Anesthesia Management of Thyroid Disease - Viva Q&A

PART 1: HYPERTHYROIDISM

• Graves disease (most common - TSH receptor autoantibodies)
• Hyperfunctioning thyroid adenoma
• Toxic multinodular goiter
• Trophoblastic tumor (excess hCG stimulation)
• Thyroiditis (subacute release of stored hormone)
• Exogenous thyroid / iodine-induced
• Struma ovarii / functioning follicular carcinoma (rare)

• Cardiovascular: tachycardia, palpitations, atrial fibrillation, hypertension, increased cardiac output, high-output cardiac failure
• Metabolic: weight loss, heat intolerance, sweating, tremor, diarrhea
• CNS: anxiety, agitation, insomnia
• Airway: goiter - possible tracheal deviation or compression, dysphagia, dyspnea, wheezing, orthopnea
• Ophthalmologic (Graves): proptosis - relevant to eye care during GA

• Best screening test for hypothyroidism: TSH alone
• For hyperthyroidism: free T3 + free T4 + TSH
• Total T4 is unreliable in isolation (affected by TBG changes in pregnancy, liver disease, estrogens, opioids)

1. Antithyroid drugs (PTU or methimazole) - inhibit synthesis of T3/T4. Note: they do NOT deplete existing stored hormone, so 6-8 weeks needed for full effect with drugs alone
2. Beta-blockers (propranolol, esmolol) - attenuate sympathetic hyperactivity; propranolol additionally impairs peripheral conversion of T4 to T3. Target HR <90 bpm. Continue until surgery
3. Potassium iodide (2-5 drops every 8h) - Wolff-Chaikoff effect: inhibits organification and hormone release; also reduces gland vascularity and size. Must start antithyroid drugs first before iodide, as iodide can transiently worsen thyrotoxicosis
4. Glucocorticoids (dexamethasone 8-12 mg/day) - reduce hormone secretion and peripheral T4-to-T3 conversion

• IV beta-blocker (esmolol infusion) to achieve HR <90 bpm
• IV methimazole or PTU
• Potassium iodide (after antithyroid drugs given)
• IV corticosteroids
• Endocrinology consultation is mandatory

• Goal: prevent thyroid storm and control sympathetic overdrive
• Continue all antithyroid drugs including the morning of surgery
• Avoid drugs that stimulate sympathetic nervous system or have indirect mechanisms (e.g., ketamine, ephedrine - use judiciously or avoid)
• Preferred induction: propofol or thiopental (thiopental has mild antithyroid properties)
• Pancuronium should be avoided (vagolytic effect worsens tachycardia)
• Adequate anesthetic depth to blunt laryngoscopy response
• Temperature monitoring is essential (early detection of thyroid storm)
• Maintain normovolemia, avoid dehydration
• Treat intraoperative tachycardia with esmolol
• Opioids (fentanyl) can help blunt sympathetic response to laryngoscopy

• Hyperthermia (often ≥40°C)
• Tachycardia + tachyarrhythmias (esp. atrial fibrillation)
• Altered mental status (agitation, delirium, coma)
• Hypotension (hypotension may follow initial hypertension)
• Diaphoresis, nausea, vomiting, diarrhea
• Congestive heart failure in ~25%
• Hypokalemia in up to 50% (very characteristic)

• Amiodarone is contraindicated in thyroid storm - causes both hypo- and hyperthyroidism
• Beta-blockers contraindicated if congestive heart failure is present
• Invasive hemodynamic monitoring (arterial line, CVP) for severe cases
• ICU admission; endocrinology consultation

PART 2: HYPOTHYROIDISM

• Hashimoto thyroiditis (most common cause overall - autoimmune)
• Post-radioactive iodine therapy (Graves treatment) - 10-60% in first year
• Post-surgical (thyroidectomy)
• Irradiation to neck
• Severe iodine depletion
• Medications: PTU, methimazole, amiodarone, lithium
• Infiltrative disease (amyloidosis, sarcoidosis)

