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Anaesthesia and The Diabetic Patient
Aparna Chatterji
Introduction
Diabetes is a chronic systemic disease as
a result of a relative or absolute lack of insulin. The cells of the body cannot metabolize sugar properly, due to a total or relative lack of insulin. The body then breaks down its own fat, proteins and glycogen to produce sugar, resulting in high sugar levels in the blood (hyperglycaemia) with excess by-products called ketones being produced by the liver. Both acute hyper- or hypoglycaemia and long-term complications are of anaesthetic relevance. Diabetics have higher morbidity and mortality as surgical patients
Types of Diabetes
Two main types
 Obesity is a common cause of Type II diabetes mellitus- the pancreas cannot make enough insulin for the body size. Diet /oral hypoglycaemics may initially be enough but eventually insulin may be required for optimal control.
Diabetes affects many organ systems, the severity of which may be related to how long the disease has been present and how well it has been controlled. Damage to small blood vessels (diabetic microangiopathy), nerves (neuropathy) throughout the body, kidneys (nephropathy) may pose problems to the anaesthetist if the patient should undergo anaesthesia.
Problems Faced by an Anaesthetist
Perioperative control of blood sugar: All elective surgery should be postponed until the blood sugars are under control. Patients on long acting oral hypoglycaemic drugs or insulin are at a risk of developing hypoglycaemia. Blood sugar control should be continued through the perioperative period and hyperglycaemia avoided. b- blocking agents in a patient with diabetes may mask the signs of hypoglycaemia (i.e. tachycardia) which may thus go undetected.
Complications of diabetes
a) Cardiovascular: Diabetics are more prone to hypertension, ischaemic heart disease, cerebrovascular disease, cardiomyopathy and myocardial infarction which may be silent.
b) Autonomic neuropathy: may result in sudden tachycardia, bradycardia or a tendency to postural hypotension. May also lead to gastric stasis and a potential full stomach necessitating a rapid sequence intubation
c) Renal: Nephropathy may already be present, often indicated by the presence of protein (albumin) in the urine. The diabetic is at risk of acute renal failure and urinary tract infection postoperatively. May have deranged renal function tests.
d) Respiratory: Increased incidence of chest infection
e) Infection: A major cause of perioperative morbidity.
f) Atlanto-occipital disease: Juvenile onset diabetics may have reduced neck movement making intubation difficult
g) Neuropathy: Peripheral neuropathy may be present, which should be documented before any regional anaesthesia techniques.
Medical conditions associated with diabetes: Hyperpituitarism, hyperthyroidism, hyperadrenalism, phaeochromocytoma, pancreatic a- cell tumour, obesity.
Concomitant drug therapy which could aggravate the diabetes: Corticosteroids, thiazide diuretics , oral contraceptive pills.
Preoperative Assessment of a Diabetic Patient
Many of the operations diabetic patients undergo are a direct result of their disease. Skin ulcers, amputations and abscesses are amongst the commonest. All except life-saving emergency surgery in the poorly controlled diabetic should be delayed until blood sugars are controlled. Badly controlled diabetics need to be admitted to hospital one or two days before surgery, if possible to allow their treatment to be stabilized.
The following investigations are necessary in a diabetic patient:
- Routine complete blood count: A raised WBC may suggest infection.
- Renal function tests: Serum creatinine may be raised indicating preexisting kidney damage (nephropathy).
- Serum electrolytes: Serum potassium may be raised (Normal: 3.5- 5 mEq/l), measures should be taken to lower it.
- Blood sugar: Fasting (Normal range: 55-85 mg/dl) and Post prandial (Normal range: < 180 mg/dl)
- Urine sugar and ketones: Urine ketones may be raised in patients with poor diabetic control.
- Chest X-ray
- ECG
Preoperative optimization includes;
- Stringent blood sugar control
- Treatment of any preoperative infection with appropriate antibiotics, which will also help in diabetic control
- Nebulisation with bronchodilators if wheeze present
- Good chest physiotherapy and incentive spirometry to be continued postoperatively so as to prevent any chest infections.
All medications should be continued up until surgery.
