Thyroid Lecture Flashcards
The blood supply to the thyroid includes
the superior and inferior thyroid arteries
superior, middle, and inferior thyroid veins
The lymphatic drainage of the thyroid includes
upper and lower deep cervical lymph node
pretracheal and paratracheal lymph node
The _________ and the external motor branch of the __________ are in intimate proximity to the thyroid gland
recurrent laryngeal nerve; superior laryngeal nerve
The thyroid gland consists of
two lobes joined by an isthmus
upper isthmus borders the cricoid cartilage
The thyroid gland is innervated by
adrenergic** and cholinergic** nervous systems
The thyroid gland takes absorbed
exogenous iodide**** (iodine is reduced to iodide in the gut) into the gland and synthesizes 2 hormones
The two thyroid hormones include:
triiodothyronine (T3)
Thyroxine (t4) **
Thyroid hormone production is dependent on
availability of exogenous iodine**
Iodine is reduced to iodide in the GI tract, absorbed into the blood stream and then is actively transported from
the plasma into the thyroid follicular cells***
_________________ are stored in the ______until they are needed and released into circulation
T3 & T4 are stored in the colloid
Iodide gets trapped inside the follicular cell and gets compounded with
tyrosine and thyroglobulin and yields monoiodotryosine and diiodotyrosine
which are then coupled to form triiodothyronine (T3)* and thyroxine (T4)*
The role of thyroid hormone
affects virtually all metabolic processes in the body
- regulates carbohydrate, lipid, and protein metabolism
- necessary for fetal development
- CNS development and activity
- Bone and tissue growth
- Gastrointestinal regulation
- Cardiac myocytes- contractility
- Vascular smooth muscle- direct vasodilation
Thyroid hormone release is the interaction between
hypothalamic-pituitary axis
thyroid gland
and thyroid hormones
The _______ controls the release of thyrotropin-releasing hormone
hypothalamus**
In the pituitary gland, the
TRH stimulates the secretion of thyroid stimulating hormone*** from the anterior pituitary
TSH acts on the
thyroid gland** to enhance synthesis and secretion of T3 & T4
A _______ exists between the hypothalamus, pituitary, and the thyroid gland
classic feedback loop**
Increased levels of thyroid hormone
INHIBIT**** secretion of TSH from the pituitary
negative feedback loop
Thyroid hormone levels are the primary determinant of
TSH secretion
The function of thyroid stimulating hormone is to
control production of thyroid hormones thyroxine (T4) & triiodothyronine (T3)
stimulates all aspects of thyroid hormone production- uptake of iodide, iodide incorporation, eventual release of T4 & T3
In hypothyroidism, the TSH level will be
ELEVATED ****
In hyperthyroidism, the TSH level will be
DECREASED**
10% of triiodothyronine (T3) is synthesized and released by
the thyroid gland
-also formed in the liver and kidneys by peripheral conversion of T4 by selenodeiodinases
T3 is ____________ than t4
3-4x’s more active*****
The half life of triiodothyronine is
1-3 days****
Triiodothyronine is _______ bound to albumin
99.7%
_________ of thyroxine (T4) is synthesized and released by the thyroid gland
90%
Thyroxine has a serum half life of
6-7 days (about 1 week)****
________ % of thyroxine (T4) is bound to thyroid binding globulin
99.9
Both T3 and T4 circulate
tightly protein bound in the blood stream
T4 is more tightly bound than T3 (leads to its longer half-life)
a larger amount of T3 circulates in the bloodstream compared to T4
It is the ______ form of T3 & T4 that is active and drives patient’s metabolic state
free
When analyzing thyroid function tests,
it is important to combine both clinical picture with laboratory tests
The principle thyroid function tests include
TSH, serum T4, serum T3, radioactive iodine uptake (RAIU)
