Endocrine - Thyroid/Parathyroid Flashcards
T3
Triiodothryonine 10% synthesized & released by the thyroid gland Also formed in liver & kidneys 3-4x more active than T4 Half-life 1-3 days 99.7% albumin bound
T4
Thyroxine
90% synthesized & released by the thyroid gland
Half-life 6-7 days
99.9% bound to thyroid binding globulin
Hypothalamus
Controls thyrotropin-releasing hormone TRH
Pituitary Gland
TRH stimulates thyroid-stimulating hormone to release from the anterior pituitary
TSH controls thyroid hormone production
Thyroid Gland
TSH action site
Synthesis & secretion T3 & T4
What’s active thyroid hormone form?
Free form
Drives patient metabolic state
Thyroid Function Tests
TSH
Serum T3/T4
Radioactive iodine uptake
TSH
Normal 0.4-5 milliunits/L
Subclinical Hyperthyroidism
TSH 0.1-0.4 milliunits/L
Normal levels free T3 & T4
Over Hyperthyroidism
TSH level <0.03 milliunits/L
↑T3 & T4
Subclinical Hypothyroidism
Myxedema
TSH level 5-10 milliunits/L
Normal levels T3 & T4
20% women over 60yo
Overt Hypothyroidism
Myxedema
TSH level >20 milliunits/L
↓T3 & T4
Pituitary Dysfunction
Admin exogenous TRH
Collect serum TSH concentration
Normal response ↑TSH
Hypothyroidism d/t pituitary disease (2° hypothyroid) TRH admin does NOT produce ↑TSH
Hyperthyroidism
TSH level <0.03 milliunits/L
↑free T3 & T4
Thyroid hormones not shutting off w/ low TSH
Hyperthyroidism Causes
Graves disease - autoimmune disease caused by thyroid-stimulating antibodies that bind to TSH receptors in the thyroid → stimulating thyroid growth, vascularity, & hypersecretion Toxic multinodular goiter Autonomously functioning thyroid nodule Thyroiditis - inflammation/infection Exogenous thyroid hormone ingestion Iodine-induced
Hyperthyroidism S/S
Anxious, restless, hyperkinetic
Flushed, diaphoretic, & heat intolerance
Protruding eyes (exophthalmos or proptosis)
Weakness, fatigue, insomnia
Tremors, weight loss, frequent bowel movements
↑MVO2, tachycardia, dysrhythmias, palpitations
Hyperthyroidism Treatment
Anti-thyroid medications
- Thionamides (Propylthiouracil) interfere w/ thyroid hormone synthesis, prevents T4 → T3 conversion, admin weeks to months, monitor thyroid function tests
Radioactive iodine (recurrent or persistent hyperthyroidism)
Thyroidectomy - only after euthyroid state achieved w/ medication
Thyroid Storm
Acute life-threatening hyperthyroidism
Mortality >20%
S/S include fever w/ diaphoresis, tachycardia (Afib or Vtach), cerebral dysfunction (confusion, psychosis, seizures), GI disorders (N/V or obstruction)
Causes - surgery, infection, IV contrast dyes, DKA, trauma, or thyroid palpation
Most often occurs postop d/t inadequately treated hyperthyroid patients
Thyroid Storm Treatment
Propylthiouracil (PTU) ↓production, conversion, & secretion thyroid hormone
Corticosteroids block T4 → T3 conversion
Ice packs & cooling
Correct acid-base abnormalities - oxygenation & ventilation
Hydration consider glucose containing fluids
Oxygen
β blockers ↓MVO2
Avoid SNS activation
Determine underlying cause
Hyperthyroidism Anesthetic Considerations
Pre-medications to block SNS
Avoid anticholinergics
Invasive monitoring (A-line)
Differentiate b/w MH & thyroid storm
Adequate anesthesia depth to avoid exaggerated SNS response
Avoid Ketamine, Ephedrine, Epi, or Dopamine
Treat hypotension w/ fluids & direct-acting vasopressor
Eye protection
Continue β blocker postop
1° Hypothyroidism
↓thyroid hormone production despite normal TSH
