Recommendations
Key Recommendations
Suspect hypothermia (core body temperature <35°C [<95°F]) based on the condition the patient is found in and/or the presence of risk factors.
Patients who are inappropriately dressed for a cold climate and have spent a long time outdoors or in a cold environment may be hypothermic.
Risk factors include immobility (e.g., due to illness or injury), substance misuse, impaired cognition (e.g., following a stroke), and homelessness.
Make sure the environment is safe before you approach the patient if you are in a pre-hospital setting.[4] Handle the patient very gently to avoid precipitating ventricular fibrillation; keep the patient in a supine position if they have features of moderate or severe hypothermia (e.g., they have stopped shivering or have a reduced level of consciousness).[24]
Assess clinical signs, and measure the patient’s core temperature (when feasible; usually in hospital). These may give an indication of the severity of hypothermia:[4]
Severe hypothermia (<28°C [<82°F]): coma, apnoea. Get urgent support from the critical care team for any patient with severe hypothermia.
Moderate hypothermia (28°C to 32°C [82°F to 90°F]): respiratory depression, bradycardia, hypotension, impaired consciousness. Shivering may also stop.[4]
Mild hypothermia (32°C to 35°C [90°F to 95°F]): tachypnoea, tachycardia, hypertension.[4]
When measuring core temperature, check your local protocols.
If the patient has severe hypothermia, common practice in hospital emergency departments in the UK is to use an oesophageal probe (a probe positioned in the lower third of the oesophagus) if the patient has a secured and protected airway, or to measure rectal temperature.
The 2021 European Resuscitation Council and 2019 Wilderness Medical Society guidelines recommend using:[4][24]
Preferably: an oesophageal probe
OR
Alternatively: a low-reading tympanic membrane thermistor-based thermometer if the patient is spontaneously breathing.
Check vital signs.[4]
Beware of diagnosing death in a patient with hypothermia, even when the patient has fixed pupils or early signs of rigor mortis; signs of life may be minimal if the patient has severe hypothermia.[25]
See Management recommendations - Cardiac arrest for management of cardiac arrest in hypothermia.
Carry out a primary survey to detect any injuries.[26]
Always order the following initial investigations in hospital:
ECG; this should be continually monitored
Blood glucose
Blood gas
Urea, electrolytes, and creatinine.
Ensure the environment is safe before you approach the patient.[4] In practice, assess:
Whether the patient is shivering. Observe this as you approach the patient.
The patient’s level of consciousness. Do they respond when you speak to them? What is their Glasgow Coma Scale score? [ Glasgow Coma Scale Opens in new window ]
For vital signs (including a carotid pulse) for up to 1 minute.[24][4]
Be aware that vital signs may be difficult to detect in a patient with hypothermia in the pre-hospital setting if you do not have access to cardiac monitoring.[4]
See Management recommendations - Cardiac arrest for management of cardiac arrest in hypothermia.
Any injuries or illness, and the mechanism of these.[4]
If the patient has been immersed in water, see our topic Drowning.
Examine and move the patient very carefully while you are assessing them. Keep the patient in a supine position if they have features of moderate or severe hypothermia (e.g., they have stopped shivering or have a reduced level of consciousness).[24] This is crucial, because movement can precipitate ventricular fibrillation, especially if the patient’s temperature is <28℃ (<82.4℉).[4]
In a pre-hospital setting, use the four-stage Swiss system (see table below) to help estimate the patient’s core temperature at the scene (if this isn’t already available).[4][25] Stages of hypothermia are based on clinical signs, which roughly correlate to the patient’s core temperature, and are used to guide management.[4][25]
Stage | Clinical findings | Core temperature (if available) |
|---|---|---|
Hypothermia IV (severe) | Apparent death; vital signs absent; not shivering | Variable2 |
Hypothermia III (severe) | Unconscious;1 vital signs present; not shivering | Below 28℃ (below 82°F) |
Hypothermia II (moderate) | Impaired consciousness;1 may or may not be shivering | 32℃ to 28℃ (90°F to 82°F) |
Hypothermia I (mild) | Conscious, shivering1 | 35℃ to 32℃ (95°F to 90°F) |
1. Shivering and consciousness may be impaired by comorbid illness (trauma, CNS pathology, toxic ingestion, etc.) or drugs (sedatives, muscle relaxants, narcotics, etc.) independent of core temperature. 2. The risk of cardiac arrest increases below 32℃, but as it is unlikely to be due solely to hypothermia until the temperature is below 28℃, alternative causes should be considered. The temperature at which consciousness is lost is variable. Patients with body temperatures below 30℃ may still be conscious. Some patients still have vital signs below 24℃, and the lowest reported temperature of a patient with vital signs is 17℃. Table reproduced and adapted with permission from Paal et al. under a CC BY creative commons licence https://creativecommons.org/licences/by/2.0[3] | ||
Ask the pre-hospital team about the condition in which the patient was found. This may provide important clues to the diagnosis; for example, patients who are inappropriately dressed for a cold climate and have spent a long time outdoors or in a cold environment may be hypothermic.
