Precautions with Diabetic Patients Undergoing Surgery

• Diabetes mellitus affects 230 million people worldwide¹
• There is a rising incidence and prevalence of diabetes mellitus¹
• About 50% of people with diabetes mellitus are unaware of their condition¹ Approximately 25% of all diabetics undergoing surgery are undiagnosed on admission to hospital.²
• Diabetics have a higher risk of certain diseases (for example they are 4 times more likely to have cardiovascular disease)³ and a higher peri-operative risk¹
• They are more likely because of their disease to require surgery and those undergoing surgery are likely to be less well controlled and to have complications from their diabetes.
• Surgeons and anaesthetists operating on diabetic patients should be familiar with the risks attached to being diabetic and to the particular risks of the particular surgery and of anaesthesia in diabetic patients.

Patients with diabetes mellitus are at risk of the complications of the disease. It is worth considering these in outline when considering how best to care for diabetic patients undergoing surgery.

• Cardiovascular disease. The high risk of large vessel coronary artery disease in diabetic patients is well recognized with data from the Framingham study showing a risk in men and women between 2.4 and 5.1 times greater.³ Diabetes is the most common cause of myocardial infarction in people under age 30 years.
• Peripheral artery disease is under recognised as it is often asymptomatic. It is present in 25-30% of diabetics and is an important marker for systemic atherosclerosis (70% of such patients die from coronary heart disease, 5-10% from stroke).⁴
• Renal disease. Diabetic nephropathy develops in close to 40% of patients with type 1 diabetes, and between 5 and 40% of patients with type 2 diabetes.
• Diabetic retinopathy occurs in up to 20% of diabetic patients.
• Neurological disease
  • Peripheral neuropathy (30% of patients)
  • Autonomic neuropathy though less common is important as it causes hypotension and may diminish the autonomic response to hypoglycaemia (pallor, sweating, tachycardia).
  • Susceptibility to nerve palsies (mononeuritis) is increased
• Skin disease
• Susceptibility to infection
• Hypoglycaemia
• Diabetic ketoacidosis

Interestingly the risk of complications after coronary artery stenting⁵ may not be increased in diabetes. In another study of complications after renal transplantation there was no difference between diabetics and non-diabetic recipients⁶ and it seems that there are other greater risk factors for poor outcome (including age of donor and recipient, time awaiting transplantation etc).⁷ This perhaps illustrates that it is important in assessing risk of complications in diabetic patients undergoing surgery to consider the specific type of surgery and anaesthetic technique. There is evidence for higher risk in diabetics undergoing surgery and when such evidence is lacking it may in part be testament to the relative safety of modern surgery and anaesthesia.
However the following risks and observations are worth considering in diabetic patients undergoing surgery:

• Myocardial infarction post-operatively (may be silent, has a greater mortality). However again it is not straightforward. In one study of cardiovascular complications in diabetics undergoing major vascular surgery, after controlling for specific comorbid conditions, the only independent association was between patients with insulin treatment and the risk of cardiovascular complications.⁸ However other studies show a clear increase in risk of peri-operative cardiac events in diabetics, for example after renal transplant⁹ carotid endarterectomy¹⁰ and vascular surgery.¹¹
• Cardiac arrest as a consequence of autonomic neuropathy
• Chronic renal failure patients (diabetic nephropathy) have a worse outcome (complications and mortality) even accounting for the increased risk of associated conditions (hypertension, peripheral vascular disease).^12,13
• Stroke.This is consistent with the generally increased risk in diabetes mellitus, although again the surgical procedure and other risk factors for stroke (for example smoking, anaesthetic technique) are important.¹⁴
• Problems with lower limb ischaemia. This is consistent with high incidence of peripheral vascular disease⁴
• Heel pressure sores, particularly with peripheral neuropathy.
• Post-operative wound infection.¹⁵
• Other infections such as chest and urinary infections are more common in diabetics. Tuberculosis can occur particularly in elderly diabetics.²
• Disruption and worsening of diabetic control (for example from the stress of surgery, lack of oral intake, postoperative vomiting etc).
• Poor perioperative diabetic control is associated with unfavourable outcomes in for example infrainguinal bypass surgery.¹⁶
• Poor intraoperative blood glucose control is associated with worse outcome after cardiac surgery in diabetic patients.^17,18
• Diabetes mellitus is a risk factor for prolonged intensive care after cardiac surgery¹⁹ and prolonged length of hospital stay after surgery.⁸

A careful preoperative assessment should be done and may help improve outcome²⁰:

• To establish the history of the patients diabetes and the state of their diabetic control
• To look for complications of diabetes mellitus
• To establish the safest method of anaesthesia and surgery

It is apparent from a review of the risks of surgery associated with diabetes mellitus that the assessment and reduction of risk require an individual assessment of the particular patient and the surgery being undertaken.

