Hypothermia

Last Updated on by FRCEM Intermediate

OVERVIEW

Hypothermia occurs when core body temperature is < 35°C

  • mild: 32-35°C
  • moderate: 28-32°C
  • severe: < 28°C

Swiss staging system

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

CAUSES

Mechanisms

  • increased heat loss
  • decreased thermogenesis
  • impaired thermogenesis

Mutliple

  • age (elderly and infants at risk)
  • environmental – exposure, drowning, alpine environment, poverty (lack of heating or shelter)
  • drugs/ tox – alcohol, sedatives, vasodilators
  • Sepsis
  • CNS disorders e.g. hypothalamic lesions, hypopituitarism
  • Endocrine/ metabolic – hypothyroidism, adrenal insufficiency, hypothermia, malnutrition
  • Trauma — burns, spinal cord injury
  • Shock
  • Skin disorders — psoriasis, exfoliating conditions
  • Iatrogenic — cold fluid administration, intra-operative, therapeutic hypothermia
  • Psychiatirc (may lead to exposure)

EFFECTS

  • CVS: bradycardia is normal; decreased Q and MAP, vasoconstriction, ECG – widening of QRS, increased PR and QT, J waves, risk of VF < 28 C, increased blood viscosity and myocardial work
  • RESP: decreased CO2 production, decreased PAO2 and PaCO2 due to increased gas solubility, increased dead space, diaphragmatic fatigue, metabolic acidosis -> pulmonary hypertension
  • GI: decreased hepatic metabolism and blood flow, decreased splanchnic circulation
  • METABOLIC: decreased BMR, shivering, left shifted oxy-Hb dissociation curve, hyperglycaemia, decreased drug metabolism
  • CNS: neuroprotection, fixed dilated pupils at < 30 C (mimics brain death)
  • HAEM: increased bleeding time, PT and APTT, VTE risk, decreased platelet and WCC
  • RENAL: decreased GFR and RBF, cold-induced diuresis

MANAGEMENT

Resuscitation

  • pulse check – palpate for up to 1 minute (consider Echo / Doppler as hard to find – do not delay CPR)
  • move patient gently if <32 degrees due to risk of triggering VF (risk is overstated)
  • Confirm for signs of Life for 1 minute
  • If VE/VT: 3 shocks, then CPR, then no shocks until > 30 C.
  • No drugs until > 30 C, then double the interval as compared to normothermic arrest until 35 C.
  • ‘not dead until warm and dead’ (30-32C)

Passive warming – useful in conscious patients who are able to shiver  (1.5C per hour)

  • keep dry
  • warm environment
  • insulation with blankets (e.g. aluminium foil) and hat
  • allow to mobilise if conscious (beware of hypotension on cessation of exercise)

Peripheral active warming

  • chemical heat pads
  • radiant methods
  • forced air warming blankets (1-2C/h)

NB. Afterdrop, a drop in core body temperature during rewarming may occur a consequence of peripheral vasodilation and release of cold peripheral blood to the body core. It is not usually significant.

Central active warming

  • warmed (40-46C) humidified inspired gases (1 C/h; 1.5°C/h ET tube)
  • warm IV fluids (42C)  (only give if need fluids, prevents cooling rather than promotes warming) – use Level 1 fluid warmer
  • body cavity lavage with 40C fluid e.g. peritoneal (3C/h), gastric, bladder, right-sided thoracic lavage (3-6C/h – use 2 ICCs for continuous flow)
  • RRT
  • ECMO/ bypass (9-18C/h)

Supportive care and monitoring

  • use esophageal probe preferentially (core temperature, minimal lag time)
  • use low reading thermometer
  • ABG measurements at 37C (temperature uncorrected values) to allow serial monitoring

Seek and treat cause and complications

REWARMING RATES FOR DIFFERENT METHODS

  • Shivering 1.5° C/hr
  • Warming Blanket 2° C/hr
  • Warm O2 1 °C/hr with mask; 1.5° C/hr ET tube
  • IV Fluids do not add, but do not take away either
  • Peritoneal Lavage 3° C/hr
  • Thoracic Lavage with Chest Tubes 3-6° C/hr
  • Cardiac Bypass 9-18° C/hr

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