Look for any signs of the underlying cause of hypothermia. For example:
Self-harm. Consider this particularly if the patient has a reduced level of consciousness or been immersed in water. Check for any signs of drug overdose or alcohol intoxication. See our topic Suicide risk mitigation.
Acute illness (e.g., stroke) or injury which has resulted in the patient lying on the ground outdoors for a long period of time.
Consider risk factors for hypothermia. These include:
Extremes of age
Immobility (e.g., due to illness or injury)
Substance misuse
Impaired cognition
Hypothyroidism
Stroke
Parkinson's disease
Homelessness
Gram-negative septicaemia.
Examine and move the patient very carefully while you are assessing them. Keep the patient in a supine position if they have features of moderate or severe hypothermia (e.g., they have stopped shivering or have a reduced level of consciousness).[24] This is crucial, because movement can precipitate ventricular fibrillation, especially if the patient’s temperature is <28℃ (<82.4℉).[4] If the patient has been immersed in water, see our topic Drowning.
Check for vital signs (including a carotid pulse) for up to 1 minute.[24][4] See Management recommendations - Cardiac arrest for management of cardiac arrest in hypothermia.
Be aware that vital signs may be very difficult to detect in a patient with hypothermia, especially in the pre-hospital setting; a very hypothermic patient may appear dead but still survive with resuscitation.[24][4]
Where possible, ECG monitoring, end-tidal CO2 and ultrasound should also be used to detect cardiac arrest.[24][4]
If you cannot feel a pulse and the patient has an organised rhythm on ECG monitoring, this may be pulseless electrical activity, or a perfusing rhythm with very weak pulses.[4]
Do not start cardiopulmonary resuscitation (CPR) in a patient with an organised, perfusing rhythm because this can risk conversion to ventricular fibrillation (a non-perfusing rhythm).[4]
Patients with hypothermia often show signs of confusion or impaired judgement. Additionally, they may be shivering, have increased urinary frequency, and show signs of frostbite. See our topic Frostbite.
Practical tip
Shivering will be absent once the patient’s core temperature drops below a certain level; the threshold varies between patients but is typically 32°C to 28°C (90°F to 82°F).[4]
Clinical signs correlate approximately to the patient’s core temperature.[4] However, bear in mind that an individual patient’s response to hypothermia may vary considerably; clinical signs can only provide an estimate of core temperature.[4] Get urgent support from the critical care team for any patient with severe hypothermia.
Clinical signs | Core temperature | Severity of hypothermia |
|---|---|---|
Coma, apnoea | <28°C (<82°F) | Severe |
Respiratory depression, bradycardia, hypotension, impaired consciousness | 28°C to 32°C (82°F to 90°F) | Moderate |
Tachypnoea, tachycardia (although this may progress to bradycardia, even in mild hypothermia), hypertension | 32°C to 35°C (90°F to 95°F) | Mild |
Some experts have suggested a further (more severe) category of profound hypothermia, at a core temperature <24°C (75.2°F) according to some and <20°C (68°F) according to others.[4] Note that this classification system differs from the four-stage Swiss System (outlined in Pre-hospital assessment above) which splits the severe group into “unconscious” (24°C-28°C) and “no vital signs” (<24°C).[25] | ||
Assess the patient for any injuries using a primary survey.[4][26]
Look for any signs of the underlying cause of hypothermia. For example:
Self-harm. Consider this particularly if the patient has a reduced level of consciousness or been immersed in water. Check for any signs of drug overdose or alcohol intoxication. See our topic Suicide risk mitigation.
Acute illness (e.g., stroke) or injury which has resulted in the patient lying on the ground outdoors for a long period of time.
Measure and monitor the patient’s core temperature.
Check your local protocols. If the patient has severe hypothermia, common practice in hospital emergency departments in the UK is to use an oesophageal probe (a probe positioned in the lower third of the oesophagus) if the patient has a secured and protected airway (i.e., tracheal tube or a supraglottic device with an oesophageal channel in place), or to measure rectal temperature.
Bear in mind, however, that the 2021 European Resuscitation Council (ERC) guideline has de-emphasised measurement of rectal temperature (or bladder temperature, which may be used if the patient requires a bladder catheter) for patients with severe hypothermia because temperature at these sites lags behind core temperature.[24]
Never measure rectal temperature if the patient is in a cold environment because this method requires the patient to be further exposed, which will increase heat loss and potentially worsen the hypothermia.[4]
Where feasible (usually in hospital) the 2021 ERC and 2019 Wilderness Medical Society guidelines recommend:
Preferably: an oesophageal probe.[24][4] An oesophageal probe correlates well with the temperature of the pulmonary artery and is the preferred method when available.[3][4]
OR
Alternatively: a low-reading tympanic membrane thermistor-based thermometer (where the thermistor touches the tympanic membrane) if the patient is spontaneously breathing.[24][4] Thermistor-based thermometers may not be widely available in some countries, including the UK.
Do not use a standard clinical thermometer to measure core temperature. This may be inadequate because it will not measure temperatures below 34.4°C (94°F). Conventional mercury thermometers are no longer recommended, owing to the risk of breakage and poisoning.
