College Answer

Definition: "severe" (usually mild 32-35, moderate 28-32, and severe < 28C). Accidental implies spontaneous decrease in core temperature, usually in a cold environment (more common in elderly, neonates, unconscious, exhausted, hypothyroid etc).

Mortality is signficant. Signs are modified by associated injuries, medications, extremes of age, etc.

Temperature control lost (become poikilothermic, cooling to ambient temperature)

Cardiac : arrhythmias (eg. bradycardia. AF and VF) decreased mean blood pressure, contractility, cardiac output

Respiratory: decreased respiratory rate, respiratory acidosis 

CNS: variable effects on mentation and motor function; impaired judgement, disorientation, hyporeflexia

Haematology: coagulopatby, platelet dysfunction

Gastrointestinal: pancreatitis 

Renal: polyuria, dehydration, ARF

Discussion

The college specifies accidental hypothermia, which means the candidate could have included in their answer the entire spectrum of horrible environment-associated problems. One does not quietly cool on a clean surface. One typically is halfway immersed in an icy lake, trapped under a dead moose, or subject to another similarly complex retrieval situation. However, the college answer bypasses the accidental nature of the hypothermia, and speaks mainly of the non-specific consequences of low body temperature.

This topic is explored in greater depth in another chapter. The table of contents from this hypothermia chapter is a good summary of the physiological consequences of hypothermia

Endocrine and metabolic consequences

• Decreased metabolism and oxygen consumption
• Decreased carbohydrate metabolism and hyperglycaemia
• Decreased drug metabolism and clearance
• Essentially unchanged electrolytes

Haematological consequences

• Increased hematocrit and blood viscosity
• Neutropenia and thrombocytopenia
• Coagulopathy and platelet dysfunction

Respiratory consequences

• Decreased respiratory rate and medullary sensitivity to CO₂
• Acid-base changes: alkalosis and hypocapnea
  • Rise of pH with falling body temperature
  • Fall of PCO₂ with falling body temperature
  • Increased oxygen solubility and O₂-haemoglobin affinity

Cardiovascular consequences

• Decreased cardiac output and bradycardia
• QT prolongation and the J wave
• Arrhythmias - classically AF and VF
• Resistance to defibrillation
• Vasoconstriction

Renal consequences

• "Cold diuresis" due to decreased vasopressin synthesis

Central nervous system effects

• Confusion and decreased level of consciousness
• Shivering
• Increased seizure threshold

Immunological consequences

• Decreased granulocyte and monocyte activity