Thyroid Gland and Anesthetic Management

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Thyroid Gland and Anesthetic Management

• Daniel Stairs CRNA, MSN, MBA
• Excela Health School of Anesthesia

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Thyroid Gland is H-shapedRight and left lobe
with isthmus
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Location of Thyroid Gland

• Anterior to trachea
• Just below cricoid cartilage
• Covering second through fourth tracheal rings
• Thyroid gland weighs about 20 gm

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Blood Supply to Thyroid Gland

• 4 to 6 cc/min/gm
• Arterial supply via inferior and superior
  arteries
• Venous supply via inferior, middle, and superior
  thyroid veins

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Nerve Supply

• Two superior laryngeal nerves and two recurrent
  laryngeal nerves supply the entire sensory and
  motor innervations to the larynx.

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Innervation
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Recurrent Laryngeal Nerve

• Most common nerve injured in throidectomy
• Motor supply
• Sensation below vocal cords
• With selective injury to abductor fibers
• (1) hoarseness
• (2) bilateral injury
• (3) obstruction

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Recurrent Laryngeal Nerve

• Selective injury to adduction fibers
• Post-operative assessment after thyroidectomy is
  via laryngoscopy and having patient phonate
  letter e
• Most common nerve injury

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Superior Laryngeal Nerve

• Motor supply to cricothyroid muscle (SLN external
  branch)
• Internal branch provides sensation above the
  vocal cords
• Injury causes possible risk for aspiration and
  hoarseness

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Essential Thyroid Hormones

• Thyroxine or T4
• Triiodothyronine or T3
• Release of these hormones into circulation
  stimulated by TSH
• T3 is less firmly bound to carrier proteins and
  disappears from circulation quicker
• T3 is 3-5 times as potent as T4 but is limited by
  its transient nature

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Thyroid Hormones

• Nearly all circulating T3 is derived from
  peripheral conversion of T4
• Major Functions of Thyroid Hormones
• (1) calorigenic effects
• (2) growth and cellular differentiation
• (3) metabolic effects
• (4) muscular effects

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Other Functions of Thyroid Hormones

• Working with growth hormone, they ensure proper
  development of the brain
• Increase protein breakdown and glucose uptake by
  cells, enhance glycogenolysis. and depress
  cholesterol levels
• In excess they may interfere with ATP synthesis
  and thus speed the exhaustion of energy in muscle
  tissues

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Thyroid Hormones

• Thyroxine
• normal serum range is 5-12 mcg/dL
• Triiodothyronine
• normal serum range is 70-90 ng/dL

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Laboratory Testing of Thyroid Hormone

• Five General Categories
• Direct tests of thyroid function
• Tests relating to the concentration and binding
  of thyroid hormones in blood
• Metabolic indexes
• Tests of homeostatic control of thyroid function
• Miscellaneous tests

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(1) Direct Tests

• In-vivo administration of radioactive iodine
• Thyroid Radioactive Iodine Uptake (RAIU) is the
  most common
• RAIU is measured 24 hours after administration of
  isotope
• Normal is 10-30 of administered dose after 24
  hours
• Values above normal indicate thyroid hyperfunction

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(2) Tests Related to Hormone Concentration and
Binding

• Are radioimmunoassays
• Highly specific and sensitive radioimmunoassays
  to measure serum T3 and T4
• Highly sensitive TSH assay is the most sensitive
  of thyroid function

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(3) Metabolic Indexes

• Although measurement of the metabolic impact of
  thyroid hormones have value in the investigative
  setting, none is sufficiently sensitive,
  specific, and easily performed for routine use
• Measurements of oxygen consumption in the BMR
  were once a mainstay in the diagnosis of thyroid
  disease, but not today

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(4) Tests of Homeostatic Control

• Basal serum TSH concentration
• Thyrotropin-releasing hormone
• Thyroid suppression test

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(5) Miscellaneous Tests

• These do not assess thyroid function but are if
  value in defining the nature of the thyroid
  disorder or in planning therapy
• Example some patients with autoimmune thyroid
  disease develop circulating antibodies against T3
  and T4 resulting in sporadic highs and lows in
  the concentration of the hormones

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Hyperthyroidism

• Clinical symptoms include nervousness,
  palpitations, intolerance to heat, weight loss,
  muscle weakness, and fatigue
• Physical exam smooth, moist skin,exopthalmus,
  presence of goiter, tachycardia, and hyperactive
  tendon reflex. Skin temperature is elevated, and
  there is fine tremor of the extended hands or a
  course tremor and jerking of trunk.

