5.3 Anesthetic management of diabetic patients: 

Many of the operations diabetic patients face are a direct result of their disease. Skin ulcers, amputations and abscesses are amongst the commonest. Successful management of the diabetic patient depends as much, if not more, on the proper management of the chronic complications of the disease as on acute glycemic management. 

5.3.1 Preoperative anesthetic management: 

A thorough preoperative search must be done for end-organ complications of diabetes mellitus. In addition to a thorough history and physical, a recent ECG, blood urea nitrogen, potassium, creatinine, glucose, and urinalysis are essential. 

5.3.1.1 Anesthetic consideration of symptoms of secondary involvement of other organs: 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. 

• Heart disease: diabetics are more prone to hypertension, ischemic heart disease, cerebrovascular disease and silent myocardial infarction. Damage to the nerves controlling the heart and blood vessels (autonomic neuropathy) may result in sudden tachycardia, bradycardia or a tendency to postural hypotension. Diabetic autonomic neuropathy may limit the heart's ability to compensate for intravascular volume changes and may predispose patients to cardiovascular instability (eg, post induction hypotension) and even sudden cardiac death, the incidence of which may be increased by the concomitant use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. A history of shortness of breath, palpitations, ankle swelling, tiredness and chest pain should therefore be sought. A routine ECG and stress testing should be done. 
• Renal disease: kidney damage may already be present, often indicated by the presence of protein (albumin) in the urine. Renal infections are common and should be treated aggressively with antibiotics. The diabetic is at risk of acute renal failure postoperatively. Blood electrolyte measurement (if possible) may reveal a raised urea and creatinine. If the potassium is high (> 5 mEql/l) then specific measures should be taken to lower it before surgery. 
• Gastrointestinal problems: 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 anesthesia. 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. Ranitidine 150mg or cimetidine 400mg plus metoclopramide 10mg orally 2 hours preoperatively to reduce the volume of stomach acid. 
• Airway: Glycosylation of collagen in the cervical and temporo-mandibular joints can cause difficulty in intubation (Fig5.1). 

• Eye disease: cataracts are common, as is an abnormal growth of blood vessels inside the eye (retinopathy). The anesthetist should try to prevent sudden rises in blood pressure that might rupture them, further damaging the eyesight. Ensure an adequate depth of anesthesia, 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 
• Hydration - Glucose in the urine (glycosuria) causes a diuresis which makes the patient dehydrated and even more susceptible to hypotension. Check for dehydration and start an intravenous infusion. 
• 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. 

5.3.2: plan ahead for blood glucose control perioperatively: 

The primary goal of intraoperative blood sugar management is to avoid hypoglycemia. Unacceptably loose blood sugar control (> 180 mg/dL) also carries risk. Hyperglycemia has been associated with hyperosmolarity (dehydration), infection, and poor wound healing. There are several perioperative management regimens for diabetic patients. 

5.3.2.1 Alternative regimen 1: In the most common, the patient receives a fraction usually half of the total morning insulin dose in the form of intermediate-acting insulin. To decrease the risk of hypoglycemia, insulin is administered after intravenous access has been established and the morning blood glucose level is checked. For example, a patient who normally takes 30 U of NPH (neutral protamine Hagedorn; intermediate-acting) insulin and 10 U of regular or Lispro (short-acting) insulin or insulin analogue each morning and whose blood sugar is at least 150 mg/dL would receive 15 U (half of 30, half the normal morning dose) of NPH subcutaneously or intramuscularly before surgery along with an infusion of 5% dextrose solution (1.5 mL/kg/h). Absorption of subcutaneous or intramuscular insulin depends on tissue blood flow 

Dedication of a small-gauge intravenous line for the dextrose infusion prevents interference with other intraoperative fluids and drugs. Supplemental dextrose can be administered if the patient becomes hypoglycemic (< 100 mg/dL). However, intraoperative hyperglycemia (> 150–180 mg/dL) is treated with intravenous regular insulin according to a sliding scale. One unit of regular insulin given to an adult usually lowers plasma glucose by 25–30 mg/dL. 

5.3.2.2 Alternative regimen 2 

Steps to select appropriate management regime 

1. Decide on the type of surgery 

• Minor - patients expected to eat and drink within 4 hours of operation (Table5.3) 
• Major - all other patients (Table5.4) 

2. Then, is the patient insulin or non-insulin dependent? 

3. Finally : 

• Are they -poorly controlled: delay surgery and change to soluble insulin three times daily but if surgery urgent, use Major surgery regime 
• Well controlled: use the appropriate regime from the Major or minor 

General Measures for all diabetics: Measure random sugar preoperatively - 4 hourly for IDDM & 8 hourly for NIDDM 

• Test urine 8 hourly for ketone and sugar 
• Place first on operating list 
• Aim for a blood glucose of 6 - 10mmol/l(120-140mg/dl) 

If the patient is taking an oral hypoglycemic agent preoperatively instead of insulin, the drug can be continued until the day of surgery, but sulfonylureas and metformin should not be used for 24–48 h before surgery because of their long half-lives. They can be started postoperatively when the patient is taking drugs per os. Metformin is restarted if renal and hepatic functions remain adequate. Because of the long duration of action, a glucose infusion is begun and blood sugars are monitored as though intermediate-acting insulin had been given.