pathology. The patient subsequently undergoes a more extensive assessment of general health closer to the time of admission for surgery. This is undertaken usually by the least experienced member of the surgical team, and in some circumstances is delegated (in part) to an experienced nurse practitioner. Identification of potential problems by these individuals relies upon their application of general medical knowledge and common sense, often assisted by the use of screening protocols developed either nationally, or locally by the anaesthetic department. When a patient is recognized to be at special risk, referral to an appropriate anaesthetist should be made. This need not be the anaesthetist ultimately responsible for the patient’s care if surgery is not urgent, provided that decisions made regarding preoperative preparation are communicated and recorded clearly in the medical notes. If surgery is more imminent, it is preferable to involve the anaesthetist who will be responsible for the patient’s perioperative care.

The need to improve efficiency of hospital bed occupancy has led to the increasing use of pre-admission clerking appointments, arranged to allow completion of the majority of the necessary administrative details. This is an ideal opportunity for anaesthetic assessment to take place, but in reality it is often not feasible to guarantee the availability of an experienced anaesthetist for these sessions. One direct consequence of this change is that patients are subsequently admitted on to the ward close to the time of surgery, allowing significantly less time for the anaesthetist to organize perioperative management. In order to optimize preparation for surgery within this system, many hospitals now use preoperative questionnaires which are completed by the patient in advance of clerking and are designed specifically to identify key features in the medical history which need further clarification. In addition, guidelines may be provided by the anaesthetic department for the surgical team or nurse practitioner to ensure that appropriate investigations are undertaken and that suitable action is taken if problems are identified.

Regardless of the timing and the individual personnel involved in clerking patients before surgery, the fundamental process of taking a detailed history and performing a systematic clinical examination remains the foundation on which preoperative assessment relies, backed up by ordering appropriate investigations where indicated. This allows the anaesthetist to concentrate on areas of particular relevance to perioperative care.

A complete history of concurrent medication must be documented carefully. Many drugs interact with agents or techniques used during anaesthesia but problems may occur if drugs are withdrawn suddenly during the perioperative period (Table 17.1). Knowledge of pharmacology is essential to permit the anaesthetist to adjust the doses of anaesthetic agents appropriately and to avoid possibly dangerous interactions. In addition, the anaesthetist must maintain up-to-date knowledge of pharmacological advances as new drugs continue to emerge on the market. Any potential interactions observed with new drugs must always be reported to the Medicines and Healthcare products Regulator Agency (MHRA), or comparable body outside the UK.

TABLE 17.1

Drugs with Potential Anaesthetic Interaction During Anaesthesia

In general terms, administration of most drugs should be continued up to and including the morning of the operation, although some adjustment in dose may be required (e.g. antihypertensives, insulin). Consideration must also be given to possible perioperative events which influence subsequent drug administration (e.g. postoperative ileus) and appropriate plans made to use an alternative route or an alternative product with similar action. It is advised that some drugs should 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 with which they are associated. Consideration must be given to the potential consequences of stopping drugs preoperatively and appropriate advice or alternative treatment provided to the patient.

There are occasions when patients with an illicit drug habit present for surgery. The patterns of abuse geographically are prone to frequent change, as are the specific drugs taken. Abuse of opioids and cocaine is not uncommon and there is significant information available about potential perioperative problems related to acute or chronic toxicity; however, the same is not true for the increasing number of ‘designer drugs’ available.

There are significant potential interactions between ‘herbal’ remedies and drugs used during the perioperative period. Garlic, ginseng and gingko are associated with increased bleeding; St John’s Wort induces cytochrome P4503A4 and cytochrome 2C9; valerian modulates GABA pathways; and traditional Chinese herbal medicines have a variety of potential adverse effects including hypertension and delayed emergence. The clinical importance of these interactions is not clear. Current guidance is that the anaesthetist should ask explicitly about their use and if possible discontinue use 2 weeks before surgery (tapering if necessary). 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 it is a drug, foods or adhesives, and the exact nature of the symptoms and signs should be elicited in order to distinguish true allergy from some other predictable adverse reaction. Latex allergy is becoming an increasing problem and requires specific equipment to be used perioperatively. Atopic individuals do not have an increased risk of anaphylaxis but may demonstrate increased cardiovascular or respiratory reactivity to any vasoactive mediators (e.g. histamine) released following administration of some drugs.

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.

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

Long-term deleterious effects of smoking include vascular disease of the peripheral, coronary and cerebral circulations, carcinoma of the lung and chronic bronchitis. It has been suggested that there are good theoretical reasons for advising all patients to cease cigarette smoking for at least 12 h prior to surgery, although there is little evidence to suggest that this influences patients’ behaviour in this period.

There are several potential mechanisms by which cigarette smoking can contribute to an adverse perioperative outcome. The cardiovascular effects of smoking are caused by the action of nicotine on the sympathetic nervous system, producing tachycardia and hypertension. Furthermore, smoking causes an increase in coronary vascular resistance; cessation of smoking improves the symptoms of angina. Cigarette smoke contains carbon monoxide, which converts haemoglobin to carboxyhaemoglobin. In heavy smokers, this may result in a reduction in available oxygen by as much as 25%. The half-life of carboxyhaemoglobin is short and therefore abstinence for 12 h leads to an increase in arterial oxygen content. Finally, the effect of smoking on the respiratory tract leads to a six-fold increase in postoperative respiratory morbidity. It has been suggested that abstinence for 6 weeks results in reduced bronchoconstriction and mucus secretion in the tracheobronchial tree.

There is some evidence to suggest that the preoperative period is an effective moment to introduce smoking cessation interventions in those patients who are motivated to stop.

Alcohol

Patients may present with acute intoxication from alcohol or sequelae of chronic consumption. The latter are mainly non-specific features of secondary organ damage such as cardiomyopathy, pancreatitis and gastritis. Establishing the diagnosis may be far from straightforward and needs to be complemented by a decision about whether to allow continued alcohol consumption during the hospital admission or risk the development of a withdrawal syndrome.

