Sports Medicine: Just the Facts

232 SECTION 3 • MEDICAL PROBLEMS IN THE ATHLETE

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39 ENVIRONMENTAL INJURIES

Brian V Reamy, MD

HYPOTHERMIA

DEFINITION

• Hypothermia occurs when the body’s core tempera-
  ture drops below 35°C (95°F).

EPIDEMIOLOGY

• Individuals younger than 2 years of age and older than
  75 years of age are most at risk.
  
  
  • Increasing homelessness and sports activities in
    inclement environments have contributed to an
    increased incidence of hypothermia in the past decade.
  
  
  • Risk factors include the use of intoxicants, psychiatric
    illness, medical illnesses, sleep deprivation, dehydra-
    tion, malnutrition, and trauma. Impaired judgement
    resulting from psychiatric illness or the use of ethanol
    is the most common predisposing factor (Danzl and
    Pozos, 1994b).
  
  
  
  

PATHOPHYSIOLOGY

• The body combats the fall in core temperature through
  shivering thermogenesis and increased gluconeogene-
  sis. When the core temperature drops below 35°C the
  victim becomes poikilothermic and cools to the ambi-
  ent temperature.


• Central nervous system(CNS) function is directly
  depressed by the cold. The electroencephalogram
  (EEG) becomes abnormal below a temperature of
  33.5°C (92.5°F) and silent at 19°C (66°F).


• Initial reflex tachypnea continues until core tempera-
  ture falls below 30°C (86°F). Failure of brainstem con-
  trol of respiratory drive and the freezing of the thoracic
  musculature eventually lead to a cessation of breathing.
  •Cold triggers peripheral vasoconstriction and tachycar-
  dia. Below 34°C (93°F), bradycardia, hypotension,
  decreased cardiac output, and a lengthening of cardiac
  electrical conduction ensue. A J-wave (Osborn hypother-
  mic hump) may be noted at the QRS–ST junction. The
  myocardium becomes increasingly irritable, and sponta-
  neous atrial and ventricular dysrhythmias can occur
  (Graham, McNaughton, and Wyatt, 2001).


• Below 28°C (82°F) ventricular fibrillation can develop
  with minor stimuli such as removing a patient’s wet
  clothing or ambulance transport.

CLINICAL FEATURES

• Nonspecific symptoms and signs predominate and
  mimic the effects of mild dementia or ethanol intoxi-
  cation. The CNS effects of cold lead to impaired
  memory, judgement, slurred speech, and decreased
  alertness. Paradoxic bradycardia and hypoventilation
  occur despite hypotension. Multiple cardiac dysrhyth-
  mias develop as the core temperature falls. A cold-
  induced ileus, abdominal spasm and rigidity can
  mimic an acute abdomen.

DIAGNOSIS

• An accurate core temperature is crucial and is ideally
  obtained with a rectal thermistor probe. At a minimum,