Summary

In study session VII you have learnt

• The thyroid gland, located immediately below the larynx on each side of and anterior to the trachea, secretes and store two major hormones, thyroxin and triiodothyronine, to increase the metabolic rate of the body.
• Hyperthyroidism results from excess circulating T3 and T4. The vast majority of cases are caused by intrinsic thyroid disease.
• The major manifestations of hyperthyroidism are weight loss; diarrhea; skeletal muscle weakness and stiffness; warm, moist skin; heat intolerance; and nervousness. The diagnosis of hyperthyroidism is confirmed by abnormal thyroid function tests, which may include an elevation in total serum T4 and serum T3.
• Medical treatment of hyperthyroidism relies on drugs that inhibit hormone synthesis, prevent hormone release, or mask the signs of adrenergic over activity. Radioactive iodine destroys thyroid cell function. Subtotal thyroidectomy is an alternative to medical therapy.
• Thyroid storm is a life-threatening exacerbation of hyperthyroidism that most commonly develops in the undiagnosed or untreated hyperthyroid patient because of the stress of surgery or non thyroid illness.
• All elective surgical procedures, including subtotal thyroidectomy, should be postponed until the patient is rendered clinically and chemically euthyroid with medical treatment.
• Preoperative assessment should include normal thyroid function tests, and a resting heart rate less than 85 beats/min has been recommended.
• In hyperthyroid patient, thiopental may be the induction agent of choice as it possesses some antithyroid activity at high doses.
• Postoperative considerations include hemorrhage, laryngeal edema, recurrent laryngeal nerve palsy, hypocalcaemia, tracheomalacia and thyroid Storm which requires immediate management
• Hypothyroidism is under secretion of thyroid hormones. Manifestation includes cretinism in children or physical and mental retardation. Clinical manifestations in the adult are from a generalized reduction in metabolic activity, resulting in lethargy, slow mental functioning, cold intolerance, and slow movements. These patients exhibit bradycardia, decreased cardiac output, and increased peripheral resistance.
• The treatment of hypothyroidism consists of oral replacement therapy with a thyroid hormone preparation, which takes several days to produce a physiological effect and several weeks to evoke clear-cut clinical improvement.
• Myxedema coma represents a severe form of hypothyroidism characterized by stupor or coma, hypoventilation, hypothermia, hypotension, and hyponatremia. This is a medical emergency, requires aggressive therapy.
• Thyroid replacement therapy is, however, indicated for patients with severe hypothyroidism or myxedema coma and for pregnant patients who are hypothyroid. Untreated hypothyroidism in pregnant patients is associated with an increased incidence of spontaneous abortion and mental and physical abnormalities in the offspring.
• Hypothyroid patients usually do not require much preoperative sedation and are very prone to drug induced respiratory depression.
• Consideration should be given to premedicating these patients with histamine H2 antagonists (ranitidine) and metoclopramide because of their decreased gastric-emptying times.
• Hypothyroid patients are more susceptible to the hypotensive effect of anesthetic agents. Ketamine is often recommended for induction of anesthesia.