Intraoperative Anesthetic Management

Intraoperative Monitoring

Available monitor including ECG, pulse oximeter, blood pressure, urine output, thermometer and serial measurement of blood glucose should be ready and applied. Stress of general anesthesia, pain and light anesthesia induce hyperglycemia. Record blood pressure and pulse every 5 minutes during the operation, and watch skin color and temperature. If the patient is cold and sweaty, then suspect hypoglycemia, check the blood glucose and treat with intravenous glucose. Monitor patient's blood sugar every 30-60 min.using glucometer. Treat as hypoglycemia if Glucose < 50 mg/dL in adult and Glucose < 40 mg/dL in child.

Another area of patient monitoring that is extremely important in the diabetic patient is positioning on the operating table. Injuries to the limbs or nerves are more likely in the patient who arrives in the operating room already compromised by diabetic peripheral vascular disease or neuropathy. The peripheral nerves may already be partly ischemic and therefore particularly vulnerable to pressure or stretch injuries.

General Anesthesia

Diabetic patients are considered as a full stomach then a rapid sequence induction should be used. A nasogastric tube can be used to empty the stomach and allow a safer awakening. There are no contraindications to standard anesthetic induction or inhalational agents, but if the patient is dehydrated then hypotension will occur and should be treated promptly with intravenous fluids. Hartmann's solution (Ringers lactate) should not be used in diabetic patients as the lactate it contains may be converted to glucose by the liver and cause hyperglycemia.

Sudden bradycardia should respond to atropine 0.3mg iv, repeated as necessary (maximum 2 mg). Tachycardia, if not due to light anesthesia or pain, may respond to gentle massage on one side of the neck over the carotid artery. If not then consider a beta-blocker (propranolol 1mg increments: max 10mg total or labetalol 5mg increments).

IV induction agents normally cause hypotension on injection due to vasodilatation. If a patient has a damaged autonomic nervous system (and many diabetics do), then they cannot compensate by vasoconstricting, and the hypotension is worsened. Reducing the dose of drug and giving it slowly helps to minimize this effect.

Anesthetic agents and diabetes: Induction agents may affect glucose homeostasis perioperatively.

  • Etomidate decreases the hyperglycemic response to surgery is a preferred induction agent. Thiopentone is preferred than ketamine. Ketamine induce sympathetic stimulation and cause hyperglycemia.
  • Benzodiazepines decrease the production of cortisol, when used in high doses during surgery. Opioid anesthetic techniques maintain metabolic stability.
  • Halothane, enflurane and isoflurane may inhibit the insulin response to glucose in a reversible and dose-dependent manner.
Regional Techniques

are useful because they get over the problem of regurgitation, possible aspiration and of course difficult intubation. Blood glucose is better maintained in regional anesthesia. However, the same attention should be paid to avoiding hypotension by ensuring adequate hydration. It is a wise precaution to chart any pre-existing nerve damage before your block is inserted. With spinals, autonomic nerve damage means the patient may not be able to keep their blood pressure in a normal range. Intervene early with ephedrine (6mg boluses) when the systolic pressure falls to 25% below normal.

Emergency Problems of Diabetic Mellitus

Hypoglycemia

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

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

Treatment - diabetic patients learn to recognize 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.

Hyperglycemia

Hyperglycemia is a high Blood Sugar. 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, 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 hyperglycemia 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 (hypokalemia) and sodium (hyponatremia) ions. The blood thickens and this may cause clotting problems such as thrombosis. 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 hypoglycemic 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 these results in high levels of waste products (ketones) in the blood and urine - this is called diabetic ketoacidosis and is a medical emergency with a significant mortality.

Diabetic Ketoacidosis

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

Treatment of ketoacidosis

  • Regular insulin 10 U IV bolus followed by an insulin infusion nominally at (blood glucose/150) U/hr
  • Isotonic IV fluids as guided by vital signs and urine output; anticipate 4-10 L deficit
  • When urine output is >0.5 mL/kg/hr, give potassium chloride 10-40 mEq/hr (with continuous ECG monitoring when the rate is greater than 10 mEq/hr)
  • When serum glucose decreased to 250 mg/dL, add dextrose 5% at 100 mL/hr
  • Consider sodium bicarbonate to correct pH < 6.9
Last modified: Sunday, 20 November 2016, 3:47 PM