Therm – Responses

Master answer

Hypothermia:

• Core body temperature < 35 degrees
  • Mild: 32-35
  • Moderate: 28-32
  • Severe: < 28

Effects via system:

1. Endocrine and metabolic consequences
   • ↓ carbohydrate metabolism and hyperglycaemia
   • ↓ drug metabolism and clearance
   • ↑ protein catabolic state
   • Impaired wound healing (due to catabolic state and wound vasoconstriction)
   • ↑ stress response (steroids and catecholamine released)
   • Altered Metabolism
     • Shivering
       • 5x ↑ general MRO2
       • ↑hypoxaemia → risk of myocardial and cerebral ischaemia
     • In absence of shivering
       • general ↓MRO2 (by up to 50%)
       • ↓BMR
2. Haematological consequences
   • ↑ hematocrit and blood viscosity
   • Neutropenia and thrombocytopenia
   • Coagulopathy and platelet dysfunction
3. Respiratory consequences
   • ↓ RR and medullary sensitivity to CO2 → ↓ MV (and in severe cases apnoea)
   • Left-shift in Hb O2 dissociation curve
   • Acid-base changes: alkalosis and hypocapnea
     • Rise of pH with falling body temperature
     • Fall of PaCO2 with falling body temperature
   • Effects on gas solubility
     • ↑ oxygen solubility and O2-haemoglobin affinity
     • ↑ solubility of gases (incl volatiles)
   • V/Q mismatching 2° to inhibition of hypoxic pulmonary vasoconstriction
   • Bronchospasm and alterations to deadspace
4. Cardiovascular consequences
   • ↓ C.O. due to direct –ve inotropic effect of cold and ↑ afterload/SVR
   • Tachycardia initially, then progressive bradycardia with ↑ cold
   • QT prolongation and the J wave
   • Arrhythmias – classically AF and VF
   • Resistance to defibrillation
   • ↑ SVR and MAP due to peripheral vasoconstriction
5. Renal consequences
   • “Cold diuresis” due to ↓ vasopressin synthesis
6. Central nervous system effects
   • Confusion and ↓ level of consciousness
   • Shivering
   • ↑ seizure threshold
   • ↓ CBF
7. Immunological consequences
   • ↓ granulocyte and monocyte activity

Gladwin 2016

Answer by Gladwin