Perioperative management of patients with hypothyroidism H.Rezvanian MD

Introduction Thyroid hormones have a wide variety of actions in virtually every organ system. They play a crucial role in regulating important functions such as cardiac contractility, vascular tone, water and electrolyte balance, and normal function of the central nervous system. It is now widely accepted that an euthyroid state marked by adequate levels of thyroid hormones is necessary to obtain the best possible results from any kind of surgical intervention.

Effects of hypothyroidism on the cardiovascular system the most important adverse effects of hypothyroidism that may predict a bad surgical outcome are those affecting cardiac function. decreased cardiac output, increased peripheral vascular resistance, and decreased blood volume. These changes may be particularly important for the surgical patient with some degree of preexisting heart failure.

Surgical outcomes  There are no randomized studies looking at surgical outcomes in hypothyroid versus euthyroid patients Two retrospective cohort studies examined peri- and postsurgical outcomes in moderately hypothyroid patients. The authors concluded that there was no evidence to justify deferring needed surgery in patients with mild to moderate hypothyroidism

Management management is to base therapeutic decisions on the severity of hypothyroidism. definitions of mild, moderate, and severe hypothyroidism can be vague A useful definition of severe hypothyroidism includes patients with myxedema coma, with severe clinical symptoms of chronic hypothyroidism such as altered mentation, pericardial effusion, or heart failure, or those with very low levels of total thyroxine (eg, less than 1.0 mcg/dL) or free thyroxine (eg, less than 0.5 ng/dL)

Moderate Hypothyroidism All other patients with overt hypothyroidism (elevated serum TSH, low free thyroxine) can be treated as having moderate disease. Subclinical hypothyroidism is defined biochemically as a normal serum free thyroxine (T4) concentration in the presence of an elevated serum thyrotropin (TSH) concentration and this is, by definition, mild disease.

Subclinical hypothyroidism we suggest not postponing surgery in patients with subclinical hypothyroidism (elevated serum TSH, normal free T4).

Moderate (overt) hypothyroidism we suggest that patients with moderate overt hypothyroidism undergo urgent or emergent surgery without delay, with the knowledge that minor perioperative complications might develop. postpone surgery until the euthyroid state in a patient being evaluated for elective surgery.

Euthyroidism in Moderate (overt) hypothyroidism young patients are started on close to full replacement doses of thyroxine (T4, 1.6 mcg/kg), while elderly patients or patients with cardiopulmonary disease are started on 25 to 50 mcg daily with an increase in dose every two to six weeks

Severe hypothyroidism these patients should be considered high risk and surgery should be delayed until hypothyroidism has been treated. If emergency surgery must be performed in a patient with severe hypothyroidism and there is concern about existing or precipitating myxedema coma,should be rapidly normalized thyroid function.

Euthyroidism in Severe hypothyroidism patients should be treated with both T3 and T4 to rapidly normalize thyroid function. As an example, T4 is given in a loading dose of 200 to 300 mcg IV followed by 50 mcg daily. T3 is given simultaneously in a dose of 5 to 20 mcg IV followed by 2.5 to 10 mcg every eight hours depending upon the patient's age and coexistent cardiac risk factors.

Angina Angina is not an absolute contraindication to thyroid hormone replacement if the patient has symptomatic hypothyroidism. Some patients will experience improvement in their angina symptoms with therapy. Presently, most patients with angina have coronary artery revascularization first and T4 is prescribed afterwards .

PTCA or CABG There were no differences between the euthyroid and hypothyroid patients undergoing PTCA Those having CABG had a higher incidence of heart failure, hyponatremia, gastrointestinal dysfunction, and fever. if hypothyroid patients need a revascularization procedure, PTCA may be a better choice if there is no time to render them euthyroid.

