Page 1420 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 103: Thyroid Disease 993

lithium level of 0.7 to 1.4 mEq/L. Caution should be exercised in patients Other analogs of thyroid hormone with reduced thyromimetic activity,
over 60 years of age. This drug acts by blocking iodide uptake and which nevertheless compete with thyroid hormone at its site of action,
hormone release by the thyroid gland. Sodium or potassium perchlorate deserve theoretical consideration. The activity of 5′-deiodinase is
67
(ClO ) competes with iodide for uptake by the thyroid gland, ultimately regulated by the concentration of T , as well as by catecholamines and
4
4
reducing the production of T . These compounds are not readily avail- other factors. PTU, glucocorticoids, propranolol, oral cholecystographic
4
able in the United States. Serious side effects, including aplastic anemia agents, and amiodarone also reduce the activity of this enzyme and thus
and nephrotic syndrome, occur rarely. decrease the generation of T , resulting in reduction of serum T con-
3
3
Successful reduction of the serum concentration of thyroid hormones centration. Severe acute or chronic nonthyroidal illness also suppresses
by means of plasma exchange has been reported in less than 100 patients. T generation in peripheral tissues.
63
3
Although there are no standard recommendations as to when to start β-Blockers, which are useful in the preparation of thyrotoxic patients
plasma exchange, most agree this should be reserved for the severely symp- for surgery, should be used with caution in thyroid storm. Whereas
tomatic patients. It may be effective in hyperthyroidism due to autoim- surgical stress clearly is related to increased catecholamine levels, and
mune causes as well as amiodarone-induced hyperthyroidism and during thyroid storm can be prevented by the use of propranolol, it is unclear
a molar pregnancy. Plasma exchange is done by ultrafiltration with dialysis whether thyroid storm induced by other mechanisms is equally respon-
and central venous access. The replacement solution is generally albumin. sive to β-blockers. However, when there is evidence of increased adren-
The range of exchanges performed was 1 to 6 per patient with a median ergic activity short of thyroid storm (ie, no evidence of hyperpyrexia or
volume of approximately 3 L replaced per patient. Filtration through a mental status changes), 1 mg propranolol can be administered by slow
63
resin bed that removes T and T has been used occasionally. Intravenous intravenous push every 5 minutes until an effect on pulse rate is seen.
64
3
4
administration of thyroxine-binding globulin has been shown experimen- Usually a total daily dose of 300 to 400 mg oral propranolol is required to
tally to decrease the transfer of thyroid hormone from blood to tissues. 65 achieve effective β blockade in the severely thyrotoxic patient. It appears
that younger patients are more susceptible to hyperadrenergic states
Prevention of Systemic Decompensation: Reduction of the body tem- with more labile courses and do better with β-blockers. By contrast,
24
perature decreases the demands on the cardiovascular system. Body elderly patients may present with “apathetic” thyrotoxicosis without
temperature can be reduced by cooling and by pharmacologic blockade elevation in body temperature and without severe tachycardia. These
of the thermoregulatory centers. Use of a cooling blanket and ice packs elderly patients more often experience cardiotoxic effects in response
alone will induce shivering; treatment with chlorpromazine, 25 to 50 mg, to β-blockers. Therefore, β-blockers should be used with caution
and meperidine, 25 to 50 mg, intravenously every 4 to 6 hours will in thyroid storm and in severe thyrotoxicosis, except in the elderly, in
decrease the severe shivering and limit further heat generation. 24 asthmatics, and in patients with evidence of dilated cardiomyopathy.
