What causes volume depletion in thyroid storm?

From the Guidelines

Thyroid storm causes volume depletion primarily due to excessive fluid losses through hyperhidrosis, tachypnea, vomiting, diarrhea, and peripheral vasodilation, as well as increased insensible losses due to fever. During thyroid storm, the body's metabolic rate is dramatically increased, leading to several mechanisms of fluid loss 1. Patients experience gastrointestinal symptoms like vomiting and diarrhea, which further contribute to fluid loss. Additionally, the hypermetabolic state causes peripheral vasodilation and increased cardiac output, which can lead to relative hypovolemia despite an increased total body water.

Key Mechanisms of Volume Depletion

• Hyperhidrosis (excessive sweating) and tachypnea (rapid breathing) increase insensible fluid losses
• Gastrointestinal symptoms like vomiting and diarrhea contribute to fluid loss
• Peripheral vasodilation and increased cardiac output lead to relative hypovolemia
• Fever exacerbates fluid losses through increased sweating

The combination of these factors results in significant volume depletion, which can worsen the clinical picture by causing hypotension and reduced organ perfusion 1. Treatment of thyroid storm must therefore include aggressive fluid resuscitation with isotonic crystalloids (typically normal saline) alongside anti-thyroid medications like propylthiouracil (PTU) or methimazole, beta-blockers, and other supportive measures to address the underlying thyrotoxicosis.

From the Research

Causes of Volume Depletion in Thyroid Storm

• Volume depletion in thyroid storm can be caused by several factors, including:
  • Increased urinary output due to hyperthyroidism 2
  • Vomiting and diarrhea, which can lead to dehydration and electrolyte imbalances 3, 4
  • Increased insensible losses due to tachypnea and fever 5
  • Decreased oral intake due to altered mental status or other symptoms of thyroid storm 6

Pathophysiology

• Thyroid storm is characterized by a hyperadrenergic state, which can lead to increased cardiac output and peripheral vasodilation, resulting in decreased systemic vascular resistance and potentially causing hypotension and volume depletion 2, 5
• The hyperthyroid state can also lead to increased renal blood flow and glomerular filtration rate, resulting in increased urinary output and potential volume depletion 3, 4

Clinical Implications

• Volume depletion in thyroid storm can exacerbate symptoms such as tachycardia, hypotension, and decreased cardiac output, and can increase the risk of multi-organ failure 2, 5
• Aggressive fluid replacement and management of volume depletion are crucial in the treatment of thyroid storm, in addition to other therapies such as antithyroid medications, beta blockers, and corticosteroids 3, 4, 6