Last Updated on December 19, 2020 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