Diabetes Mellitus
Intraoperative: Keep blood sugar below 180 mg/dL but avoid hypoglycemia as well. Hyperglycemia increases the risk of infection, risk of poor wound healing, and mortality. For common perioperative management of patients with insulin-dependent diabetes with either bolus technique or continuous infusion. One unit of regular insulin lowers plasma glucose by 25 to 30 mg/dL. If using oral hypoglycemic agents preoperatively, continue until day of surgery. Sulfonylureas and metformin should be discontinued 24 to 48 hours preoperatively. Patients may need insulin perioperatively because of stress hyperglycemia. Monitor blood sugar every hour if the patient is on insulin infusion or has type 1 diabetes (every 2–3 hours for type 2 diabetes). Patients on NPH have increased risk of allergic reaction to protamine sulfate.
Two Common Techniques for Perioperative Insulin Management in Diabetes Mellitus
Postoperative: Continue to monitor blood sugar closely because of variations in onset and duration of insulin preparations. Also monitor for stress hyperglycemia.
Complications: Hypertension, coronary artery disease, peripheral and cerebrovascular disease, peripheral and autonomic neuropathies; life-threatening risks of diabetic ketoacidosis (DKA), hyperosmolar nonketotic coma, and hypoglycemia
1. DKA: Anion-gap metabolic acidosis caused by ketone bodies often precipitated by infection. Clinical manifestations: Tachypnea, abdominal pain, nausea and vomiting, mental status change. Treatment: Correct hypovolemia, hyperglycemia, and total body potassium deficit. Decrease blood glucose 75 to 100 mg/dL/hr with insulin infusion. Add D5W when plasma glucose is 250 mg/dL to avoid hypoglycemia. Monitor potassium frequently because of risk for hypokalemia.
2. Hyperosmolar nonketotic coma: Hyperglycemia-induced diuresis leads to dehydration and hyperosmolality (>360 mOsm/L). May cause renal failure, lactic acidosis, and factitious hyponatremia. Clinical manifestations: Change in mental status and seizures. Treatment: Normal saline, relatively small insulin doses, potassium supplementation.
3. Hypoglycemia: Excess insulin relative to carbohydrate intake (plasma glucose <50 mg/dL). Clinical manifestations: diaphoresis, tachycardia, anxiety, lightheadedness, confusions, convulsions, coma. Treatment: Intravenous (IV) 50% glucose in anesthetized or critically ill patients. Oral glucose liquid in awake patients.
Hypothyroidism
Causes: Autoimmune disease (Hashimoto thyroiditis), thyroidectomy, radioactive iodine, antithyroid medications, iodine deficiency, or failure of hypothalamic-pituitary axis. Clinical manifestations: During neonatal development, congenital hypothyroidism is associated with physical and mental retardation. In adults, symptoms include infertility, weight gain, cold intolerance, muscle fatigue, lethargy, constipation, hypoactive reflexes, and depression as well as decreased myocardial contractility, stroke volume, and cardiac output. Extremities are cool and mottled. Pleural, pericardial, abdominal effusions are common. Diagnosis: Low free thyroxine (T4). Primary hypothyroidism is differentiated from secondary disease by elevated thyroid-stimulating hormone (TSH). Euthyroid sick syndrome with normal TSH and low triiodothyronine (T3) is seen in critical illness. Treatment: Oral replacement therapy.
Myxedema coma: Extreme hypothyroidism precipitated by infection, surgery, or trauma. Characterized by impaired mentation, hypoventilation, hypothermia, hyponatremia, and congestive heart failure. Treatment includes IV T3 and steroid replacement (hydrocortisone 100 mg IV every 8 hr) plus ventilatory support and warming if needed.
Preoperative management: Patients with uncorrected severe hypothyroidism or myxedema coma should not have elective surgery. Treat these patients with IV T3, before emergency surgery. Mild to moderate hypothyroidism is not an absolute contraindication to surgery. Use minimal preoperative sedation because these patients are prone to drug-induced respiratory depression. Continue thyroid medication on the morning of surgery, but missing one dose will have little consequence because of the long half-lives of these drugs.
Intraoperative management: Decreased cardiac output, blunted baroreceptor reflexes, and hypovolemia lead to hypotension with anesthetic agents. Consider adrenal insufficiency if the patient has refractory hypotension. Other coexisting conditions include hypoglycemia, anemia, hyponatremia, a large tongue causing difficult intubation, and hypothermia.
Postoperative management: Delayed recovery because of hypothermia, respiratory depression, and slow drug biotransformation. A multimodal pain management approach recommended to decrease opioid requirements and thus respiratory depression.
Hyperthyroidism
Clinical manifestations: Weight loss, heat intolerance, muscle weakness, diarrhea, hyperactive reflexes, and nervousness. Cardiac signs include new-onset atrial fibrillation, sinus tachycardia, and congestive heart failure.
Treatment: Propylthiouracil and methimazole (inhibit thyroid hormone synthesis), potassium and sodium iodide (prevent hormone release), and beta blockers (mask adrenergic overactivity). Propranolol decreases peripheral conversion of T4 to T3. Radioactive iodine destroys thyroid cell function.
Preoperative management: Elective procedures postponed until patient is euthyroid. Continue antithyroid medications and beta blockers through the morning of surgery. Use esmolol infusion to control hyperdynamic circulation in setting of emergency surgery.
Intraoperative management: Monitor cardiovascular function and temperature. Exophthalmos increases risk of corneal abrasion. Avoid drugs that stimulate the sympathetic nervous system. Incompletely treated hyper-thyroid patients may be hypovolemic and prone to hypotensive response to induction. Caution with neuromuscular blockers in patients with thyrotoxicosis as there is increased risk of myopathies and myasthenia gravis.
Postoperative management: Thyroid storm (hyperpyrexia, tachycardia, and altered consciousness) usually occurs 6–24 hours after surgery. Treat with hydration, cooling, IV beta blocker, propylthiouracil, then sodium iodide. Cortisol is used to prevent complications from adrenal gland suppression. Thyroidectomy complications include recurrent laryngeal nerve palsy, hematoma formation causing airway compromise, and hypocalcemia (in 12–72 hours) due to unintentional parathyroid gland removal.
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