Obstructive Sleep Apnoea

Patients with obstructive sleep apnoea have a higher incidence of difficult airway management and current recommendations are that they should have careful observation in the postoperative period. The gold standard for diagnosis is polysomnography. However, this is not always available and current guidance supports the use of screening tools such as the Berlin or STOP–BANG questionnaires (Tables 17.2a and 17.2b).

TABLE 17.2a

Berlin Questionnaire

High likelihood of obstructive sleep apnoea is indicated by 2 or more positive categories.

Category 1 is positive with ≥ 2 positive responses.

Category 2 is positive with ≥ 2 positive responses.

Category 3 is positive with ≥ 1 positive responses.

TABLE 17.2b

STOP–BANG Questionnaire

S: Do you snore loudly (louder than talking or loud enough to be heard through closed doors)?

T: Do you often feel tired, fatigued, or sleepy during daytime?

O: Has anyone observed you stop breathing during your sleep?

P: Do you have or are you being treated for high blood pressure?

STOP (alone): High risk of OSA: Yes to ≥ 2 questions out of 4.

BMI: > 35 kg m^− 2

Age: > 50 years

Neck circumference: > 40 cm

Gender: Male

STOP–BANG: High risk of OSA: Yes to ≥ 3 questions from 8 questions of STOP–BANG

Physical Examination

A physical examination should be performed on every patient admitted for surgery and the findings documented in the medical notes. It might be argued that this is unnecessary in young healthy patients undergoing short or minor procedures. However, the exercise is a simple and safe method for confirming good health or otherwise, and provides important information in case unexpected morbidity arises postoperatively, e.g. foot drop as a result of incorrect positioning on the operating theatre table, prolonged sensory anaesthesia following local anaesthetic techniques, etc. The information obtained from clinical examination should complement the patient’s history and allows the anaesthetist to focus further on features of relevance (Table 17.3).

TABLE 17.3

Features of the Clinical Examination Relevant to the Anaesthetist

System	Features of Interest
General	Nutritional state, fluid balance
	Condition of the skin and mucous membranes (anaemia, perfusion, jaundice)
	Temperature
Cardiovascular	Peripheral pulse (rate, rhythm, volume)
	Arterial pressure
	Heart sounds
	Carotid bruits
	Dependent oedema
Respiratory	Central vs. peripheral cyanosis
	Observation of dyspnoea
	Auscultation of lung fields
Airway	Mouth opening
	Neck movements
	Thyromental distance
	Dentition
Nervous	Any dysfunction of the special senses, other cranial nerves, or peripheral motor and sensory nerves

In addition, the anaesthetist must assess the patient for any potential difficulty in maintaining the airway during general anaesthesia. The teeth should be inspected closely for the presence of caries, caps, loose teeth and particularly protruding upper incisors. The extent of mouth opening is assessed, together with the degree of flexion of the cervical spine and extension of the atlanto-occipital joint. The thyromental distance should also be documented. Specific features associated with difficulty in performing tracheal intubation are described elsewhere (Ch 22).

Special Investigations

In general, the results of many investigations may be predicted if a detailed history and examination have been performed. Routine laboratory tests in patients who are apparently healthy on the basis of the history and clinical examination are invariably of little use and a waste of resources. Before ordering extensive investigations, the following questions should be considered:

Will this investigation yield information not revealed by clinical assessment?

Will the results of the investigation give additional information on diagnosis or prognosis relevant to planned surgery?

Will the results of the investigation alter the management of the patient?

In order to reduce the volume of routine preoperative investigations, the following suggestions are made. It should be noted that these are guidelines only and should be modified according to the assessment obtained from the history and clinical examination (Table 17.4). Attention should be paid to ensuring that the results of any investigations requested are seen by the surgical team and properly documented, and that this process is undertaken in a timely manner to allow any necessary intervention with the patient’s management to be considered and implemented. The National Institute for Health and Clinical Excellence in the UK has produced a comprehensive summary of suggested testing approaches based on the patient and nature of surgery. The European Society of Anaesthesiology has also adopted these recommendations.

TABLE 17.4

Guidelines for Preoperative Investigations

Urinalysis	All patients
Full blood count	All female adults
	Before surgery which is likely to result in significant blood loss
	When indicated clinically, e.g. history of blood loss, previous anaemia or haemopoietic disease, cardiovascular disease, malnutrition, etc.
Urea, creatinine and electrolytes	All patients over 65 years (increased likelihood of CVS disease), or with a positive urinalysis result
	Any patient with cardiopulmonary disease, or taking cardiovascular active medication, diuretics or corticosteroids
	Patients with renal or liver disease, diabetes or abnormal nutritional status
	Patients with a history of diarrhoea, vomiting or metabolic disorder
	Patients receiving intravenous fluid therapy for greater than 24 h
Blood glucose	Patients with diabetes mellitus, vascular disease or taking corticosteroids
Liver function tests	Any history of liver disease, alcoholism, previous hepatitis or an abnormal nutritional state
Coagulation screen	Any history of a coagulation disorder, drug abuse, significant chronic alcohol abuse, acute or chronic liver disease or anticoagulant medication
ECG	Male smokers older than 45 years; all others older than 50 years
	Any history (actual or suspected) of heart disease or hypertension
	Any patient taking medication active on the cardiovascular system or a diuretic
	Patients with chronic or acute-on-chronic pulmonary disease
Chest X-ray	Rarely indicated unless active cardiac or respiratory disease or possible pulmonary metastases.
	Previously abnormal chest X-ray is not an indication in its own right to repeat a chest X-ray

Urine Analysis

This should be performed in every patient. It is inexpensive and may reveal undiagnosed diabetes mellitus or the presence of urinary tract infection. Positive results should be confirmed by seeking further evidence of pathology.

