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N935 Advanced Pathophysiology II > Thyroid Pathophysiology > Flashcards

Thyroid Pathophysiology Flashcards

1
Q

Parts of thyroid gland

A
  • right lobe
  • left lobe
  • isthmus (part in the middle)
  • some have pyramidal lobe (extra, not everyone has it)
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2
Q

blood supply to thyroid

A
  • superior and inferior arteries

- superior, middle, and inferior thyroid veins

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3
Q

lymphatic drainage of thyroid

A
  • upper and lower deep cervical lymph node

- pretracheal and paratracheal lymph nodes

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4
Q

what nerves are in close proximity to the thyroid gland

A
  • recurrent laryngeal nerve

- external motor branch of superior laryngeal nerve

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5
Q

thyroid gland

A
  • weighs 20g
  • two lobes joined by isthmus
  • upper isthmus borders cricoid cartilage
  • innervated by adrenergic and cholinergic nervous systems
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6
Q

thyroid gland function

A

-takes absorbed exogenous iodide (iodine reduced to iodide in gut) into the gland and synthesizes the two thyroid hormones T3 and T4

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7
Q

two thyroid hormones

A
  • triiodothyronine (T3), 10%

- thyroxine (T4), 90%

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8
Q

colloid in thyroid gland

A

where the thyroid hormones are made

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9
Q

thyroid hormone production

A
  • depends on availability of exogenous iodine
  • iodine reduced to iodide in GI tract
  • absorbed into blood stream
  • active transport from plasma into thyroid follicular cells
  • iodide trapped in follicular cell and compounded with tyrosine and thyroglobulin –> T1 and T2
  • T1 and T2 coupled to make T3 and T4
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10
Q

T1 and T2

A
  • monoiodotyrosine

- diiodotyrosine

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11
Q

where are T3 and T4 stored?

A

colloid of the follicular cells

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12
Q

thyroid hormone roles

A
  • regulated carb, lipid, and protein metabolism
  • necessary for fetal development
  • CNS development and activity
  • bone and tissue growth
  • GI regulation
  • cardiac myocytes (for contractility)
  • vascular smooth muscle (for direct vasodilation)
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13
Q

thyroid hormone release

A
  • interaction between three things…
  • hypothalamic-pituitary axis
  • thyroid gland
  • thyroid hormone
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14
Q

hypothalamus in thyroid function

A

controls release of thyrotropin releasing hormone (TRH)

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15
Q

pituitary gland in thyroid function

A

TRH stimulates secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary

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16
Q

thyroid gland in thyroid function

A

TSH acts on gland to ehance synthesis and secretion of T3 and T4

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17
Q

pituitary thyroid feedback loop

A
  • classic NEGATIVE feedback loop exists between hypothalamus, pituitary, and thyroid gland
  • increased levels of TH inhibit the secretion of TSH from the pituitary (and also TRH from the hypothalamus)
  • TH levels are the primary determinant of TSH secretion
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18
Q

TSH function

A
  • controls production of thyroid hormones T3 and T4
  • stimulates all aspects of thyroid hormone production –> uptake of iodide from GI tract, iodide incorporation, eventual release of T3 and T4
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19
Q

TSH in hypothyroidism

A

elevated

low levels of T3 and T4, body says what the heck we need more so increase release of TSH to try and get more T3 and T4

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20
Q

TSH in hyperthyroidism

A

decreased

HIGH levels of T3 and T4, body again says what the heck, we need LESS so the amount of TSH is decreased

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21
Q

T3

A
  • triiodothyronine
  • 10% synthesized and release by thyroid gland
  • also formed in the liver and kidneys by peripheral conversion of T4 to T3 by selenodeiodinases
  • 3-4x more active than T4
  • half life is 1-3 days
  • 99.7% bound to albumin
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22
Q

T4

A
  • thyroxine
  • 90% synthesized and release by the thyroid gland
  • half life of 6-7 days (about 1 week)
  • 99.9% is bound to thyroid binding globulin
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23
Q

