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Perioperative management of patients with hypothyroidism

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Title: 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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