What is the most likely mechanism of heatstroke in a patient with hyperthermia, confusion, and tachycardia after running a marathon?

Inadequate Heat Dissipation is the Most Likely Mechanism of Heatstroke in this Marathon Runner

The most likely mechanism of this patient's condition is inadequate dissipation of body heat (option D). This marathon runner is experiencing exertional heatstroke, characterized by hyperthermia (40°C/104°F), confusion, tachycardia, and neurological symptoms after intense physical exertion in hot conditions 1.

Pathophysiology of Exertional Heatstroke

Exertional heatstroke occurs when the body's heat production exceeds its ability to dissipate heat effectively. The pathophysiological process involves:

1. Heat Generation:

   • Strenuous exercise (marathon running) dramatically increases metabolic rate and heat production
   • Laboratory studies confirm that heat directly induces tissue injury, with severity proportional to degree and duration of hyperthermia 1

2. Failed Thermoregulation:

   • The body attempts to increase heat dissipation through:
     • Cutaneous vasodilation (explaining the warm skin)
     • Sweating (though in this case, the skin is dry, suggesting sweating mechanisms are overwhelmed)
   • When these mechanisms fail to maintain normal body temperature, core temperature rises rapidly 1

3. Systemic Effects:

   • Hyperthermia (40°C) triggers central nervous system dysfunction (confusion, disorientation)
   • Tachycardia (155/min) reflects increased sympathetic nervous system outflow
   • Hypotension (100/60 mmHg) results from peripheral vasodilation 1

Why Other Options Are Less Likely

• Depletion of total body potassium (A): While electrolyte abnormalities can occur in heat-related illness, they are consequences rather than primary mechanisms. Potassium loss alone wouldn't explain the severe hyperthermia and neurological symptoms 1.

• Depletion of total body sodium (B): Sodium depletion may contribute to heat exhaustion but doesn't adequately explain the severe hyperthermia and CNS dysfunction seen in this case 1.

• High-output cardiac failure (C): While circulatory alterations occur in heatstroke, they typically manifest as distributive shock rather than primary cardiac failure. Myocardial failure is rare in heatstroke 1, 2.

• Release of creatine kinase from muscle cells (E): Rhabdomyolysis is a consequence of heatstroke, not its primary mechanism. Elevated creatine kinase occurs after tissue damage from hyperthermia 1.

Clinical Manifestations Supporting Inadequate Heat Dissipation

The patient's presentation aligns perfectly with exertional heatstroke:

• Context: Marathon running in summer (high environmental temperature, strenuous exercise)
• Vital signs: Hyperthermia (40°C), tachycardia (155/min), relative hypotension (100/60 mmHg)
• Neurological symptoms: Confusion, disorientation, unsteady gait
• Skin findings: Warm and dry skin (suggesting overwhelmed sweating mechanisms)
• Timing: Symptoms developed during intense physical exertion

Management Implications

Understanding that inadequate heat dissipation is the primary mechanism guides immediate management:

• Rapid cooling is the most critical intervention to prevent irreversible organ damage and death 1
• Immersion in cold water is particularly effective for young, athletic individuals with exertional heatstroke 1
• Hemodynamic support with careful fluid resuscitation is essential, as circulatory failure occurs in 20-65% of heatstroke patients 1

Conclusion

The clinical presentation of hyperthermia, confusion, tachycardia, and warm dry skin in a marathon runner clearly points to inadequate heat dissipation as the primary mechanism of this patient's condition. This understanding should guide immediate cooling interventions to prevent progression to multi-organ failure and death.