TH in the bloodstream

A
  • both T3 and T4 circulate tightly bound in the blood
  • T4 more tightly bound than T3 (part of which leads to its longer half life)
  • larger amount of T3 (0.4%) circulates in blood as compared to T4 (0.04%)
  • FREE FORM = active and drives the patient’s metabolic state
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24
Q

principle thyroid function tests

A
  • TSH
  • serum T3
  • serum T4
  • radioactive iodine uptake (RAIU)
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25
Q

aging and TSH

A

-increase in baseline TSH

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26
Q

normal TSH level

A

0.4-5.0 mu/L

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27
Q

subclinical hyperthyroidism

A
  • TSH 0.1-0.4 mu/L

- normal levels of free T3 and T4

28
Q

overt hyperthyroidism

A
  • TSH level below 0.03 mu/L

- elevated T3 and T4

29
Q

subclinical hypothyroidism

A
  • TSH level 5.0-10 mu/L

- normal T3 and T4

30
Q

overt hypothyroidism

A
  • TSH level higher than 20 mu/L

- reduced T3 and T4

31
Q

diagnosis of pituitary dysfunction

A
  • TRH test
  • inject exogenous TRH by rapid IVP
  • serum concentration of TSH collected at 15 and 30 min intervals over 2-3 hours
  • normally = TSH rise
  • if secondary hypothyroidism admin of TRH does not produce increase in TSH
32
Q

hyperthyroidism

A
  • wide clinical spectrum ranging from subclinical to a life threatening thyroid storm
  • lab values = low TSH and high T3/T4
33
Q

causes of hyperthyroidism

A
  • graves disease
  • toxic multinodular goiter
  • autonomously functioning thyroid nodule
  • thyroiditis (inflammation/infection)
  • exogenous thyroid hormone ingestion
  • iodine induced
34
Q

graves disease

A

autoimmune disease caused by thyroid stimulating antibodies that bind to the TSH receptors in the thyroid, stimulating thyroid growth, vascularity and hypersecretion

35
Q

S/S hyperthyroidism

A
  • anxious, restless, hyperkinetic
  • warm skin, sweating, flushed, heat intolerance
  • protruding eyes (exopahtalmos or proptosis)
  • weakness
  • fatigue/inability to sleep
  • tremors
  • weight loss
  • frequent bowel movements
  • increased cardiac work, tachycardia, dysrhythmias, palpitations
36
Q

morbidity and mortality of hyperthyroidism-

A
  • increased HR –> stroke, MI, ectopy, CHF, PVCs and A fib
  • hypermetabolism –> increase CO2 –> increased Ve –> weakness in resp muscles
  • myopathies
37
Q

treatment of hyperthyroidism

A
  • antithyroid medications
  • radioactive iodine may be used for recurrent or persistent hyperthyroidism
  • thyroidectomy (only if euthyroid state has been achieved)
38
Q

propylthiouracil (PTU) or methimazole

A
  • thionamides
  • interfere with synthesis (coupling) of thyroid hormones in the thyroid gland
  • PTU also prevents conversion of T4 to T3 in the periphery
  • meds given for weeks to months and then thyroid function tests used to ensure euthyroid state
39
Q

thyroid storm

A
  • acute life-threatening form of hyperthyroidism
  • significant associated mortality
  • most often occurs in postop period of inadequately treated hyperthyroid patient
40
Q

clinical signs of thyroid storm

A
  • temp elevation with diaphoresis (as high as 106 degrees)
  • marked tachycardia (can manifest as afib or Vtach)
  • cerebral dysfunction (confusion, psychosis, seizures)
  • GI disorders (N/V, obstruction)
41
Q

thyroid storm precipitating evnets

A
  • surgery
  • infection
  • IV contrast dyes
  • DKA
  • trauma
  • Vigorous palpation of thyroid
42
Q

thyroid storm treatment

A
  • decrease production, conversion and secretion of TH (PTU and corticosteroids)
  • supportive care –> treat temp, acid/base disturbance (oxygenation and ventilation), hydration (glucose containing fluids due to hypermetabolism), oxygen
  • beta blockers (propranolol, esmolol)
  • determine underlying cause
  • consider avoiding SNS activation (avoid ketamine, epi, etc)
43
Q

preop management of emergency surgery in patient with hyperthyroid

A
  • good premedication (benzos/narcotics)

- avoid anticholinergics (may precipitate tachycardia)

44
Q

intraop management of emergency surgery in patient with hyperthyroid

A
  • consider invasive monitoring (a line)
  • differentiate between MH and thyroid storm
  • adequate anesthetic depth to avoid exaggerated SNS
  • avoid ketamine, ephedrine, epi, dopa due to effect on SNS
  • hypotension - consider fluids and direct acting vasopressor (like phenylephrine)
  • succs, NDMR, and N2O okay
  • eye protection (lube or pads due to exopathalmos)
45
Q

postop management of emergency surgery in patient with hyperthyroid

A

continue beta blocker therapy because half life of T4 is 6-7 days

46
Q

hypothyroidism (or myxedema)