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Hyperthyroidism

• Long-standing thyrotoxicosis
• Mild anemia and lymphocytosis are common
• Approximately 20 will have reduction in total
  WBC count

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Hyperthyroidism

• Affects approximately 2 of women and 0.2 of men

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Causes of Hyperthyroidism

• Graves disease (diffuse goiter and
  opthalmopathy) is the most common
• Graves disease typically occurs in women 20 to
  40 years of age
• An autoimmune pathogenesis for Graves disease is
  suggested by presence of immunoglobulin G
  autoantiobodies

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Causes of Hyperthyroidism

• Iatrogenicsecond most common cause. May result
  from administration of T3/T4
• Toxic nodular goiter nodules functioning
  independently of normal feedback regulation
• Thyroiditis inflammation-induced release of
  thyroid hormones

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Treatment of Hyperthyroidism

• Antithyroid Drugs
• Usual initial medical management
• Propylthiouracil,carbimazole, methimazole
• These drugs inhibit synthesis of inorganic iodide
  and coupling of iodothyronines
• Graves disease often initially treated with
  antithyroid drugs in hope of inducing a remission
  or achieving euthyroidism before surgery

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Treatment of Hyperthyroidism

• Pregnant females should be treated with
  propylthiouracil (of antithyroid drugs it crosses
  placenta least), minimizing the risk of goiter
  any hypothyroidism in fetus
• Serious side effects of antithyroid drugs include
  agranulocytosis
• Intraoperative bleeding, from drug-induced
  thrombocytopenia or hypoprothrombinemia has been
  reported in patients on propylthiouracil
• Hypothyroidism is a risk of antithyroid drugs so
  patient may receive supplemental T4

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Treatment of Hyperthyroidism

• Beta-Adrenergic Antagonists
• useful adjunctive therapies for patients with
  Graves disease diminish some of the S/S
  (tachycardia, anxiety, tremor) more rapidly than
  can antithyroid drugs
• Nadolol and atenolol have a longer duration than
  propranolol
• These drugs do not block the synthesis and
  secretion of thyroid hormones

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Treatment of Hyperthyroidism

• Inorganic Iodine
• Iodine in pharmacologic doses (Lugols solution,
  5 iodine, 10 potassium iodide in water)
  inhibits the release of T3 and T4 for a limited
  time (days to weeks) after which its antithyroid
  activity is lost
• Inorganic iodine is principally used to prepare
  pts. for surgery and treat thyrotoxic crisis

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Treatment of Hyperthyroidism

• Radioiodine Therapy
• Often selected as tx of choice for
  hyperthyroidism that recurs following therapy
  with antithyroid drugs
• Objective is to destroy sufficient thyroid tissue
  to cure hyperthyroidism
• Permanent hypothyroidism is the only important
  complication of this therapy
• Pregnancy is an absolute contraindication as it
  may cause ablation of the fetal thyroid gland

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Treatment of Hyperthyroidism

• Subtotal Thyroidectomy
• Used to treat Graves disease when radioiodine is
  refused, or for rare pts. With large goiters
  causing tracheal compression or cosmetic concerns
• If elective, pt. needs to be rendered euthyroid
  with drugs
• In emergency, pts. can be prepared for surgery in
  less than 1 hour by IV administration of esmolol

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Treatments to Render Hyperthyroid Pts. Euthyroid
Prior to Surgery

• Emergency Surgery
• Esmolol 100-300 mcg/kg/min IV until heart rate
  lt100/min
• Elective Surgery
• Oral administration of Beta-adrenergic
  antagonist (propranolol, nadolol, atenolol) until
  heart rate lt100/min
• Antithyroid drugs
• Antithyroid drugs plus potassium iodide
• Potassium iodide plus Beta-adrenergic
  antagonist

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Subtotal Thyroidectomy

• Some uncommon complications include damage to
  recurrent laryngeal nerves, postop bleeding into
  the neck with resultant tracheal compression, and
  hypoparathyroidism
• Most common nerve injury is damage to abductor
  fibers of recurrent laryngeal
• This injury when unilateralhoarseness, and
  paralyzed vocal cord assuming an intermediate
  position

