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Preoperative Assessment


The majority of patients undergoing elective surgery will attend a preoperative assessment clinic before they are admitted to hospital. The decision to operate and what is to be done will have already been made in the surgical out-patient clinic and the preoperative assessment clinic builds on this work. The main focus is to assess the patient’s fitness for surgery (including their fitness for anaesthesia), and organise any necessary preoperative investigations. This helps to identify patients who are not fit for surgery, thereby preventing unnecessary cancellations and wasted theatre slots. Importantly, patients who are not currently fit for surgery but could be after some adjustments to their treatments or lifestyle are also identified and dealt with appropriately. This process generally helps to make the provision of elective surgery more efficient. This article will outline who is involved in preoperative assessment and their different roles. It will also cover different preoperative investigations, when it is appropriate for them to be done, and what to do with specific medications.


Participants in Preoperative Assessment

The Surgeon:

(nb. the surgeon may not be involved directly in the preoperative assessment clinic and, as mentioned above, their tasks will probably be done in their own out-patient clinic)

  • will decide (along with the patient) whether an operation is the most appropriate treatment and whether the procedure should be done electively or as an emergency.
  • will explain the planned procedure, including any specifics like the use of drains or catheters.
  • will explain any necessary preoperative preparations, such as starving, as well as the plans for post-op care. 
  • will answer any questions the patient may have.
  • will obtain explicit written consent from the patient. The surgeon who will perform the operation should do this and should explain any potential complications. Some will be specific to the operation, but there are always general risks. For example, failure of the procedure, damage to local structures, bleeding, infection, and death.


The Anaesthetist:

(nb. may be part of the general preoperative assessment clinic, or run their own specific clinics)

  • will assess the patient's fitness for anaesthesia. They will particularly be concerned with cardio-respiratory fitness and will cover this in the past medical history and by asking about exercise tolerance. Another important consideration is the presence of reflux disease which may need optimisation prior to anaesthesia, or may even warrant the patient being anaesthetised by rapid sequence induction.
  • will choose the method of anaesthesia (e.g. general anaesthetic, local anaesthetic, regional anaesthetic). If a patient is not fit for general anaesthesia it is often possible to consider doing the operation under local anaesthetic, especially if it involves a peripheral part of the body.
  • will assess the airway and try to identify a potentially difficult intubation. A history of difficult intubation is the clearest indicator of future difficulty, but spotting any abnormalities of the bony or soft tissue structures of the upper airway will identify potential difficulties. Consideration of things like BMI, facial shape, mouth opening, quality of dentition, and the range of neck movement can be helpful in this respect, but there are several specific screening tests available. These are best used in combination. They are described in more detail below. A history of rheumatoid arthritis affecting the neck is also important as this means the cervical verterbrae may be unstable. Xray assessment of the neck should be acquired before intubation is attempted.
  • will identify potential anaesthetic complications by asking about previous experience with anaesthesia and family history of anaesthetic complications. Patients are often concerned about things like "awareness during anaesthesia", postoperative nausea and vomiting, and postoperative pain. These are important, but the anaesthetist will also want to identify any potentially important drug allergies and if there is a risk of specific complications like malignant hyperthermia or suxamethonium apnoea.


The Junior Doctor:

  • will clerk the patient for their admission. This involves taking a history and examining the patient.
  • should ensure that the patient doesn’t need emergency admission.
  • should ensure that the patient is fit for the planned surgery and undergoing an anaesthetic. This will involve checking that the patient does not have a concurrent illness and that any preoperative investigations already done are within normal limits.
  • will order any additional investigations required according to local protocols. For example, if a new murmur is found on examination then an ECHO may be indicated.
  • where patients are not routinely seen in advance of their surgery by the anaesthetist there will be a system for referring patients in whom abnormalities are discovered or there is some concern about their fitness for anaesthetic. The junior doctor will often make referrals for these cases.
  • will write the drug chart for admission. Always consider thromboprophylaxis, analgesia, antiemetics, and preoperative antibiotics.
  • should ensure that the patient knows what to do with regard to their regular medications.


The Nurse:

  • will help to admit the patient and fill out important clerking documents with the patient.
  • will record important baseline observations, including vital signs and BMI.
  • will organise or perform routine investigations where required, allowing patients to get a complete assessment in a single visit.
  • will ensure the patient is prepared for the postoperative period, including checking that they will have transport home and that people will be available to care for them whilst they recover.

Mallampati Score

Grades for mallampati assessment

Perhaps the most widely used airway assessment tool is the Mallampati score. The test involves sitting opposite the patient and asking them to open their mouth as widely as possible. The score given corresponds to the best view obtained and this view indicates how much of the vocal cords will be visible at laryngoscopy. Grade 1 indicates a good view at laryngoscopy and a straightforward intubation. Grades 3-4 suggest little or none of the vocal cords will be visible and so intubation will be potentially difficult. See the diagram opposite for examples fo the different grades.

