The Pre-Operative Assessment

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Last updated: July 3, 2021
Revisions: 39

Last updated: July 3, 2021
Revisions: 39

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The pre-operative assessment is an opportunity to identify co-morbidities that may lead to patient complications during the anaesthetic, surgical, or post-operative period. Patients scheduled for elective procedures will generally attend a pre-operative assessment 2-4 weeks before the date of their surgery.

In this article, we shall look at the components of an effective pre-operative history, examination, and routine investigations that can be performed.

Pre-Operative History

The pre-operative history follows the same structure as typical history taking, with the addition of some anaesthetic and surgery specific topics.

History of the Presenting Complaint

A brief history of why the patient first attended and what procedure they have subsequently been scheduled for. One should also confirm the side on which the procedure will be performed (if applicable)

There may be aspects of the disease or condition requiring surgery that are important for the anaesthetist to be aware of; for example, head and neck surgery may indicate the presence of abnormal airway anatomy.

Past Medical History

A full past medical history (PMH) is required, with the following specifically asked about:

  • Cardiovascular disease, including hypertension; exercise tolerance is a useful indicator of cardiovascular fitness and, particularly for patients undergoing major surgery, can help predict their risk of post-operative complications and level of care needed post-operatively
    • Screening questions may elucidate undiagnosed disease and prompt further investigation, e.g. the presence of exertional chest pain, syncopal episodes, or orthopnoea
  • Respiratory disease, as adequate oxygenation and ventilation is essential in reducing the risk of acute ischaemic events in the peri-operative period
    • Questions including whether the patient is able to lie flat for a prolonged period or has a chronic cough are key as these may preclude spinal anaesthesia; also screen for symptoms and signs of obstructive sleep apnoea, if the patient has any risk factors
  • Renal disease, including their baseline renal function and any renal-specific medications
  • Endocrine disease, specifically diabetes mellitus and thyroid disease
  • Gastro-oeseophageal reflux (GORD), as the aspiration of gastric contents can potentially be fatal and the presence of GORD will likely alter anaesthetic technique
    • Whilst this may be overlooked as a diagnosis or in their past medical history, particularly if patient managed with over-the-counter medicines, it is important to ask about at the pre-operative assessment

Other specific questions it may be useful to ask themselves the following questions:

  • Pregnancy – as part of the pre-operative checklist on the day of surgery, for females of reproductive age a urinary pregnancy test is mandatory in the majority of hospitals
  • Sickle Cell Disease – could they have undiagnosed sickle cell disease, especially if their country of birth does not have routine screening for sickle cell

Past Surgical History

Has the patient had any previous operations? If so, what, when, and why?

If the patient is having a repeat procedure, this can significantly change both the surgical time and ease of operation, and hence influence the anaesthetic technique used

Past Anaesthetic History

Has the patient had anaesthesia before? If so, for what operation and what type of anaesthesia? Were there any problems? Did the patient experience any post-operative nausea and vomiting?

Drug History

full drug history is required, as some medications require stopping or altering prior to surgery. Ask about any known allergies, both drug and non-drug allergies

Family History

Whilst most hereditary conditions relating to anaesthesia are extremely rare, such as malignant hyperthermia, it is important to ask about any known family history of problems with anaesthesia

Social History

Ensure to ask the patient about smoking history, alcohol intake, and any recreational drug use

Other important social factors to make note of include:

  • Language spoken and the need for an interpreter
  • Living situation, as the absence of an adult at home may require an admission overnight

Pre-Operative Examination

In the pre-operative examination, two distinct examinations are performed; the general examination (to identify any underlying undiagnosed pathology present) and the airway examination (to predict the difficulty of airway management e.g. intubation). If appropriate, the area relevant to the operation can also be examined.

Perform a full general examination, looking closely for any obvious cardiovascular (in particular undiagnosed murmurs or signs of heart failure), respiratory, or abdominal signs. An anaesthetic examination, including an airway assessment (typically using the Mallampati score), will also be performed by the anaesthetist prior to any surgery

American Society of Anaesthesiologists Grade

On all anaesthetic charts, a patient will be given an American Society of Anaesthesiologists (ASA) grade after their pre-operative assessment, which has been subjectively assessed and based on the criteria below. A patient’s ASA grade directly correlates with their risk of post-operative complications and absolute mortality.

