What is poikilothermia?

Poikilothermia: Definition, Pathophysiology, and Clinical Implications

Poikilothermia is a rare condition characterized by the inability to maintain a constant core body temperature independent of ambient temperature, resulting in body temperature that varies with environmental temperature.

Pathophysiology

Poikilothermia represents a fundamental failure of thermoregulatory mechanisms that normally maintain homeostasis. The condition involves:

• Impaired thermoregulatory effector mechanisms affecting both heat conservation and heat dissipation 1
• Defective central temperature regulation, most commonly of hypothalamic origin 2
• Compromised peripheral responses including:
  • Reduced or absent peripheral vasoconstriction in cold environments
  • Diminished or absent shivering response
  • Severely reduced sweating capacity and evaporative heat loss 3
  • Decreased resting metabolic rate compared to normal individuals 1

Clinical Manifestations

Patients with poikilothermia present with:

• Fluctuating core temperature that mirrors environmental temperature changes
• Hypothermia in cool environments without appropriate compensatory responses
• Hyperthermia in warm environments without adequate heat dissipation
• Afterdrop phenomenon - continued decrease in core temperature even after moving to a warmer environment 2
• Altered mental status that varies with body temperature
• Physical dysfunction related to temperature extremes 1

Diagnosis

Diagnosis of poikilothermia requires:

1. Documentation of variable core temperature that follows environmental temperature
2. Demonstration of impaired thermoregulatory responses through:
   • Heat challenge testing showing reduced sweating and evaporative weight loss
   • Cold challenge testing showing absent/reduced peripheral vasoconstriction and shivering
   • Testing of sweat gland function using acetylcholine injection or pilocarpine iontophoresis 3

Clinical Implications and Management

Poikilothermia has significant implications for patient health:

• Increased morbidity and mortality due to complications of both hypothermia and hyperthermia
• Neurological effects: At low temperatures, patients may become confused, uncoordinated, and somnolent, potentially progressing to coma around 30°C 4
• Cardiovascular effects: Hypothermia initially causes increased sympathetic tone but can progress to bradycardia, arrhythmias, and eventually ventricular fibrillation at severe levels 4
• Respiratory effects: Hypothermia can lead to decreased minute ventilation, increased secretions, and atelectasis 4
• Hematological effects: Coagulation abnormalities occur with hypothermia, with impaired platelet function between 33-37°C and decreased activity of clotting factors below 33°C 4

Management Approach:

1. Environmental temperature control is the cornerstone of management
2. Regular monitoring of core temperature using reliable methods (esophageal or nasopharyngeal measurements are most accurate) 4
3. Proactive temperature management to prevent extremes:
   • In cold environments: External warming devices, insulated clothing, heated environments
   • In warm environments: Cooling measures, air conditioning, avoiding heat exposure
4. Patient and caregiver education about recognizing temperature extremes and appropriate interventions
5. Treatment of underlying cause when possible (e.g., hypothalamic lesions)

Special Considerations

• Measurement technique matters: Esophageal and nasopharyngeal temperatures are most accurate for core temperature assessment, while axillary measurements can be up to 1.9°C below actual core temperature 4
• Diagnosis of brain death cannot be made while a patient has severe hypothermia; patients must be rewarmed to at least 34°C 4
• Medication metabolism may be altered at temperature extremes, requiring dose adjustments

Prevention of Complications

Careful monitoring and maintaining normothermia are essential to:

• Improve quality of life
• Prevent serious complications from both hypothermia and hyperthermia
• Reduce risk of coagulopathies, cardiac arrhythmias, and neurological impairment
• Prevent rhabdomyolysis and renal injury that can occur with severe temperature fluctuations

Poikilothermia requires vigilant management focused on environmental temperature control and proactive intervention to maintain core temperature within safe limits.