Introduction		Major Surgery - Alternative Regime
Preoperative Assessment		Treatment of Diabetic Ketoacids
Anaesthetic Management		Anaesthetic Technique
Which Regime?		Summary
Minor Surgery		References
Major Surgery

Introduction

Diabetes is a condition where the cells of the body cannot metabolise 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.

There are two main types of diabetes (table 1) which classically affect different age groups. In reality there is a huge overlap between age groups.

Diabetes causes disease in 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) and nerves (neuropathy) throughout the body results in many pitfalls for the unwary anaesthetist. The following guidelines should help to identify these problems and cope with them. 

Preoperative assessment.

Specific problems arise:

Cardiovascular- diabetics are more prone to hypertension, ischaemic heart disease, cerebrovascular disease, myocardial infarction which may be silent and cardiomyopathy. Damage to the nerves controlling the heart and blood vessels (autonomic neuropathy) may result in sudden tachycardia, bradycardia or a tendency to postural hypotension. A history of shortness of breath, palpitations, ankle swelling, tiredness and of course chest pain should therefore be sought and a careful examination for heart failure (distended neck veins, ankle swelling, tender swollen liver, crackles heard on listening to the chest) made. A preoperative ECG should be performed. Heart failure is a very serious risk factor and must be improved before surgery with diuretics. Table 2 describes how to test clinically for autonomic neuropathy.

Renal - kidney damage may already be present, often indicated by the presence of protein (albumin) in the urine. Urine infections are common and should be treated aggressively with antibiotics. The diabetic is at risk of acute renal failure and retention postoperatively. Blood electrolyte measurement (if possible) may reveal a raised urea and creatinine. If the potassium is high (> 5 mmol/l) then specific measures should be taken to lower it before surgery.

Respiratory - diabetics, especially if obese and smokers, are particularly prone to chest infections. Chest physiotherapy pre and postoperatively are indicated, with nebulised oxygen and regular bronchodilators (salbutamol 2.5-5mg in 5ml saline) if wheeze is heard. A chest X-ray, blood gases and spirometry are the gold standard investigations, but careful repeated clinical assessment willusually reveal when a patient is as good as they are going to get. Non-emergency surgery should be delayed until this point.

Airway - thickening of soft tissues occurs eg ligaments around joints. If the neck is affected there may be difficulty extending the neck, making intubation difficult. To test if the patient is at risk, ask them to bring their hands together as in praying. If they cannot have the fingers of each hand flat against the other hand, then they probably have ligament thickening of the finger joints, and difficult intubation should also be anticipated.

Gastrointestinal - the nerves to the gut wall and sphincters can be damaged. Delayed gastric emptying and increased reflux of acid make them more prone to regurgitation and at risk of aspiration on induction of anaesthesia. A history should be sought of heartburn and acid reflux when lying flat; if present they should have a rapid sequence induction with cricoid pressure, even for elective procedures. If available, prescribe an H2 antagonist and metoclopramide as a premedication. Ranitidine 150mg or cimetidine 400mg plus metoclopramide 10mg orally 2 hours preoperatively to reduce the volume of stomach acid.

Eyes - cataracts are common, as is an abnormal growth of blood vessels inside the eye (retinopathy). The anaesthetist should try to prevent sudden rises in blood pressure that might rupture them, further damaging the eyesight. Ensure an adequate depth of anaesthesia, especially at induction.

Infection - diabetics are prone to getting infections that can upset their sugar control. If possible, delay surgery until these are treated. Wound infections are common. Great care should be paid to aseptic techniques when any procedure is undertaken.

Miscellaneous - diabetes may be caused or worsened by treatment with corticosteroids, thiazide diuretics and the contraceptive pill. Thyroid disease, obesity, pregnancy and even stress can affect diabetic control.

Blood and urine glucose monitoring - meter analysis (most accurate) or reagent strips (which employ a visual colour comparison with a pre-printed chart) are commonly available. It is vital that the instructions are properly followed for whatever method is used. Out-of-date strips will give an inaccurate reading. If strips are cut in half for economy (not recommended), then the unused portion must be carefully stored in a dry place. When using meters, ensure that the testing strips are properly matched for the meter. Remember, false readings could lead to the wrong, even life threatening treatment being given. Strips or tablets can also be used to test the urine for glucose or ketones. The same precautions apply. 

Anaesthetic management:

Many of the operations diabetic patients face are a direct result of their disease. Skin ulcers, amputations and abscesses are amongst the commonest.

Preoperative assessment-

Timing - diabetic patients should be placed first on the operating list. This shortens their preoperative fast. Badly controlled diabetics need to be admitted to hospital one or two days before surgery if possible to allow their treatment to be stabilised.

Hydration - Glucose in the urine (glycosuria) causes a diuresis which makes the patient dehydrated and even more susceptible to hypotension. Check for dehydration (Table 3) and start an intravenous infusion.