With aging, there is _________ in baseline TSH
an increase
Normal thyroid stimulating hormone (TSH) is
0.4-5.0 milliunits/L *****
Subclinical hyperthyroidism is defined as
TSH level of 0.1-0.4 milliunits/L with normal levels of free T3 and free T4
Overt hyperthyroidism is defined as
TSH level below 0.03 milliunits/L with elevated T3 and T4
Subclinical hypothyroidism is defined as
TSH level of 5.0-10 milliunits/L with normal levels of T3 and T4
Overt hypothyroidism is defined as
a TSH level higher than 20.0 milliunits/L with reduced levels of T3 and T4
A diagnosis of pituitary dysfunction can be performed from
thyrotropin releasing hormone test- injection of exogenous TRH by rapid IV push
serum concentration of TSH is collected at 15 and 30 min intervals over 2-3 hours
normally TSH would rise in concentration
If hypothyroidism is due to pituitary disease (secondary hypothyroidism) administration of TRH
does not produce an increase in TSH
Thyroid pathophysiology includes
hyperthyroidism
hypothyroidism
goiter & thyroid tumors
Hyperthyroidism has a wide clinical spectrum ranging from
subclinical to life-threatening thyroid storm*
Hyperthyroidism laboratory values will display
low TSH and high free T4 and T3
In subclinical hyperthyroidism the TSH is
low but free T4 and free T3 are normal
Causes of hyperthyroidism include
Graves disease*** (most common) toxic multinodular goiter autonomously functioning thyroid nodule thyroiditis exogenous thyroid hormone ingestion iodine induced
Graves disease is an
autoimmune disease caused by thyroid-stimulating antibodies that bind to TSH receptors in the thyroid, stimulating thyroid growth, vascularity, and hypersecretion
Signs and symptoms of hyperthyroidism include
hypermetabolic state
- anxious, restless, hyperkinetic
- warm skin, sweating, flushed, heat intolerance
- protruding eyes (exophthalmos or proptosis)
- weakness, fatigue, inability to sleep
- tremors, weight loss, frequent bowel movements
- increased cardiac work, tachycardia, dysrhythmias, palpitations
Increased heart rate as a result of hyperthyroidism can lead to
stroke, MI, ectopy, CHF, PVCs, and a fib
Hypermetabolism results in
-increased CO2 production–> increased minute ventilation–> weakness in respiratory muscles
Morbidity and mortality related to hyperthyroidism includes
increased HR
hypermetabolism
myopathies
Treatment of hyperthyroidism includes
antithyroid medications
radioactive iodine
thyroidectomy
A thyroidectomy should only be performed after
euthyroid state has been achieved with medication
Radioactive iodine may be used for
recurrent or persistent hyperthyroidism
Anti-thyroid medications include
thionamides- Propylthiouracil (PTU) or methimazole
interferes with coupling of thyroid hormones in the thyroid
Thyroid storm is an
acute life-threatening form of hyperthyroidism
significant associated mortality (>20%)
The diagnosis of thyroid storm is ffrom
temperature elevation with diaphoresis (as high as 106 degrees) marked tachycardia (can manifest as afib or Vtach) cerebral dysfunction (confusion, psychosis, seizures, etc.) Gastrointestinal disorders (N/V, obstruction)
Precipitating events for thyroid storm can include
surgery, infection, IV contrast dyes, DKA, trauma, and even vigorous palpation of the thyroid
Thyroid storm most often occurs
in the postoperative period of inadequately treated hyperthyroid patients
Treatment of thyroid storm includes
decrease production, conversion, and secretion of thyroid hormone (propylthiouracil, corticosteroids)
supportive care- aggressive tx. of temperature, acid-base abnormalities oxygenation & ventilation, oxygen, hydration- consider glucose containing fluids for hypermetabolism
beta blockers- propranolol, esmolol
determine underlying cause
consider avoiding SNS activation (ketamine, epi, etc.)