All women of childbearing age should have pregnancy excluded before surgery. For many, this will involve a urine test on the day of surgery.

Full Blood Count

This provides information about the haemoglobin concentration, white blood cell count and platelet count, together with details of red cell morphology. Haemoglobin concentration tends to be of greatest interest to the anaesthetist. Patients whose ethnic origin or family history suggests that a haemoglobinopathy may be present should have their haemoglobin concentration measured and haemoglobin electrophoresis undertaken if it has not been performed previously or if the result is not available. If such patients are scheduled for emergency surgery, a Sickledex test may be requested and, if positive, haemoglobin electrophoresis should be undertaken as soon as possible. However, this should not delay emergency surgery because, in practice, in teenagers and adults without a personal history of sickle disease, the result is unlikely to change management.

Moderate degrees of anaemia increase the risk of requiring blood transfusion. Preoperative assessment clinics should have agreed processes for investigation and/or treatment to avoid either missing important pathology such as bowel malignancy or undertaking unnecessary investigations.

Blood Chemistry

The measurements available include the serum concentrations of urea, creatinine and electrolytes, blood glucose concentration and liver function tests. There are specific conditions in which knowledge of preoperative values is important (e.g. diuretic therapy, impaired renal function, chronic alcohol abuse). Beyond these situations, the value of preoperative screening is less clear and detection of an unexpected abnormality seldom alters anaesthetic management. Blood sugar measurement is informative in patients receiving corticosteroid drugs and in those who have diabetes mellitus or vascular disease; a fasting sample is usually required.

Coagulation Tests

These should be ordered solely if the patient has a high likelihood of a bleeding disorder. This is based on the history (alcohol, liver disease, bleeding/bruising tendency, family history, drug history, etc.). They have no value as a screening test. They do not detect abnormalities of platelet function so have no role in patients taking antiplatelet drugs.

Chest X-Ray

This investigation should be reserved for patients with a clear indication and if the clinician believes that the result will change management significantly. There is little evidence that chest X-rays change management even in a higher risk population. It has little value as a preoperative baseline because postoperative abnormalities are treated predominantly on the basis of their clinical relevance.

Other X-rays

Cervical spine X-rays should be considered in any patient in whom there is a possibility of vertebral instability, e.g. in the presence of rheumatoid arthritis. Thoracic inlet X-rays may be required in patients with thyroid enlargement.

Cardiac Investigation

The extent of cardiac investigation should be based on the urgency of surgery, the presence of active cardiac conditions which require treatment, the risk of complications from surgery and the patient’s physical fitness. A schematic of an approach to patients at risk of cardiac events is shown in Figure 17.1.

FIGURE 17.1 Approach to investigation of patients at risk of cardiac complications. Simplified from European and American Guidelines.
METs: metabolic equivalents – inability to climb two flights of stairs or run a short distance equates to < 4 METs.
Cardiac risk factors:

➢ Angina pectoris

➢ Prior MI

➢ Heart failure

➢ Stroke/transient ischaemic attack

➢ Renal dysfunction (serum creatinine > 170 mmol L^− 1 or 2 mg dL^− 1 or a creatinine clearance of < 60 mL min^− 1)

➢ Diabetes mellitus requiring insulin therapy

Surgical risk of MI and cardiac death within 30 days after surgery

Low risk (< 1%)	Intermediate risk (1–5%)	High risk (> 5%)
Breast Dental Endocrine Eye Gynaecology Reconstructive Orthopaedic – minor Urology – minor	Abdominal Carotid surgery Peripheral angioplasty Endovascular aneurysm repair Head and neck Neurological Orthopaedic – major Transplant Urology – major	Aortic/major vascular Peripheral vascular

ECG

A 12-lead electrocardiogram can demonstrate many acute or longstanding pathological conditions affecting the heart, particularly changes in rhythm or the occurrence of myocardial ischaemia or infarction. It has little value as a preoperative baseline in patients with known or potential cardiovascular disease; in the resting state, the trace may appear normal despite the presence of clinically significant coronary artery disease. More extensive investigations are available in many departments to supplement the 12-lead ECG and these are discussed elsewhere (see Chs 18 and 34).

Echocardiography

Echocardiography is indicated in patients with undiagnosed heart murmurs. It should be noted that systolic murmurs are common and, in the absence of cardiac symptoms, they are unlikely to represent significant valve disease. Static (i.e. non-exercise/non-dobutamine) transthoracic echocardiography gives some information about the presence of left ventricular hypertrophy and function but is not a good investigation for patients with suspected ischaemic heart disease. As with all investigations, echocardiography should be requested only if the result is likely to change management. Formal protocols detailing which patients should be referred for echocardiography should be agreed between the anaesthesia and cardiology departments.

Dobutamine stress echocardiography (DSE) utilizes an infusion of dobutamine to increase heart rate and work whilst monitoring cardiac function using transthoracic echocardiography, usually to a maximum heart rate of 120 beats min^− 1 in patients aged over 65 years. It is used to assess left ventricular wall motion abnormalities, which occur in heart failure or ischaemic cardiomyopathy. The test is considered positive if symptoms of angina, headaches, vomiting, ST depression or elevation, or hypotension occur. DSE has a low (25–30%) positive predictive value but a high (95%) negative predictive value for perioperative cardiovascular complications after major surgery. A patient who has a positive DSE test should be referred to a cardiologist for consideration of coronary angiography and revascularisation.

Pulmonary Function Tests

Pulmonary function tests (peak expiratory flow rate (PEFR), forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV₁)) have a poor predictive value for postoperative problems apart from possibly some specific situations such as thoracic surgery and correction of spinal deformity.

Patients with stable asthma do not require PFTs, but note should be made of home recorded PEFR if patients are poorly controlled.

