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N935 Pathophysiology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Describe the blood supply to the thyroid

A

superior and inferior thyroid arteries

superior middle and inferior thyroid veins

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2
Q

Describe lymphatic drainage around the thyroid

A

upper and lower deep cervical lymph node

pre-tracheal and paratracheal lymph node

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3
Q

What two nerves are in close proximity to the thyroid?

A

recurrent laryngeal nerve

external motor branch of the superior laryngeal nerve

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4
Q

How much does the thyroid weigh?

A

20g

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5
Q

Describe the structure of the thyroid

A

two lobes joined by isthmus

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6
Q

What does the isthmus border?

A

cricoid cartiledge

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7
Q

What is the thyroid gland innervated by?

A

adrenergic and cholinergic nervous systems

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8
Q

What is the purpose of the thyroid?

A

takes absorbed exogenous idodide (iodine is reduced to iodide in the gut) into the gland and synthesizes 2 thyroid hormones

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9
Q

What are the two hormones of the thyroid

A

triiodothyronine (T3)

thyroxine (t4)

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10
Q

What does thyroid hormone production depend on?

A

availability of exogenous iodine (i2)

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11
Q

Describe thyroid hormone production

A

iodine is reduced to iodide (I-) in the GI tract absorbed into the blood stream and then is actively transported from the plasma into the thyroid follicular cells
iodide gets trapped inside the follicular cell and gets compounded with tyrosine and thyroglobulin and yields monoiodotryosine and diiodotyrosine
then they are coupled into T3 and T4

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12
Q

Where are T3 and T4 stored til needed and released into circulation?

A

colloid

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13
Q

What are the 7 roles of thyroid hormone?

A

regulates carbohydrate, lipid, protein metabolism
necessary for fetal development
CNS development and activity
bone and tissue growth
gastrointestinal regulation
cardiac myocytes (contractility)
vascular smooth muscle (direct vasodilation)

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14
Q

What are the interactions between thyroid hormone that allow release?

A

hypothalamic-pituitary axis
thyroid gland
thyroid hrormones

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15
Q

What is the role of the hypothalamus in the regulation of thyroid function?

A

controls the release of thyrotropin-releasing hormone (TRH)

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16
Q

What is the role of the pituitary gland in thyroid function?

A

TRH stimulates the secretion of thyroid secreting hormone (TSH) form the anterior pituitary

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17
Q

What is the role of the thyroid gland in thyroid function?

A

TSH acts on the thyroid gland to enhance synthesis and secretion of T4 and T3

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18
Q

What exists between the hypothalamus, pituitary, and the thyroid gland?

A

classic feedback loop

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19
Q

Describe the negative feedback loop of thyroid function

A

increase levels of thyroid hormone INHIBIT secretion of TSH from the pituitary

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20
Q

What are the primary determinant of TSH secretion?

A

thyroid hormone levels

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21
Q

What is the composition of thyroid stimulating hormone?

A

211 amino acids

2 subunits

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22
Q

What is the function of thyroid stimulating hormone?

A

controls production of thyroid hormones T4 adn T3

stimulates all aspects of thyroid hormone production

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23
Q

What specific roles of thyroid hormone production is stimulated with TSH?

A

uptake of iodide
iodide incorporation
eventual release of T4 and T3

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24
Q

In hypothyroidism, TSH will be

A

elevated

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25
Q

In hyperthyroidism, TSH will be

A

decreased

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26
Q

Which thyroid hormone is more active?

A

T3

3-4x more active then T4

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27
Q

What is the half life of T3?

A

1-3 days

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28
Q

How much is T3 bound to albumin?

A

99.7%

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29
Q

T3 is synthesized in the thyroid gland, but also formed in the

A

liver and kidneys by peripheral conversion of T4 by selenodeiodinases

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30
Q

How much is thyroxine synthesized and released by the thyroid gland?