Preoperative management of anesthesia in the emergent patient with hyperthyroidism includes
good premedication (benzos/narcs) avoid anticholinergics- may precipitate tachycardia
Intraoperative management of anesthesia in the emergent patient with hyperthyroidism includes
consider invasive monitoring (e.g. a-line)
-differentiate between MH and thyroid storm
-adequate anesthetic depth to avoid exaggerated SNS response
-avoid ketamine, ephedrine, epinephrine, dopamine due to effect on SNS
hypotension- consider fluids and direct acting vasopressor (phenylephrine)
succs, NDMR, and N2O are okay
eye protection (lubricant, pads)
Postoperative management of anesthesia in the emergent patient with hyperthyroidism includes
continue beta blocker for 7-8 days
Hypothyroidism or myxedema can be
primary hypothyroidism (90-95% of all cases) autoimmune hypothyroidism secondary hypothyroidism
Describe primary hypothyroidism:
decreased production of thyroid hormones despite normal TSH
most common causes are ablation of the gland by radioactive iodine therapy or surgery
Describe autoimmune hypothyroidism:
autoantibodies block TSH receptors in the thyroid
this immune response destroys receptors (instead of stimulating)
Describe secondary hypothyroidism:
secondary to hypothalamic or pituitary disease
Hashimoto’s thyroiditis is
autoimmune disorder, goiter, and hypothyroidism
commonly in middle aged women
Signs and symptoms of hypothyroidism include
slow, progressive
mild-tires easily, weight gain despite decreased appetite
Signs and symptoms of moderate to severe hypothyroidism include
fatigue, apathy, listlessness
slow speech
cold intolerance, decreased sweating, constipation, menorrhagia, slow motor function
slowed gastrointestinal function
dry hair, skin, large tongue, periorbital edema
cardiomyopathy, impaired baroreceptor function, bradycardia, hyponatremia
impaired ventilatory response to hypoxia and hypercarbia
Describe the diagnosis of primary versus secondary hypothyroidism
primary- reduced levels of T4, T3 and elevated TSH
secondary (pituitary)- reduce levels of T4, T3 and reduced TSH
A _________ test can confirm pituitary pathology as a cause of hypothyroidism
TRH stimulation test
-in primary hypothyroidism 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
Treatment of hypothyroidism is
L-Thyroxine (levothyroxine sodium) “synthroid”**
pharmacology: levothyroxine is a synthetic form of thyroxine
Onset of action: oral 3 to 5 days, peak effect may required 4 to 6 weeks
Anesthetic considerations for the patient with hypothyroidism includes ***
airway compromise secondary to a swollen oral cavity, edematous vocal cords, or goiter
decreased gastric emptying increases the risk of aspiration
hypodynamic cardiovascular system
decreased ventilatory responsiveness to hypoxia and hypercarbia
risk for hypothermia
hematologic abnormalities
increased sensitivity to sedatives/narcotics
Describe the hypodynamic cardiovascular system as it relates to hypothyroidism & anesthetic considerations
decreased CO, SV, HR, baroreceptor reflexes, and intravascular volume may be compromised by surgical stress and cardiac-depressant anesthetic agents
Describe the hematologic abnormalities as it relates to hypothyroidism and anesthetic considerations
anemia, platelet dysfunction, electrolyte imbalances, & hypoglycemia
Management of anesthesia in emergency with a patient who has hypothyroidism includes
potential for severe intraoperative CV instability & myxedema coma
IV thyroid replacement- IV triiodothyronine is effective in 6 hours
steroid coverage
phosphodiesterase inhibitors such as milrinone may be effective in the tx. of reduced myocardial contrality
The mortality rate of myxedema coma is
50%
Myxedema coma is a
medical emergency & requires IV thyroxine or triiodothyronine and IV steroids for possible adrenal insufficiency
Myxedema coma most commonly occurs in
elderly women with a long history of untreated hypothyroidism
Myxedema coma is a
rare, severe form of hypothyroidism characterized by delirium or unconsciousness, hypoventilation, hypothermia, bradycardia, hypotension, and a severe dilutional hyponatremia
Goiter is the
swelling of the thyroid gland
can be a result of hypothyroidism or hyperthyroidism
Causes of goiter include
deficient intake of iodine
ingestion of a dietary agent (e.g. cassava)
pharmacologic goitrogen
defect in the hormonal biosynthetic pathway
Anesthetic management of the patient with goiter includes
careful airway evaluation and extreme caution with any respiratory depressants prior to securement of the airway
Nontoxic goiters are
euthyroid but can lead to toxic multinodular goiter
Complications of thyroid surgery includes
superior laryngeal nerve injury
recurrent laryngeal nerve injury
Superior laryngeal nerve injury results in
weakness of the voice in ability to create high tones
Recurrent laryngeal nerve injury can be
unilateral or bilateral
unilateral= hoarseness
bilateral= airway obstruction, may require tracheostomy
paralysis of the abductor vocal cord muscle results in median/paramedian cord position
Ideally, the patient with thyroid issues should be
euthyroid prior to any surgical procedure- may require delay of elective surgery for 6-8 weeks
Thyroid surgery anesthetic considerations include
use of recurrent laryngeal nerve monitor
airway compromise with large goiters may be present with nerve compression, tracheal deviation, and erosion
1-2 months of medication treatment followed by recent TSH and T3/T4 may indicate optimal treatment effectiveness
Additional complications of thyroid surgery include
tracheal compression & hypoparathyroidism
Describe the complication of tracheal compression
due to expanding hematoma
hematoma evacuation is first-line treatment- at bedside if necessary
Describe the complication of hypoparathyroidism
can result from damage to the blood supply of the parathyroid gland, not usually inadvertent removal
- hypocalcemia 24-48 postoperatively
- stridor/laryngospasm- treatment is IV calcium