Patients with significant dyspnoea on mild or moderate exertion may require PFTs as part of a diagnostic work-up to elucidate the cause. Reversibility with bronchodilators is an important question to be answered as this may have an impact on perioperative management. Arterial blood gas analysis is prudent in patients with dyspnoea at rest and in patients scheduled for elective thoracotomy; the information is a useful supplement to spirometry values. In patients with progressive disease, these investigations may serve as a useful reference for future admissions.

Cardiopulmonary Exercise Testing

Cardiopulmonary exercise (CPEX) testing has been used in respiratory and sports medicine for some time, but has more recently been applied to the assessment of physical fitness in patients scheduled for major surgery. The usual protocol for CPEX testing is that patients exercise on a bicycle against progressively increasing resistance while ECG, oxygen consumption, carbon dioxide production and other variables are measured. These variables include anaerobic threshold (AT, the oxygen consumption at the point where anaerobic metabolism starts to occur) and ventilatory equivalents for CO₂ and O₂ (V_E/VCO₂ and V_E/VO₂, expired volume required for adequate CO₂ exchange or oxygen intake). All of these reflect physical fitness, cardiac and pulmonary function. Peak oxygen consumption, V_E/VCO₂ and AT have been related to outcome and long-term survival after major surgery.

Alternatively, simple measures of exercise tolerance such as the Incremental Shuttle walk test may be used to quantify aerobic fitness.

PREDICTION OF PERIOPERATIVE MORBIDITY OR MORTALITY

After the patient’s history, examination and relevant investigations have been collated the anaesthetist must answer two questions:

Is the patient in optimum physical condition for anaesthesia and surgery?

Are the anticipated benefits of surgery greater than the combined risks of undergoing anaesthesia and surgery, taking into account any concurrent disease?

In principle, if there is any medical condition which may be improved (e.g. pulmonary disease, hypertension, cardiac failure, chronic bronchitis, renal disease), surgery should be postponed and appropriate therapy instituted. The reasoning behind such a decision must be recorded clearly in the patient’s medical notes, with the anticipated time required to achieve reasonable improvement. At this stage, the patient should be reassessed and the decision about when or whether to proceed with surgery reviewed.

There is continued interest in quantifying factors preoperatively which correlate with the occurrence of postoperative morbidity and mortality. Some accuracy is possible for populations of patients, but precision does not extend to accurate prediction of risk for an individual patient. Frequently, the decision to proceed may be made only by discussion between surgeon and anaesthetist.

Scoring systems for determining the likelihood of adverse outcome may be divided into two main groups:

general scoring systems designed to predict nonspecific undesirable events

systems which focus on prediction of specific morbidity or technical difficulty, e.g. adverse cardiac events, difficulty with tracheal intubation.

Prediction of Non-Specific Adverse Outcome

Over a broad range of operations and age, the overall mortality rate within 7 days of surgery is approximately 4% across Europe as a whole. This is many times greater than the incidence of deaths to which anaesthesia has made a significant contribution or has been the sole cause (approximately 1 in 10 000). In many large studies of mortality, e.g. NCEPOD reports, common factors which have emerged as contributing to anaesthetic mortality include inadequate assessment of patients in the preoperative period, inadequate supervision and monitoring in the intraoperative period and inadequate postoperative supervision and management. It remains difficult to evaluate formally whether the patient’s characteristics, the surgical features or the anaesthetic technique are the most influential in terms of final outcome. This is primarily a result of the high standards of practice which exist, the relative infrequency with which significant perioperative morbidity or mortality occurs and the multifactorial background for many adverse events.

However, there is an increasing body of evidence to suggest that postoperative complications are not benign. Patients who have postoperative complications and who survive the postoperative period have an increased mortality several months and even years after their operation compared to those without. Some data indicate that reducing complications improves outcome, suggesting that this link is not solely identifying patients with poor reserve.

Any prospective studies intended to evaluate predictive factors of perioperative risk rely upon the incorporation of large numbers of patients and scrupulous design. Those that have been published tend to agree on several factors identified from physiological, demographic and laboratory data which can combine to indicate the likelihood of adverse outcome (Table 17.5).

TABLE 17.5

Typical Preoperative Features which may Increase the Likelihood of Significant Perioperative Complications or Mortality

Demographic/Surgical	Pathophysiological	Laboratory
Age > 70 years	Dyspnoea at rest or on minimal exertion	Serum urea > 20 mmol L^–1
Major thoracic, abdominal or cardiovascular surgery	MI within 30 days or unstable angina, untreated heart failure or high grade arrhythmias	Serum albumin < 30 g L^–1
Perforated viscus (excluding appendix), pancreatitis or intraperitoneal abscess	Cardiac symptoms requiring medical treatment	Haemoglobin < 10 g dL^–1
Intestinal obstruction	Confusional state
Palliative surgery	Clinical jaundice
Smoking	Significant weight loss (> 10%) in 1 month
Cytotoxic or corticosteroid treatment	Productive cough with sputum, especially if persistent
Controlled diabetes	Haemorrhage or anaemia requiring transfusion

In an effort to better manage patients with increased risk of postoperative morbidity and mortality, clinicians have been encouraged to document the predicted risk of complications both before and after surgery. There is reasonable evidence that clinical judgement alone is not a particularly good predictor of the need for critical care in the postoperative period.

ASA (American Society of Anesthesiologists) Grading

The ASA grading system (Table 17.6) was introduced in the 1960s as a simple description of the physical state of a patient, along with an indication of whether surgery is elective or emergency. Despite its apparent simplicity, it remains one of the few prospective descriptions of the patient which correlates with the risks of anaesthesia and surgery. However, it does not embrace all aspects of anaesthetic risk, as there is no allowance for inclusion of many criteria such as age or difficulty in intubation. In addition, it does not take into account the severity of either the presenting disease or the surgery proposed, nor does it identify factors which can be improved preoperatively in order to influence outcome. Nevertheless, it is extremely useful and should be applied to all patients who present for anaesthesia.