IS PREOPERATIVE MEASUREMENT OF TSH NECESSARY? Despite the relatively high prevalence of thyroid disease in the general population, we believe there is no need to screen for thyroid disease during the preoperative medical consultation. if the history and physical examination are suggestive of thyroid disease, it is reasonable to try to make the diagnosis

Perioperative management of patients with hyperthyroidism with

HYPERTHYROIDISM hyperthyroidism affects many bodily systems that might influence perioperative outcome. Patients with hyperthyroidism have an increase in cardiac output, due both to increased peripheral oxygen needs and increased cardiac contractility. Heart rate is increased, pulse pressure is widened, and peripheral vascular resistance is decreased.

HYPERTHYROIDISM Atrial fibrillation occurs in about 8 percent of patients with hyperthyroidism and is more common in elderly patients. Dyspnea may occur for a variety of reasons, including increased oxygen consumption and CO2 production, respiratory weakness, and decreased lung volume. Weight loss is due primarily to increased calorigenesis, and secondarily to increased gut motility and the associated hyperdefecation and malabsorption; these changes can cause the patient to be malnourished.

Management In patients with untreated or poorly controlled hyperthyroidism, an acute event such as surgery can precipitate thyroid storm, a potentially life-threatening condition. Thus, all elective surgeries should be postponed in patients with newly discovered overt hyperthyroidism until the patient has achieved adequate control of their thyroid condition (usually three to eight weeks).

subclinical hyperthyroidism patients with subclinical hyperthyroidism (low TSH, normal free T4 and T3) can typically proceed with elective surgeries. Unless contraindicated, we typically administer a beta blocker preoperatively to older patients (>50 years) or younger patients with cardiovascular disease, and taper after recovery.

Preoperative preparation for urgent surgery Such patients require preoperative preparation, typically with beta blockers and thionamides. If hyperthyroidism is severe and the need for surgery is urgent, we also add SSKI one to five drops three times daily) one hour after thionamides.

Preoperative preparation for urgent surgery Extreme caution is necessary before administering SSKI to a patient with known or suspected toxic nodular goiter since iodine, in the absence of a thionamide to block organification, may exacerbate the hyperthyroidism.

Urgent surgery Patients with toxic nodular goiter who are intolerant or unable to take thionamides should be pretreated with beta blockers alone

urgent surgery In contrast, in patients with Graves' disease, exogenous iodine is unlikely to exacerbate hyperthyroidism by acting as substrate. Thus, for patients with Graves’ hyperthyroidism who are allergic to or are intolerant of thionamides, the combination of beta blockers and iodine can be used for preoperative preparation

Beta blockers beta blockers administered preoperatively effectively control the clinical manifestations of hyperthyroidism and are as effective as a thionamide for preoperative preparation of the hyperthyroid patient

Beta blockers The longer acting beta blockers are preferred in patients who are candidates for therapy because an oral dose taken one hour before surgery will usually maintain adequate beta blockade until the patient is able to take oral medications postoperatively .

Beta blockers Patients with relative contraindications to beta blockade may better tolerate beta 1-selective agents, such as metoprolol

Thionamides Thionamides block de novo thyroid hormone synthesis but have no effect upon the release of preformed hormone from the thyroid gland, and will therefore not have a significant effect on thyroid hormone levels over only a few preoperative days. Nevertheless, once the diagnosis of hyperthyroidism is established, thionamides should be initiated with the aim of controlling hyperthyroidism in the postoperative period.

Thionamides Methimazol 10 mg two to three times daily or 20 to 30 mg once daily) is usually preferred to PTU except during pregnancy, because of its longer duration of action (allowing for single daily dosing) and a lesser degree of toxicity.

IODINE Iodine blocks release of T4 and T3 from the gland and thereby shortens the time to achieving a euthyroid state. we suggest adding iodine.

Thyroid storm The therapeutic options for thyroid storm are essentially the same as those for uncomplicated hyperthyroidism, except that the drugs are given in higher doses and more frequently. In addition, infection needs to be identified and treated, and hyperpyrexia should be aggressively corrected.

Thyroid storm Acetaminophen is preferable to aspirin, which can increase serum free T4 and T3 concentrations by interfering with protein binding. Cooling blankets can be used if hyperthermia develops during surgery. Full support of the patient in an intensive care unit is essential, since the mortality rate of thyroid storm is substantial