Level 2 of 6Must-remember

Hypothermia: recognition, rewarming and cold arrest

Assess, manage and stay safe — enough on its own

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The card — assess, manage, caution

Assessment— look, ask, measure

Define it by the number: hypothermia is an unintentional fall in core body temperature below 35°C (95°F), the point at which the compensatory mechanisms that conserve and generate heat begin to fail.
Ask why, not only how cold: primary (accidental) hypothermia is environmental cold overwhelming intact thermoregulation, while secondary hypothermia results from sepsis, hypothyroidism, hypoglycaemia, overdose, stroke, adrenal insufficiency or trauma — mortality is substantially higher in secondary hypothermia and the two frequently coexist.
Use a low-reading probe: a standard clinical thermometer does not read below about 35°C and tympanic and skin devices are not calibrated below 35.5°C — an accurate core temperature requires a probe measuring down to 25°C, oesophageal (lower third) preferred in the intubated patient, rectal the pragmatic standard, bladder a useful ancillary site.
Rectal readings lag during rapid change, so a cooling patient looks warmer than they are; trend the temperature, never measure it once.
Severity bands: mild 32–35°C, moderate 28–32°C, severe below 28°C, with some authorities adding profound below 24°C.
Where no probe is available, stage clinically (Swiss system): Stage I conscious and shivering; Stage II drowsy with shivering stopped; Stage III unconscious with vital signs present; Stage IV unconscious with no detectable vital signs — it overestimates severity in about 20% of cases, and where staging and thermometer disagree, treat the more severe of the two.
A fast bedside guide: a person who feels icy to the touch over the abdomen, groin and axillae is probably substantially hypothermic, and if also clammy, uncooperative or sleepy the core temperature is almost certainly below 32°C.
Cessation of shivering is deterioration, not settling: shivering raises heat production two- to fivefold but consumes glycogen and fails between 29°C and 31°C.
Capillary glucose in the first minute: cold stress drives glycogenolysis so hyperglycaemia is common, but the malnourished and alcohol-dependent become hypoglycaemic, and hypoglycaemia both causes and complicates hypothermia.
Look for signs by stage: mild — vigorous shivering, amnesia, apathy, dysarthria, ataxia, poor judgement, cold diuresis; moderate — shivering ceases, depressed consciousness, dilated pupils, sluggish then absent reflexes, rigidity, hypoventilation, loss of airway reflexes, J waves, paradoxical undressing and hallucinations; severe — coma, fixed dilated pupils, areflexia, absent corneal and oculocephalic reflexes, apnoea, profound bradycardia or asystole, extreme oliguria.
People in severe hypothermia look dead, and pulses may be genuinely undetectable in a patient who is still perfusing.
Assess for signs of life for a full 60 seconds with the monitor gain at maximum, because QRS amplitude is reduced; capnography or echocardiography confirms perfusion.
Get a 12-lead ECG: bradycardia, prolonged PR, QRS and QT, slow atrial fibrillation, ectopy and the J (Osborn) wave — a positive deflection at the QRS–ST junction maximal in II, V5 and V6, which enlarges as temperature falls and resolves with rewarming.
Danger signs: cessation of shivering while still cold; core temperature below 30°C (maximal VF risk, triggerable by movement alone); deterioration during handling or transfer (rescue collapse); tachycardia disproportionate to the temperature; persistent hyperventilation; marked depression of consciousness with only mild hypothermia (32–35°C); areflexia that may hide a spinal cord lesion; a rigid abdomen from cold-induced ileus that may mask peritonitis; and hypotension unresponsive to fluid and rewarming.
Immersion times worth knowing: dangerous hypothermia develops after 30–60 minutes in water of 15–20°C, and below 12°C limbs become numb and weak within minutes; hypothermia also occurs indoors below about 8°C with poor heating, clothing and nutrition.
In neonates and infants think sepsis: they cool within minutes when wet and undressed, do not shiver effectively, present floppy, poorly responsive, feeding poorly with grunting, apnoea, mottling and prolonged capillary refill — neonatal hypothermia is a presentation of sepsis until proved otherwise and is strongly associated with hypoglycaemia and inborn errors of metabolism.