A

90%

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31
Q

what is the serum half life of T4

A

6-7 days (1 week)

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32
Q

What % is t4 bound to thyroid binding globulin?

A

99.9%

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33
Q

How do T3 and T4 circulate the blood stream?

A

circulate tightly protein bound

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34
Q

Which hormone is more tightly bound?

A

t4

leads to the longer 1/2 life

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35
Q

Which hormone has a larger amount circulating in the blood stream?

A

t3

0.4 vs 0.04%

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36
Q

What state of the thyroid hormone drives the patient’s metabolic state?

A

free form and active

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37
Q

When performing thyroid test, what is important to look at?

A

clinical picture and laboratory tests

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38
Q

What are principle thyroid function tests?

A

TSH
serum T4
serum T3
radioactive iodine uptake

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39
Q

What occurs to thyroid tests with aging?

A

increase in baseline TSH

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40
Q

What is a normal range of T4?

A

4.5-12ug/dL

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41
Q

What is a normal range of T3?

A

90-200mcg/dL

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42
Q

What is a normal range of TSH?

A

0.4-4.5ug/dL

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43
Q

What is a normal range of free t4?

A

0.7-1.6mg/dL

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44
Q

What is a normal range of free t3?

A

230-420mg/L

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45
Q

What is a normal range of RAIU?

A

8-35% at 24hour

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46
Q

What is subclinical hyperthyroidism diagnosis?

A

TSH level of 0.1-0.4mu/L with normal levels of free T3 and free T4

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47
Q

What is overt hyperthyroidism diagnosis?

A

TSH below 0.03mu/L with elevated T3/T4

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48
Q

What is subclinical hypothyroidism diagnosis?

A

TSH level of 5-10mu/L with normal levels of T3 adn T4

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49
Q

What is overt hypothyroidism diagnosis?

A

TSH level higher than 20 mu/L with reduced levels of T3 and T4

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50
Q

How do you diagnosis pituitary dysfunction?

A

Thyrotropin releasing hormone test

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51
Q

What occurs when TRH is administered with second hypothyroidism?

A

does not produce an increase in TSH

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52
Q

How can you test for pituitary dysfunction?

A

injection of exogenous TRH by rapid IV push
serum concentration of TSH is collected at 15 and 30 minute intervals over 2-3 hours
normally TSH would rise in concentration

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53
Q

What is a life threatening emergency in hyperthyroidism?

A

thyroid storm

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54
Q

Thyrotoxicosis

A

clinical syndrome caused by increased thyroid hormone levels, regardless of cause

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55
Q

Hyperthyroidism

A

syndrome caused by an intrinsic abnormality of the thyroid, but the two terms are used interchangeably

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56
Q

What will laboratory levels reveal in hyperthyroidism?

A

low TSH and high free T4 and T3

57
Q

In subclinical hyperthyroidism, lab levels reveal

A

TSH is low but free t4 and free T3 are normal

58
Q

Hyperthyroidism is most caused by by

A

primary thyroid abnormality but may result from a TSH producing pituitary adenoma

59
Q

Symptoms of hyperthyroidism

A 
fatigue
weight loss
sensitivity to cold
depression
memory problems
goiter
hair loss
muscle pain
trembling hands
infertility
anxious
restless
hyperkinetic
warm skin, sweating, flushed, heat intolerance
protruding eyes (exophthalmos or proptosis
weakness
frequent bowel movements
increased cardiac work, tachycardia, dysrhythmias, palpitations
60
Q

What are causes of hyperthyroidism?

A 
graves disease
toxic multinodular goiter
autonomously functioning thyroid nodule
thyroiditis
exogenous thyroid hormone ingestion
iodine induced
61
Q

What % of hyperthyroidism cases are Graves disease?

A

85%

62
Q

What is graves disease?

A

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

63
Q

What can cause morbidity adn mortality of hyperthyroidism?