  1. View of the faucial pillars, soft palate and the uvula
  2. View of the faucial pillars and soft palate
  3. View of the soft palate only
  4. None of the above structures visible

Other Airway Assessment Techniques

  1. Thyromental distance: with the patient's head extended measure the distance from the thryoid notch to the tip of the mandible. The normal measurement is >6.5cm and if it is >7cm intubation is likely to be straightforward. If it is <6cm intubation will be challenging.
  2. Sternomental distance: with the patient's head extended measure the distance from the sternal notch to the tip of the mandible. A measurement <12.5cm is a predictor of difficult intubation.
  3. Protrusion of the mandible: if the patient is unable to move their lower incisors further forward than the upper incisors this suggests mandibular movement is limited and intubation may be difficult.

ASA Grades and Severity of Surgery

American Society of Anasthesiologists (ASA) GradesGrades of Surgery

Choosing Preoperative Investigations

Evidence suggests that routinely investigating patients preoperatively doesn’t necessarily improve surgical outcomes and is not cost effective. Current NICE guidance recommends that the decision to investigate should be based upon the following conditions:

  1. Age
  2. ASA grade (see table)
  3. Grade of surgery (see table)
  4. Co-morbidities


The idea is that investigations should be targeted at patients who are at greater risk of morbidity/mortality through undergoing surgery. Clearly, having more major surgery puts the patient at greater risk and so preoperative investigations are more likely to affect outcomes. Similarly, older patients generally have less functional reserve to cope with the insult of surgery and so any operation is potentially more serious for them. Older patients are also more likely to have co-morbidities, something which is accounted for by the ASA grade. More thorough assessment of fitness for surgery is therefore warranted where patient age or ASA grade is increased. Finally, the relevant co-morbidities that warrant specific investigation are cardiovascular disease, respiratory disease, and renal disease. Patients with conditions in these categories undergoing anaesthsia are at increased risk and so they often require investigations like ECG, chest xray or spirometry, and U&E blood testing respectively. NICE has produced grids to recommend appropriate investigations for all ages, all ASA grades and all co-morbidities undergoing all grades of surgery. Two example grids can be seen below.


Investigations that should be considered preoperatively are listed below. For full guidance as to when they are appropriate see the NICE website.

  • FBC – preoperative Hb is a useful baseline where there is expected blood loss or the patient could be anaemic.
  • U&E’s – are useful for assessing renal function, especially as renal impairment can affect required drug doses.
  • Haemostasis – clotting function should be considered if there is a high risk of bleeding, especially if the patient is already taking anticoagulants. Where blood products may be required a “group and save” sample should also be taken.
  • ECG – will show cardiac ischaemia and arrhythmias. This should be considered in older patients or those with a known history of heart disease.
  • ECHO – should be considered where there is a murmur or known cardiac dysfunction.
  • Chest xray – may be useful if there is known lung disease or suspected acute lung disease (e.g. pneumonia). There are a few circumstances where it is essential, for example, in thoracic or head and neck surgery.
  • Spirometry – to assess respiratory function and reserve where there is known respiratory disease.
  • Urine dip – evidence for its use is equivocal, but it is a cheap and easy test that can show infection and occult diabetes.
  • Pregnancy test – should be considered in all women who could be pregnant.


Examples of NICE Guidance Tables

ASA grade 1 adults undergoing grade 2 surgeryASA grade 1 adults undergoing grade 4 surgery

Preoperative Medications

An important consideration in preoperative assessment is ensuring that the patient knows what to do with their regular medications. Often the nursing staff will explain this, but the junior doctor may also need to, especially if a prescription is required. The following are medications that are relevant prior to elective surgery: 

  • Clopidogrel – should be stopped 7 days prior to surgery.
  • Aspirin – the risk of stopping should be weighed against the risk of bleeding during surgery.  Usually it should be continued as normal, but if stopped should be done so 7 days prior to surgery. Follow local guidelines.
  • Warfarin – should be stopped 5 days prior to surgery. Aim for INR  <1.5 for surgery (reversal with vitamin K may be required). High risk patients (e.g. those with metallic heart valves) should have bridging anticoagulation in the form of LMWH.
  • Oral diabetes medications – should be continued as normal, but the morning dose on the day of surgery should be omitted (as the patient will be starved). Restart once the patient is eating again. Cover with an insulin sliding scale if blood sugar control is poor.
  • Insulin - should be continued as normal, but the morning dose on the day of surgery should be omitted (as the patient will be starved). Restart the normal regimen once the patient is eating again. An insulin sliding scale may be required during surgery and the patient may need to be admitted earlier to optimise treatment.
  • Steroids – should be continued as normal. Increased doses may be required postoperatively to cope with the stress response. 


References and Further Reading

  1. Patient UK. Pre-Operative Assessment – Examination and Tests. (accessed 11th December 2011).
  2. National Institute for Health and Clinical Excellence. Preoperative Tests – the use of routine preoperative tests for elective surgery 2003. (accessed 11th December 2011).
  3. Hurley N, Dawson J, Sanders S, Eccles S (eds.). Oxford Handbook for the Foundation Programme 2nd ed. Oxford: Oxford University Press, 2008: 128-130.
  4. Surgical Tutor. Pre-operative Assessment. (accessed 11th December 2011).
  5. Patient UK. Precautions for Patients on Steroids Undergoing Surgery. (accessed 11th December 2011).
  6. Patient UK. Precautions with Diabetic Patients Undergoing Surgery. (accessed 11th December 2011).

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