13. DIABETES

Diabetic patients present the anaesthetist with two special problems. One is the control of the patient’s blood sugar in the perioperative period and the other is the long-term effect of the diabetes on their health (end-organ disease). Hypoglycaemia must be avoided.

The anaesthetic management will depend on how well the diabetes is controlled, how urgent the surgery is and which type of treatment the patient is receiving for their diabetes.

Preoperative Assessment

As the major risk factors for all diabetics undergoing surgery are end-organ diseases associated with diabetes, all diabetics must have a complete preoperative assessment and treatment. This assessment should focus on heart disease, kidney disease, joint abnormalities and neuropathies.

Cardiovascular Assessment

50% of patients who are diabetic and have hypertension will have autonomic neuropathy compared to only 10% in diabetics without hypertension. All diabetic patients should be assessed for autonomic neuropathy. The presence of autonomic neuropathy may make the perioperative period more dangerous. These patients are more likely to have intra-operative or postoperative cardiorespiratory arrest, have a higher rate of painless myocardial ischaemia, may have cardiovascular instability and are more likely to have delayed emptying of stomach contents (gastroparesis) and therefore are at an increased risk of pulmonary aspiration. Symptoms of autonomic neuropathy include: lack of sweating, fall in blood pressure when standing (orthostatic hypotension), penis erectile problems, severe constipation or night-time diarrhoea. Signs of autonomic neuropathy include orthostatic hypotension (fall of 20 mmHg in systolic or 10 mmHg in diastolic blood pressure for more than 3 minutes after standing), lack of pulse rate change with breathing (less than a 5 beat/min change in pulse rate on deep inspiration) and loss of electrocardiogram R-R interval variability.

Diabetic patients have an increased incidence of atherosclerosis and all its complications. Unfortunately they may have painless myocardial ischaemia so the anaesthetist cannot rely on a history of chest pain to assess the patient’s risk. The anaesthetist should carefully assess for myocardial ischaemia in all diabetics who are obese, physically inactive, over 55 years of age or who have chonically elevated blood glucose (greater than 11 mmol/l). In diabetic patients, the risk of coronary artery disease is two to four times higher than the general population. A good indication of the severity of ischaemic heart disease is the patient’s exercise tolerance. If the patient can climb a flight of stairs, walk up a hill or run a short distance then their risk is probably low. An electrocardiogram may not show signs of myocardial ischaemia.

Renal Assessment

Blood testing of the kidney may show reduced function.

Musculo-Skeletal Assessment

Diabetics can have stiffness of the alanto-occipital joint making intubation of the trachea difficult. All diabetic patients need careful assessment of their airway.

Preoperative Management

The better the control of a patient’s diabetes the lower the perioperative risk. Poorly treated diabetics having elective surgery should be postponed until their diabetic treatment is improved. Adequacy of treatment can be assessed by history and investigation. Those patients who are still symptomatic or who have a raised glycosylated haemoglobin (HbA1C) are likely to have poor diabetic control. Glycosylated haemoglobin gives the best evidence of blood glucose control over the previous 1 to 2 months. If the HbA1C is greater than 9%, the patient’s diabetic control is inadequate.

Recommendation

If the patient’s diabetes is well treated (asymptomatic, HbA1C less than 9%):

Diet control only. No change in treatment.

Oral hypoglycaemic. All oral hypoglycaemics should be omitted on the day of surgery.

Insulin. Arrange for the patient to be first on the morning or afternoon operating list. If on the morning list then omit the morning insulin and monitor the blood glucose level. If on an afternoon operating list the patient should have a light early morning breakfast with half their normal insulin dose.

Blood glucose should be measured at least every second hour until the patient is eating and drinking.

All patients should have a blood sugar measurement on admission to the hospital. If the blood sugar level (BSL) is less than 5 mmol/l or greater than 10 mmol/l the patient needs further treatment.

If the patient’s diabetes is poorly treated:

If the surgery is elective the case should be cancelled and the patient’s treatment of the diabetes improved. The case can be rebooked in 4 to 6 weeks.

If the surgery is urgent and the patient is treated with only oral hypoglycaemics then stop all hypoglycaemic tablets, begin 6 hourly Actrapid insulin injections according to a sliding scale and give 5% dextrose (80 ml/h) when fasting. Measure the BSL every 2 hours and hourly intra-operatively.

If the surgery is urgent and the patient is treated with insulin, then stop the normal insulin, begin 6 hourly Actrapid insulin injections according to a sliding scale and give 5% dextrose (80 ml/h) when fasting. Measure the BSL every 2 hours before surgery and at least hourly intra-operatively.