Peri-op care - Diabetes

Question 1

How are blood glucose levels affected by surgery? Explain why.

Answer 1

Surgery causes development of insulin resistance with free fatty acids becoming primary source of energy. Results in HYPERGLYCAEMIA:

1. increased adrenaline, ACTH, cortisol and GH antagonise actions and secretion of insulin… promotes catabolism: glycogenolysis, proteolysis, lipolysis
2. increased gluconeogenesis in liver and kidney and reduced glucose uptake by muscle and adipose tissue

Question 2

What is the target range for capillary blood glucose (CBG) in peri-op diabetic patients?

Answer 2

6-10 mmol/L

4-12 mmol/L may be acceptable

Question 3

Why is a high CBG (>13 mmol/L) unacceptable unless surgery is critically urgent?

Answer 3

RISK OF KETOACIDOSIS

Without insulin, lipolysis is stimulated… ketogenesis with increased plasma levels of ketone bodies… metabolic acidosis

Question 4

How should peri-op glucose levels be managed in patients with diet-controlled diabetes?

Answer 4

• Majority do not require specific intervention.

- Blood glucose must be monitored daily by BM stix (if rises >11mmol/L seek advice from diabetic team).

Question 5

How should peri-op glucose levels be managed in diabetic patients on oral hypoglycaemics anticipate to only miss 1 meal before surgery?

Answer 5

• Omit dose of oral hypoglycaemic on morning of operation. Can be resumed once Pt starts eating post-op.
• BMs must be measured and if very high, can be brought own by small doses of subcutaneous soluble insulin. If this fails or in cases of major surgery, convert treatment to a sliding scale.

Question 6

How should peri-op glucose levels be managed in diabetic patients on oral hypoglycaemics anticipate to miss more than 1 meal before surgery?

Answer 6

Start Pt on variable rate insulin infusion.

Question 7

How should peri-op glucose levels be managed in diabetic patients on insulin?

Answer 7

If only 1 missed meal and well controlled diabetes, may need to reduce/alter/omit insulin dose on day prior to or day of surgery.

If more than 1 meal missed or poorly-controlled diabetes, start Pt on variable rate insulin infusion.

Question 8

If a patient is on a variable rate insulin infusion for surgery, what else should they be given?

Answer 8

1. 5% or 10% dextrose infusion to balance insulin given and make up for lack of dietary intake.
2. Potassium (as insulin drives K+ into cells)

Question 9

Name 3 investigations that should be included in the pre-op assessment of a diabetic patient.

Answer 9

1. Serial blood glucose and glycosylated haemoglobin measurements - for evaluation of current diabetic control
2. ECG - to assess potential cardiovascular complications (with Valsalva manoeuvre to look for autonomic neuropathy)
3. U and Es - to assess possible renal complications

Question 10

Suggest specific perioperative problems in patients with diabetes.

Answer 10

Cardiovascular:

1. predisposition to ischaemic heart disease - greater risk of perioperative MI
2. increased danger of cardiac arrest due to autonomic neuropathy
3. predisposition to peripheral vascular disease - greater risk of strokes and lower limb sequelae
4. Renal problems due
   to predisposition to diabetic nephropathy and chronic renal failure
5. Increased incidence of post-op infection in wound, lungs or urinary tract
6. Risk of hyperglycaemia (due to lack of insulin) or hypoglycaemia (due to insulin-replacement therapy)