TABLE 17.6

ASA Classification of Physical Status and the Associated Mortality Rates (for Elective and Emergency Cases)

More recently, the combination of ASA with age of patient, urgency and extent of surgery has been shown to be a reliable predictor of outcome at a population level and uses information readily available preoperatively.

POSSUM

This stands for ‘Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity’. First reported in 1991, this tool was developed to compare mortality and morbidity over a wide range of general surgical procedures, and takes into account 12 physiological and six operative factors which are either readily available or predictable in the immediate preoperative period (Table 17.7). These factors are weighted according to their value, and a logistic regression formula applied to calculate ‘risk’ of mortality or morbidity. Some groups have modified the formula (P-POSSUM) after suggestions that the original system overestimated the risk of death in low-risk patient groups, and others have produced speciality-specific variants (e.g. V-POSSUM for elective vascular surgery). It should be emphasized that the POSSUM scoring system was designed to compare observed with expected death rates among populations rather than to predict mortality for an individual, and should be applied only in this way.

TABLE 17.7

Factors Contributing to the POSSUM Score for Risk of Perioperative Mortality and Morbidity. A Higher Score is Awarded for Increasing Deviation from the ‘Normal’ Value or Range

Physiological Factors	Operative Factors
Age (years)	Operative complexity
Cardiac status	Single vs. multiple procedures
Respiratory status	Expected blood loss
Systolic blood pressure	Peritoneal contamination (blood, pus, bowel content)
Pulse rate	Extent of any malignant spread
Glasgow Coma Score	Urgency of surgery
Haemoglobin concentration
White cell count
Serum urea concentration
Serum sodium concentration
Serum potassium concentration
ECG rhythm

Prediction of Specific Adverse Events

The Difficult Airway

There are specific medical or surgical conditions which are associated with potential airway problems during anaesthesia, such as obesity, the later stages of pregnancy, a large neck, mediastinal tumours and some faciomaxillary deformities. Apart from these, it requires an experienced anaesthetist to collate various physical features which can predict likely difficulty. Several classifications or scoring systems have been designed for this purpose, although none is entirely reliable; they are discussed elsewhere (see Chs 21 and 22).

Adverse Cardiac Events

Over 25 years ago, Goldman and colleagues published a retrospective analysis of preoperative risk factors which were associated with an adverse cardiac event following non-cardiac surgery. This topic has been re-evaluated extensively in the intervening years, with many studies agreeing broadly with Goldman’s conclusions. However, conflicting opinions exist regarding identification of the most accurate predictors, probably as a result of the diversity of methods used in these studies together with the significant and continued advances made in the understanding and management of cardiovascular pathophysiology. The most widely used risk index currently is Lee’s Revised Cardiac Risk Index (Table 17.8).

TABLE 17.8

Lee’s Revised Cardiac Risk Index

	Indicators
High risk surgical procedures	Intraperitoneal Intrathoracic Suprainguinal vascular
History of ischaemic heart disease	History of myocardial infarction History of positive exercise test Current ischaemic chest pain Use of nitrate therapy ECG with pathological Q waves
Congestive heart failure	History of congestive heart failure, pulmonary oedema or paroxysmal nocturnal dyspnoea Physical examination showing bilateral rales or S3 gallop Chest X-ray showing pulmonary vascular redistribution
Cerebrovascular disease	History of transient ischaemic attack or stroke

Risk for Major Cardiac Event (Myocardial Infarction, Pulmonary Oedema, Ventricular Fibrillation, Primary Cardiac Arrest, and Complete Heart Block): Complication Rates in Patients with 0, 1, 2, or More than 2 of these Variables were Reported as 0.4%, 1.0%, 7% and 11%.

Reprinted from Thomas H. Lee, Edward R. Marcantonio, Carol M. Mangione et al. Derivation and Prospective Validation of a Simple Index for Prediction of Cardiac Risk of Major Noncardiac Surgery. Circulation. 1999;100:1043–1049.

It should be noted that many aspects of perioperative care have changed since the production of these cardiac risk indices.

Respiratory Complications

Patients at risk of developing postoperative pulmonary complications include smokers, those with pre-existing lung disease, the obese and those undergoing thoracic or abdominal surgery. Unfortunately, predicting the likelihood and severity of such adverse events remains difficult. Sophisticated tests of pulmonary function (e.g. functional residual capacity, closing capacity, pulmonary diffusing capacity, etc.) are no more valuable in assessment of lung disease than simple spirometric tests, particularly vital capacity, FVC and FEV₁. Blood gas analysis should be performed preoperatively if there is concern about postoperative lung function; the presence of a preoperative arterial oxygen tension of less than 9 kPa, together with the presence of dyspnoea at rest, is the most sensitive method of predicting the need for mechanical ventilation in the postoperative period.

There are scoring tools available for prediction of postoperative respiratory complications such as pneumonia and respiratory failure.

PREOPERATIVE PREPARATION

Having taken a full clinical history, performed a physical examination and reviewed the relevant investigations, the anaesthetist should decide whether further measures are required to prepare the patient satisfactorily before proceeding to anaesthesia and surgery. This is the time to address any factors which place the patient at increased risk of adverse outcome and which could be improved to the patient’s benefit before surgery. It is also appropriate to consider factors such as preoperative fasting; providing information to the patient and obtaining consent to proceed; ensuring blood products are available during the perioperative period if this is thought necessary; and organizing appropriate staff and equipment within the operating theatre suite.

Postponing Surgery for Clinical Reasons

There are several common reasons for postponing surgery, some of which are mentioned below. One key issue relates to communication; the reason(s) for the decision to postpone surgery must be clear to the patient, the surgical team and any other staff who have been contacted to review the patient (e.g. cardiologists, physiotherapists). This helps to ensure that the time course for any improvement remains realistic and apparent to everyone involved, and that it can be balanced against the possible detriment of delaying surgery.

Acute Upper Respiratory Tract Infection

Although many patients may admit to the presence of a cold, clarification of such an admission should be made. In general, the presence of nasal secretions, pyrexia or the unexpected presence of physical signs on clinical examination of the chest indicate that non-urgent surgery should be postponed for a few weeks until the patient has recovered.

