Hypothermia is defined by a core body temperature <35°C (<95°F).
Classified as mild, moderate, or severe according to the patient’s core temperature and clinical features. 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.
Core temperature measured in the lower third of the oesophagus correlates well with pulmonary artery temperature and is preferred in patients with a secure airway.
Initial management should focus on stopping further cooling. This includes removing the patient from the cold environment, careful removal of wet or cold clothing, insulation, warming the body, securing the airway, monitoring breathing and circulation, and maintaining circulation using warm intravenous fluids.
Choice of re-warming strategy (passive external, active external, active internal) is based on the patient’s core temperature and clinical features; a combination of techniques may be used.
Patients who have sustained a hypothermic cardiac arrest should ideally be re-warmed in a specialist centre using extracorporeal life support (ECLS).
Accidental hypothermia is characterised by the unintentional lowering of core body temperature below physiological normal limits, typically <35°C (<95°F).
A threshold of 36°C (96.8°F) has been adopted in patients with trauma. In this patient group, even milder degrees of hypothermia have devastating consequences in both military and civilian populations.
This topic covers accidental hypothermia in adults.
History and exam
Key diagnostic factors
- presence of risk factors
- cold exposure and body temperature <35°C (<95°F)
- cognitive impairment
Other diagnostic factors
- tachypnoea, tachycardia, hypertension
- respiratory depression, bradycardia, hypotension
- coma and apnoea
- cold-induced diuresis
- general anaesthetic use
- older age
- very young age
- substance misuse
- impaired cognition
- Parkinson's disease
- gram-negative septicaemia
- neuroleptic medication
- beta-blocker medication
- sedative hypnotic medication
1st investigations to order
- core temperature measurement
- 12-lead ECG
- blood glucose
- blood gas
- serum urea, electrolytes, and creatinine
- clotting screen
- chest x-ray
Investigations to consider
- serum creatine kinase
- myoglobin levels
- end-tidal CO₂
moderate or severe hypothermia in cardiac arrest: ≤32°C (≤90°F)
moderate or severe hypothermia not in cardiac arrest: ≤32°C (≤90°F)
mild hypothermia: >32°C to 35°C (>90°F to 95°F)
Alexander Alexiou, MBBS, BSc, DCH, FRCEM, Dip IMC RCSEd
Emergency Medicine Consultant
Barts Health NHS Trust
Physician Response Unit Consultant
London’s Air Ambulance
Royal London Hospital
AA declares that he has no competing interests.
Melvyn Jenkins-Welch, MBBS, BSc, MSc, FRCA, FFICM
Consultant Critical Care Medicine
Cardiff and Vale ULHB
MJW declares that he has no competing interests.
BMJ Best Practice would like to gratefully acknowledge the previous expert contributors, whose work has been retained in parts of the content:
Emmanuel Atta Agaba, MD, FRCSEd, FACS
Assistant Professor of Surgery
Montefiore Medical Center at Albert Einstein College of Medicine
Rafael Barrera, MD, FACP
Surgical Intensive Care Unit
Long Island Jewish Medical Center
New Hyde Park
Patrick Morgan, MBChB, FRCA, FFICM, Dip IMC RCSEd, DiMM
Consultant in Anaesthesia
North Bristol NHS Trust
Pre-hospital and Retrieval Doctor
Emergency Medical Retrieval and Transfer Service (EMRTS) Cymru
PM is Medical Director, HM coastguard (UK). PM has been a medical expert witness in hypothermia, cold water-immersion and drowning. PM is a Research Associate/student at the Extreme Environments Laboratory, University of Portsmouth.
Section Editor, BMJ Best Practice
AS declares that she has no competing interests.
Lead Section Editor, BMJ Best Practice
TAO declares that she has no competing interests.
Drug Editor, BMJ Best Practice
AM declares that he has no competing interests.
Comorbidities Editor, BMJ Best Practice
JC declares that she has no competing interests.
- European Resuscitation Council guidelines for resuscitation 2021
- Clinical practice guidelines for the out-of-hospital evaluation and treatment of accidental hypothermia
Glasgow Coma ScaleMore Calculators
- Log in or subscribe to access all of BMJ Best Practice
Use of this content is subject to our disclaimer