• Cardiovascular: bradycardia, decreased cardiac output, increased peripheral resistance, pericardial effusion (low-voltage ECG), cardiomyopathy, prolonged QTc
• Respiratory: hypoventilation, depressed response to hypoxia and hypercapnia (potentiated by sedatives, opioids, GA), obstructive sleep apnea
• Airway: enlarged tongue (macroglossia), hoarse voice, goiter, vocal cord edema
• Neurological: lethargy, cognitive dysfunction, slow mental functioning, slow reflexes, peripheral neuropathy
• GI: decreased motility, constipation, ileus, gastric atrophy (aspiration risk)
• Metabolic: hypothermia, cold intolerance, weight gain, hypoglycemia
• Haematological: anemia, acquired von Willebrand syndrome (coagulopathy, bleeding)
• Electrolytes: hyponatremia (impaired free water clearance), hypoglycemia
• Endocrine: blunted stress response, may have adrenal insufficiency in severe/longstanding disease

• Mild to moderate hypothyroidism: No compelling reason to postpone. Evidence shows no increase in serious perioperative complications, though there may be higher rates of intraoperative hypotension and post-op GI/neuropsychiatric complications.
• Severe hypothyroidism: Surgery should be postponed until at least partially treated due to risks of cardiac and respiratory decompensation.
• Hypothyroid with CAD: Balance replacement against risk of precipitating myocardial ischemia. In unstable cardiac ischemia, thyroid replacement may be delayed until after coronary revascularization.
• Thyroid medications are continued on the day of surgery (including the morning of surgery).

• Induction: Ketamine is preferred (stimulates sympathetic nervous system, counteracts hemodynamic depression). Propofol/thiopental can be used carefully.
• Maintenance: Both IV and inhalational agents are acceptable. MAC for volatile agents is not significantly decreased.
• Regional anesthesia is a good alternative if intravascular volume is well-maintained.
• Avoid or use judiciously: narcotics, sedatives, long-acting agents (prolonged emergence, exacerbated respiratory depression)
• Rapid sequence induction may be warranted in severe disease due to aspiration risk and delayed gastric emptying

• Maintain normothermia (hypothermia is a major risk - use forced-air warming)
• Watch for hypotension, bradycardia, congestive heart failure
• Monitor glucose and electrolytes
• Anticipate difficult airway (macroglossia, vocal cord edema, goiter)
• Post-op: prolonged sedation, ventilatory depression, sleep apnea

PART 3: ANESTHESIA FOR THYROID SURGERY

• Failed medical therapy for hyperthyroidism
• Underlying thyroid cancer
• Symptomatic goiter (compressive symptoms)
• Patient preference over long-term medical therapy

• Incidence of difficult intubation: 5-8% in goiter surgery
• Thyroid cancer increases risk but goiter size alone is not predictive
• Pre-op review of CT/MRI is mandatory for large goiters
• Large goiters with airway obstruction or tracheal deviation - consider awake intubation
• Substernal goiters behave like anterior mediastinal masses - can cause intrathoracic airway obstruction AFTER induction of GA (life-threatening)
• Standard approach: general endotracheal anesthesia
• LMA is increasingly used: allows real-time vocal cord visualization with spontaneous breathing
• Limited thyroidectomy: can be done under bilateral superficial cervical plexus block
• Robot-assisted transaxillary and transoral approaches require nasal intubation for the transoral route
• Tracheomalacia may occur with substernal goiters - risk of pneumothorax

• Special ETT with paired electrodes embedded just above the cuff that contact the vocal cords
• Used for intraoperative recurrent laryngeal nerve (RLN) monitoring
• Provides EMG signal when the nerve is stimulated by the surgeon
• Requires: no muscle relaxants after intubation, no topical laryngeal anesthesia
• Intubation can be facilitated with succinylcholine or small dose of rocuronium, but effect must wear off before monitoring begins
• Tube position must be verified after head/neck repositioning for surgical exposure

HIGH-YIELD SUMMARY TABLE