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Subtotal Thyroidectomy

• Bilateral recurrent nerve injury results in
  aphonia and paralyzed vocal cords
• The cords can collapse together, producing total
  airway obstruction during inspiration
• Selective injury of adductor fibers of recurrent
  laryngeal nerves leaves the adductor fibers
  unopposed and pulmonary aspiration a hazard

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Subtotal Thyroidectomy

• Airway obstruction that occurs soon after
  tracheal extubation, despite normal vocal cord
  function, suggests tracheomalacia
• This reflects a weakening of tracheal rings by
  chronic pressure of a goiter
• Airway obstruction postop (PACU) may be due to
  tracheal compression by a hematoma

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Subtotal Thyroidectomy

• Hypoparathyroidism resulting from accidental
  removal of parathyroid gland rarely occurs after
  subtotal thyroidectomy
• If damage to parathyroids does occur,
  hypocalcemia typically develops 24 to 72 hours
  postop, but may manifest as early as 1-3 hours
  postop
• Laryngeal muscles sensitive to hypocalcemiamay
  go from inspiratory stridor progressing to
  laryngospasm. Prompt IV calcium till laryngeal
  stridor ceases is tx.

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Subtotal Thyroidectomy
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Thyroid Storm (Thyrotoxic Crisis)

• Medical Emergency characterized by abrupt
  appearance of clinical signs of hyperthyroidism
  (tachycardia, hyperthermia, agitation, skeletal
  muscle weakness, CHF, dehydration, shock) due to
  the abrupt release of T4 and T3 into the
  circulation
• Can occur intraop but is more likely to occur
  16-18 hours postoperative

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Thyroid Storm (Thyrotoxic Crisis)

• When thyroid storm occurs intraop it may mimic
  malignant hyperthermia
• Treatment includes cooled crytalloids and
  continuous IV infusion of esmolol to maintain
  heart rate at acceptable level (usually lt
  100/min)
• When hypotension is persistent, the
  administration of cortisol, 100-200 mg IV may be
  a consideration

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Thyroid Storm (Thyrotoxic Crisis)

• Propylthiouracil is given in dose of 100mg every
  6 hours po or by NG tube to take advantage of the
  drugs ability to inhibit extrathyroidal
  conversion of T4 to T3
• Potassium Iodide is also administered to block
  the release of T4 to T3
• Also important to treat any suspected infection
  in these patients

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Management of Anesthesia

• Elective surgery should be deferred until the
  patient has been rendered euthyroid and the
  hyperdynamic cardiovascular system has been
  controlled with Beta adrenergic antagonists, as
  evidenced by an acceptable heart rate

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Management of Anesthesia

• When surgery cannot be delayed in symptomatic
  hyperthyroid patients, the continuous infusion of
  Esmolol, 100 to 300 mcg/kg/min IV may be useful
  for controlling cardiovascular responses evoked
  by the sympathetic nervous system

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Management of Anesthesia

• Preoperative Medication
• (a) benzodiazepines
• (b) use of anticholinergics not recommended as
  these drugs could interfere with the bodys own
  heat-regulating mechanisms and contribute to an
  increased heart rate

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Management of Anesthesia

• Preoperative
• Evaluation of the upper airway for evidence of
  obstruction (goiter compressing on trachea) is
  extremely important
• Be prepared and have available in the O.R. needed
  equipment for a difficult airway and difficult
  intubation

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Management of Anesthesia

• Induction
• Propoful/Pentothal for induction
• Ketamine is not a likely selection as it can
  stimulate the sympathetic nervous system leading
  to a tachycardia
• Succinylcholine or non-depolarizers that do not
  affect the cardiovascular system for intubation
  (would avoid pancuronium)

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Maintenance of Anesthesia

• Goals in maintenance of anesthesia in patients
  with hyperthyroidism are
• Avoid administration of drugs that stimulate that
  stimulate the sympathetic nervous system
• Provide sufficient anesthetic-induced sympathetic
  nervous system depression to prevent exaggerated
  responses to surgical stimulation

