Endocrine - Thyroid/Parathyroid

Question 1

T3

Answer 1

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

Question 2

T4

Answer 2

Thyroxine
90% synthesized & released by the thyroid gland
Half-life 6-7 days
99.9% bound to thyroid binding globulin

Question 3

Hypothalamus

Answer 3

Controls thyrotropin-releasing hormone TRH

Question 4

Pituitary Gland

Answer 4

TRH stimulates thyroid-stimulating hormone to release from the anterior pituitary
TSH controls thyroid hormone production

Question 5

Thyroid Gland

Answer 5

TSH action site

Synthesis & secretion T3 & T4

Question 6

What’s active thyroid hormone form?

Answer 6

Free form

Drives patient metabolic state

Question 7

Thyroid Function Tests

Answer 7

TSH
Serum T3/T4
Radioactive iodine uptake

Question 8

TSH

Answer 8

Normal 0.4-5 milliunits/L

Question 9

Subclinical Hyperthyroidism

Answer 9

TSH 0.1-0.4 milliunits/L

Normal levels free T3 & T4

Question 10

Over Hyperthyroidism

Answer 10

TSH level <0.03 milliunits/L

↑T3 & T4

Question 11

Subclinical Hypothyroidism

Answer 11

Myxedema
TSH level 5-10 milliunits/L
Normal levels T3 & T4

20% women over 60yo

Question 12

Overt Hypothyroidism

Answer 12

Myxedema
TSH level >20 milliunits/L
↓T3 & T4

Question 13

Pituitary Dysfunction

Answer 13

Admin exogenous TRH
Collect serum TSH concentration
Normal response ↑TSH
Hypothyroidism d/t pituitary disease (2° hypothyroid) TRH admin does NOT produce ↑TSH

Question 14

Hyperthyroidism

Answer 14

TSH level <0.03 milliunits/L
↑free T3 & T4
Thyroid hormones not shutting off w/ low TSH

Question 15

Hyperthyroidism Causes

Answer 15

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

Question 16

Hyperthyroidism S/S

Answer 16

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

Question 17

Hyperthyroidism Treatment

Answer 17

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

Question 18

Thyroid Storm

Answer 18

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

Question 19

Thyroid Storm Treatment

Answer 19

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

Question 20

Hyperthyroidism Anesthetic Considerations

Answer 20

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

Question 21

1° Hypothyroidism

Answer 21

↓thyroid hormone production despite normal TSH
Most common causes are thyroid gland ablation d/t radioactive iodine therapy or surgery
90-95% all cases

Question 22

2° Hypothyroidism

Answer 22

Hypothalamic or pituitary disease

5% all cases

Question 23

Autoimmune Hypothyroidism

Answer 23

Autoantibodies block TSH receptors in the thyroid

Immune response destroys receptors rather than stimulating

Question 24

Hashimoto Thyroiditis

Answer 24

Autoimmune disorder, goiter, & hypothyroidism

Common in middle-aged women

Question 25

Hypothyroidism S/S

Answer 25

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

Question 26

Hypothyroidism Diagnosis

Answer 26

1° (thyroid) ↓T3 & T4 levels ↑TSH 2° (pituitary) ↓T3 & T4 levels AND ↓TSH Identify primary vs. secondary w/ TRH stim test

Question 27

Hypothyroidism Treatment

Answer 27

``` L-thyroxine (Levothyroxine/Synthroid) Synthetic T4 thyroxine T4 → T3 Onset 3-5 days PO (peak therapeutic effect 4-6 weeks) IV 6-8 hours ```

Question 28

Hypothyroidism Anesthetic Considerations

Answer 28

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

Question 29

Myxedema Coma

Answer 29

``` 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 ```

Question 30

Goiter

Answer 30

Thyroid gland swelling Hyper OR hypothyroidism Non-toxic goiters euthyroid → toxic multinodular goiter Airway evaluation Caution w/ respiratory depressants prior to airway airway securement

Question 31

Thyroid Surgery | Anesthetic Considerations

Answer 31

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

Question 32

Thyroid Surgery Complications

Answer 32

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)

Question 33

RLN Injury

Answer 33

Abductor vocal cord muscle paralysis results in median/paramedian cord position Unilateral = hoarseness Bilateral = airway obstruction (reintubate or trach)

Question 34

SLN Injury

Answer 34

Voice weakness | Unable to create high tones "E"

Question 35

Parathyroid Glands

Answer 35

4 parathyroid glands Produce parathyroid hormone (PTH) Maintains normal plasma calcium concentration

Question 36

Parathyroid Hormone

Answer 36

PTH Released into bloodstream via negative feedback Dependent on plasma calcium concentration Half-life 4 minutes Average PTH level 8-51 pg/mL

Question 37

Hypocalcemia → | Hypercalcemia →

Answer 37

Releases parathyroid hormone | Suppresses PTH synthesis & release

Question 38

Calcitonin

Answer 38

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)

Question 39

Vitamin D

Answer 39

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

Question 40

Calcium

Answer 40

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)

Question 41

pH & Ca2+

Answer 41

Acidosis ↑serum Ca2+ ↓pH ↓protein binding (more available ionized fraction) Each 0.1 ↓pH ↑iCal by 0.05mmol/L Alkalosis ↓serum Ca2+

Question 42

PTH Disorders

Answer 42

``` ↓PTH - DiGeorge syndrome - CATCH 22 - Autoimmune Parathyroid gland adenomas ```

Question 43

Hyperparathyroidism

Answer 43

Excessive PTH production | Most common cause of hypercalcemia >10.4mg/dL

Question 44

1° Hyperparathyroidism

Answer 44

``` Parathyroid gland destruction Excessive PTH secretion - Benign adenoma - Hyperplasia - Carcinoma 50% patients asymptomatic ```

Question 45

2° Hyperparathyroidism

Answer 45

Appropriate response to hypocalcemia (CKD)

Question 46

Hyperparathyroidism S/S

Answer 46

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

Question 47

Hyperparathyroidism Diagnosis

Answer 47

``` PTH assay Vitamin D & Ca2+ levels Renal function CT scans Previous thyroid surgery ```

Question 48

Hyperthyroidism Treatment

Answer 48

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

Question 49

Hypoparathyroidism

Answer 49

Absence or PTH secretion deficiency Peripheral tissues resistant to hormone effects Iatrogenic - surgical removal (thyroidectomy) Results in hypocalcemia

Question 50

Hypocalcemia S/S

Answer 50

``` Neuronal irritability Fatigue Mental status changes Skeletal muscle spasms Tetany Seizures Prolonged QT interval CHF (chronic) Hypotension (acute) ``` Acute hypocalcemia - stridor, laryngospasm, & apnea

Question 51

Hypocalcemia Treatment

Answer 51

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

Question 52

Hypocalcemia Anesthetic Considerations

Answer 52

``` Treat hypoglycemia prior to surgery Anesthetic risks include ↓cardiac contractility & dysrhythmias Tetany Altered response to muscle relaxants Laryngospasm risk ```

Question 53

Parathyroidectomy Surgical Considerations

Answer 53

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

Question 54

Parathyroid Surgery

Answer 54

``` 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 ```

Question 55

PTH Sampling

Answer 55

Baseline PTH Time 0 when parathyroid removed Time 5/10/15 min post parathyroid removal