A

increased HR
hypermetabolism
myopathies

64
Q

What an increased HR in hyperthyroidism cause?

A

can lead to stroke, MI ectopy, CHF PVCs and a fib

65
Q

What can hypermetabolism cause with hyperthyroidism?

A

increased CO2 production-> increased minute ventilation-> weakness in respiratory muscles

66
Q

How do you treat hyperthyroidism?

A

anti-thyroid medications
radioactive iodine
thyroidectomy

67
Q

What is an example of an anti-thyroid medication?

A

thionamides

propylthiouracil (PTU) or methimazole

68
Q

MOA of propylthiouracil (PTU)

A

interferes with synthesis (coupling) of thyroid hormones in the thyroid
prevents the conversion of T4 to T3 in the periphery
medications are given for weeks to months and then thyroid function tests are used to ensure euthyroid state

69
Q

When should you perform a thyroidectomy?

A

should only be performed after euthyroid state has been achieved with medication

70
Q

When should radioactive iodine be used?

A

used for recurrent or persistent hyperthyroidism

71
Q

What is thyroid storm?

A

an acute life threatening form of hyperthyroidism

significant associated mortality (>20%)

72
Q

How do you diagnosis thyroid storm?

A

clinically
temperature elevation with diaphoresis (as high at 106 degrees)
marked tachycardia (can manifest as afib or v-tach)
cerebral dysfunction (confusion, psychosis, seizures)
GI disorders (NV obstruction)

73
Q

What can cause thyroid storm?

A 
surgery
infection
IV contrast dyes
DKA
trauma
vigorous palpitation of thyroid
74
Q

When does thyroid storm most likely occur?

A

postoperatively treated of inadequately treated hyperthyroidism patients

75
Q

How do you treat thyroid storm?

A

decrease production, conversion and secretion of thyroid hormone
PTU/ Corticosteroids
Supportive care
beta blocks (propranolol, esmolol)
determine underlying cause
consider avoiding SNS activation (ketamine, epi)

76
Q

What is supportive care for thyroid storm?

A

aggressive treatment of temperature
acid-base abnormalities (oxygenation and ventilation
hydration (consider glucose containing fluids for hypermetabolism
oxygen

77
Q

What is the typical adult dose of antithyroid agents (PTU) ?

A

1200-1500mg/day given in 200-250mg increaments PO or via gastric tube

78
Q

What is the typical adult dose of antithyroid agents methimazole?

A

120mg given in 20mg increments PO or via gastric tube

79
Q

What is the MOA of antithyroid agents, PTU

A

prevents production of more T4 and T3 in the thyroid, and blocks the conversion of T4 to T3 outside the thyroid

80
Q

What is the MOA of antithyroid agents, methimazole

A

prevents production of stored thyroid hormone from the thyroid gland

81
Q

What is the dose for lugols solution

A

10 drops BID PO or via gastric tube

82
Q

What is the dose for saturated solution of potassium iodide (Pima, SSKI)

A

8 drops every 6 hours PO or via gastric tube

83
Q

What are iodides?

A

lugol drops

saturated solution of potassium iodide

84
Q

What is the MOA of iodides?

A

blocks release of stored thyroid hormone form thyroid gland

85
Q

What is the adult dose of glucocorticoids, dexamethasone?

A

2mg Q6 PO or IV

86
Q

What is the adult dose of glucocorticoids, hydrocortisone?

A

100mg IV every 8 hours

87
Q

What is the MOA of glucocorticoids?

A

blocks conversion of T4 to T3

88
Q

What is an adult dose of beta blockers, propranolol?

A

1mg/min IV as required than 60-80mg q4 hours PO or gastric tube

89
Q

What is an adult dose of beta blockers, esmolol?

A

500mcg/kg/min for 1 min then 50-100mcg/kg/min for 4 minute

90
Q

What is the MOA of BB?

