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