Patients in thyroid storm lose excessive amounts of fluid because of Cardioselective β-blockers such as metoprolol or atenolol can be used
(1) increased insensible water loss associated with hyperthermia and with caution in patients with asthma or COPD. When surgery is indi-
tachypnea, (2) decreased levels of antidiuretic hormone, and (3) vomiting cated in such patients, careful titration of the adverse adrenergic cardio-
and diarrhea associated with increased intestinal motility. Thus patients vascular effects (tachycardia, large pulse pressure) can be implemented
may present with either high- or low-output congestive heart failure. with shorter-duration β-blockers (esmolol) preceded by maximal bron-
Solutions containing crystalloid (for volume replacement) and dextrose chodilator therapy in asthmatic patients or right-sided heart catheteriza-
(to replenish hepatic glycogen stores and minimize the breakdown tion in elderly patients and those with prior heart failure.
of body protein) are used. Treatment with high doses of propranolol,
as discussed below, can make it necessary to use 5% to 10% dextrose Treatment of Precipitating Events: Without an antecedent history of
solutions. Multivitamins often are administered to replenish the surgery, any patient with thyroid storm should be suspected of being
B-complex vitamins. septic until proven otherwise. Blood, urine, and other body secretions
Treatment of congestive heart failure usually is supportive. While (ie, ascites or pleural fluid and sputum) should be Gram stained and
reduction of the high body temperature should be attempted before cultured. Empirical use of broad-spectrum antibiotics is recommended.
specific treatment is instituted, the judicious use of inotropic agents In a seriously ill patient in whom an infection or other precipitating
and diuretics should also be considered. Since patients are often volume cause, such as diabetic ketoacidosis, cannot be identified, pulmonary
depleted, diuretics should be used carefully and always with meticulous thromboembolism 68,69 or bowel infarction should be considered.
monitoring of intravascular volume. Impending shock should be treated
with rapid correction of volume and with inotropic agents, as indicated. Thyroid Storm in Pregnancy: The approach to treatment of thyroid storm
Atrial fibrillation is a known complication of thyrotoxicosis. Control of in pregnant patients is similar to that outlined earlier. Thyroid storm is
ventricular response can be achieved with β-blockers, but conversion to clearly a life-threatening condition for the mother. The basic approach
sinus rhythm can be achieved only after the patient is made euthyroid. to prevent decompensation is aggressive fluid replacement along with
Since relative hypoadrenalism is thought to occur in thyroid storm treatment of the precipitating event and antithyroid therapy. Because
because of accelerated metabolism of glucocorticoids, it is prudent to β-blockers may have deleterious effects on the fetus at all stages of fetal
give 300 mg hydrocortisone intravenously, followed by 100 mg every development, their use must be weighed against maternal safety. While
8 hours to provide adequate stress levels. In addition, glucocorticoids administration of iodide often results in the development of massive
can be beneficial for their effect in reducing the conversion of T to fetal goiter, PTU can be given to the toxic pregnant patient with only a
4
T in peripheral tissue. Use of parenteral H blockers or proton-pump small likelihood of adverse effects on the fetus.
3
2
inhibitors are indicated to reduce the likelihood of ulcer formation. In
thyrotoxicosis, there is rapid clearance of drugs. Therefore, doses of ANESTHESIA AND SURGERY: RISKS
digoxin, insulin, and antibiotics need to be increased to be effective. AND MANAGEMENT IN THYROTOXIC PATIENTS
Two exceptions are adrenergic drugs and anticoagulants. It is necessary
66
to remember to reduce these drug doses as the thyrotoxicosis resolves. The Swiss surgeon Emil Theodor Kocher (1841-1917), who was the first
to operate on hyperthyroid patients, was also among the first to recog-
Reduction of Thyroid Hormone Action on Body Tissues: The effects of thy- nize that thyroidectomy carried a high rate of mortality in “unprepared”
roid hormone can be reduced by (1) decreasing its conversion to the active thyrotoxic patients. The stress of any form of surgery or anesthesia alone
form, T , (2) counteracting its sympathomimetic effects, (3) displacing could push a mildly decompensated thyrotoxic patient into a thyroid
3
it from its receptor, and (4) reducing its transport to tissues. crisis, a life-threatening condition (see above). Therefore, it is important
The oral cholecystographic agents, as discussed earlier, may act in to control thyrotoxicosis prior to surgery. Ideally, the FT I should be below
4
part by displacing T from its site of action at the receptor in cell nuclei. the upper limit of normal. Unfortunately, even in the presence of a rapid
3

section08.indd 993 1/14/2015 8:28:37 AM