Pre-Operative Care

Before going to theatre for an operation there are a number of things that need to be addressed:

  • Pre-op assessment
  • Consent
  • Bloods (including groups and save / crossmatch)
  • Fasting
  • Medication changes
  • Venous thromboembolism assessment


Pre-Operative Assessment

Patients need to be assessed individually for whether they are fit to undergo an operation. This will involve their co-morbidities, risk of anaesthetic, frailty, cardiovascular and respiratory fitness.

They require a full history of:

  • Past medical problems
  • Previous surgery
  • Previous anaesthetic
  • Medications
  • Allergies
  • Smoking
  • Alcohol use


Consider pregnancy in women of childbearing age, they may require a pregnancy test. Consider asking about a family history of sickle cell disease. A general examination is performed to look for cardiovascular and respiratory disease.

Patients who may be malnourished (e.g. BMI under 18.5 or significant unintentional weight loss) may need input from a dietician and additional nutritional support before surgery and during admission.


ASA Grade

The American Society of Anesthesiologists (ASA) grading system classifies the physical status of the patient for anaesthesia. Patients are given a grade on their anaesthetics. The grades are:

  • ASA I – normal health patient
  • ASA II – mild systemic disease
  • ASA III – severe systemic disease
  • ASA IV – severe systemic disease that constantly threatens life
  • ASA V – “moribund” and expected to die without the operation
  • ASA VI – declared brain-dead and undergoing an organ donation operation before death
  • E – this is used for emergency operations


Pre-Operative Investigations

There is a NICE guideline from 2016 on routine preoperative tests for elective surgery that gives guidance on which investigations are required depending on individual patient factors and the size of the operation. There will also be local guidelines. If in doubt, get advice from an anaesthetist.

Investigations may be required prior to surgery depending on the co-morbidities:

  • ECG if there is known or possible cardiovascular disease
  • Echocardiogram if there are heart murmurs, cardiac symptoms or heart failure
  • Lung function tests may be required if there is known or possible respiratory disease
  • Arterial blood gas testing may be required if there is known or possible respiratory disease
  • HbA1C (within the last 3 months) for people with known diabetes
  • U&Es for people risk of acute kidney injury
  • FBC may be required if there is possible anaemia, cardiovascular or kidney disease
  • Clotting testing may be required if there is known or possible liver disease


Group and save refers to sending off a sample of the patient’s blood to establish their blood group. The sample is saved in case they require blood to be matched to them for a blood transfusion. No blood is assigned to the patient at this stage. This is done routinely where there is a lower probability that they will require blood products.

Crossmatching involves the process of actually taking a unit or more of blood off the shelf and assigning it to the patient in case they need it quickly. This is done where there is a higher probability they will require blood products so that the blood is ready to go if required.

MRSA screening is routinely performed on all patients being admitted to hospital. This is usually arranged automatically by the nursing staff so you don’t need to think about this.


Fasting before Surgery

Patients are “fasted” before surgery to ensure an empty stomach at the time of the operation. The aim is to reduce the risk of reflux of food during the operation, with aspiration into the lungs occurring.

Typically fasting for an operation involves:

  • 6 hours of no food or feeds before operation
  • 2 hours no clear fluids (fully “nil by mouth”)


TOM TIP: When you assess an acutely unwell surgical patient, always consider whether there is any possibility they require emergency surgery. Acutely unwell surgical patients that potentially require emergency surgery are made nil by mouth and given maintenance IV fluids. Allowing them to eat and drink could have significant consequences if they need emergency surgery, and the anaesthetist and senior surgeon won’t be happy. This will often be reversed on the post-take ward round if the consultant or senior surgeon decides they are unlikely to need to go to theatre.


Specific Medications

Follow local guidelines for medication alterations around the operation.

Anticoagulants need to be stopped before major surgery. The INR can be monitored in patients on warfarin to ensure it returns to normal before the operation. Warfarin can be rapid reversed with vitamin K in acute scenarios. Treatment dose low molecular weight heparin or an unfractionated heparin infusion may be used to bridge the gap between stopping warfarin and surgery in higher-risk patients (e.g. mechanical heart valves or recent VTE),  and stopped shortly before surgery depending on the risk of bleeding and thrombosis. DOACs (e.g. apixaban, rivaroxaban or dabigatran) are stopped 24-72 hours before surgery depending on the half-life, procedure and kidney function.

Oestrogen-containing contraction (e.g. the combined contraceptive pill) or hormone replacement therapy (e.g. in perimenopausal women) need to be stopped 4 weeks before surgery to reduce the risk of venous thromboembolism (NICE guidelines 2010).

Long-term corticosteroids, equivalent to more than 5mg of oral prednisolone, require additional management around the time of surgery. Surgery adds additional stress to the body, which normally increases steroid production. In patients on long-term steroids, there is adrenal suppression that prevents them from creating the extra steroids required to deal with this stress. Management involves:

  • Additional IV hydrocortisone at induction and for the immediate postoperative period (e.g. first 24 hours)
  • Doubling of their normal dose once they are eating and drinking for 24 – 72 hours depending on the operation



Stress of surgery increases blood sugar levels, however fasting may lead to hypoglycaemia. In general, the risk of hypoglycaemia is greater than hyperglycaemia.

Certain oral anti-diabetic medications may need to be adjusted or omitted around surgery:

  • Sulfonylureas (e.g. gliclazide) can cause hypoglycaemia and are omitted until eating and drinking
  • Metformin is associated with lactic acidosis, particularly in patients with renal impairment
  • SGLT2 inhibitors (e.g. dapagliflozin) have a risk of diabetic ketoacidosis in dehydrated or acutely unwell patients


In patients on insulin going for surgery (follow the local policy):

  • Continue a lower dose (BNF recommends 80%) of their long-acting insulin
  • Shop short-acting insulin whilst fasting or not eating, until eating and drinking again
  • Have a variable rate insulin infusion alongside a glucose, sodium chloride and potassium infusion (“sliding-scale”) to carefully control their insulin, glucose and potassium balance


VTE Prophylaxis

Every patient admitted to hospital should be assessed for their risk of venous thromboembolism (VTE). Surgery, particularly where the patient is likely to be immobilised (e.g. orthopaedic surgery), significantly increases the risk of venous thromboembolism. There are local and national policies on reducing the risk that involve:

  • Low molecular weight heparin (LMWH) such as enoxaparin
  • DOACs (e.g. apixaban or rivaroxaban) may be used as an alternative to LMWH
  • Intermittent pneumatic compression (inflating cuffs around the legs)
  • Anti-embolic compression stockings


Last updated March 2021
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