History and examination

• Assessment of control (records of HBAIC etc)
• Cardiovascular disease.
  • Evidence of angina, intermittent claudication
  • Examine for peripheral vascular disease
  • Examine for postural hypotension (systolic fall of >30 mmHg on standing)
• Neurological disease.
  • Symptoms of numbness, pain, paraesthesia, leg ulcers, transient ischaemic attacks etc.
  • Postural hypotension gives a late indication of autonomic neuropathy.
  • An assessment of heart rate variability (HRV) during deep breathing is a much better way of detecting autonomic neuropathy earlier.²¹
• Renal disease. Symptoms of polyuria may reflect glycosuria or renal failure. Anaemia and hypertension should be detected as possible associated conditions.
• Skin, feet etc. The skin should be examined for sepsis and the pressure areas (heels, buttocks etc) examined for sores.

Should include:

• Blood glucose (Serial readings) and HbA1c (more relevant for long term control). Blood glucose should be maintained at 4-10 mmol/l and it is very important to avoid hypoglycaemia. If blood sugar cannot be maintained below 13 mmol/l surgery should be deferred (risk of ketoacidosis or hyperosmolar state.
• Full blood count
• ECG (with Valsalva manoeuvre) to assess for ischaemic and other cardiovascular disease.
• U & Es (assess for renal complications) and eGFR if available
• Urine analysis. Ketones (poor control), protein (possible renal complications) and bacteriology (for infection).
• CXR. This may be indicated to screen for pulmonary infection, including tuberculosis.

• Local or general anaesthesia can be used
• Local anaesthesia:
  • Reduces the stress response
  • Hypoglycaemia readily detectable with patient awake
  • Postoperative nausea reduced
  • Easy postoperative diabetic control
  There are disadvantages of regional blocks with cardiovascular disease and some neurological conditions.
• General anaesthesia. Consideration should be given to:
  • The presence of cardiovascular and renal disease
  • Prevention of intraoperative hypoglycaemia
  • Autonomic neuropathy. It can mask hypoglycaemia and may exacerbate respiratory depression with opioids
  • Avoidance of hypotension (increased risk of spinal cord infarction)
  • Protection of pressure areas

Type 1 diabetes mellitus

It is usually best to admit patients 2-3 days before elective surgery particularly if outpatient adjustments are difficult. There are different recommended routines but it is important that ward staff and those responsible for postoperative care have clear instructions. Complicated regimens can cause confusion amongst staff.

• Ensure good pre-operative control usually with short acting insulin (or a mixture of short and intermediate acting insulin) twice daily. Extra short acting insulin can be added if necessary.
• Monitor blood glucose throughout the day.
• On day of surgery starve from midnight and do not give first dose of insulin
• Operation as early as possible (ie put the diabetic first on the list)
• Check glucose and electrolytes early on the day of surgery (defer if glucose >13mmol/l or if significant electrolyte disturbance).
• Start IV infusions of dextrose (500mls 10% dextrose plus 10 units soluble insulin plus 10 mol KCl at 125mls per hour). Check blood glucose and electrolytes at end of operation or at 1-2 hour intervals.
• Monitor blood glucose preoperatively at least every 30 minutes. Continue this as long as blood glucose between 5-10mmol/litre. Reduce insulin to 5 units if less than 5mmol/litre and increase to 15 units if blood glucose 10-20 mmol/litre (new infusion needed of course)
• After surgery check glucose every 2 hours and electrolytes every 6-12 hours adjusting infusions as necessary.
• Continue infusions but when eating normally, restart subcutaneous insulin (as before surgery).

Type 2 diabetes mellitus

• Preoperatively control should be assessed.
• Patients controlled by diet alone do not usually need any special measures providing control on diet is adequate.
• It is better to use short acting drugs (for example glipizide).
• Remember that the hypoglycaemic effect of sulphonylureas is enhanced by some drugs (for example aspirin, sulphonamides, anticoagulants).
• If control is inadequate insulin may be needed.
• Insulin can be required in the postoperative phase temporarily.

• On the day of surgery keep 'nil by mouth' as usual and omit short acting sulphonylurea.
• Monitor blood glucose as for type 1 diabetes above. If blood glucose >13mmol/l use insulin to control (small doses of soluble insulin).
• For major surgery or where there is prolonged postoperative starvation, use glucose and insulin infusions as set out above.

In general, emergency or non elective cases must have blood glucose controlled with insulin, glucose and potassium infusions as above with special attention being given to rehydration before surgery.

• Diabetic ketoacidosis. This can present as abdominal pain and vomiting with the vomiting usually preceding the pain (unlike in the acute abdomen when pain usually precedes vomiting). If diabetic ketoacidosis does not respond to treatment it should be remembered that the acute abdomen may have triggered diabetic ketoacidosis.
• Anaesthesia and surgery in diabetic ketoacidosis is hazardous but is occasionally required (eg for perforated diverticular abscess) For example there is a risk of cerebral oedema (resulting from swings in serum osmolarity) and the effects of acidosis on ventilation can cause problems.
• Hyperosmolar non-ketotic diabetic coma. These patients rarely require surgery but if required it is high risk. Heparinisation is usually required.
• Lactic acidosis should be suspected when there is acidosis but no ketosis. It can be caused by the effects of biguanides but occurs also in septicaemia, pancreatitis, hepatic and renal failure.