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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
In hyperthyroidism, TSH will be
decreased
26
Which thyroid hormone is more active?
T3 | 3-4x more active then T4
27
What is the half life of T3?
1-3 days
28
How much is T3 bound to albumin?
99.7%
29
T3 is synthesized in the thyroid gland, but also formed in the
liver and kidneys by peripheral conversion of T4 by selenodeiodinases
30
How much is thyroxine synthesized and released by the thyroid gland?
90%
31
what is the serum half life of T4
6-7 days (1 week)
32
What % is t4 bound to thyroid binding globulin?
99.9%
33
How do T3 and T4 circulate the blood stream?
circulate tightly protein bound
34
Which hormone is more tightly bound?
t4 | leads to the longer 1/2 life
35
Which hormone has a larger amount circulating in the blood stream?
t3 | 0.4 vs 0.04%
36
What state of the thyroid hormone drives the patient's metabolic state?
free form and active
37
When performing thyroid test, what is important to look at?
clinical picture and laboratory tests
38
What are principle thyroid function tests?
TSH serum T4 serum T3 radioactive iodine uptake
39
What occurs to thyroid tests with aging?
increase in baseline TSH
40
What is a normal range of T4?
4.5-12ug/dL
41
What is a normal range of T3?
90-200mcg/dL
42
What is a normal range of TSH?
0.4-4.5ug/dL
43
What is a normal range of free t4?
0.7-1.6mg/dL
44
What is a normal range of free t3?
230-420mg/L
45
What is a normal range of RAIU?
8-35% at 24hour
46
What is subclinical hyperthyroidism diagnosis?
TSH level of 0.1-0.4mu/L with normal levels of free T3 and free T4
47
What is overt hyperthyroidism diagnosis?
TSH below 0.03mu/L with elevated T3/T4
48
What is subclinical hypothyroidism diagnosis?
TSH level of 5-10mu/L with normal levels of T3 adn T4
49
What is overt hypothyroidism diagnosis?
TSH level higher than 20 mu/L with reduced levels of T3 and T4
50
How do you diagnosis pituitary dysfunction?
Thyrotropin releasing hormone test
51
What occurs when TRH is administered with second hypothyroidism?
does not produce an increase in TSH
52
How can you test for pituitary dysfunction?
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
53
What is a life threatening emergency in hyperthyroidism?
thyroid storm
54
Thyrotoxicosis
clinical syndrome caused by increased thyroid hormone levels, regardless of cause
55
Hyperthyroidism
syndrome caused by an intrinsic abnormality of the thyroid, but the two terms are used interchangeably
56
What will laboratory levels reveal in hyperthyroidism?
low TSH and high free T4 and T3
57
In subclinical hyperthyroidism, lab levels reveal
TSH is low but free t4 and free T3 are normal
58
Hyperthyroidism is most caused by by
primary thyroid abnormality but may result from a TSH producing pituitary adenoma
59
Symptoms of hyperthyroidism
``` 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
What are causes of hyperthyroidism?
``` graves disease toxic multinodular goiter autonomously functioning thyroid nodule thyroiditis exogenous thyroid hormone ingestion iodine induced ```
61
What % of hyperthyroidism cases are Graves disease?
85%
62
What is graves disease?
autoimmune disease caused by thyroid-stimulating and antibodies that bind to TSH receptors in the thyroid, stimulating thyroid growth, vascularity, and hyper-secretion
63
What can cause morbidity adn mortality of hyperthyroidism?
increased HR hypermetabolism myopathies
64
What an increased HR in hyperthyroidism cause?
can lead to stroke, MI ectopy, CHF PVCs and a fib
65
What can hypermetabolism cause with hyperthyroidism?
increased CO2 production-> increased minute ventilation-> weakness in respiratory muscles
66
How do you treat hyperthyroidism?
anti-thyroid medications radioactive iodine thyroidectomy
67
What is an example of an anti-thyroid medication?
thionamides | propylthiouracil (PTU) or methimazole
68
MOA of propylthiouracil (PTU)
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
When should you perform a thyroidectomy?
should only be performed after euthyroid state has been achieved with medication
70
When should radioactive iodine be used?
used for recurrent or persistent hyperthyroidism
71
What is thyroid storm?
an acute life threatening form of hyperthyroidism | significant associated mortality (>20%)
72
How do you diagnosis thyroid storm?
