Hypothermia exists when the core body temperature is below 35°C and is classified arbitrarily as mild (32-35°C), moderate (28-32°C), or severe (<28°C).

The Swiss staging system, based on clinical signs, can be used by rescuers at the scene to describe victims:

• I – clearly conscious and shivering
• II – impaired consciousness without shivering
• III – unconscious
• IV – not breathing
• V – death due to irreversible hypothermia

Risk factors for hypothermia include the following:

• Environmental exposure
• Unsatisfactory housing
• Poverty
• Lack of cold awareness (autonomic neuropathy, dementia)
• Drugs (sedatives, anti-depressants)
• Alcohol
• Acute confusion
• Hypothyroidism
• Sepsis

The clinical features of hypothermia vary depending upon the severity:

1. At 32-35°C:

• Apathy
• Amnesia
• Ataxia
• Dysarthria

2. At 30-32°C:

• Decreased conscious level/coma
• Hypotension
• Arrhythmias
• Respiratory depression
• Muscular rigidity

3. Below 30°C:

• Ventricular fibrillation
• VF may be precipitated by excessive movement or invasive procedures

Diagnosis of hypothermia can be confirmed by checking the core temperature with an oesophageal probe. Alternatively use a rectal or tympanic probe with a low reading thermometer. Rectal and tympanic temperatures lag behind core temperature and are unreliable in hypothermia.

Investigations that should be carried out include:

• Bloods
  • U&Es, FBC, toxicology and clotting screen
  • Blood glucose
  • Amylase
  • Blood cultures
  • Arterial blood gas
• ECG
  • Bradyarrhythmias
  • Osborne Waves (= J waves)
  • Prolonged PR, QRS and QT intervals
  • Shivering artefact
  • Ventricular ectopics
  • Cardiac arrest due to VT, VF or asystole
• Chest X-ray
  • Look for LRTI, aspiration and LVF
• CT Head
  • If suspected head injury or CVA

J-waves (Osborne-waves): In hypothermia, a small extra wave is seen immediately after the QRS complex. This additional wave is called a J wave or Osborne wave after the individual who first described it. This wave disappears with the warming of body temperature. The mechanism is unknown.

The management of hypothermia is as follows:

1. Basic principles:

• Support ABCs
• Treat in a warm room (>21°C)
• Remove wet clothes and dry the skin
• Place on a cardiac monitor and monitor the ECG
• Warmed, humidified O₂ by face mask
• Correct hypoglycaemia with IV 50% glucose
• Handle patient gently to avoid precipitating VF arrest

2. Re-warming methods:

• Aim for a rate of 0.5-2°C per hour
• Passive re-warming
  • Easy, non-invasive and suitable for mild cases
  • Wrap in warm blankets
  • Bair hugger/polythene sheets
• Surface re-warming
  • Water bath at 37-41°C useful for acute immersion hypothermia
  • Can cause core temperature after drop and hypotension (this is due to peripheral vasodilation)
• Core re-warming
  • Airway re-warming – heated, humidified O₂
  • Peritoneal lavage. 0.9% Saline run via DPL catheter
  • Extracorporeal re-warming via cardiopulmonary bypass – this is the method of choice in severe hypothermia / cardiac arrest

3. Hypothermic cardiac arrest:

• If CPR is required, give chest compressions and ventilations at standard rates
• Check for signs of life for up to 1 minute (palpate a central artery)
• Hypothermia can cause stiffness of the chest wall and make chest compression difficulty – consider the use of a mechanical chest compression device
• The hypothermic heart may be resistant to cardioactive drugs – avoid drugs until core temperature >30°C
• Once 30°C has been reached the interval between drugs should be doubled until approaching normothermia
• Defibrillate at usual energies but if three shocks are unsuccessful then defer further shocks until core temperature >28-30°C

Header image used on licence from Shutterstock

Thank you to the joint editorial team of www.mrcemexamprep.net for this article.