Hypothyroidism 

 

 

 

Considerations

 

  • Possible difficult airway:

    • Enlarged goiter: anatomical deviation/obstruction

    • Anterior mediastinal mass

    • Recurrent laryngeal nerve involvement

    • Prior neck radiation

  • Aspiration risk 

  • Physiologic manifestations:

    • Cardiovascular: congestive heart failure, ↓ CO (↓ contractility/rate), hypotension, pericardial effusion, autonomic instability, hypovolemia

    • Respiratory: hypoventilation, ↓ response to hypoxemia/hypercarbia

    • Electrolytes: hyponatremia 

    • Endocrine: hypoglycemia, adrenal insufficiency (cortical atrophy)

    • Hypothermia

    • ↓ metabolic rate

  • Interactions with anesthetic:

    • ↓ MAC 

    • Delayed emergence

    • Sensitivity to respiratory depressents

    • Perioperative endocrine supplementation (thyroid, steroids)

  • Potential for myxedema coma

  • Thyroid surgery:

    • Shared airway

    • Post-operative airway obstruction (recurrent laryngeal nerve injury, tracheomalacia, hematoma, hypocalcemia)

 

 

Optimization

 

  • Euthyroid patient preoperatively

  • Optimize volume status, give steroids, & manage glucose & sodium 

 

 

Conflicts

 

  • Thyroid replacement & coronary artery disease (can precipitate myocardial ischemia)

  • Potential for over-sedation vs. difficult airway (post-operative analgesia)

 

 

Myxedema Coma

 

  • Life-threatening form of hypothyroidism (mortality > 50%) precipitated by stress 

  • Exaggerated features of hypothyroidism:

    • ↓ LOC

    • Risk of aspiration

    • ↑ sensitivity to neuromuscular blockers & sedatives

    • ↓ cardiac output/heart rate, congestive heart failure, pulmonary edema

    • Respiratory depression

    • Hypothermia

    • Metabolic: SIADH, hypoglycemia, adrenal suppression

    • High risk for delayed emergence & need for post-operative ventilation

  • Treatment:

    • IV thyroxine

    • IV T3 0.2mcg/kg q6h (onset 6-24 hrs)

    • T4 200-300mcg IV over 5-10 mins then 100mcg IV q24

    • Risk of precipitation of myocardial ischemia with IV T3/T4 supplementation in those with CAD

    • Hydrocortisone 100mg IV then 25mg q6h (common association with adrenal suppression)

    • Passive rewarming with blankets 

    • Post-operative ventilation, fluids, pressors, inotropes

    • ICU & endocrinology consult