17
Preoperative Assessment and Premedication
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.
THE PROCESS OF PREOPERATIVE ASSESSMENT
History
Direct questions should be asked about the following items of specific relevance to anaesthesia.
Drug History
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 Many drugs interact with agents or techniques used during anaesthesia but problems may occur if drugs are withdrawn suddenly during the perioperative period (Table 17.1).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.
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
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.
TABLE 17.2b
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
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 |