Perioperative Insulin Regime
Surgery causes a stress response which will change the patient’s insulin requirements. Treatment will need to be adjusted according to:
the extent/type of the surgery
Minor- patients who are expected to eat and drink within 4 hours of surgery
Major- all other patients whether the patient is insulin dependant (IDDM) or non-insulin dependant (NIDDM) the quality of their blood sugar control.: poorly controlled: delay surgery and change to soluble insulin but if surgery urgent, use Major surgery regime well controlled: use the appropriate regime from the Major or Minor regime
The aim is to keep the blood sugar level (random sugar) within the range 108 – 180 mg/dl at all times.
Minor Surgery regime: Table 2
Major surgery regime: Table 3
IDDM and NIDDM patients who are poorly controlled (blood sugar >180 mg/dl). NIDDM become insulin dependent during major surgery and will need to be managed as such (converted to insulin perioperatively, some even preoperatively if poorly controlled on oral hypoglycaemics)
Continue normal medication until day of operation
Regime 1 - If no infusion pump available.
Start intravenous infusion of 5 or10 % dextrose (500 ml bags) over 4 - 6 hours and add Insulin and Potassium Chloride (KCl) to each 500 ml bag as below. Change bag according to blood sugar level readings:-
Regime 2 - for use with infusion pumps (Sliding scale)
The insulin and dextrose infusions are given via separate infusion pumps. Allows better control than regime 1, but care is needed to ensure the separate lines do not become blocked, or that one infusion runs out leaving the other infusing alone.
Insulin infusion - 50 units insulin made up to 50 ml with saline (i.e. concentration is 1 unit per ml)
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If it is difficult to reduce the blood sugar level, then consider increasing the rate of insulin for each glucose level or also giving a bolus of Actrapid of 3 - 5 units.
Patients normally on higher doses of insulin will need higher rates of insulin infusion.
Dextrose infusion - 5 or 10% dextrose infused at 100 ml per hour. Add 10 mEq KCl to each 500 ml of solution.
Anaesthetic Management
Diabetic patients should be placed first on the operating list. This shortens the duration of preoperative fasting. Blood sugars should be well controlled (range of 108-180 mg/dl ) in all except life-saving emergency surgery.
Intraoperative monitoring: Routine perioperative monitoring ECG, pulse oximetry, capnography, blood pressure and heart rate. Other advanced monitoring as per individual patient requirement. If the patient is cold and sweaty, suspect hypoglycaemia, check the blood glucose and treat with intravenous glucose.
Premedication: should be given as usual
General Anaesthesia: If risk of gastric stasis (due to autonomic neuropathy) is suspected, rapid sequence intubation should be performed to secure the airway. The standard anaesthetic induction or inhalational agents may be used, but if the patient is dehydrated, sudden severe hypotension might occur and should be treated promptly with intravenous fluids.
IV induction agents should be administered slowly (giving a sleep dose) so as to prevent sudden hypotension which may be aggravated in diabetics with a damaged autonomic nervous system. They cannot compensate by vasoconstriction, and the hypotension is worsened. Reducing the dose of drug and giving it slowly helps to minimise this effect.
Ringers lactate should not be used in diabetic patients as the lactate it contains may be converted to glucose by the liver and cause hyperglycaemia. Sudden bradycardia or tachycardia may occur during the course of anaesthesia (in those with autonomic neuropathy). Bradycardia should respond to atropine 0.3mg iv, repeated as necessary (maximum 2 mg). Tachycardias, if not due to light anaesthesia or pain, may respond to gentle massage on one side of the neck over the carotid artery
Regional anaesthesia: Useful as it overcomes the problem of regurgitation, possible aspiration and of course difficult intubation. However, attention should be paid to avoid hypotension by ensuring adequate hydration. Any pre-existing nerve damage due to peripheral neuropathy should be documented prior to giving the block.
With a spinal or epidural anaesthesia, the patient may not be able to keep their blood pressure in a normal range due to damage to their autonomic nervous system. Ephedrine (6 mg boluses) should be used when the systolic pressure falls to 25% below normal.
Summary
A diabetic patient presents many challenges to the anaesthetist . Watching for the clinical signs of perioperative hypoglycaemia and rapid action to prevent the same should see them safely through their surgery. The goal is to keep things as normal as possible. Regional techniques are often safer than general anaesthesia, but require the same amount of care and vigilance.
References
1. Hirsch IB, McGill JB, Cryer PE, White PF. Perioperative management of surgical patients with diabetes mellitus. Anesthesiology 1991; 74 : 346-59.
2. Alberti KGMM. Diabetes and surgery. Anesthesiology 1991; 74 : 209-11.
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