A
  • affects 0.5-0.8% of population
  • primary
  • autoimmune
  • secondary
47
Q

primary hypothyroidism

A
  • 90-95%
  • decreased production of TH despite normal TSH
  • most common causes are ablation of gland by radioactive iodine therapy or surgery
48
Q

autoimmune hypothyroidism

A
  • autoantibodies block TSH receptors in thyroid gland

- immune response destroys receptors (instead of stimulating)

49
Q

secondary hypothyroidism

A
  • 5% of all cases

- secondary to either hypothalamic or pituitary disease

50
Q

hashimoto’s thyroiditis

A
  • autoimmune disorder, goiter, hypothyroidism

- common in middle aged women

51
Q

mild s/s of hypothyroidism

A
  • tires easily

- weight gain despite decreased appetite

52
Q

moderate to severe s/s hypothyroidism

A
  • fatigue, apathy, listlessness
  • slow speech
  • cold intolerance, decreased sweating, constipation, menorrhagia, slow motor function
  • slowed GI function
  • dry hair, skin
  • large tongue, periorbital edema
  • cardiomyopathy, impaired baroreceptor function, bradycardia, hyponatremia
  • impaired ventilatory response to hypoxia and hypercarbia
53
Q

dianosis of hypothyroidism

A
  • primary - reduced T4/T3 and elevated TSH

- secondary (pituitary) = reduced T3 and T4 and TSH

54
Q

levothyroxine sodium (synthroid)

A
  • synthetic form of thyroxine (T4)
  • can be converted to T3
  • onset oral 3-5 days (peak may require 4-6 weeks)
  • onset IV 6-8 hours
55
Q

anesthetic considerations for hypothyroidism

A
  • airway compromise
  • decreased gastric emptying
  • hypodynamic CV system
  • decreased ventilatory responsiveness to hypoxia and hypercarbia
  • risk for hypothermia
  • hematologic abnormalities (anemia, plt dysfunction, electrolyte imbalances, hypoglycemia)
  • increased sensitivity to sedatives/narcs
56
Q

anesthesia management of emergency surgery in patient with hypothyroid

A
  • potential for severe intraop CV instability and myxedema coma
  • IV thyroid replacement may be needed
  • steroid coverage
  • PDE-i like milrinone may be effective in treatment of reduced myocardial contractility because MOA does not depend on beta receptors (which may be reduced or have decreased sensitivity in hypothyroid)
57
Q

myxedema coma

A
  • rare, severe form of hypothyroid characterized by delirium or unconsciousness, hypoventilation, hypothermia, bradycardia, hypotension, and severe dilutional hyponatremia
  • most common in elderly women with LONG history of hypothyroidism
  • mortality > 50%
  • MEDICAL emergency –> requires IV synthroid and IV steroids
58
Q

goiter

A
  • swelling of thyroid
  • can occur in hyper or hypothyroidism
  • nontoxic goiters are euthyroid but can lead to toxic multinodular goiter
59
Q

goiter causes

A
  • deficient intake of iodine
  • ingestion of dietary substance that decreases iodine (raw cassava = cyanide)
  • pharmacologic goitrogen
  • defect in hormonal biosynthetic pathway
60
Q

goiter anesthetic management

A
  • careful airway eval

- extreme caution with resp depressants prior to airway securement

61
Q

thyroid surgery anesthetic considerations

A
  • euthyroid (IDEAL) before any elective procedure
  • airway compromise with large goiter may be present with nerve compression, tracheal deviation, and erosion
  • use of RLN monitor (NIMS)
62
Q

complications of thyroid surgery

A
  • morbidity approaches 13%
  • recurrent laryngeal nerve injury
  • superior laryngeal nerve injury
  • hypoparathyroidism
  • tracheal compression from expanding hematoma
63
Q

RLN injury

A
  • paralysis of abductor vocal cord muscles results in median/paramedian cord position
  • unilateral = hoarseness
  • bilateral = airway obstruction, resp distress, stridor; may require a trach
64
Q

SLN injury

A

weakness of voice in ability to create high tones

65
Q

hypoparathyroid during thyroid surgery

A
  • usually result of damage of blood supply to parathyroid gland NOT inadvertent removal
  • hypocalcemia 24-48 hrs post op
  • stridor/laryngospasm (treatment IV calcium)

N935 Advanced Pathophysiology II (16 decks)

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