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
What can cause thyroid storm?
``` surgery infection IV contrast dyes DKA trauma vigorous palpitation of thyroid ```
74
When does thyroid storm most likely occur?
postoperatively treated of inadequately treated hyperthyroidism patients
75
How do you treat thyroid storm?
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
What is supportive care for thyroid storm?
aggressive treatment of temperature acid-base abnormalities (oxygenation and ventilation hydration (consider glucose containing fluids for hypermetabolism oxygen
77
What is the typical adult dose of antithyroid agents (PTU) ?
1200-1500mg/day given in 200-250mg increaments PO or via gastric tube
78
What is the typical adult dose of antithyroid agents methimazole?
120mg given in 20mg increments PO or via gastric tube
79
What is the MOA of antithyroid agents, PTU
prevents production of more T4 and T3 in the thyroid, and blocks the conversion of T4 to T3 outside the thyroid
80
What is the MOA of antithyroid agents, methimazole
prevents production of stored thyroid hormone from the thyroid gland
81
What is the dose for lugols solution
10 drops BID PO or via gastric tube
82
What is the dose for saturated solution of potassium iodide (Pima, SSKI)
8 drops every 6 hours PO or via gastric tube
83
What are iodides?
lugol drops | saturated solution of potassium iodide
84
What is the MOA of iodides?
blocks release of stored thyroid hormone form thyroid gland
85
What is the adult dose of glucocorticoids, dexamethasone?
2mg Q6 PO or IV
86
What is the adult dose of glucocorticoids, hydrocortisone?
100mg IV every 8 hours
87
What is the MOA of glucocorticoids?
blocks conversion of T4 to T3
88
What is an adult dose of beta blockers, propranolol?
1mg/min IV as required than 60-80mg q4 hours PO or gastric tube
89
What is an adult dose of beta blockers, esmolol?
500mcg/kg/min for 1 min then 50-100mcg/kg/min for 4 minute
90
What is the MOA of BB?
reduces symptoms tachycardia, tremor, restlessness, caused by a heightened response to catecholamines; blocks conversion T4 and T3
91
What drugs do you avoid in hyperthyroidism?
aspirin amiodarone caution with beta blocks
92
Why is aspirin CKA in hyperthyroidism?
associated with displacement of thyroid hormone bind from thyroid binding globulin-> increased free thyroid hormone
93
Why is amiodarone CKA in hyperthyroidism?
an iodine containing drug | largerly because of effects on peripheral deiondination of t4 to t3
94
What do you caution BB with hyperthyroidism?
a moderate degree of compensatory tachycardia may be necessary to maintain adequate in some patients
95
Pre-operative Anesthesia Implications in Trauma patient with hyperthyroidism
good premedication (benzo/narcotics)
96
Intra-operative Anesthesia Implications in Trauma patient with hyperthyroidism
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
postoperative Anesthesia Implications in Trauma patient with hyperthyroidism
continue beta blocker (1/2 life of T4 is 7-8days)
98
What drugs need to be avoid in hyperthyroidism due to effect on SNS?
epi, ketamine, dopamine, ephedrine
99
What is primary hypothyroidism?
decreased production of thyroid hormones despite normal TSH
100
What are the most common cause of hypothyroidism?
ablation of the gland by radioactive iodine therapy or surgery
101
What is autoimmune hypothyroidism?
autoantibodies block TSH in the thyroid
102
What happens to the receptors in autoimmune hypothyroidism?
destorys receptors (instead of stimulating)
103
What is secondary hypothyroidism?
secondary to hypothalamic or pituitary disease
104
What is hashimoto's thyroiditis?
autoimmune disorder, goiter, hypothyroidism | commonly in middle-aged women
105
What are mild signs and symptoms of hypothyroidism?
tires easily, weight gain despite decreased appetite
106
What are moderate to severe symptoms of hypothyroidism?