Management— do this, in order

Handle the patient minimally and keep them horizontal: cardiac output and cerebral blood flow are already low and fall further if the patient is sat up, stood or suspended in a harness — below 30°C, movement alone can precipitate ventricular fibrillation.
Stop ongoing heat loss before adding heat: remove wet clothing, dry the patient, cover them including the head, insulate from cold surfaces and warm the environment — this costs nothing and is often worth more than anything that follows.
Rewarm the trunk, not the limbs, since heat applied to the extremities causes vasodilatation and precipitates afterdrop; treat the cause concurrently, not afterwards.
Oxygen for everyone: the leftward shift of the oxyhaemoglobin dissociation curve impairs tissue oxygen delivery even when saturations look acceptable, and pulse oximetry is unreliable in the vasoconstricted patient; where available give it heated and humidified to 40–45°C, which eliminates respiratory heat loss and adds 1–2°C per hour.
Airway: if protective reflexes are absent, gentle endotracheal intubation is indicated — adequate preoxygenation is what prevents intubation-associated ventricular arrhythmia.Doctor / NurseNot available at your setup — Endotracheal intubation kit.
Glucose within the first minute: for documented hypoglycaemia give adult 50 mL of 25% glucose IV (or 100 mL of 10%), child 2 mL/kg of 10% glucose IV — never 25% or 50% in a neonate — and recheck at 15 minutes.Doctor / Nurse
Fluid: dehydration is the rule in chronic hypothermia, so give a crystalloid bolus — 0.9% sodium chloride is preferable to lactated Ringer's or Hartmann's because the cold liver metabolises lactate inefficiently; warm it to 38–42°C; adult 500–1000 mL, child 20 mL/kg, reassessing between boluses.Doctor / Nurse
Tubes: a gastric tube prevents dilatation from cold-induced ileus, and a urinary catheter monitors cold diuresis and gives an ancillary temperature site.
Passive external rewarming — drying, covering including the head, insulating and a warm environment — achieves 0.5–2°C per hour and suits the previously healthy patient with acute, mild, primary hypothermia; in the uninjured, alert, mildly hypothermic patient physical activity is safe and recommended, raising core temperature by around 2°C per hour, and hot sweet drinks may be given.
Active rewarming is necessary for any of: core temperature below 32°C; cardiovascular instability; extremes of age; CNS dysfunction; hormone insufficiency; or suspicion of secondary hypothermia.
Active external rewarming is best delivered by forced-air heating blankets to the trunk at 0.1–3.4°C per hour; alternatives are circulating-water heat-exchange pads, radiant heat sources and wrapped chemical heat packs to the axillae, groins and trunk; a 40°C bath is effective for mild hypothermia in the fully alert only.
Active core rewarming without a cardiac unit: heated humidified oxygen 40–45°C adds 1–2°C/h; bladder lavage with 300 mL warm saline instilled, drained and repeated gives 1–2°C/h; gastric lavage is minimal but worth combining in arrest; closed thoracic lavage gives 2–3°C/h and is the most efficient method where extracorporeal support is unavailable.
Aim for a controlled rise of roughly 1°C per hour in the perfusing patient — there is no evidence that extremely rapid rewarming improves survival in perfusing patients; speed matters only in cardiac arrest.
Blood pressure: target a mean arterial pressure of at least 60 mmHg early; most hypothermic hypotension responds to warmed crystalloid and rewarming, and where it does not, low-dose dopamine 2–5 micrograms/kg/min IV is the specifically recommended agent (same weight-based dose in children); perfusion may also improve with low-dose intravenous glyceryl trinitrate.Doctor / Nurse
Drug rule: below 30°C withhold adjunctive medications (adrenaline, amiodarone and the rest); between 30°C and 35°C double the interval between doses or use a lower dose — where adrenaline is given above 30°C the paediatric dose is 10 micrograms/kg IV/IO (0.1 mL/kg of 1:10 000).Doctor / Nurse
Hypothermic arrest: confirm arrest over a full 60 seconds; high-quality continuous chest compressions (intermittent CPR may still be effective below 28°C where continuous is impossible); defibrillate VF or pulseless VT with up to three shocks at maximal energy below 30°C (paediatric 4 J/kg) then delay further shocks until the core temperature exceeds 30°C; rewarm aggressively and in combination; continue resuscitation until the core temperature is at least 32°C before considering termination.Doctor / NurseNot available at your setup — Defibrillator.
Frostbite: do not thaw if refreezing is possible — pad and splint instead; otherwise immerse in circulating water at 37–39°C for 30–60 minutes until the part is soft and distally flushed, preceded by ibuprofen 400 mg orally and morphine 0.1 mg/kg IV titrated (child 0.1 mg/kg with paracetamol 15 mg/kg), then elevate, leave haemorrhagic vesicles intact, dress loosely and continue ibuprofen 400–600 mg 8–12-hourly (paediatric 5–10 mg/kg 8-hourly).Doctor / Nurse