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Maintenance of Anesthesia

• Volatile anesthetics
• isoflurane, desflurane, sevoflurane, are good as
  they offset adverse sympathetic nervous system
  responses to surgical stimulation, but do not
  sensitize the heart to catecholamines
• Remember sevoflurane and potential concern with
  nephrotoxicity caused by an increased production
  of fluoride owing to accelerated metabolism of
  this anesthetic

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Maintenance of Anesthesia

• Monitor and keep track of patients body
  temperature (keep in mind thyroid storm)
• Vigilant monitoring of vital signs
• Pts. With exopthalmos prone to corneal
  ulcerations
• For antagonism of neuromuscular blockade with
  anticholinergics, it is best to avoid atropine
  and use glycopyrrolate as it has fewer
  chronotropic effects

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Maintenance of Anesthesia

• Treatment of Hypotension
• When using sympathomimetic drugs must consider
  the possibility of exaggerated responsiveness of
  hyperthyroid pts. to endogenous or exogenous
  catecholamines
• Therefore, decreased doses of direct-acting
  vasopressors such as phenylephrine may be a
  better choice than ephedrine, which acts in part
  by provoking the release of catecholamines

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Regional Anesthesia for Hyperthyroid Patients

• Causes a sympathetic nervous system blockade
• May be a useful choice in hyperthyroid patients,
  assuming there is no evidence of high-output
  congestive heart failure
• Continuous epidural may be preferable to spinal
  because of the slower onset of sympathetic
  nervous system blockade

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Regional Anesthesia for Hyperthyroid Patients

• If hypotension occurs, decreased doses of
  phenylephrine are recommended
• Epinephrine should not be added to local
  anesthetics, as systemic absorption of this
  catecholamine could produce exaggerated
  circulatory responses

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Hypothyroidism

• Decreased circulating concentration of T3 and T4
• Present in 0.5 to 0.8 of adults
• Diagnosis based on clinical S/S plus confirmation
  of decreased thyroid gland function as
  demonstrated by appropriate tests

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Hypothyroidism

• Causes The etiology of hypothyroidism is
  categorized as
• Primarydestruction of the thyroid gland
• Secondarycentral nervous system dysfunction
• Chronic thyroiditis (Hashimotos thyroiditis) is
  the most common cause

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Etiology of Hypothyroidism

• Primary Hypothyroidism
• Thyroid Gland Dysfunction
• Hashimotos thyroiditis
• Previous subtotal thyroidectomy
• Previous radioiodine therapy
• Irradiation of the neck

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Etiology of Hypothyroidism

• Primary hypothyroidism
• Thyroid hormone deficiency
• Antithyroid drugs
• Excess iodide (inhibits release)
• Dietary iodine deficiency

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Etiology of Hypothyroidism

• Secondary hypothyroidism
• Hypothalamic dysfunction
• Thyrotropin-releasing hormone
• deficiency
• Anterior pituitary dysfunction
• Thyrotropin hormone deficiency

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Hypothyroidism

• Signs and Symptoms
• -Decreased metabolic activity
• -Lethargy is prominent
• -Intolerance to cold
• -Cardiovascular changes are often the earliest
  clinical manifestations
• -bradycardia
• -decreased stroke volume and contractility
• -decreased cardiac output

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Hypothyroidism

• -increased SVR
• -systemic hypertension, especially diastolic
  hypertension occurs in about 15 of hypothyroid
  patients
• -narrow pulse pressure
• -increased circulating concentrations of
  catecholamines
• -overt CHF is unlikely, but if present may
  indicate co-existing heart disease

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Hypothyroidism

• Patients with hypothyroidism are predisposed to
  pericardial effusions
• The EKG may reveal low voltage, prolonged PR,
  QRS, and QT intervals due to pericardial effusion
• Conduction abnormalities may predispose patients
  to ventricular tachycardia, especially torsades
  de pointes

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Hypothyroidism

• Thyroid hormone is necessary for normal
  production of pulmonary surfactant
• Chronic hypothyroidism is associated with pleural
  effusions
• Ventilatory drive to hypoxia and hypercapnia is
  decreased in patients with severe hypothyroidism
• BMR can be decreased up to 50 due to the
  hypothermia that occurs

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Hypothyroidism

• Peripheral vasoconstriction characterized by
  cool, dry skin
• There is often atrophy of the adrenal cortex and
  associated decreases in the production of
  cortisol
• Inappropriate secretion of ADH can result in
  hyponatremia owing to the impaired ability of
  renal tubules to excrete free water

