Surgery in Patients with Diabetes

Diabetes presents several special problems during surgery.
Fasting causes particular problems in type 1 diabetes. Such
patients need basal insulin to prevent ketosis, and develop
hypoglycaemia without additional carbohydrate intake. Fasting
is of little signifi cance in type 2 diabetes, unless the patient
has received oral hypoglycaemic agents.
Metabolic changes include the following.
• Increases in circulating adrenaline, adrenocorticotrophic
hormone, cortisol and growth hormone aggravate insulin
defi ciency and insulin resistance. These changes are a normal
response to surgery and proportional to the severity of
the operation. They antagonize the actions of insulin and its
secretion, resulting in catabolism with increased glycogenolysis,
gluconeogenesis, proteolysis and lipolysis. In diabetes,
the effects are compounded by insulin defi ciency.
• Gluconeogenesis from precursors such as lactate, pyruvate,
alanine and glutamine is increased in the liver and kidney,
and muscle and adipose tissue take up less glucose. The resultant
hyperglycaemia is more pronounced in patients with
diabetes than in non-diabetic patients.
• Without insulin, lipolysis is stimulated and leads to ketogenesis.
Plasma levels of free fatty acids, glycerol and ketone
bodies increase, and metabolic acidosis may develop even in
the presence of near-normal plasma glucose.
All these changes are aggravated by some types of anaesthesia,
particularly high doses of opiates or regional blockade.
They increase insulin requirements in patients with type 1
diabetes, and may cause those with type 2 diabetes to become
temporarily insulin-requiring.
Recognizing hypoglycaemia may be difficult in unconscious
patients.
Subcutaneous insulin absorption is poor or unpredictable
when peripheral vessels are constricted.

Principles of management

The fundamental principle of surgical management in diabetes
is that capillary blood glucose is measured regularly and
accurately, and that these results are recorded and acted on.
Most problems occur because staff have forgotten to measure
blood glucose, or because very low values have been ignored
or wrongly attributed to faulty meters.
Target glucose – during surgery, blood glucose should be
7–11 mmol/litre. At normal levels, patients are too close to
hypoglycaemia. At levels above 11 mmol/litre, urine output
increases and dehydration may ensue.
Fluids – any other fl uids given during the surgical period
should not contain glucose. Use of Hartmann’s solution
(Ringer lactate) in patients with diabetes remains controversial.
The lactate contained in this crystalloid is used for
gluconeogenesis, particularly in starved or catabolic patients.
In patients with type 2 diabetes, an infusion of Hartmann’s
solution may cause blood glucose levels to rise signifi cantly.
If fluids have to be restricted, glucose may be given as a
20% or 50% solution. This must be administered via a central
venous catheter, to avoid venous thrombosis.
Electrolytes – potassium levels should be monitored regularly
perioperatively. Serum potassium varies according to:
• the effects of insulin, which promotes potassium uptake
by muscle, liver and adipose tissue
• dehydration, which may cause a shift in potassium from
the intracellular to the extracellular space
• acidosis, which leads to hydrogen and potassium exchange
in the kidneys, potassium retention and hyperkalaemia.
Most patients with normal renal function require 20 mmol
potassium/litre fl uid given, but the requirement is often higher
in patients with diabetes.
Analgesia – in the past, there was a view among anaesthetists
that regional blockade (including spinal and epidural)
was undesirable in diabetes. This originated from fear
of aggravating (possibly latent) neuropathy, of uncontrolled
hypotension in those with signifi cant autonomic neuropathy,
or of causing infection at the site of the block. This view is no
longer valid. The advantages of regional blockade, which provides
excellent analgesia and blunting of the stress response,
outweigh any disadvantages in most patients with diabetes.