Coexisting Medical Disease and Drug Therapy

If the patient has coexisting medical disease which may affect outcome adversely if not under optimum control, there is a strong argument to postpone non-urgent surgery until further specialized advice has been sought. Examples include thyroid disease, and acute exacerbations of inflammatory diseases such as multiple sclerosis, inflammatory bowel disease and autoimmune diseases.

Emergency Surgery for Which the Patient has not been Resuscitated Adequately

In some emergency patients, it may be necessary to delay surgery to optimize the patient’s physiology, but this should be balanced against the risks of deterioration due to the underlying disease process. Acutely unwell patients with surgical pathology are unlikely to make significant improvements if the underlying condition is not addressed, unless they are grossly hypovolaemic. In practice, resuscitation should proceed at the same time that preparations for surgery are made.

Surgery for haemorrhage control in trauma is discussed elsewhere (see Ch 37).

Recent Ingestion of Food

In general, anaesthesia for elective surgery should not be undertaken within 6 h of ingestion of food, although clear fluids may be taken up to 2 h before surgery (see below).

Failure to Obtain Consent

Consent for surgery should be obtained from all adult patients unless the patient is incapable of providing consent and the treatment proposed is clearly in his or her best interests (see below). If there is any doubt regarding the validity of the consent, surgery should be postponed where feasible until appropriate advice has been obtained.

Preoperative Fasting

The time of last oral intake of solid and fluid must be established. One of the commonest causes of anaesthetic-related mortality and morbidity is aspiration of gastric contents.

Many anaesthetic departments have re-evaluated their standing orders on the issue of preoperative fasting for clear fluids in light of clinical studies which have demonstrated the speed of gastric emptying in healthy adults. Several important points need to be emphasized on this topic:

There are many factors which can increase the likelihood of significant gastric content regardless of the period of starvation (e.g. pain, anxiety, some drugs and premedication including opioid analgesics, paralytic ileus, later stages of pregnancy, etc.).

The normal daily secretion of gastric fluid can approach 2000 mL in adults; consequently, the stomach is never truly ‘empty’.

Clinical studies which encourage changes in practice should be scrutinized carefully to ensure that the results are not extrapolated beyond the sample of the population upon which they were based.

Providing Information to the Patient and Obtaining Consent

Consent for anaesthesia is a vital part of preoperative preparation. It is discussed more fully in Chapter 19. It must be obtained by an individual with sufficient knowledge of the procedure and the risks involved. In order for consent to be valid, it must encompass three elements:

The patient must have the capacity to consent to the treatment offered.

The patient must have sufficient information to enable him/her to make a balanced decision to consent.

The consent must be voluntary.

Capacity to consent refers to the patient’s ability to comprehend the information provided, come to a decision on what is involved and communicate that decision. There is no fixed age limit below which a minor cannot consent to treatment, although caution should be exercised when dealing with patients aged less than 16 years; if in doubt, consent should also be sought from a person with parental responsibility. Capacity may also be invalidated by a patient’s confusion, pain, shock or fatigue, and administration of some drugs such as opioid analgesics or benzodiazepine premedication. Appropriate advice should be sought if there is any concern.

Patients are confronted by a barrage of information on arrival in hospital, in addition to having to comply with an often alien environment with its own routines and practices. It is common for surgical consent forms to include consent to anaesthesia, despite the fact that the surgical team rarely has the knowledge to inform the patient fully on this subject. During the preoperative visit, the anaesthetist must ensure that the patient has been given an adequate amount of information about the proposed anaesthetic technique, and in particular its nature and consequences. The amount of information provided should be determined by an assessment of the needs of the patient to receive detailed information and the likelihood of adverse events.

All patients should be told of common complications associated with the proposed anaesthetic technique (e.g. succinylcholine pains, postdural puncture headache).

All patients should be told what they may experience in the perioperative period, including temporary numbness and weakness in the postoperative period if a local or regional technique is to be used.

If a technique of a sensitive nature (e.g. insertion of an analgesic suppository) is to be used during anaesthesia, the patient should be informed.

Patients should be informed of any increased risk related to their preoperative condition (e.g. damage to loose or crowned teeth, or cardiac complications in the presence of severe coronary artery disease).

All patients should be given the opportunity to ask questions, and specific questions relating to anaesthesia must be answered honestly; if the questions relate to surgery, then the anaesthetist should ensure that a surgeon speaks to the patient before anaesthesia is induced.

A summary of the matters discussed, the risks explained and the techniques agreed should be documented on the anaesthetic record.

In many hospitals, patients receive information leaflets which describe anaesthesia and its associated risks.

Blood Transfusion Requests

Blood products are an expensive commodity and blood transfusion carries small but finite risks of incompatibility reactions and transmission of infection. In addition, there is the potential for supplies to be short, and the need for transfusion should be considered very carefully. The object of transfusion is to ensure that adequate oxygen delivery to the tissues can be maintained throughout the perioperative period. The amount of blood ordered from the blood transfusion service depends on both the patient’s preoperative haemoglobin concentration and the anticipated extent of surgery. Consideration should also be given to the use of anaesthetic techniques which reduce intraoperative blood loss, the use of cell salvage techniques perioperatively if available, preoperative red cell donation immediately before surgery or acute normovolaemic haemodilution.

Common operations should have agreed policies in place regarding transfusion requests. With the advent of electronic issue of blood in many hospitals, formal cross-matching before surgery is less commonly needed than previously.

Preoperative Organization of the Operating Theatre and the Postoperative Period

The process of preoperative assessment provides the anaesthetist with a wealth of information about the patient and the proposed surgery. This allows the anaesthetist to plan various aspects of perioperative management. Some aspects must be conveyed to staff in the operating theatre suite in advance. Examples include the planned use of invasive monitoring, issues related to patient positioning and any special needs the patient might have, such as an interpreter. If senior anaesthetic assistance is needed, this should be arranged in advance, and organization of appropriate postoperative care should also be initiated.