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Hypothyroidism

• Treatment
• -Oral administration of T4
• -Pts. With ischemic heart disease and
  hypothyroidism may not tolerate even modest
  amounts of T4 without developing angina
• -If angina appears or worsens during T4
  therapy, coronary angiography and CABG may be
  necessary before adequate T4 therapy can be
  achieved

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Myxedema Coma

• Rare complication of hypothyroidism
• Manifests as loss of deep tendon reflexes,
  spontaneous hypothermia, hypoventilation,
  cardiovascular collapse, coma, and death
• Sepsis in elderly or exposure to cold may be an
  initiating event

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Myxedema Coma

• Treatment is with IV administration of T3, which
  exerts a physiologic effect within 6 hours
• Digitalis, as used to treat CHF, is used
  sparingly because the hypothyroid patients heart
  cannot easily perform increased myocardial
  contractile work
• Fluid therapy is important, but remember these
  patients may be vulnerable to water intoxication
  and hyponatremia

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Hypothyroidism

• Management of Anesthesia
• -Elective surgery should be deferred if
  symptomatic
• -T4 drug has long half-life (7 days) and
  administration of it on day of surgery is
  optional
• -T3 drug has shorter half-life (1.5 days) so it
  may be prudent to have pt. take it on day of
  surgery

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Hypothyroidism

• -Opioid premedication may be exaggerated in the
  hypothyroid patient
• -Supplemental cortisol may be considered if there
  is concern that surgical stress could unmask
  decreased adrenal function that may accompany
  hypothyroidism

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Maintenance of Anesthesia

• Induction with pentothal, ketamine, or propoful
• Tracheal intubation with succinylcholine, or
  NDMR, but keep in mind that co-existing skeletal
  muscle weakness could be associated with an
  exaggerated drug effect

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Maintenance of Anesthesia

• Often achieved with nitrous oxide short-acting
  opioids, benzodiazepines, or ketamine
• Volatile anesthetics may not be recommended in
  overtly symptomatic hypothyroid pts. for fear of
  inducing exaggerated cardiac depression

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Maintenance of Anesthesia

• Vasodilation produced by anesthetic drugs in the
  presence of hypovolemia could result in abrupt
  decrease in systemic blood pressure
• Pancuronium, because of its mild cardiovascular
  stimulating effects, may be selected for skeletal
  muscle paralysis
• Intermediate and short-acting NDMRs are good as
  they are less likely to produce a prolonged
  neuromuscular blockade

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Maintenance of Anesthesia

• Monitoring hypothyroid pts. during anesthesia is
  intended to facilitate prompt recognition of
  exaggerated cardiovascular depression, and
  detection of onset of hypothermia
• Consider arterial line for long surgical
  procedures, or those associated with significant
  blood loss

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Maintenance of Anesthesia

• IV fluids used should contain sodium to decrease
  likelihood of hyponatremia
• To treat hypotension it is best to use small
  increments of ephedrine 2.5 to 5.0 mg IV
• Phenylephrine could adversely increase SVR in the
  presence of a heart that cannot reliably increase
  its contractility

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Maintenance of Anesthesia

• Suspect acute adrenal insufficiency when
  hypotension persists despite treatment with
  fluids and/or sympathomimetic drugs
• Maintain patients body temperature with use of a
  warming blanket or convection system, and warming
  of IV fluids

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Perioperative Period Possibilities

• Increased sensitivity to depressant drugs
• Hypodynamic cardiovascular system
  responsesdecreased heart rate, decreased cardiac
  output
• Slow metabolism of drugs
• Hypovolemia
• Delayed gastric emptying
• Hyponatremia

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Perioperative Period Possibilities

• Impaired ventilatory responses to arterial
  hypoxemia or hypercarbia
• Hypothermia
• Hypoglycemia
• Adrenal insufficiency

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Postoperative Management

• Recovery from sedative effects of anesthetic
  drugs may be delayed
• Tracheal extubation should be delayed until the
  hypothyroid patient responds appropriately and
  their body temperature is near 37 degrees C
• Due to increased sensitivity to opioids, may want
  to consider nonopioid analgesic

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Extreme Goiter
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Goiter
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Shift of Trachea from Enlarged Right Lobe of
Thyroid Gland