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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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