If the preferred methods for measuring core temperature are not available (e.g., in a pre-hospital setting), suspect hypothermia from the history and setting, and assess whether the patient’s trunk feels cold.[24]
Practical tip
Cold water or snow in the patient’s ear canal can lead to localised cooling of the tympanic membrane, which may result in a falsely low core temperature reading.
In addition to temperature, measure and monitor other vital signs, including:
Pulse rate
Blood pressure
Respiratory rate
Oxygen saturations.
Key investigations
Always order these key tests in all patients.
ECG
Monitor the ECG continuously.
This is essential for detecting arrhythmias, which may be fatal. Where possible, ECG monitoring should also be used to detect cardiac arrest.[4][24]
Arrhythmias can occur at any stage of hypothermia, and also during re-warming. Initially, in mild hypothermia, the ECG may show tachycardia. In more severe cases of hypothermia, the ECG may show progressive sinus bradycardia, atrial or ventricular fibrillation, junctional rhythms, ST segment changes, T-wave inversion, prolongation of the QT interval, and eventually asystole.[5] With the exception of ventricular fibrillation, these changes are likely to improve without treatment as the patient’s core temperature increases.[4][24]
J waves (or Osborn waves) occur in most, but not all, patients.[27] However, they do not correlate well with temperature.[28]
[Figure caption and citation for the preceding image starts]: A 12 lead ECG obtained from a hypothermic patient; note Osborn waves (arrows), which have an extra deflection at the end of the QRS complexAydin M, Gursurer M, Bayraktaroglu T, et al. Tex Heart Inst J. 2005;32(1):105 [Citation ends].
Blood glucose
Bear in mind that glucose levels may be normal, high (owing to increased secretion of stress hormones - cortisol, growth hormones, and catecholamines - and reduced insulin secretion, together with increased peripheral resistance to insulin), or low (owing to cold-induced inhibition of hepatic glucose production).
Monitor blood glucose even after the patient is normoglycaemic because rebound hypoglycaemia may develop when normal insulin production resumes.
Treat hypoglycaemia promptly. Hypoglycaemia can stop shivering (because the central control of shivering is dependent on glucose), leading to subsequent heat loss.[29]
Blood gas
Note that blood gases may show respiratory alkalosis, metabolic acidosis, or a mixture of both.
As core temperature decreases, respiration is depressed, resulting in hypoxaemia and hypercapnia.
A combined respiratory and metabolic acidosis occurs as a result of hypoventilation, retention of carbon dioxide, decreased bicarbonate, impaired hepatic metabolism of organic acid production (owing to impaired hepatic perfusion), and increased lactic acid production. It is important to note that blood pH rises by 0.015 for every 1°C (1.8°F) drop in body temperature.
In general, use blood gas results without adjustment for temperature to guide treatment decisions.[30]
Be aware that there is debate in the literature about how to interpret blood gases in patients with hypothermia.[3][30] This is a complex issue, because blood gas analysers warm the blood sample to 37℃ (98.6℉) - higher than the patient’s temperature if they are hypothermic - and pH, PO2 and PCO2 all vary with temperature.[3][30] Therefore, interpretation of uncorrected blood gas results is a widely used approach because clinicians are more familiar with this.[30]
In practice, perform a venous rather than an arterial blood gas; a venous blood gas is associated with less risk than an arterial blood gas and gives adequate results for most patients.
Monitor blood gases to ensure resolution of hypoxia and normalisation of pH.
Urea, electrolytes, and creatinine
Hypokalaemia may occur as a result of the hypothermia or the associated treatment. Hyperkalaemia may occur during re-warming.
For a patient in cardiac arrest, hyperkalaemia can also indicate that hypoxia preceded hypothermia (e.g., if the patient was found in an avalanche).[4]
Hyperkalaemia is part of the HOPE (Hypothermia Outcome Prediction after ECLS re-warming for hypothermic arrested patients) score for prognostication of successful re-warming.[4][24] Initial serum potassium >12 mmol/L (12 mEq/L) is associated with irreversible death if the patient is in cardiac arrest.[3]
Renal function may be impaired due to dehydration, cold exposure, or rhabdomyolysis.
Further investigations
Always order the following investigations, but bear in mind that they are less useful for the acute assessment and management of hypothermia.
Full blood count
May show elevated haemoglobin and haematocrit, and low platelet and WBC counts.
Clotting screen
Prothrombin time and PTT tend to be prolonged, although the cause for this is unknown.[31]
Chest x-ray
A chest x-ray is particularly important if the patient has an altered level of consciousness.
It may show pulmonary oedema or infiltrates.
If the patient has been immersed in water, it may show inhaled foreign bodies, such as false teeth or debris from the water, which will need to be removed. See our topic Foreign body aspiration.
Investigations to consider
If the patient may have been lying on the ground outdoors for a long time and they have not been immersed in water, check for rhabdomyolysis by ordering:
Serum creatine kinase
Myoglobin levels.
See our topic Rhabdomyolysis.
If you cannot detect vital signs, use the following investigations, where possible, to confirm cardiac arrest:[24][4]
End-tidal CO2
Ultrasound.
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