List the clinical effects of severe accidental hypothermia.
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
Renal: polyuria, dehydration, ARF
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
- Increased hematocrit and blood viscosity
- Neutropenia and thrombocytopenia
- Coagulopathy and platelet dysfunction
- Decreased respiratory rate and medullary sensitivity to CO2
- Acid-base changes: alkalosis and hypocapnea
- Decreased cardiac output and bradycardia
- QT prolongation and the J wave
- Arrhythmias - classically AF and VF
- Resistance to defibrillation
Central nervous system effects
The above-referenced chapter on hypothermia has extensive references.
In order to simplify revision, I have identified four articles which cover this topic with a wealth of detail.
Wong, K. C. "Physiology and pharmacology of hypothermia." Western Journal of Medicine 138.2 (1983): 227.
Polderman, Kees H. "Application of therapeutic hypothermia in the intensive care unit." Intensive care medicine 30.5 (2004): 757-769.
Polderman, Kees H. "Mechanisms of action, physiological effects, and complications of hypothermia." Critical care medicine 37.7 (2009): S186-S202.
Mallet, M. L. "Pathophysiology of accidental hypothermia." Qjm 95.12 (2002): 775-785.