Anesthetic Considerations in Hyperthyroidism

🌡️ Etiology of Hyperthyroidism

Cause

Description

Graves’ Disease

Autoimmune stimulation of TSH receptors (most common)

Toxic multinodular goiter

Autonomous nodules producing hormone

Toxic adenoma

Solitary hyperfunctioning nodule

Thyroiditis

Hormone leakage due to inflammation

Factitious thyrotoxicosis

Exogenous intake of thyroid hormone

TSH-secreting pituitary adenoma

Secondary hyperthyroidism

🧪 Pathophysiology

  • ↑ Basal metabolic rate
  • ↑ Adrenergic activity → tachycardia, tremors, anxiety
  • ↑ Oxygen consumption and CO₂ production
  • ↓ SVR, ↑ cardiac output → high-output heart failure
  • Heat intolerance, weight loss
  • Muscle wasting, weakness
  • Menstrual disturbances

📋 Clinical Features

System

Manifestations

CVS

Palpitations, tachycardia, AF, widened pulse pressure, ↑ CO

CNS

Nervousness, anxiety, tremors, insomnia

Resp

↑ RR, dyspnea, ↑ VO₂

GI

Diarrhea, weight loss

Skin

Warm, moist, heat intolerance

Musculoskeletal

Proximal myopathy, tremors

Eyes

Exophthalmos (Graves’), lid lag

📊 Thyroid Function Tests

Test

Change

TSH

↓ (in primary hyperthyroidism)

Free T3, T4

↑↑

T3:T4 Ratio

Elevated

TRAb (TSI)

Positive in Graves’

❗ Thyroid Storm (Thyrotoxic Crisis)

Life-threatening emergency due to exaggerated thyrotoxicosis:

Precipitating factors:

  • Surgery/anesthesia
  • Infection
  • Trauma
  • Withdrawal of antithyroid meds

🔺 Clinical Features (Remember “5 H’s”):

  • Hyperpyrexia (> 104°F)
  • Hypertension → hypotension → shock
  • Hyperactivity of CNS: agitation, delirium, coma
  • Hypermetabolism: ↑ VO₂, lactic acidosis
  • Heart: tachyarrhythmias, CHF

🆘 Management of Thyroid Storm

Step

Drug

↓ Thyroid synthesis

PTU 600–1000 mg PO/NGT initially, then 150 mg q6h

↓ T4→T3 conversion

IV Hydrocortisone + PTU

↓ Hormone release

Lugol’s iodine 1 h after PTU

Control SNS symptoms

Propranolol 1 mg IV or PO (titrate)

Supportive

Cooling, oxygen, fluids, vasopressors if needed

✅ Preoperative Optimization

Goal

Management

Achieve euthyroid state

ATDs: Carbimazole, Propylthiouracil (PTU)

Adrenergic control

Propranolol (most effective), Atenolol

Inhibit T3 conversion

Steroids (hydrocortisone)

Avoid iodine-containing agents

(e.g., amiodarone, contrast) pre-op

Monitor for AF or CHF

ECG, Echo

Evaluate airway

Large goiters may cause difficult intubation

Elective surgery should be deferred until euthyroid unless emergent.

💉 Anesthetic Considerations

🛌 Premedication

Drug

Rationale

Benzodiazepines

Anxiolysis, avoid agitation

Avoid anticholinergics

May ↑ HR

Beta-blockers

Reduce tachycardia, anxiety, prevent thyroid storm

⚠️ Intraoperative Goals

Parameter

Target

HR

60–80 bpm

Temperature

Normothermia

Depth

Adequate to suppress SNS

Avoid

Ketamine (↑ HR), pancuronium, stress, pain

🔍 Induction

Drug Class

Agent of Choice

Induction

Etomidate, Propofol

Muscle Relaxants

Rocuronium, Vecuronium (avoid pancuronium)

Opioids

Fentanyl, remifentanil for blunting SNS

Inhalational agents

Sevoflurane (smooth, hemodynamically stable)

🚨 Special Considerations

  • Large goiters → difficult airway
  • Avoid hypoxia, hypercapnia (triggers SNS)
  • Adequate depth of anesthesia to suppress stress
  • Use short-acting drugs due to hypermetabolic clearance
  • Anticipate thyroid storm intra/post-op

🛌 Regional Anesthesia

✅ Regional anesthesia is safe, especially in well-optimized patients.

🛑 Caution in unoptimized patients or those with CVS instability.

🧯 Postoperative Management

  • Close monitoring for:
    • Thyroid storm
    • Arrhythmias
    • Temperature
  • Pain control (avoid NSAIDs that interfere with thyroid hormones)
  • Restart antithyroid therapy post-op
  • Monitor ECG and electrolytes
  • Provide calm, low-stimulation environment

💡 Viva Triggers

Question

Answer

Most common cause of hyperthyroidism?

Graves’ disease

When is thyroid storm most likely?

6–18 hours post-op in unoptimized patient

Mechanism of PTU?

Inhibits TPO + peripheral T4→T3 conversion

Beta-blocker of choice?

Propranolol (also inhibits T4→T3)

Which anesthetic to avoid?

Ketamine (↑ HR, BP), Pancuronium (↑ HR)

🎯 MCQ Nuggets

  1. First-line drug in thyroid storm?
    → Propylthiouracil (PTU)
  2. Definitive treatment for Graves’?
    → Surgery or radioiodine
  3. Best beta-blocker in hyperthyroidism?
    → Propranolol
  4. Why iodine is given after PTU?
    → Prevents further release, given after hormone synthesis is blocked
  5. Key sign of impending thyroid storm?
    → Sudden rise in temperature, HR, agitation