Anaesthetic Pre-op Assessment

Doing endless pre-op assessments is one of the less well publicised duties of the house officer. This is probably because it does not engender the same sense of immediacy and subsequent fear as responding to a cardiac arrest call, and nor does it engender the same sense of tedium as filling out forms upon forms upon forms.

However, when called to do it, it is often not done as well as it might be. This is because as medical students we are often taught the theory behind it, without being given a clear structure for how to do it. Therefore, we all know why a good pre-op assessment is necessary, but are often slightly lost as to exactly how to do it. This article aims to fill that vacuum and therefore to optimise practice.

As we all acknowledge, putting someone to sleep is a risky procedure, and the whole point of the pre-op assessment is to recognise and quantify this risk, and reduce it as much as possible. The all-important question is ‘Is this person as well as they can be?’ If they are not, why are they not, and what can be done to optimise their condition?

History

Active Problems

Anaesthetic drugs have a profound effect on the cardiac and respiratory systems, as can surgery itself, so the history must begin with a systematic enquiry relating to symptoms caused by cardiovascular and respiratory diseases:

• Chest pain
• Breathlessness
• Orthopnoea/ PND
• Ankle swelling
• Palpitations
• Cough
• Sputum production
• Wheeze
• Recurrent infections

When any of these symptoms are present, as with any history, an attempt MUST be made to quantify them and relate them to function and how it affects the person in everyday life, e.g. by gauging exercise tolerance. This will help in coming to a diagnosis, if one has not already been made, as happens fairly often. A patient may come in for surgery who gets chest infections every winter, gets short of breath on walking one hundred metres, and regularly coughs up white sputum. It may be you who suspects the diagnosis of COPD and acts accordingly in order to make them ‘as well as they can be’ – i.e. advising them to stop smoking, ordering a chest X-ray and pulmonary function tests, and making any necessary referrals in order to start inhalers and have follow-up care.

Past history

Again it’s wise to start with the respiratory and cardiac systems here, but one also has to widen the net a little bit in order to find out about all the possible pathology that may affect the anaesthesia and the surgery. Conditions to ask about specifically and directly are in bold as they are very important and sometimes missed when the patient is simply asked if there are any previous medical problems.

• CVS - angina/coronary artery disease, previous myocardial infarction, hypertension, congestive heart failure, valvular disease, arrhythmia, peripheral vascular disease
• Respiratory - asthma, COPD, upper respiratory tract infection, pneumonia, fibrotic lung disease, malignancy
• GI – gastro-oesophageal reflux disease, liver disease, ulcers, inflammatory bowel disease
• Renal – chronic kidney disease, dialysis
• CNS – stroke, TIA, epilepsy, spinal disease
• Endocrine – diabetes, thyroid disease, adrenal disease
• MSK – rheumatoid arthritis, osteoarthritis
• Other – pregnancy

NB – learning point on rheumatoid arthritis. This is important because of the risk of C-spine subluxation during intubation if there is arthritis at the atlanto-axial joint. Therefore previous imaging will have to be viewed, and if there is any hint of C-spine instability, further CT or MRI imaging may be required, possibly followed by stabilisation surgery. The crux of this, as with most complicated things, is that discussion with a senior will be necessary.

Again, as with any other history, any previous problems found should be explored in terms of what problems it causes for the patient, how long it has been known, what treatment options have been attempted and with what kind of success. This will help when discussing the patient with the anaesthetist, in order to come to decisions about whether and when the patient will undergo surgery. In the example of rheumatoid arthritis, it would be important to elicit if there are neck symptoms, if there are neurological symptoms, and if there has been previous imaging of the neck.

Previous anaesthetic history

It is important to find out about and document what previous experience the person has had of anaesthesia, if they have been intubated before, any complications, and how they recovered. One should ask specifically if there were any adverse reactions to anaesthetic drugs.