This information should be discussed, as a minimum, at the preoperative briefing. Clearly, many of these issues need addressing before this time.

PREMEDICATION AND OTHER PROPHYLACTIC MEASURES

Premedication refers to the administration of drugs in the period 1–2 h before induction of anaesthesia. The traditional intramuscular opioid premedication is no longer a routine part of preoperative preparation, but the need for premedication must be considered after all of the relevant factors have been identified. The objectives of premedication are to:

allay anxiety and fear

reduce postoperative nausea and vomiting

assist with intra- and postoperative analgesia

reduce secretions

reduce the volume and increase the pH of gastric contents

attenuate vagal reflexes

attenuate sympathoadrenal responses.

Relief from Anxiety

Surgical patients have a high incidence of anxiety and there is a significant inverse relationship between anxiety and smoothness of induction of anaesthesia. Relief from anxiety is accomplished most effectively by non-pharmacological means, which may be termed psychotherapy. This is effected at the preoperative visit by establishment of rapport, explanation of events which occur in the perioperative period and reassurance regarding the patient’s anxieties and fears. There is good evidence that this approach has a significant calming effect.

In some patients, reassurance and explanation may be insufficient to allay anxiety. In these patients, it is appropriate to offer anxiolytic medication; benzodiazepine drugs are the most effective for this purpose.

Sedation

Sedation is not synonymous with anxiolysis. Some drugs, e.g. barbiturates and to a lesser extent opioids, provide sedation but have no anxiolytic properties. In general, it is unnecessary to use a sedative preoperatively. An exception to this may be in paediatric practice. It is unwise to administer any sedative medication if the patient is in a critical condition, particularly if the airway and/or respiratory function are at risk of compromise.

Postoperative Antiemesis

Nausea and vomiting are extremely common after anaesthesia. Opioid drugs administered during and after operation are often responsible. Antiemetics may be given usefully as an oral premedication, particularly in day-case surgery.

Analgesia

Paracetamol: Paracetamol is a cheap and effective analgesic when given as an oral premedication. Many day-case and children’s surgery units do this as routine. Logistical reasons prevent many main theatre units from doing this, but the anaesthetist should always consider prescribing paracetamol at the preoperative visit.

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): Similarly to paracetamol, NSAIDs can be given safely and effectively as premedication, with due consideration to contraindications and ensuring that a second dose is not given inadvertently in theatre or the recovery room.

Opioid Analgesics: The main indication for preoperative opioid therapy is treatment of pain but, otherwise, premedication with opioids is rarely used now. Opioids should always be used in combination with an antiemetic agent.

Reduction in Secretions

Ether stimulates the production of secretions from pharyngeal and bronchial glands and premedication with an anticholinergic agent was common before ether anaesthesia. This problem occurs rarely with modern anaesthetic agents and anticholinergic premedication is no longer used as a routine. However, premedication with an anticholinergic drug is advisable for patients in whom an awake fibreoptic intubation is planned (when excessive salivation can create extra difficulty), or before using ketamine.

Reduction in Gastric Volume and Elevation of Gastric pH

In patients who are at risk of vomiting or regurgitation (e.g. emergency patients with a full stomach or elective patients with hiatus hernia), it may be desirable to promote gastric emptying and elevate the pH of residual gastric contents. Gastric emptying may be enhanced by the administration of metoclopramide, which also possesses some antiemetic properties, while elevation of the pH of gastric contents may be produced by administration of sodium citrate. This topic is described in greater detail in Chapter 37.

Reduction in Vagal Reflexes

Premedication with an anticholinergic drug may be considered in specific situations in which vagal bradycardia may occur.

Traction of the eye muscles, particularly the rectus medialis, during squint surgery may result in bradycardia and/or arrhythmias (the oculocardiac reflex). Premedication with atropine protects against this but it is not as effective as the intravenous administration of atropine at induction of anaesthesia or in anticipation of traction of the muscles.

Repeated administration of succinylcholine often results in bradycardia, which sometimes proceeds to asystole. Administration of atropine should always precede the administration of a second dose of succinylcholine.

Surgical stimulation during a balanced anaesthetic technique may be associated with bradycardia – particularly during laparoscopy.

The administration of propofol to patients with a slow heart rate may result in dangerous degrees of bradycardia.

Limitation of Sympathoadrenal Responses

Induction of anaesthesia and tracheal intubation may be associated with marked sympathoadrenal activity, manifest by tachycardia, hypertension and elevation of plasma catecholamine concentrations. These responses are undesirable in the healthy individual and may be harmful in patients with hypertension or ischaemic heart disease. A β-blocker drug or clonidine may be given as premedication in order to attenuate these responses.

Drugs Used for Premedication

Some of the objectives listed above may be achieved by administration of drugs at induction or during maintenance of anaesthesia. The ability to achieve all objectives by administration of a variety of drugs either preoperatively or at induction is responsible for the wide variation in prescribing habits among anaesthetists.

Benzodiazepines

Benzodiazepines possess several properties which are useful for premedication, including anxiolysis, sedation and amnesia. The extent of each of these effects differs among individual drugs. Diazepam was the first drug of this group to be used commonly, although temazepam (10–30 mg) is now often preferred because of its shorter duration of action. Lorazepam (1–5 mg) produces a greater degree of amnesia than the other drugs in this group. Benzodiazepines produce anxiolysis in doses which do not produce excessive sedation and this is advantageous if respiratory function is compromised; however, great caution should be exercised in these patients because depression of ventilation may be precipitated even by small doses. Some benzodiazepines may be administered by intramuscular injection but evidence suggests that oral administration gives better results. There is a very wide variation in response to benzodiazepines and effects may be unpredictable. A specific antagonist (flumazenil) is available.