Most common causes are thyroid gland ablation d/t radioactive iodine therapy or surgery
90-95% all cases
2° Hypothyroidism
Hypothalamic or pituitary disease
5% all cases
Autoimmune Hypothyroidism
Autoantibodies block TSH receptors in the thyroid
Immune response destroys receptors rather than stimulating
Hashimoto Thyroiditis
Autoimmune disorder, goiter, & hypothyroidism
Common in middle-aged women
Hypothyroidism S/S
Slow, progressive
Mild - fatigues easily & weight gain despite ↓appetite
Moderate to severe - fatigue, apathy, listless, slow speech, cold intolerance, ↓sweating, constipation, menorrhagia, slow motor function, ↓GI function, dry hair & skin, large tongue, periorbital edema, cardiomyopathy, impaired baroreceptor function, bradycardia, hyponatremia, impaired ventilatory response to hypoxia & hypercarbia
Hypothyroidism Diagnosis
1° (thyroid) ↓T3 & T4 levels ↑TSH
2° (pituitary) ↓T3 & T4 levels AND ↓TSH
Identify primary vs. secondary w/ TRH stim test
Hypothyroidism Treatment
L-thyroxine (Levothyroxine/Synthroid) Synthetic T4 thyroxine T4 → T3 Onset 3-5 days PO (peak therapeutic effect 4-6 weeks) IV 6-8 hours
Hypothyroidism Anesthetic Considerations
Airway compromise 2° swollen oral cavity, edematous vocal cords, or goiter
↓gastric emptying ↑aspiration risk
Hypodynamic CV system ↓HR/SV/CO (phosphodiesterase inhibitors treat reduced myocardial contractility MOA not β receptor dependent)
↓ventilatory response to hypoxia & hypercarbia
Hypothermia risk
Anemia, platelet dysfunction, electrolyte imbalances, & hypoglycemia
↑sensitivity to sedatives & narcotics
Myxedema Coma
Rare, severe form hypothyroidism Delirium or unconsciousness, hypoventilation, hypothermia, bradycardia, hypotension, & severe dilutional hyponatremia Elderly women w/ hypothyroidism history Mortality rate >50% MEDICAL EMERGENCY - IV thyroxine or triiodothyronine - IV steroids
Goiter
Thyroid gland swelling
Hyper OR hypothyroidism
Non-toxic goiters euthyroid → toxic multinodular goiter
Airway evaluation
Caution w/ respiratory depressants prior to airway airway securement
Thyroid Surgery
Anesthetic Considerations
Euthyroid prior to surgery
Delay elective surgery 6-8 weeks
Airway compromise w/ goiters - nerve compression, tracheal deviation, & erosion
1-2 mos treatment w/ recent TSH & T3/T4 to evaluate treatment effectiveness
Recurrent laryngeal nerve monitor
Thyroid Surgery Complications
RLN or SLN injury
Hypoparathyroidism d/t parathyroid gland blood supply damage
- Hypocalcemia 24-48H postop
- Stridor/laryngospasm (treatment IV calcium)
Tracheal compression d/t expanding hematoma (1st line treatment evacuation)
RLN Injury
Abductor vocal cord muscle paralysis results in median/paramedian cord position
Unilateral = hoarseness
Bilateral = airway obstruction (reintubate or trach)
SLN Injury
Voice weakness
Unable to create high tones “E”
Parathyroid Glands
4 parathyroid glands
Produce parathyroid hormone (PTH)
Maintains normal plasma calcium concentration
Parathyroid Hormone
PTH
Released into bloodstream via negative feedback
Dependent on plasma calcium concentration
Half-life 4 minutes
Average PTH level 8-51 pg/mL
Hypocalcemia →
Hypercalcemia →
Releases parathyroid hormone
Suppresses PTH synthesis & release
Calcitonin
Opposes PTH effects - lowers blood calcium
- Inhibits osteoclast activity in bones to promote Ca2+ storage
- Inhibits renal tubular cell Ca2+ reabsorption
- Inhibits Ca2+ absorption via intestines
Secreted by parafollicular cells in the thyroid
Stimulated by ↑serum calcium (hypercalcemia)
