Environmental Emergencies
Question 288 of 300
A 32 year old man is brought to the Emergency Department after being pulled from a lake. He was in the water for 10 minutes. The lake temperature was recorded at 4°C. You ask for the patient's core temperature to be recorded to classify the severity of hypothermia. Below what core temperature would the severity be classed as "severe" hypothermia?
Answer:
Hypothermia is defined as a body core temperature below 35°C:- Mild: 32 – 35°C
- Moderate: 28 – 32°C
- Severe: < 28°C
Hypothermia
Environmental Emergencies
Last Updated: 14th December 2023
Hypothermia is defined as a body core temperature below 35°C:
- Mild: 32 – 35°C
- Moderate: 28 – 32°C
- Severe: < 28°C
Swiss staging system for hypothermia
The Swiss staging system based on clinical signs can be used by rescuers at the scene to describe victims:
- Stage I: mild hypothermia; conscious, shivering, core temperature 32 – 35°C
- Stage II: moderate hypothermia; impaired consciousness without shivering, core temperature 28 – 32°C
- Stage III: severe hypothermia; unconscious, vital signs present, core temperature 24 – 28°C
- Stage IV: cardiac arrest or low flow state (no or minimal vital signs), core temperature < 24°C
- Stage V: death due to irreversible hypothermia, core temperature < 13.7°C
Diagnosis of hypothermia
- Accidental hypothermia may be under-diagnosed in countries with a temperate climate; when thermoregulation is impaired (e.g. elderly and very young) hypothermia may follow a mild insult; the risk of hypothermia is increased by alcohol or drug ingestion, exhaustion, illness, injury or neglect
- Hypothermia may be suspected from the clinical history or a brief examination of the collapsed patient
- A low-reading thermometer is needed to measure core temperature and confirm the diagnosis; the core temperature in the lower third of the oesophagus correlates well with heart temperature
- Tympanic measurement using a thermocouple is a reliable alternative but may be considerably lower than core temperature if the environment is very cold, the probe is not well insulated or the external auditory canal is filled with snow or water; commonly used tympanic thermometers based on infrared technique do not seal the ear and are not designed for low core temperature readings
- Once in hospital, use a consistent core temperature measurement site throughout resuscitation and rewarming; bladder and rectal temperatures lag behind core temperature and are not recommended in patients with severe hypothermia
Decision to resuscitate the hypothermic patient
- Cooling of the human body decreases cellular oxygen consumption by about 6% per 1°C decrease in core temperature; in some cases hypothermia can exert a protective effect on the brain and vital organs and intact neurological recovery is possible, even after prolonged cardiac arrest if deep hypothermia develops before asphyxia
- Hypothermia can produce a very slow, small-volume pulse and unrecordable blood pressure; in a hypothermic patient, no signs of life alone are unreliable for declaring death; at 18°C the brain can tolerate periods of circulatory arrest for ten times longer than at 37°C
- Intermittent CPR during rescue can be of benefit if continuous CPR cannot be delivered (alternating every 5 minutes)
- In the prehospital setting, CPR should only be withheld only if clear reason e.g. obvious signs of lethal injury or irreversible death, a valid DNACPR decision, conditions unsafe for rescuer, avalanche burial ≥ 60 min and airway packed with snow and asystole
Modifications to ALS in the hypothermic patient
- Check for signs of life for up to 1 minute; palpate a central artery and assess the cardiac rhythm; if there is any doubt, start CPR immediately
- Hypothermia can cause stiffness of the chest wall making ventilation and chest compressions difficult; consider the use of mechanical chest compression devices
- Do not delay careful tracheal intubation where indicated; the advantages of adequate oxygenation and protection from aspiration outweigh the minimal risk of triggering VF by performing tracheal intubation
- Once CPR is underway, confirm hypothermia with a low-reading thermometer
- The hypothermic heart may be unresponsive to cardioactive drugs, attempted electrical pacing and defibrillation; drug metabolism is slowed leading to potentially toxic plasma concentrations of any drugs given:
- Withhold adrenaline and other CPR drugs until the patient has been warmed to a core temperature of ≥ 30°C
- Once 30°C has been reached, the intervals between drug doses should be doubled when compared to normothermia (i.e. adrenaline every 6 - 10 minutes
- As normothermia is approached (≥ 35°C), standard drug protocols should be applied
- If VF is detected, defibrillate according to standard protocols; if VF persists after 3 shocks, delay further attempts until core temperature is ≥ 30°C; CPR and rewarming may have to be continued for several hours to facilitate successful defibrillation
- In-hospital prognostication of successful rewarming should be based on the HOPE or ICE scores.