ASA Grade Definition Absolute Mortality (%)
I Normal healthy patient 0.1
II Mild systemic disease 0.2
III Severe systemic disease 1.8
IV Severe systemic illness that is a constant threat to life 7.8
V Moribund, who is not expected to survive without the operation 9.4
E Suffix added if an emergency operation

Pre-Operative Investigations

The nature of the exact investigations required depends on a number of factors, including co-morbidities, age, and the nature of the procedure.

The urgency of the surgery will also dictate which conditions need further investigation and management prior to surgery. For example, elective surgery is often delayed for poorly controlled blood glucose levels in diabetic patients, to allow time for optimisation

Each specific hospital is likely to provide local guidelines, however it is useful to understand the tests than could be done pre-operatively and have an appreciation as to why each may be requested. NICE produce a colour traffic light table which can further guide your investigative decisions.

Blood Tests

  • Full Blood Count (FBC)
    • Most patients will get a full blood count, predominantly used to assess for any anaemia or thrombocytopenia, as this may require correction pre-operatively to reduce the risk of cardiovascular events or allow for preparation of blood products
  • Urea & Electrolytes (U&Es)
    • To assess the baseline renal function, which help inform fluid management and drug decisions, both for anaesthesia and post-operative analgesia (e.g. morphine is generally avoided in those with CKD)
  • Liver Function Tests (LFTs)
    • Important in the assessing liver metabolism and synthesising function, useful for peri-operative management; if there is suspicion of liver impairment, LFTs may help direct medication choice and dosing
  • Condition-specific blood tests
    • There are several conditions or diseases that may require specific bloods, such as HbA1C or thyroid function tests (TFTs)
  • Clotting Screen
    • Any indication of deranged coagulation, such as iatrogenic causes (e.g. warfarin), inherited coagulopathies (e.g. haemophilia A/B), or liver impairment, will need identifying and correcting or managing appropriately in the peri-operative period
  • Group and Save (G&S) +/- cross-matching

Group and Save versus Cross-Match

Group and Save (G&S) and Cross-Match (X-match) are two tests that are slightly different in their aims:

  • A G&S determines the patient’s blood group (ABO and RhD) and screens the blood for any atypical antibodies; the process takes around 40 minutes and no blood is issued
    • A G&S is recommended if blood loss is not anticipated, but blood may be required should there be greater blood loss than expected
  • A cross-match involves physically mixing the patient’s blood with the donor’s blood, in order to see if any immune reaction takes places; if it does not, the donor blood is issued and can be transfused in to the patient, otherwise alternative blood is trialled
    • This process also takes ~40 minutes (in addition to the 40 minutes required to G&S the blood, which must be done first), and should be done pre-emptively if blood loss is anticipated

Cardiac Investigations

An ECG is often performed in individuals with a history of cardiovascular disease or for those undergoing major surgery. It can indicate any underlying cardiac pathology and provide a baseline for comparison if there are post-operative  concerns for cardiac ischaemia.

An echocardiogram (ECHO) provides very useful information for the anaesthetist as it helps to risk stratify and tailor the intra-operative care of the patient. It may be considered if the person has (1) a heart murmur (2) ECG changes (3) signs or symptoms of heart failure.

For patients with untreated ischaemic heart disease, or symptoms of angina, myocardial perfusion scans are often performed to look for inducible ischaemia.

Respiratory Investigations

If a patient has a chronic lung condition e.g. COPD, spirometry may be of use in assessing current baseline and predicting post-operative pulmonary complications in these patients. Patients may also be referred for spirometry if there are symptoms and signs of undiagnosed pulmonary disease.

Plain film chest radiographs (CXR) are less commonly performed routinely pre-operatively and should be used only when necessary

Other Tests


Especially for urological procedures, a urinalysis must be performed to assess if there is any evidence or suspicion of ongoing urinary tract infection

MRSA Swabs

All patients will have swabs taken from the nostril and perineum for MRSA colonisation. If this is isolated, decontamination hair and body wash, along with topical ointment applied to the nostrils, will be given.

Cardiopulmonary Exercise Testing

High-risk patients undergoing major surgery may be referred for cardiopulmonary exercise testing (CPET). This usually involves a graded intensity period on a stationary bicycle whilst wearing a mask, as well as ECG monitoring. It provides useful information, such as the VO2max and anaerobic threshold, which can be used to risk-stratify patients for post-operative complications and need for higher level care environments