Perioperative management of patients with hypothyroidism

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Perioperative management of patientswith
hypothyroidism

• H.Rezvanian MD

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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.

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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.

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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

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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)

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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.

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Subclinical hypothyroidism

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

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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.

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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

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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.

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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.

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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 .

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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.

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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

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Perioperative management of patients with
hyperthyroidismwith
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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.

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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.

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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).

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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 (gt50 years) or
  younger patients with cardiovascular disease, and
  taper after recovery.

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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.

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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.

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Urgent surgery

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

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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

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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

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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 .

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Beta blockers

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

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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.

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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.

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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.

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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.

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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

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