Thyroid Flashcards
Where is the thyroid located?
Immediately below larynx, anterior and to each side of the trachea
How much does the thyroid gland weigh?
15-20 grams in adults
What is the #1 and #2 endocrinopathy?
DM - #1
Thyroid disease - #2
What does the thyroid gland do?
regulates the metabolic rate of the body
What does a complete lack of thyroid secretion result in?
Basal metabolic rate decrease of 40-50%
What does an extreme excess of thyroid secretion result in?
Increase basal metabolic rate by 60-100% above normal
The SLN and RLN are branches of what nerve?
CN X (Vagus nerve)
Where does the phrenic nerve come down from?
C3, 4, 5
What hormones does the thyroid produce?
- Thyroxine (T4)
-Triiodothyronine (T3)
-reverse T3 (rT3)-inactive - calcitonin (important for calcium regulation)
What kind of cells is the thyroid made of?
Follicles of cuboidal epithelial cells surrounding colloid matrix
What substance is required for thyroid hormone synthesis?
IODINE
What is the colloid matrix?
A substance made of a protein called thyroglobulin which is responsible for the formation and storage of thyroid hormone
What is tyrosine?
An amino acid
(amino acids are building blocks of protein= tyrosine is the building block of thyroglobulin)
What does iodine combine with to form T3 and T4?
Iodine combines w thyroglobulin in the colloid to form T3 and T4
T3 is _______ T4 which occurs in the target tissues
T3 is de-iodinated T4 which occurs in the target tissues
(T3 loses and iodine atom)
What two hormones are the most important thyroid hormones for metabolic control?
Thyroxine (T4) and Triiodothyronine (T3)
How do T4 and T3 differ?
The function of the 2 hormones are qualitatively the same but they differ in their rapidity and intensity of action
In what percentage does the thyroid secrete thyroxine (T4)?
93% (though nearly all is converted to T3 in the tissues)
In what percentage does the thyroid secrete triiodothyronine (T3)?
7% (T3 is mostly produced outside thyroid gland)
T3 is _________ x more potent than T4, but is more _____and is _______ more rapidly
T3 is 4x more potent than T4, but is more scarce and is cleared more rapidly
What is released by the hypothalamus?
Thyrotropin-releasing hormone (TRH)
What does TRH cause the release of, and from where?
thyroid-stimulating hormone (TSH) by the anterior pituitary
What does TSH cause the release of and from where?
Thyroid hormones (T3, T4) from the thyroid gland
What hormones are active?
T3 and T4
but over 99% is bound to protein (thyroxine-binding globulin (TBG) or albumin
Peripheral tissues contain enzymes that convert what?
T4 to T3 (T3 is more metabolically active)
TH activate intracellular processes, these increase gene transcription, protein and enzyme production which increase metabolic rate
What do T3 and T4 (TH) increase?
TH increases the size, and number of mitochondria, which are the energy generators of the cells.
What cells are targets for thyroid hormones?
It is likely that all cells in the body are targets for thyroid hormones
- thyroid hormones effect metabolism, growth, and development
What are the thyroid hormone effects?
- Stimulation of carbohydrate metabolism
(increased uptake of glucose by cells and GI tract, enhances glycolysis, gluconeogenesis, and insulin secretion) - Stimulation of fat metabolism
(mobilizes lipids, decreases fat stores, decreases cholesterol)
-Increased requirement for vitamins
(Vitamins are needed for increased enzyme synthesis)
- Increased Basal metabolic rate
(increased metabolism in almost all cells) - Decreased body weight
(Does not always occur bc appetite is also increased) - Brings up blood sugar
What are the cardiovascular effects of thyroid hormones?
-Increase blood flow secondary to vasodilation
-Increased CO
-increased heart strength and HR
- Increase SBP, decreased DBP, increase pulse pressure (normal MAP)
-Increase respiration (d/t more CO2 produced)
-Increased number and affinity of beta-adrenergic receptors
-Decreased number of cardiac alpha-adrenergic receptors
What are the CNS effects of thyroid hormone?
increased mentation
increased anxiety
increased neurosis
What are the muscular effects of thyroid hormone?
Muscles more vigorous, become weak w protein catabolism
What are the effects on sleep by thyroid hormone?
causes exhaustive sleep states (Hypo)
excitable effects (hyper) - constantly tired but can’t sleep
Hypothyroid pts can sometimes need 12-14 hrs a day of sleep
What are the endocrine effects of thyroid hormone?
increases secretion by glands but also the need for hormone from peripheral tissues
What are the reproductive effects of thyroid hormone?
lack of thyroid hormone causes loss of libido
excess causes impotence
- inconsistent menstrual changes occur
What are the symptoms of Hypothyroidism?