A

reduces symptoms tachycardia, tremor, restlessness, caused by a heightened response to catecholamines; blocks conversion T4 and T3

91
Q

What drugs do you avoid in hyperthyroidism?

A

aspirin
amiodarone
caution with beta blocks

92
Q

Why is aspirin CKA in hyperthyroidism?

A

associated with displacement of thyroid hormone bind from thyroid binding globulin-> increased free thyroid hormone

93
Q

Why is amiodarone CKA in hyperthyroidism?

A

an iodine containing drug

largerly because of effects on peripheral deiondination of t4 to t3

94
Q

What do you caution BB with hyperthyroidism?

A

a moderate degree of compensatory tachycardia may be necessary to maintain adequate in some patients

95
Q

Pre-operative Anesthesia Implications in Trauma patient with hyperthyroidism

A

good premedication (benzo/narcotics)

96
Q

Intra-operative Anesthesia Implications in Trauma patient with hyperthyroidism

A

invasive monitoring
differiential Diagnosis (MH vs thyroid storm)
adequate anesthetic depth to avoid exaggerated SNS response
treat hypotension (fluids, direct acting vasopressor)
succinylcholine, NDMR and N2O
eye protection

97
Q

postoperative Anesthesia Implications in Trauma patient with hyperthyroidism

A

continue beta blocker (1/2 life of T4 is 7-8days)

98
Q

What drugs need to be avoid in hyperthyroidism due to effect on SNS?

A

epi, ketamine, dopamine, ephedrine

99
Q

What is primary hypothyroidism?

A

decreased production of thyroid hormones despite normal TSH

100
Q

What are the most common cause of hypothyroidism?

A

ablation of the gland by radioactive iodine therapy or surgery

101
Q

What is autoimmune hypothyroidism?

A

autoantibodies block TSH in the thyroid

102
Q

What happens to the receptors in autoimmune hypothyroidism?

A

destorys receptors (instead of stimulating)

103
Q

What is secondary hypothyroidism?

A

secondary to hypothalamic or pituitary disease

104
Q

What is hashimoto’s thyroiditis?

A

autoimmune disorder, goiter, hypothyroidism

commonly in middle-aged women

105
Q

What are mild signs and symptoms of hypothyroidism?

A

tires easily, weight gain despite decreased appetite

106
Q

What are moderate to severe symptoms of hypothyroidism?

A 
fatigue apathy listlessness
slow speech
cold intolerance
decreased sweating 
constipation
menorrhagia
slow motor function
slowed GI function
dry hair skin large togue periorbital edema
cardiomyopathy
impaired baroreceptor function
bradycardia
hyponatremia
impaired ventilatory response to hypoxia and hypercarbia
107
Q

How do you diagnosis primary hypothyroidism?

A

reduced levels of T4, T3, and elevated TSH

108
Q

How do you diagnosis secondary hypothyroidism?

A

reduced levels of T4, T3 and reduced TSH

109
Q

What can confirm pituitary pathology as the diagnosis of hypothyroidism?

A

TRH stimulation test

110
Q

What occurs in primary hypothyroidism with a TRH stimulation test?

A

basal levels of TSH are elevated and the elevation is exaggerated after TRH administration
with pituitary dysfunction there is a blunted or absent response to TRH

111
Q

How do you treat hypothyroidism?

A

L thyroxine (levothyroxine sodium) synthyroid

112
Q

What is the MOA of snthyroid?

A

T4 can be converted to T3
thyroid hormones bind to thyroid receptor proteins in the cell nucleus and exert metabolic effects through control of DNA transcription and protein synthesis in multiple sites throughout the body; involved in normal metabolism, growth, and development; promotes gluconeogenesis, increases utilization and mobilization of glycogen stores and stimulates protein synthesis, increases basal metabolic rate

113
Q

What is the PO onset of action for Synthyroid?

A

3-5 days

114
Q

What is the IV onset of action for Synthyroid?