Table 3: Clinical signs of dehydration
Sign	Water loss (% body weight)
Thirst Dry mouth	< 5 %
Capillary refill > 2 seconds * Decreased skin turgor * Orthostatic hypotension * Low intraocular pressure (soft eyes) Reduced urine output Low CVP/JVP	5 - 10 %
Shock Unconscious	> 10 %
* Capillary refill - lift limb above level of heart, press on skin for 5 seconds, release and observe colour returning to area. Normal is < 2 seconds. Skin turgor - pinch skin on back of hand and release. Normally the fold of skin quickly falls back flat but if dehydrated stays folded or returns slowly. Orthostatic hypotension - a severe fall in BP when patient stands up causing fainting.

Medication - all medications should be continued up until surgery. Surgery causes a stress response which will change the patient's insulin requirements. Treatment will need to be adjusted according to:

• the extent of the anticipated surgery
• whether the patient is insulin dependant (IDDM) or non-insulin dependant (NIDDM)
• the quality of their blood sugar control.

In general, if the patient can be expected to eat and drink within 4 hours of surgery, then it is classified as MINOR. All surgery other than minor is classified as MAJOR. Figures 1-4 give regimes for major and minor surgery and for NIDDM and IDDM.

The aim is to keep the blood glucose level within the range 6 -10 mmol/l at all times.

Special problems.

Low Blood Sugar (hypoglycaemia)-

The main danger to diabetics is low blood sugar levels (blood glucose < 4mmol/l). Fasting, alcohol, liver failure, septicaemia and malaria can cause this. The characteristic signs and symptoms of early hypoglycaemia are tachycardia, light-headedness, sweating and pallor. If hypoglycaemia persists or gets worse then confusion, restlessness, incomprehensible speech, double vision, convulsions and coma will ensue. If untreated, permanent brain damage will occur, made worse by hypotension and hypoxia.

Anaesthetised patients may not show any of these signs. The anaesthetist must therefore monitor the blood sugar regularly if possible, and be very suspicious of any unexplained changes in the patient's condition. If in doubt, regard them as indicating hypoglycaemia and treat.

Treatment - diabetic patients learn to recognise the early signs and often carry glucose with them to take orally. If unconscious, 50ml of 50% glucose (or any glucose solution available) given intravenously and repeated as necessary is the treatment of choice. If no sugar is available, 1mg of glucagon intramuscularly will help.

High Blood Sugar (hyperglycaemia)-

This is defined as a fasting blood sugar level > 6 mmol/l. It is a common problem found in many conditions other than diabetes eg - pancreatitis, sepsis, thiazide diuretic therapy, ether administration, glucose infusions, parenteral nutrition administration and most importantly, any cause of stress such as surgery, burns or trauma. Slightly elevated levels are thus commonly found after routine major surgery. It is usual to treat this only if the level is above 10 mmol/l. At this level, sugar is present in the urine and causes a diuresis which may result in dehydration, loss of potassium (hypokalaemia) and sodium (hyponatraemia) ions. The blood thickens and this may cause clotting problems such as thrombosis, and could precipitate a crisis in a patient with sickle cell disease.

Assess the patient, rehydrate them and delay surgery if necessary. Remember the aim is a sugar level of 6-10 mmol/l. If the sugar is below 10 mmol/l, observe and recheck it hourly throughout the operation. Should it be above 10 mmol/l, then follow the regimes in figures 1-4, according to the extent of the surgery planned.

After surgery, the insulin requirements fall as the stress response subsides. Newly diagnosed diabetics need further investigation to establish whether they will need insulin therapy, oral hypoglycaemics or indeed just diet control.

Sometimes when the blood sugar has become very high, the patient becomes comatose (diabetic coma). It is vital to correct this by adhering to the general guidelines and regimes already mentioned. Aim to reduce the sugar levels to below 10 mmol/l. When this has happened over a few days, the body uses its own fat to produce energy, and this results in high levels of waste products (ketones) in the blood and urine - this is called diabetic ketoacidiosis and is a medical emergency with a significant mortality.

Diabetic ketoacidosis

This may be triggered by infections or other illnesses such as bowel perforations and myocardial infarction. The patient will be drowsy or even unconscious with fast, deep breathing due to acid in the blood. The ketones make their breath smell sweetly, like acetone. Ketones can also be detected by the use of urine and blood testing strips.

Diarrhoea, vomiting, gastric dilatation (insert a nasogastric tube) or even severe abdominal pain may be present which can be misinterpreted as an acute surgical problem! As severe dehydration is usually present, surgery must be delayed until fluid resuscitation has commenced in order to avoid disastrous hypotension with induction agents. A urinary catheter will help monitor fluid balance, and an ECG and CVP line (to estimate the fluid deficit) are helpful. The aim is to slowly return the body chemistry to normal.

Give high flow oxygen therapy.

Although the blood potassium level is usually high, the body has actually lost large amounts in the urine, and extra potassium is required intravenously. It is important to lower the blood sugar level slowly, as reducing it too fast can result in further complications such as brain oedema and convulsions. Search for infections (chest X-ray, blood and urine cultures) and treat with antibiotics. Blood gases and electrolyte measurements may also help management. figure 5 gives a regime for treatment. 

(Continued ...)

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