Drug history

These may need to be continued, stopped or the dose or route of administration changed. Most drugs can be continued until the day of surgery, with notable exceptions being certain antibiotics (because of their enzyme inhibitory action), the oral contraceptive pill (because of the risk of developing a DVT). There will normally be a local protocol for diabetic medication, involving being first on the list and the use of an insulin sliding scale if necessary. Steroids are also important, and cover for these while the patient is nil by mouth may need to be organised in order to prevent Addisonian crisis.

Family history

Again, one should ask specifically about reactions to anaesthetic drugs. In particular, one must be wary of malignant hyperthermia and cholinesterase abnormalities (which can cause slow breakdown of suxamethonium).

Social history

One must ask about alcohol, cigarettes and use of any other drugs.

Examination

Airway

This should involve a general inspection of the size and shape of the neck and the mouth, paying particular attention to obesity. The size of the jaw and tongue and visualization of the uvula should also be noted, and these are all covered by using the Mallampati visual score:

• class 1 - able to visualize soft palate, fauces, uvula, ant and post tonsillar pillars
• class 2 - able to visualize all of the above, except anterior and posterior tonsillar pillars are hidden by the tongue
• class 3 - only the soft palate and base of the uvula are visible
• class 4 - only the soft palate can be seen (uvula not visualized)

Systems Examination

A full examination should then be done of all systems in order to further evaluate any problems elicited in the history, as well as to pick up anything that may have been missed or may not yet have been discovered, e.g. heart murmurs, abnormal breath sounds or local skin infections.

Investigations

Which investigations are done will depend on the procedure, and what has been elicited from the history and examination. There are usually local protocols for which procedures will require investigations as standard, regardless of the patient’s clinical presentation. A few common investigations are discussed below

• Urine dipstick – Cheap, easy test to detect undiagnosed diabetes or UTI. Can also do beta-hCG test at the same time in women
• Bloods
  • Haematology - A full blood count is indicated in those known or suspected to be anaemic from history and examination and those taking any sort of anticoagulant medication. Sickle cell tests may also be indicated in high risk groups i.e. Afro-Caribbeans. There will be local protocols for which procedures will require group and save or cross-matching.
  • Biochemistry – Renal function and electrolytes should be checked before major operations as it will affect which drugs can be given, and it what doses, as well as giving a baseline because the operation itself can cause electrolyte disturbances.
• ECG – should be done in anyone with cardiovascular risk factors, including age over 50. Further testing may also be required such as exercise ECG and echocardiography, the latter particularly if there is a murmur or any question of ventricular dysfunction.
• Radiography – A chest X-ray is not routinely required, but should be ordered if there is any suspicion of heart or lung disease. Cervical spine X-ray should be ordered for all of those with rheumatoid arthritis or ankylosing spondylitis, and further imaging may also be required, as discussed in the Past history section.
• Lung function – Spirometry will be useful in those with restrictive or obstructive lung defects.

NB – In those patients requiring investigations such as exercise ECG, echocardiography, cervical imaging and spirometry, the patient will definitely need assessment by an anaesthetist, and ideally this should be discussed before ordering the investigations, as it should not be the house officer’s responsibility to interpret them.

ASA Rating

The house officer would not be expected to do this for a patient, but it is definitely worth knowing about the rating scale which anaesthetists use to quantify fitness for anaesthesia. It is important to remember that this is not the only factor to take into account during pre-op, as it is necessary to compare the risk of the procedure with the actual benefit which will be derived from it.

Bringing it all together, the important factors to remember are to take a thorough, well structured history and examination, and think about which investigations are actually going to be useful before ordering them, using local guidelines where available. And always keep in mind the point of the assessment, which is to quantify the risk of being anaesthetised.

References

Avidan A, Harvey AMR, Ponte J, Wendon J, Ginsburg R. Perioperative Care, Anaesthesia, Pain Management and Intensive Care. Edinburgh: Churchill Livingstone 2003.

Behar JM, Gogalniceanu P, Bromley L. Anaesthesia: introduction and pre-operative assessment. studentBMJ. 2007; 15: 12-14.

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