Anticholinergic Agents

The three anticholinergic agents used commonly in anaesthesia are atropine, hyoscine and glycopyrronium. Atropine and hyoscine are tertiary amines which cross the blood–brain barrier; glycopyrronium is a quaternary amine which does not cross the blood–brain barrier and which is not absorbed from the gastrointestinal tract. Although atropine is absorbed from the gastrointestinal tract, this occurs in an unpredictable manner and is dependent on gastric content, pH and motility.

These three drugs differ in respect of their dose-response effects at various cholinergic receptors. In standard clinical doses, hyoscine 0.4 mg produces a greater antisialagogue effect than atropine 0.6 mg and has little action on cardiac vagal receptors. Hyoscine possesses sedative and amnesic actions and, in contrast to atropine, does not cause stimulation of higher centres. Hyoscine should be avoided in the elderly (over 60 years of age) as it can produce dysphoria and restlessness. Glycopyrronium has no central effects, a much longer duration of action and, in a standard clinical dose of 0.4 mg, causes less change in heart rate than atropine 0.6 mg.

Anticholinergic drugs are used clinically to produce the following effects:

Antisialagogue effects. Glycopyrronium and hyoscine are more potent than atropine in this respect. These drugs block secretions when irritant anaesthetic gases are used and reduce excessive secretions and bradycardia associated with succinylcholine when it is given either repeatedly or as an infusion.

Sedative and amnesic effects. In combination with morphine, hyoscine produces powerful sedative and amnesic effects.

Prevention of reflex bradycardia. Anticholinergics are given for both prophylaxis and treatment of bradycardia. Atropine is used commonly as premedication in ophthalmic surgery to block the oculocardiac reflex in patients undergoing squint surgery and has been used also in small children to reduce the bradycardia which may occur in association with halothane anaesthesia.

Side-effects of anticholinergic drugs include the following:

CNS toxicity. The central anticholinergic syndrome is produced by stimulation of the CNS (usually by atropine). Symptoms include restlessness, agitation and somnolence and, in extreme cases, convulsions and coma. With hyoscine, there is more commonly prolonged somnolence. Physostigmine 1–2 mg i.v. has been recommended to reverse the central anticholinergic syndrome, but is no longer available in the UK. Diazepam has been reported to have a beneficial effect but the patient must be observed closely and steps taken if necessary to deal with depression of ventilation or upper airway obstruction.

Reduction in lower oesophageal sphincter tone. Theoretically, a reduction in tone may lead to an increased risk of gastro-oesophageal reflux, although in clinical practice there is no suggestion that the use of anticholinergics for premedication is associated with an increased incidence of regurgitation and aspiration.

Tachycardia, which should be avoided in patients with cardiac disease (e.g. obstructive cardiomyopathy, valvular stenosis or ischaemic heart disease) or when a hypotensive anaesthetic technique is planned.

Mydriasis and cycloplegia, which lead to visual impairment. This may be troublesome, but is not a serious side-effect. Theoretically, mydriasis may be associated with reduced drainage of aqueous humour from the anterior chamber of the eye, thereby increasing intraocular pressure in patients with glaucoma. However, this effect is not important in practice and atropine may be prescribed safely to patients with glaucoma provided that appropriate therapy is maintained.

Pyrexia. By suppressing secretion of sweat, anticholinergics predispose to an increase in body temperature. These drugs should therefore be avoided in the presence of pyrexia, particularly in children.

Excessive drying. Although anticholinergics are given for the specific purpose of producing antisialagogue effects, this may be most unpleasant for the patient.

Increased physiological dead space. Atropine and hyoscine increase physiological dead space by 20–25%, but this is compensated for by an increase in ventilation.

β-Blockers

The use of β-blockers (e.g. atenolol) during the perioperative period limits the haemodynamic response to nociceptive stimuli, such as tracheal intubation and surgical stimulation, and inhibits the neuroendocrine stress response. Recent studies concerning the use of β-blockers in patients at risk of coronary artery disease are still controversial. Current advice is not to prescribe prophylactic β-blockers indiscriminately in the perioperative period, but withdrawal of β-blockers in patients receiving chronic treatment may be harmful; such patients should continue their β-blocker therapy.

Clonidine and Dexmedetomidine

These are α₂-agonists which potentiate anaesthetics by decreasing central noradrenergic activity. Dexmedetomidine is more specific for the α₂-receptor and probably has greater potential as a premedicant. Administration results in decreased intraoperative requirements for inhaled anaesthetic agents or propofol, although recovery times may be prolonged. These agents may also have a role in attenuating sympathoadrenal responses at induction of anaesthesia.

Other Prophylactic Measures

Thought should be given to the value of giving prophylactic treatment for the specific situations summarized in Table 17.9.

TABLE 17.9

Prophylactic Measures Against Specific Complications

Complication	Methods of Prophylaxis
Deep vein thrombosis	Early postoperative mobilization
	Leg exercises (active/passive)
	Pneumatic compression of limbs
	Electrical stimulation of calf muscles
	Graduated stockings
	Low-dose subcutaneous heparin
	Warfarin anticoagulation
	(Regional anaesthetic techniques, especially for orthopaedic lower-limb procedures)
Aspiration of gastric contents	Nil by mouth
	Antacids: sodium citrate
	H₂-antagonists
	Omeprazole
	Metoclopramide
Infection
Surgical procedure	Directed by local or national practice with advice of microbiologists
Infective endocarditis	Follow guidelines of the Endocarditis Working Party
Adrenocortical suppression – suggested for patients who have received exogenous systemic steroids (> 10 mg prednisolone/day) during the 2 months preceding surgery	Hydrocortisone 25 mg 6-hourly, or continue usual steroids if this is in excess of the current requirements (i.e. > 300 mg hydrocortisone equivalent, which is the maximum daily production in response to stress). Consult local guidance.

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Preoperative Assessment and Premedication

Preoperative Assessment and Premedication

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