What is the management approach for a patient presenting with hypothermia, hyponatremia, and a low normal Thyroid-Stimulating Hormone (TSH) level?

Management of Hypothermia with Hyponatremia and Low-Normal TSH

This patient requires immediate active rewarming to achieve normothermia, correction of hyponatremia with fluid restriction (not hypertonic saline unless symptomatic), and urgent evaluation for severe hypothyroidism despite the low-normal TSH, as myxedema coma can present with paradoxically low or normal TSH levels and carries high mortality if untreated. 1, 2, 3

Immediate Temperature Management

Core temperature of 35°C represents mild hypothermia requiring both passive and active rewarming measures. 1

• Remove all wet clothing immediately and move patient to warm environment 1
• Apply passive rewarming with warm blankets while simultaneously initiating active external rewarming 1, 4
• Use forced-air warming blankets, heating pads, or radiant heaters (Level 2 strategies) - these increase rewarming rates to approximately 2.4°C/hour versus 1.4°C/hour with passive methods alone 4
• Administer warmed intravenous fluids and humidified oxygen 1, 4
• Monitor core temperature every 5-15 minutes until reaching 36°C, then cease active rewarming at 37°C as higher temperatures worsen outcomes 4
• Place insulation between heat sources and skin to prevent burns, checking frequently for skin injury 1

Critical Pitfall in Temperature Monitoring

Always measure core body temperature with esophageal, bladder, or rectal thermometers - never rely on axillary measurements which read 1.5-1.9°C below actual core temperature and can lead to undertreatment 4, 5. Clinical presentation may not match severity; patients can appear alert with severe hypothermia based on core temperature 5.

Hyponatremia Management

The combination of hypothermia and hyponatremia suggests severe hypothyroidism until proven otherwise, even with low-normal TSH. 2, 3

• Implement fluid restriction as first-line treatment for mild-moderate hyponatremia in hypothyroid patients 2
• Do NOT use hypertonic saline (3% NaCl) unless patient exhibits hyponatremic encephalopathy (altered mental status, seizures, coma) 6, 2
• If hypertonic saline is required for symptomatic hyponatremia, administer through large vein with extreme caution - rapid correction risks osmotic demyelination syndrome 6
• Avoid rapid correction of hyponatremia - this is potentially dangerous with risk of serious neurologic complications 6

Monitoring During Correction

• Check serum sodium every 2-4 hours during active treatment 2
• Monitor for signs of overcorrection - confusion, dysarthria, dysphagia, lethargy 2
• Evaluate for other contributing factors: medications (diuretics, SSRIs), adrenal insufficiency, infections 2

Thyroid Evaluation and Treatment

Low-normal TSH with hypothermia and hyponatremia is concerning for myxedema coma, which requires immediate empiric treatment before confirmatory labs return. 3

Diagnostic Approach

• Obtain immediate TSH, free T4, free T3, and cortisol levels 4, 3
• Do not wait for results to initiate treatment if clinical suspicion is high - myxedema coma has mortality rates exceeding 25-60% without prompt intervention 3
• Low-normal or even normal TSH does not exclude severe hypothyroidism in critically ill patients due to sick euthyroid syndrome 2, 3

Empiric Thyroid Hormone Replacement

If myxedema coma is suspected based on clinical presentation (hypothermia, hyponatremia, altered mental status, bradycardia):

• Administer intravenous liothyronine (T3) 5-20 mcg bolus, then 2.5-10 mcg every 8 hours 3
• Give oral levothyroxine (T4) 200-400 mcg loading dose via nasogastric tube if unable to take orally 3
• Administer stress-dose hydrocortisone 100 mg IV every 8 hours empirically before thyroid hormone to prevent adrenal crisis, as hypothyroidism can mask concurrent adrenal insufficiency 3

Response Monitoring

• Expect improvement in hypothermia and bradycardia within 24-48 hours of liothyronine initiation 3
• Continue IV liothyronine for 5-7 days, then transition to oral levothyroxine alone 3
• Monitor for cardiac arrhythmias during rewarming - hypothermia impairs cardiac conduction but bradycardia may be physiologically appropriate 4

Additional Critical Considerations

Rule Out Precipitating Factors

• Evaluate for infection - sepsis commonly precipitates myxedema coma 3
• Check for medication causes of hyponatremia: lithium, carbamazepine, SSRIs, diuretics 6, 2
• Assess for adrenal insufficiency - can coexist with hypothyroidism and cause both hypothermia and hyponatremia 2, 3

Complications to Monitor

• Coagulopathy: each 1°C drop in temperature reduces coagulation factor function by 10% 1
• Cardiac arrhythmias: atrial fibrillation common during rewarming, but aggressive treatment not indicated unless hemodynamically unstable 5
• Rhabdomyolysis: check creatine kinase and maintain adequate hydration 5
• Rewarming shock: monitor blood pressure closely as peripheral vasodilation occurs 4

When to Escalate Care

Activate emergency response system if patient develops: 1

• Decreased level of responsiveness, confusion, or inability to participate in care
• Pallor, cyanosis, or frozen skin
• Temperature drops below 32°C (moderate hypothermia)
• Hemodynamic instability despite initial measures

Transfer to ICU for: 3

• Suspected myxedema coma requiring IV liothyronine
• Need for invasive monitoring or mechanical ventilation
• Severe hyponatremia requiring hypertonic saline
• Core temperature <32°C requiring advanced rewarming techniques