Caution— what harms

Do not diagnose death in a cold patient: cold is neuroprotective and 'you are not dead until you are warm and dead' is literal guidance — do not stop because the pupils are fixed and dilated, the reflexes absent, or the patient looks dead.
Brainstem death cannot be diagnosed in a hypothermic patient — exclude and correct hypothermia first.
Chest compressions given to a perfusing patient may convert a perfusing rhythm to a non-perfusing one — hence the full 60-second assessment at maximum monitor gain.
Never warm the limbs first: heat applied to the extremities causes vasodilatation and precipitates core afterdrop; and never use an electric blanket, because vasoconstricted skin burns easily and the patient cannot feel it.
Avoid in the cold heart: deep insertion of a central venous catheter into the right atrium, pulmonary artery catheterisation (the non-compliant cold artery perforates) and transvenous pacing, all of which can precipitate refractory arrhythmia; and a thoracostomy tube in the left chest of a perfusing patient.Not available at your setup — Central venous access.
Do not correct the blood gas for temperature and do not hyperventilate: an uncorrected pH of 7.42 with PCO₂ 40 mmHg reflects appropriate ventilation at any core temperature, and at 28°C a 10 mmHg fall in PCO₂ produces double the 0.08 rise in pH it produces at 37°C.Not available at your setup — Arterial blood gas.
A falsely high PaO₂ is reported when a cold sample is analysed at 37°C — about 7% per °C between 37°C and 33°C; oximeter SaO₂ is correct, but a PaO₂ back-calculated from it needs downward correction.Not available at your setup — Arterial blood gas.
Laboratory results mislead systematically: haematocrit rises about 2% for every 1°C fall so a normal haemoglobin may conceal anaemia or haemorrhage; a normal white count does not exclude infection; coagulation studies run at 37°C look normal while the patient bleeds from a genuine cold coagulopathy; and the ECG changes of hyperkalaemia are obscured by hypothermia, so trust the number, not the trace.Not available at your setup — Serum electrolytes, Coagulation (PT/INR).
Do not treat the arrhythmias: atrial arrhythmias including slow atrial fibrillation are monitored without intervention and most convert spontaneously during rewarming; bradycardia is appropriate to the temperature, atropine is ineffective, and there is limited evidence to recommend any specific antiarrhythmic — the definitive antiarrhythmic is heat.
Doses that appear ineffective in the cold become toxic during rewarming because target organs respond minimally while protein binding rises and metabolism and excretion are impaired — digoxin and insulin are the classical examples.
Platelets and fresh frozen plasma do not correct cold coagulopathy and are reserved for actual haemorrhage; the treatment for the cold defect is rewarming.Not available at your setup — Blood & blood products.
Parenteral levothyroxine given to a euthyroid hypothermic patient is potentially hazardous — treat on historical clues or the prolonged Achilles relaxation phase, not empirically while results are awaited; likewise empirical steroid is usually not warranted unless the history suggests steroid dependence or hypoadrenalism, or standard rewarming fails.
Passive rewarming fails in the malnourished, the elderly and the alcohol-dependent because it depends absolutely on sufficient glycogen for endogenous thermogenesis.
Anticipate the complications of rewarming rather than discovering them: core temperature afterdrop, rewarming shock from vasodilatation onto unrecognised hypovolaemia, rewarming lactic acidosis, ventricular fibrillation and other arrhythmias, and rescue collapse triggered by handling or transfer below 30°C — keep defibrillation capability immediately available and keep warmed fluid running.Not available at your setup — Defibrillator.
Shaking rigors from infection are commonly mistaken for shivering, and hypothermia obscures fever and leucocytosis — in the elderly, hypothermia more often complicates another acute illness (pneumonia, stroke, fracture) than occurs alone.

Refer / escalate

Refer or transfer urgently any patient below 32°C, any patient with cardiovascular instability, arrest, CNS dysfunction, suspected secondary hypothermia or extremes of age — to a centre with extracorporeal life support if arrest or instability is present, moving them horizontal, minimally handled, insulated, with warmed fluid and heated humidified oxygen running and defibrillation capability at the trolley.

The card — assess, manage, caution

Hypothermia: recognition, rewarming and cold arrest — Level 1: CorePrevious Hypothermia: recognition, rewarming and cold arrest — Level 3: Core practiceNext

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