``` 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
How do you diagnosis primary hypothyroidism?
reduced levels of T4, T3, and elevated TSH
108
How do you diagnosis secondary hypothyroidism?
reduced levels of T4, T3 and reduced TSH
109
What can confirm pituitary pathology as the diagnosis of hypothyroidism?
TRH stimulation test
110
What occurs in primary hypothyroidism with a TRH stimulation test?
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
How do you treat hypothyroidism?
L thyroxine (levothyroxine sodium) synthyroid
112
What is the MOA of snthyroid?
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
What is the PO onset of action for Synthyroid?
3-5 days
114
What is the IV onset of action for Synthyroid?
peak therapeutic effect may require 4-6 weeks | within 6-8 hours
115
What are airway considerations for hypothyroidism?
``` airway compromise decreased gastric emptying hypo-dynamic cardiovascular system decreased ventilatory responsiveness hypothermia hematologic abnormalities ```
116
Why do you have airway compromise in hypothyroidism?
s/c to a swollen oral cavity, edematous vocal cords, or goiter
117
What does decreased gastric emptying in hypothyroidism placed the patient at risk for?
risk of aspiration
118
What hemodynamic changes are seen in hypothyroidism?
decreased CO, SV, baroreceptor reflexes, and intravascular volume may be compromised by surgical stress and cardiac-depressant anesthetic agents
119
What are the hematologic abnormalities seen with hypothyroidism?
anemia platelet dysfunction electrolyte imbalances and hypoglycemia
120
How do you manage hypothyroidism in an anesthesia emergency?
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
What is myxedema coma?
rare, severe form of hypothyroidism characterized by delirium or unconsicousness, hypoventilatoin, hypothermia, bradycardia, hypotension, and severe dilutional hyponatremia
122
When is myxedema coma?
most commonly in elderly women with a long history of hypothyroidism
123
What is the treatment of myedema coma?
IV T4 or T3 and IV steroids for possible adrenal insufficiency
124
What is a goiter?
swelling of the thyroid gland
125
What can cause a goiter?
``` hypothyroidism or hyperthyroidism deficient intake of iodine ingestion of a dietary pharmacologic goiterogen defect in the hormonal biosynthetic pathway ```
126
Why does a goiter occur?
compensatory hypertrophy and hyperplasia of follicular epithelium secondary to a reduction in thyroid hormone output
127
What are nontoxic goiters?
euthyroid
128
What can nontoxic goiters lead to?
toxic multinodular goiter
129
What is anesthetic management for a goiter?
anesthetic management includes careful airway evaluation and extreme caution with any respiratory depressant prior to securement of the airway
130
What are the anesthetic considerations prior to thyroid surgery?
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
What indicates optimal treatment for effectiveness for thyroid surgery?
1-2 months of medication treatment followed by recent TSH and T3/T4`
132
What are complications of thyroid surgery?
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
What is seen with an SLN injury?
weakness of the voice in ability to create high tones
134
What is seen in unilateral RLN?
hoarseness
135
What is seen in bilateral RLN?
airway obstruction, may require tracheostomy
136
How does hypoparatyhroidism occur in thyroid surgery?
result from damage to the blood supply of the parathyroid gland, not usually inadvertent removal
137
What are signs of hypoparathyroidism in thyroid surgery?
hypocalcemia 24-48 hrs postoperatively | stridor/laryngeal spasm (treatment IV calcium)
138
How does tracheal compression occur in thyroid surgery?
expanding hematoma
139
What is the treatment of expanding hematoma?
evacuation is first line treatment

N935 Pathophysiology (6 decks)

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