What is the hormonal pathway leading up to the release of thyroid hormones?
TRH (hypothalamus) --> TSH (anterior pituitary) --> T3/T4 bind to TBG (thyroid) --> TBG carries T3/T4 throughout the bloodstream
TRH: Thyroid Releashing Hormone
TSH: Thyroid Stimulating Hormone
TBG: thyroxine binding globulin
What is the first line screening test for thyroid dysfunction?
Why is this useful?
What values indicate hyper-, eu-, and hypo-thyroid states?
Iodine and T3/T4 (thyroid hormones) inhibit TRH and TSH secretion, so the level of TSH is a reflection of circulating T3/T4
What is the primary negative feedback loop involved in thyroid hormone regulation?
TRH and TSH stimulate thyroid hormone secretion
Iodine and thyroid hormone inhibit TRH and TSH secretion
Why are T4 levels a poor indicator of thyroid function?
T4 levels are not reliable due to extensive protein binding to TBG.
80% of T3 is produced by this process...
Extra-thyroidal de-iodination of T4
Compared to T4, T3 is ___ potent and _____ protein bound.
How much T3/T4 is free circulating hormone?
<0.1% of the T3 and T4 produced by the body.
What are some symptoms of hyperthyroidism?
Increased pulse pressure
What are some intrinsic causes of hyperthyroidism?
What are some extrathyroid causes of hyperthyroidism?
How should hyperthyroid patients be optimized?
They should be euthyroid on DOS.
This can take 6-8 weeks (NaI/KI --> PTU, methimazole)
In hyperthyroid pts, what meds should you avoid?
Sympathetic system stimulating meds (ketamine, pancuronium/pavulon, ephedrine, halothane)
Hyperthyroidism is commonly accompanied by this autoimmune disease. What is the disease and how does it effect our anesthetic plan?
We need to reduce our initial NMB dose.
Thyroidectomies are common surgeries that hyperthyroid patients undergo.
What are some common post-op complications of thyroidectomies?
Superior and Recurrent Laryngeal Nerve damage
HypoPTH (leads to hypo Ca++) w/ stridor
Corneal injury (due to exophthalmos of Graves)
Stridor can last 24-96 hours post-op
What are risk factors for the occurrence of thyroid storm? (Think Sx situations and disease states)
Thyroid Storm Is Deadly Man:
Mental status changes
What diseases/intra-op malignancies do thyroid storms resemble?
What are intra-operative treatments for thyroid storm?
Beta-blockade (esp with propranolol which inhibits T4->T3 conversion)
Decadron (reduces thyroid secretion and inhibits T4->T3 conversion)
PTU/methimaxole (via NGT)
What are absolutely contraindicated in the treatment of thyroid storm?
Any drugs that increase sympathetic output or hyperthermia
Aspirin! (can increase T3/T4 levels)
What are symptoms of hypothyroidism?
Decreased response to hypoxia/hypercapnia
What are primary and secondary causes of hypothyroidism?
What are the effects of decreased thyroid function on MAC?
What are some pre-op and intra-op concerns with hypothyroidism?
No real pre-op concern; pt does not have to be euthyroid unless severe
Watch out for bradycardia, etc.. ; no agents absolutely contraindicated
Consider A-line to manage CV
What is myxedema coma?
What is its mortality rate?
When does it occur?
What are its symptoms?
How do we treat it?
An outcome of severe hypothyroidism with a mortality rate of 25-50%
Usually occurs after stressful events (MI, infection drugs)
Symptoms: Stupor, hypoventilation, HoTN, hyponatremia
Treatment: IV thyroid replacement, steroids, warming
~50% of your body's serum Ca++ is bound to this protein. What is it?
What is the rest bound to?
The other 45% are ionized free (bound to nothing)
What are the functions of PTH (parathyroid hormone)?
Maintain serum Ca and Mg (renal reabsorption, bone resorption as well as GI absorption which requires vit D)
Phosphate excretion (occurs renally as Ca++ is reabsorbed)
Note: Mg+ will tend to follow Ca++
What is Calcitonin?
Where does it come from?
What does it do?
It is a hormone secreted from the thyroid gland?
It inhibits PTH (wastes Ca/Mg, save phosphate)
Vitamin __ assists Ca++ absorption from the ______________.
D, GI tract
HyperPTH means a high level of this ion.
What are some primary causes of hyperPTH?
Hyperplasia (too much cell growth)
MEN (multiple endocrine neoplasia) syndrome
Ectopic production (tumor)
What are some secondary causes of hyperPTH?
What are symptoms of hyperPTH?
Stones Bones Groans Moans:
kidney Stones (nephrolithiasis)
GI problems (ulcers)
Psychiatric overtones (fatigue, depression, thirst)
bradycardia, HTN, short QT, heart block
What are some treatments for HyperCa++?
IVF + Lasix
What population of patients are especially susceptible to the negative effects of hyperPTH and should be surgically treated?
Pregnant women due to high maternal/fetal mortality
Unlike many other electrolytes, excessive amounts of calcium tend to be excitatory/depressive. (choose one)
What are some post-op complications associated with parathryoidectomies?
Electrolyte imbalance (Ca/Mg/Phos)
Hungry bone syndrome (bones absorb Ca++ at high rates in response to surgery)
What are some causes of hypoparathyroidism?
What electrolyte imbalance does it cause?
Removal of PTH glands
Severe hypoMg (Ca++ and Mg+ follow each other)
What are some signs of HypoCa++?
Latent tetany (Trousseau)
Bonus. What is another name for Versed?
Midazolam. Good job, you're awesome.
Most common cause of hyperthyroidism is..
How do you distinguish between thyroid storm and MH?
Hyperventilation of pt will not decrease PaCO2 in MH but will decrease in thyroid storm.
(Gauge through ABGs)