-Cold intolerance (body not producing heat)
-constipation
-depression
-fatigue
-muscle/joint pain
-paleness
-thin, brittle fingernails
-thin, brittle hair
-weakness
-wt gain
-decreased taste and smell
-hoarseness
-menstrual disorders
-puffy face, hands, and feet- d/t loss of proteins (can also see pleural/pericardial effusions)
- slow speech
-thickening of skin
-thinning of eyebrows
More common in females
What is Primary hypothyroidism?
T3, T4 are not produced bc of problems w thyroid gland
Causes:
Hashimoto’s
Surgical removal
Inadequate iodine
Radiation exposure
Lithium
TSH elevated
Low T4
What is secondary hypothyroidism? (5-10% of cases)
Inadequate T3, t4 d/t TSH not being released from the pituitary
TSH low
What is Tertiary Hypothyroidism (<5% of cases)
inadequate T3, t4 d/t Thyrotropin-releasing hormone (TRH) from the hypothalamus
Hypothyroidism that occurs in infancy leads to?
mental retardation and growth defects (cretinism)
What is the most severe form of hypothyroidism?
Myxedema coma
- Triggered by illness, stroke, infection/sepsis, exposure to the cold, medicines
Myxedema Coma is a state of decompensated hypothyroidism. All symptoms of a slow metabolism. Most cases of hypothyroidism are mild symptoms unlike myxedema coma. Myxedema coma is named after the symptoms it causes- Myxedema (non-pitting edema) Coma (altered state of consciousness/ mental status, hyper somnolent *not necessarily a coma)
What are the symptoms of Myxedema coma?
- coma
-decreased breathing
-decreased blood sugar
-decrease BP
-decreased temperature
Near total or total lack of thyroid hormone
What medications can cause myxedema coma?
Amiodarone or lithium can cause myxedema coma d/t iodine richness
How do you test for hypothyroidism?
Serum T4 assay is the standard test for thyroid gland function.
When are blood levels of rT3 high?
Euthyroid sick states (critical illness)
What is Levothyroxine (Synthroid)?
T4 (most commonly used)
what is Armour thyroid?
both T3 and T4
When do Thyroxine binding globulin (TBG) levels change?
liver disease and pregnancy
When should surgery be done?
Once the euthyroid state is achieved
What are some problems that can occur with a pt with hypothyroidism and anesthesia?
-lethargy
-HoTN
- bradycardia
-CHF
-gastroparesis
-hypoglycemia
-Hypothermia
-hypoventilation
-Hyponatremia
What induction is ideal to use in the hypothyroid pt?
Ketamine (but all meds can be used)
Anesthetic management of hypothyroidism:
-Be aware of the “crash on induction” possibility
-Ketamine “ideal” but all meds can be used
-MAC is usually not affected, potent volatile agents may worsen myocardial depression
-Regional anesthesia preferred if surgery permits
-Pancuronium/Rocuronium have vagolytic/sympathomimetic effects
-Aline is indicated with PA catheter in setting of cardiac failure
-Hypoventilation is very serious. Avoid any pre-op sedation prior to going to OR. Diminished response to hypoxia and hypercarbia
What is Hashimotos?
form of hypothyroidism. Associated w other forms of autoimmune (DM, adrenal insufficiency, myasthenia gravis)
What is thyroiditis?
-Thyroiditis: inflammation of the thyroid which causes release of excessive hormone but not increased production
Hyperthyroid is excess gland activity and thyrotoxicosis is increased hormones
What is thyrotoxicosis?
oversupply of thyroid hormones on peripheral tissues
What are the symptoms of hyperthyroidism?
- Palpitations
-Nervousness
-breathlessness
-fatigue
-tachycardia
-muscle weakness
-hair loss
-heat intolerance
-insomnia
-increased bowel movements - light or absent menstrual periods
-trembling hands
-warm moist skin
-staring gase (exophthalmos)
Tachycardia/ a-fib common. CO can double or triple normal
What’s the most common cause of hyperthyroidism?
Grave’s disease (60-90% of cases) - an autoimmune disease
-Autoantibodies activate the TSH receptor.
-Causes multinodular goiter
-Stimulates thyroid hormone synthesis, secretion and thyroid growth (goiter formation)
-Exophthalmos is caused by inflammation of the eye muscles by attacking autoantibodies.
More common in females 40-60 years old (caused by genetics, stress, or cigarette smoking)
What is the treatment for hyperthyroidism?
