N935 Advanced Pathophysiology II > Thyroid Pathophysiology > Flashcards

Thyroid Pathophysiology Flashcards

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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
aging and TSH
-increase in baseline TSH
26
normal TSH level
0.4-5.0 mu/L
27
subclinical hyperthyroidism
- TSH 0.1-0.4 mu/L | - normal levels of free T3 and T4
28
overt hyperthyroidism
- TSH level below 0.03 mu/L | - elevated T3 and T4
29
subclinical hypothyroidism
- TSH level 5.0-10 mu/L | - normal T3 and T4
30
overt hypothyroidism
- TSH level higher than 20 mu/L | - reduced T3 and T4
31
diagnosis of pituitary dysfunction
- 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
hyperthyroidism
- wide clinical spectrum ranging from subclinical to a life threatening thyroid storm - lab values = low TSH and high T3/T4
33
causes of hyperthyroidism
- graves disease - toxic multinodular goiter - autonomously functioning thyroid nodule - thyroiditis (inflammation/infection) - exogenous thyroid hormone ingestion - iodine induced
34
graves disease
autoimmune disease caused by thyroid stimulating antibodies that bind to the TSH receptors in the thyroid, stimulating thyroid growth, vascularity and hypersecretion
35
S/S hyperthyroidism
- 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
morbidity and mortality of hyperthyroidism-
- increased HR --> stroke, MI, ectopy, CHF, PVCs and A fib - hypermetabolism --> increase CO2 --> increased Ve --> weakness in resp muscles - myopathies
37
treatment of hyperthyroidism
- antithyroid medications - radioactive iodine may be used for recurrent or persistent hyperthyroidism - thyroidectomy (only if euthyroid state has been achieved)
38
propylthiouracil (PTU) or methimazole
- 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
thyroid storm
- acute life-threatening form of hyperthyroidism - significant associated mortality - most often occurs in postop period of inadequately treated hyperthyroid patient
40
clinical signs of thyroid storm
- 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
thyroid storm precipitating evnets
- surgery - infection - IV contrast dyes - DKA - trauma - Vigorous palpation of thyroid
42
thyroid storm treatment
- 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
preop management of emergency surgery in patient with hyperthyroid
- good premedication (benzos/narcotics) | - avoid anticholinergics (may precipitate tachycardia)
44
intraop management of emergency surgery in patient with hyperthyroid
- 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
postop management of emergency surgery in patient with hyperthyroid
continue beta blocker therapy because half life of T4 is 6-7 days
46
hypothyroidism (or myxedema)
- affects 0.5-0.8% of population - primary - autoimmune - secondary
47
primary hypothyroidism
- 90-95% - decreased production of TH despite normal TSH - most common causes are ablation of gland by radioactive iodine therapy or surgery
48
autoimmune hypothyroidism
- autoantibodies block TSH receptors in thyroid gland | - immune response destroys receptors (instead of stimulating)
49
secondary hypothyroidism
- 5% of all cases | - secondary to either hypothalamic or pituitary disease
50
hashimoto's thyroiditis
- autoimmune disorder, goiter, hypothyroidism | - common in middle aged women
51
mild s/s of hypothyroidism
- tires easily | - weight gain despite decreased appetite
52
moderate to severe s/s hypothyroidism
- 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
dianosis of hypothyroidism
- primary - reduced T4/T3 and elevated TSH | - secondary (pituitary) = reduced T3 and T4 and TSH
54
levothyroxine sodium (synthroid)
- 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
anesthetic considerations for hypothyroidism
- 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
anesthesia management of emergency surgery in patient with hypothyroid
- 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
myxedema coma
- 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
goiter
- swelling of thyroid - can occur in hyper or hypothyroidism - nontoxic goiters are euthyroid but can lead to toxic multinodular goiter
59
goiter causes
- deficient intake of iodine - ingestion of dietary substance that decreases iodine (raw cassava = cyanide) - pharmacologic goitrogen - defect in hormonal biosynthetic pathway
60
goiter anesthetic management
- careful airway eval | - extreme caution with resp depressants prior to airway securement
61
thyroid surgery anesthetic considerations
- 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
complications of thyroid surgery
- morbidity approaches 13% - recurrent laryngeal nerve injury - superior laryngeal nerve injury - hypoparathyroidism - tracheal compression from expanding hematoma
63
RLN injury
- 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
SLN injury
weakness of voice in ability to create high tones
65
hypoparathyroid during thyroid surgery
- usually result of damage of blood supply to parathyroid gland NOT inadvertent removal - hypocalcemia 24-48 hrs post op - stridor/laryngospasm (treatment IV calcium)
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