Rewarming after hypothermia
- General principles
- General measures for all victims include removal from the cold environment, prevention of further heart loss and rapid transfer to the hospital
- In the field, a patient with moderate or severe hypothermia should be immobilised and handled carefully (to decrease risk of VF provoked by limb movement or invasive procedures), oxygenated adequately, monitored and the whole body dried and insulated
- Remove wet clothes while minimising excessive movement of the patient
- Patients with mild hypothermia can mobilise as exercise rewarms a person more rapidly than shivering
- Patients will continue cooling after removal from a cold environment (afterdrop), this can result in a life-threatening decrease in core temperature triggering a cardiac arrest during transport
- Patients who stop shivering (e.g. hypothermia stage II - IV, sedated or anaesthetised) will cool faster
- Prehospital rewarming and transfer
- In hypothermia stage I, passive rewarming is appropriate as patients are still able to shiver
- In hypothermia stages II - IV, the application of chemical heat packs to the trunk has been recommended; if the patient is unconscious and the airway not secured, arrange the insulation around the patient lying in a recovery (lateral decubitus) position
- Rewarming in the field with heated intravenous fluids and warm humidified gases is not feasible
- Intensive active rewarming must not delay transport to a hospital where advanced rewarming techniques, continuous monitoring and observation are available
- In hypothermia stage I, patients should be transferred to the nearest hospital
- In hypothermia stages II - IV, consider direct transfer to a hospital with facilities for ECLS, especially when there is cardiac instability
- In hypothermia stage V, in the absence of any reason for withholding CPR, start CPR and transfer the patient to an ECLS centre
- In-hospital rewarming and post-resuscitation care
- Rewarm using active external methods and minimally invasive methods;
- Mild hypothermia is treated with passive external rewarming
- Moderate and refractory mild hypothermia are treated with active external rewarming
- Severe and refractory moderate hypothermia are treated with active internal rewarming
- With a core temperature < 32°C and K+ < 8 mmol/L, consider ECLS rewarming where available; veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is the preferred method because it can be made available more rapidly, needs less anticoagulation and can provide prolonged cardiorespiratory support after rewarming (as compared to cardiopulmonary bypass)
- Continuous haemodynamic monitoring and warm IV fluids are essential; patients will require large volumes of IV fluids during rewarming as vasodilation causes expansion of the intravascular space; avoid hyperthermia during and after rewarming
- Once ROSC has been achieved, use standard post-resuscitation care
- Rewarm using active external methods and minimally invasive methods;
Rewarming techniques:
- Passive external rewarming:
- Remove wet clothes and dry whole body
- Mobilise conscious individuals
- Remove from cold environment and treat in warm environment
- Full body insulation with wool blankets, aluminium foil, cap
- Active external rewarming:
- Warm blankets
- Heating pads
- Warm baths
- Forced warm air e.g. Bair Hugger
- Active internal rewarming:
- Warm intravenous fluids
- Warm humidified oxygen
- Forced peritoneal lavage
- Extracorporeal life support (ECLS)
Characteristic ECG changes in hypothermia
- Prolonged RR, PR, QRS and QT intervals
- Delayed repolarisation J-waves (Osborne waves)
- Bradycardia
- Arrhythmias
Osborn wave seen in hypothermia. (Image by Jer5150 [CC BY-SA 3.0 , via Wikimedia Commons)
Complications of hypothermia
- Cardiac arrhythmias at temperatures below 30 - 32°C
- Infection
- Aspiration pneumonia
- Pulmonary oedema
- Pancreatitis
- Bleeding diathesis
- Bladder atony
- Frostbite
- Electrolyte abnormalities e.g. hyperkalemia, hypoglycemia
- Coagulopathy
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
