The thyroid is located below the larynx and anterior to the trachea (see Figure 4.3). The thyroid gland produces two iodine-dependent hormones: thyroxine (T4) and triiodothyronine (T3). A third hormone known as thyrocalcitonin (calcitonin) is produced by the C cells of the thyroid gland in response to calcium levels. The C cell makes calcitonin that helps to regulate calcium levels in the blood. These hormones play a role in regulating the metabolic processes controlling the rate of growth, oxygen consumption, contractility of the heart, and calcium absorption.
FIGURE 4.3 Thyroid and parathyroid glands.
Hypothyroidism occurs when thyroid hormone production is inadequate. The thyroid gland often enlarges to compensate for a lack of thyroid hormone, resulting in a goiter. Another cause for development of a goiter is a lack of iodine in the diet. Other causes of primary hypothyroidism include genetic defects that prevent the metabolism of iodine. In the infant, this is known as cretinism. Other causes include eating a diet high in goitrogens, such as turnips, cabbage, spinach, and radishes, or taking the medications lithium, phenylbutazone, and para-aminosalicylic acid. Secondary hypothyroidism, known as myxedema, is the result of a lack of pituitary production of thyroid-stimulating hormone.
Signs and symptoms of hypothyroidism in the adult are as follows:
- Fatigue and lethargy
- Decreased body temperature
- Decreased pulse rate
- Decreased blood pressure
- Weight gain
- Edema of hands and feet
- Hair loss
- Thickening of the skin
In severe cases, myxedema coma can occur. Symptoms of myxedema include coma, hypotension, hypothermia, respiratory failure, hyponatremia, and hypoglycemia. Myxedema coma can be brought on by withdrawal of thyroid medication, anesthesia, use of sedatives, narcotics, surgery, or hypothermia.
Signs and Symptoms of Hypothyroidism in the Infant
As mentioned earlier, hypothyroidism in an infant is called cretinism. The following list gives you the signs and symptoms of cretinism:
- Decreased respirations
- Changes in skin color (jaundice or cyanosis)
- Poor feeding
- Hoarse cry
- Mental retardation in those not detected or improperly treated
Diagnostic studies for cretinism include evaluation of T3 and T4 levels using test doses of thyroid-stimulating hormone.
Management of the client with hypothyroidism includes the replacement of thyroid hormone, usually in the form of synthetic thyroid hormone levothyroxine sodium (Synthroid). Clients should be instructed to take Synthroid in the morning one hour prior to meals with water only because food can alter absorption. Soy products should be limited because soy can also alter absorption. The client’s history should include other drugs the client is taking. Prior to administering thyroid medications, the pulse rate should be evaluated. If the pulse rate is above 100 in the adult or 120 in the infant, the physician should be notified. The client requires a warm environment due to alteration in metabolic rate affecting temperature. Another problem associated with a slower metabolic rate is constipation. A high-fiber diet is recommended to prevent constipation. Treatment of myxedema coma includes treatment of hypotension, glucose regulation, and administration of corticosteroids.
Hyperthyroidism or thyrotoxicosis is caused by excessive thyroid hormone. Because the thyroid gland is responsible for metabolism, the client with hyperthyroidism often experiences increased heart rate, increased stoke volume, weight loss, and nervousness. The cause of hyperthyroidism is multifactorial. Some of these causes are autoimmune stimulation such as Graves’ disease, hypersecretion of thyroid-stimulating hormone (TSH), thyroiditis, or neoplasms of the thyroid gland.
Graves’ disease results from an increased production of thyroid hormone. The most common cause of hyperthyroidism is hyperplasia of the thyroid, commonly referred to as a toxic diffuse goiter.
Signs and symptoms of hyperthyroidism include
- Increased heart rate and pulse pressure
- Tremors or nervousness
- Moist skin and sweating
- Increased activity
- Atrial fibrillation
- Increased appetite and weight loss
A thyroid storm is an abrupt onset of symptoms of hyperthyroidism due to Graves’ disease, inadequate treatment of hyperthyroidism, trauma, infection, surgery, pulmonary embolus, diabetic acidosis, emotional upset, or toxemia of pregnancy. Fever, tachycardia, hypertension, tremors, agitation, anxiety, and gastrointestinal upset occur. The treatment for a thyroid storm includes maintenance of a patent airway and medication to treat hypertensive crises. Propylthiouracil (PTU) and methimazole (Tapazole) are two antithyroid drugs used to treat thyroid storm. These drugs work by blocking the synthesis and secretion of thyroid hormone. Soluble solution of potassium iodine (SSKI) or Lugol’s solution can be given to stop the release of thyroid hormone already in the gland. This drug can also be given prior to thyroid surgery to prevent a thyroid storm. The client should be taught to take the medication with a fruit juice high in ascorbic acid, such as orange or tomato juice, to increase the absorption of the medication and mask the taste. Taking the medication through a straw can also increase the palatability of the medication. Propranolol (Inderal) or other beta-blocking agents can be given to slow the heart rate and decrease the blood pressure. If fever is present, the client can be treated with a nonaspirin medication such as acetaminophen (Tylenol) or ibuprofen.
Diagnosis of hyperthyroidism involves the evaluation of T3 and T4 levels and a thyroid scan with or without contrast media. These thyroid function studies tell the physician whether the client has an adequate amount of circulating thyroid hormone. A thyroid scan can clarify the presence of an enlargement of tumor of the thyroid gland.
Management of the client with hyperthyroidism includes
- The use of antithyroid drugs (propylthiouracil or Tapazole)
- Radioactive iodine, which can be used to test and destroy portions of the gland
- Surgical removal of a portion of the gland
Prior to thyroid surgery, the client is given Lugol’s solution (SSKI)—an iodine preparation—to decrease the vascularity of the gland. Postoperatively, the client should be carefully assessed for the following:
- Edema and swelling of the airway (the surgical incision is located at the base of the neck anterior to the trachea).
- Bleeding (check for bleeding behind the neck).
- Tetany, nervousness, and irritability (complications resulting from damage to the parathyroid). Calcium gluconate should be kept available to treat hypocalcemia.
Because the thyroid gland is located anterior to the trachea, any surgery in this area might result in swelling of the trachea. For that reason, it is imperative that the nurse be prepared for laryngeal swelling and occlusion of the airway. The nurse should keep a tracheostomy set at the bedside and call the doctor if the client has changes in her voice or signs of laryngeal stridor. The nurse should instruct the client to keep her head and neck as straight as possible. Vital signs should be monitored, and the client should be evaluated for signs of hypoparathyroidism. Those signs include tingling around the mouth. The nurse should check for hypocalcemia by checking Chvostek’s sign. This is elicited when cranial nerves 7 and 5 are stimulated and result in facial grimacing when the cheek is tapped with the examiner’s finger. Trousseau’s sign is also an indication of hypocalcemia and is elicited by placing a blood pressure cuff on the arm and watching for carpopedal spasms. Refer to Figures 2.4 and 2.5 in Chapter 2, “Fluid and Electrolyte and Acid/Base Balance,” for more information about Chvostek’s sign and Trousseau’s sign.