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Title: Thyroid Gland and Anesthetic Management


1
Thyroid Gland and Anesthetic Management
  • Daniel Stairs CRNA, MSN, MBA
  • Excela Health School of Anesthesia

2
Thyroid Gland is H-shapedRight and left lobe
with isthmus
3
Location of Thyroid Gland
  • Anterior to trachea
  • Just below cricoid cartilage
  • Covering second through fourth tracheal rings
  • Thyroid gland weighs about 20 gm

4
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

5
Nerve Supply
  • Two superior laryngeal nerves and two recurrent
    laryngeal nerves supply the entire sensory and
    motor innervations to the larynx.

6
Innervation
7
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

8
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

9
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

10
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

11
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

12
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

13
Thyroid Hormones
  • Thyroxine
  • normal serum range is 5-12 mcg/dL
  • Triiodothyronine
  • normal serum range is 70-90 ng/dL

14
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

15
(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

16
(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

17
(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

18
(4) Tests of Homeostatic Control
  • Basal serum TSH concentration
  • Thyrotropin-releasing hormone
  • Thyroid suppression test

19
(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

20
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.

21
Hyperthyroidism
  • Long-standing thyrotoxicosis
  • Mild anemia and lymphocytosis are common
  • Approximately 20 will have reduction in total
    WBC count

22
Hyperthyroidism
  • Affects approximately 2 of women and 0.2 of men

23
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

24
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

25
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

26
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

27
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

28
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

29
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

30
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

31
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

32
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

33
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

34
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

35
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.

36
Subtotal Thyroidectomy
37
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

38
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

39
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

40
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

41
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

42
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

43
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

44
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)

45
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

46
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

47
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

48
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

49
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

50
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

51
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

52
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

53
Etiology of Hypothyroidism
  • Primary Hypothyroidism
  • Thyroid Gland Dysfunction
  • Hashimotos thyroiditis
  • Previous subtotal thyroidectomy
  • Previous radioiodine therapy
  • Irradiation of the neck

54
Etiology of Hypothyroidism
  • Primary hypothyroidism
  • Thyroid hormone deficiency
  • Antithyroid drugs
  • Excess iodide (inhibits release)
  • Dietary iodine deficiency

55
Etiology of Hypothyroidism
  • Secondary hypothyroidism
  • Hypothalamic dysfunction
  • Thyrotropin-releasing hormone
  • deficiency
  • Anterior pituitary dysfunction
  • Thyrotropin hormone deficiency

56
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

57
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

58
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

59
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

60
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

61
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

62
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

63
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

64
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

65
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

66
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

67
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

68
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

69
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

70
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

71
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

72
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

73
Perioperative Period Possibilities
  • Impaired ventilatory responses to arterial
    hypoxemia or hypercarbia
  • Hypothermia
  • Hypoglycemia
  • Adrenal insufficiency

74
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

75
Extreme Goiter
76
Goiter
77
Shift of Trachea from Enlarged Right Lobe of
Thyroid Gland
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