Vitamin D
Fat-soluble
↑intestinal absorption Ca2+, magnesium, & phosphate
D2 (cholecalciferol) synthesis dependent on sun exposure
D3 (ergocalciferol)
Ca2+ homeostasis & metabolism
Receptors located intestines, kidneys, bone, & parathyroid gland
Calcium
Total (bound & free) serum Ca2+ 9.5-10.5mg/dL
iCal 4.75-5.7mg/dL
50% bound to albumin, 40% ionized, 10% bound to chelating agents (phosphate, citrate, sulfate)
99% bone
1% coagulation factors, nerve & muscle excitability, & metabolic regulation (hormones & enzyme regulation)
pH & Ca2+
Acidosis ↑serum Ca2+
↓pH ↓protein binding (more available ionized fraction)
Each 0.1 ↓pH ↑iCal by 0.05mmol/L
Alkalosis ↓serum Ca2+
PTH Disorders
↓PTH - DiGeorge syndrome - CATCH 22 - Autoimmune Parathyroid gland adenomas
Hyperparathyroidism
Excessive PTH production
Most common cause of hypercalcemia >10.4mg/dL
1° Hyperparathyroidism
Parathyroid gland destruction Excessive PTH secretion - Benign adenoma - Hyperplasia - Carcinoma 50% patients asymptomatic
2° Hyperparathyroidism
Appropriate response to hypocalcemia (CKD)
Hyperparathyroidism S/S
Symptomatic when Ca2+ 11.5-12mg/dL
Skeletal muscle weakness
Polyuria & polydipsia
↓GFR or kidney stones
Anemia
Prolonged PR interval, shortened QT, systemic HTN
Abdominal pain, vomiting, peptic ulcer, pancreatitis
Skeletal demineralization & pathologic fractures
Somnolence, ↓pain sensation, psychosis
Hyperparathyroidism Diagnosis
PTH assay Vitamin D & Ca2+ levels Renal function CT scans Previous thyroid surgery
Hyperthyroidism Treatment
Medical management to treat mild, asymptomatic disease
- Mild hypercalcemia 12mg/dL (hydration)
- Moderate to severe hypercalcemia 13-15mg/dL (IV saline hydration & Furosemide to promote Na+/Ca2+ diuresis)
Surgical removal = definitive treatment
- Intraop PTH assay before & after adenoma removal
- Multiple gland hyperplasia need to identify all parathyroid glands
Hypoparathyroidism
Absence or PTH secretion deficiency
Peripheral tissues resistant to hormone effects
Iatrogenic - surgical removal (thyroidectomy)
Results in hypocalcemia
Hypocalcemia S/S
Neuronal irritability Fatigue Mental status changes Skeletal muscle spasms Tetany Seizures Prolonged QT interval CHF (chronic) Hypotension (acute)
Acute hypocalcemia - stridor, laryngospasm, & apnea
Hypocalcemia Treatment
Electrolyte replacement
Ca2+ & vitamin D
PO or IV magnesium replacement
Severe symptomatic 10% Ca2+ gluconate 10-20mL (peripheral) or 10% Ca2+ chloride 3-5mL (central) followed by continuous infusion 1-2mg/kg/hr
Hypocalcemia Anesthetic Considerations
Treat hypoglycemia prior to surgery Anesthetic risks include ↓cardiac contractility & dysrhythmias Tetany Altered response to muscle relaxants Laryngospasm risk
Parathyroidectomy Surgical Considerations
Monitor cardiac dysrhythmias 2° hypercalcemia (↓refractory period ↑ventricular excitability)
NIMs ETT to monitor RLN
Neuromuscular blocking agents unpredictable consider qualitative monitoring
Careful positioning d/t fractures risk
Postop complications similar to thyroid surgery
Acute hypocalcemia
Parathyroid Surgery
Supine w/ arms tucked Ether screen Neck extension Video to place NIMs ETT 2 PIVs PTH sampling (saphenous vein) NIBP cuff above sample IV to act as tourniquet Consider A-line Antiemetics ↓pressure Inhalational agent Remifentanil infusion Consider TIVA (risk PONV) No muscle relaxant
PTH Sampling
Baseline PTH
Time 0 when parathyroid removed
Time 5/10/15 min post parathyroid removal