A

peak therapeutic effect may require 4-6 weeks

within 6-8 hours

115
Q

What are airway considerations for hypothyroidism?

A 
airway compromise
decreased gastric emptying
hypo-dynamic cardiovascular system
decreased ventilatory responsiveness
hypothermia
hematologic abnormalities
116
Q

Why do you have airway compromise in hypothyroidism?

A

s/c to a swollen oral cavity, edematous vocal cords, or goiter

117
Q

What does decreased gastric emptying in hypothyroidism placed the patient at risk for?

A

risk of aspiration

118
Q

What hemodynamic changes are seen in hypothyroidism?

A

decreased CO, SV, baroreceptor reflexes, and intravascular volume may be compromised by surgical stress and cardiac-depressant anesthetic agents

119
Q

What are the hematologic abnormalities seen with hypothyroidism?

A

anemia
platelet dysfunction
electrolyte imbalances and hypoglycemia

120
Q

How do you manage hypothyroidism in an anesthesia emergency?

A

potential for severe intraoperative cardiovascular instability and myxedema coma
V thyroid replacement (IV tT3 is effective in 6 hours)
Steroid coverage
Phosphodiesterase inhibitors (milirnone) can reduce myocardial contractility

121
Q

What is myxedema coma?

A

rare, severe form of hypothyroidism characterized by delirium or unconsicousness, hypoventilatoin, hypothermia, bradycardia, hypotension, and severe dilutional hyponatremia

122
Q

When is myxedema coma?

A

most commonly in elderly women with a long history of hypothyroidism

123
Q

What is the treatment of myedema coma?

A

IV T4 or T3 and IV steroids for possible adrenal insufficiency

124
Q

What is a goiter?

A

swelling of the thyroid gland

125
Q

What can cause a goiter?

A 
hypothyroidism or hyperthyroidism
deficient intake of iodine
ingestion of a dietary
pharmacologic goiterogen
defect in the hormonal biosynthetic pathway
126
Q

Why does a goiter occur?

A

compensatory hypertrophy and hyperplasia of follicular epithelium secondary to a reduction in thyroid hormone output

127
Q

What are nontoxic goiters?

A

euthyroid

128
Q

What can nontoxic goiters lead to?

A

toxic multinodular goiter

129
Q

What is anesthetic management for a goiter?

A

anesthetic management includes careful airway evaluation and extreme caution with any respiratory depressant prior to securement of the airway

130
Q

What are the anesthetic considerations prior to thyroid surgery?

A

patient is euthyroid (may delay elective procedure 6-8 weeks)
airway compromised with large goiters can present wiht nerve compression, tracheal deviation, and erosion
use of RLN monitor

131
Q

What indicates optimal treatment for effectiveness for thyroid surgery?

A

1-2 months of medication treatment followed by recent TSH and T3/T4`

132
Q

What are complications of thyroid surgery?

A

higher morbidity
recurrent laryngeal injury (unilateral or bilateral)
paralysis of abductor vocal cord muscle results in median/ paramedian cord position
superior larygneal nerve injury
hypoparathyroidism
tracheal compression

133
Q

What is seen with an SLN injury?

A

weakness of the voice in ability to create high tones

134
Q

What is seen in unilateral RLN?

A

hoarseness

135
Q

What is seen in bilateral RLN?

A

airway obstruction, may require tracheostomy

136
Q

How does hypoparatyhroidism occur in thyroid surgery?

A

result from damage to the blood supply of the parathyroid gland, not usually inadvertent removal

137
Q

What are signs of hypoparathyroidism in thyroid surgery?

A

hypocalcemia 24-48 hrs postoperatively

stridor/laryngeal spasm (treatment IV calcium)

138
Q

How does tracheal compression occur in thyroid surgery?

A

expanding hematoma

139
Q

What is the treatment of expanding hematoma?

A

evacuation is first line treatment

N935 Pathophysiology (6 decks)

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