Suppressive medicines–> surgical or radioisotope therapy
Antithyroid drugs inhibit the production of Th
-Methimazole and propylthiouracil (PTU)
-Beta-blockers (Propranolol)
High dose iodine deceased thyroid activity
How do Methimazole and propylthiouracil (PTU) work?
inhibit iodination of thyroglobulin and conversion of T4 to T3
How do beta-blockers (propranolol) work in hyperthyroidism?
-L-isomer causes beta-blockade, treats tachycardia, tremor, palpitations, anxiety, and heat intolerance
-D-isomer inhibits the conversion of T4 to T3
any beta-blocker can be used but propranolol is most common
What is radioactive iodine?
one time dose in pill form, results in destruction of thyroid tissue
What kind of surgery would be done for hyperthyroidism?
Partial or total thyroidectomy
Not used extensively in the absence of cancer as meds are effective and risk of removing parathyroids or recurrent laryngeal nerve
What is thyroid storm?
An extreme form of hyperthyroidism
occurs 6-18 hrs post-op
80% of pts not suspected of having thyroid probs
What are the signs and symptoms of thyroid storm?
-Hyperthermia
-tachycardia
-dysrhythmias
-CHF
-Shock
What are the causes of thyroid storm?
-Surgery (especially of the thyroid gland)
-infection
-trauma
-toxemia
-DKA
What is the treatment for thyroid storm?
Hyperthyroid: Sodium iodide, Inderal/labetalol, Cortisol (increased utilization of cortisol), PTU
Hyperthermia: acetaminophen, cooling blankets
Hydration: Fluids and glucose (increased metabolism)
How do you prepare for surgery for a hyperthyroid pt?
-checking the airway
-administering antithyroid drugs,
-treating sxs of hyperdynamism
-treating volume depletion and electrolyte problems
-Check airway for goiter, wheezing, obstruction
Treatment for hyperthyroidism before surgery:
Sodium iodide and propranolol lead to euthyroidism in about 10 days
Antithyroid drugs 6-8 weeks before surgery include sodium iodide and propylthiouracil
Treat hyperdynamism with beta blockers
Treat hypovolemia with crystalloids
What drugs should be avoided in the pt w hyperthyroidism?
Avoid sympathomimetic drugs:
Atropine
Robinul
Ketamine
Pancuronium
Halothane
how do you prepare your hyperthyroid pt for emergency surgery?
-Check for upper airway obstruction
-Administer antithyroid drugs: sodium iodide, cortisol (blocks the peripheral conversion of T4 to T3, making rT3 instead), PTU
-Hydrate to compensate for hypovolemia
-Treat hyperdynamic vitals with propranolol
-Premedicate to decrease anxiety may require larger doses
-Treat heart failure with Digitalis and symptomatic support
What causes goiters?
Chronic stimulation by TSH
Can occur in iodine deficiency states (table salt contains iodine)
Not always visible
What will you be monitoring during a thyroidectomy and with what?
EGM with dragonfly nerve monitor or nim tube
What are you assessing for post-op thyroidectomy?
RLN damage:
unilateral= hoarseness
bilaterally= aphonia, stridor, aspiration
SLN damage: abnormal voice in upper registers
Hematoma: airway emergency–> decompression and intubation
Hypocalcemia: d/t inadvertent removal of parathyroids
can end w cv collapse
Tracheomalacia -tracheal softening= airway collapse w inspiration
What can happen with hypocalcemia?
Hypocalcemia- monitor Ca+ levels.
Laryngeal stridor can progress to laryngospasm, often an early sign of hypocalcemic tetany.
CV collapse if Ca+ is not replaced.
Tracheomalacia or a tracheal compression from hematoma.
What are the functional units of the thyroid gland?
follicles (each lobule is composed of 20-40 follicles)
How much ingest iodine is required each week to form normal quantities of thyroid hormones?
1 mg
What’s the most vascular organ?
Thyroid
Where are hormones made and stored?
colloid matrix
what do you need in your every day diet?
tyrosine and iodine
Thyroglobulin is responsible for:
the formation and storage of thyroid hormone
What are the causes of Primary Hypothyroidism?
-Hashimoto’s
-Surgical removal
-inadequate iodine
-radiation exposure
-lithium
What are the 2 roles of propranolol?
L-isomer causes beta blockade
D-isomer inhibits conversion of T4 to T3
What meds should be avoided in Hyperthyroidism?
-Halothane
-Atropine
-Robinul (glycopyrrolate)
-Ketamine
-Pancuronium
Sympathomimetic drugs
What will you see with hypocalcemia?
-Weakness
-Tetany
-Laryngospasm
(24-72hrs later)
