Hypothermia: Causes, Symptoms, Treatment

Author: Payal Patal, MD; Blake Briggs, MD

Introduction 

Hypothermia is defined as a core body temperature < 35°C. The stage of hypothermia, based on core temperature, impacts intervention. The classification of hypothermia is as follows¹:

• Mild hypothermia: Core temperature is 32 to 35°C (90 to 95°F).
• Moderate hypothermia: Core temperature is 28 to 32°C (82 to 90°F).
• Severe hypothermia: Core temperature is < 28°C (82°F).

Causes of Hypothermia²

• Environmental
• Metabolic: hypoglycemia, DKA, hypothyroid, adrenal insufficiency, thiamine deficiency 
• Toxicologic: sedatives or drugs that decrease catecholaminergic drive (e.g. beta-blockers, cholinergics, ethanol, opioids, benzodiazepines).
• Sepsis
• Malnutrition
• Elderly population

Clinical Pearl:
When evaluating hypothermia, consider a broad differential. Environmental exposure is less common in the ED compared to multifactorial causes (e.g., elderly on beta-blockers, cold ambient temperature, sepsis).

Evaluation

Obtain temperature with a thermometer at more than one site, preferably in the esophagus or rectum. However, if unable to obtain, use the Swiss hypothermia staging as shown in the table below. Keep in mind that the signs and symptoms do not correlate well with the degree of hypothermia. 

One of the first things to establish is an airway; endotracheal intubation is often immediately needed in an unresponsive patient with moderate-severe hypothermia. 

All wet clothing should immediately be removed and warming blankets applied.

Patients can also benefit from the administration of warm humidified oxygen and warm IV fluids.

There are some classic features of hypothermia you have to know. We summarize them in the table below.

Diagnostic Testing 

There are a lot of weird laboratory changes when patients have dramatic changes in their temperature. Some of these changes are easily testable, and it is good to know for clinical practice because they may erroneously lead you to make rash decisions. Expect hemoconcentration, hypo/hyperkalemia, hypo/hyperglycemia, and abnormal PT/INR/PTT results. 

Hypothermia can cause noncardiogenic pulmonary edema, be on the lookout for this and don’t confuse it for pneumonia. 

EKG in severe cases may show J (Osborne) waves, prolonged intervals, and arrhythmias.⁴  Shown below is an EKG with Osborne waves.⁵ 

Interventions

Passive external rewarming (blankets and oral hydration) is done for cases of mild hypothermia. For moderate hypothermia, a combination of both passive and active external rewarming is done. This includes warm air, blankets, warm IV fluids. 

Lastly, for severe hypothermia, active internal rewarming is the preferred method. This includes warm IV fluids, and discussion of aggressive methods like warm bladder or gastric lavage, central arteriovenous or venovenous rewarming, and dialysis.⁴

For hemodynamic instability, cardiac arrest, or severe rhabdomyolysis with hyperkalemia, consider ECMO or cardiopulmonary bypass (CPB).

• CPB can rewarm at rates up to 9.5°C/hour.
• ECMO is preferred for severe pulmonary edema due to prolonged oxygenation and circulatory support.
• Meta-analysis shows 44% survival with ECMO compared to 31% with CPB, though CPB shows 87% better neurologic outcomes compared to 75% with ECMO.^6,7

If hypothermia is secondary to infection or suggestive of sepsis, empiric broad-spectrum antibiotics should be started. Coverage should account for gram-positive and gram-negative, fungal, and rarely viruses. Antibiotics such as carbapenem or piperacillin-tazobactam should be started. If an organism is unknown, physicians should account for the following⁸:

• MRSA (with unlikelihood of Pseudomonas): Start IV Vancomycin with 
  • Third generation (ceftriaxone or cefotaxime) or fourth generation cephalosporin (cefepime) 
  • Beta-lactam inhibitor (piperacillin-tazobactam) 
  • Carbapenem (imipenem or meropenem) 
• Pseudomonas: Start Vancomycin with 1-2 of the following:
  • Antipseudomonal cephalosporin (ceftazidime, cefepime) 
  • Antipseudomonal carbapenem (imipenem, meropenem)
  • Antipseudomonal beta-lactam inhibitor (piperacillin-tazobactam) 
  • Fluroquinolone (ciprofloxacin) 

References

1. Giesbrecht GG. Cold stress, near drowning and accidental hypothermia: a review. Aviat Space Environ Med. 2000 Jul;71(7):733-52. PMID: 10902937.
2. Vassallo SU, Delaney KA. Thermoregulatory Principles. In: Nelson LS, Howland M, Lewin NA, Smith SW, Goldfrank LR, Hoffman RS. eds. Goldfrank’s Toxicologic Emergencies, 11e. McGraw-Hill
3. Brown DJ, Brugger H, Boyd J, Paal P. Accidental hypothermia. N Engl J Med. 2012 Nov 15;367(20):1930-8. doi: 10.1056/NEJMra1114208. Erratum in: N Engl J Med. 2013 Jan 24;368(4):394. PMID: 23150960.
4. https://www.saem.org/about-saem/academies-interest-groups-affiliates2/cdem/for-students/online-education/m4-curriculum/group-m4-environmental/hypothermia
5. Van Heukelom J. Osborn Waves in a Severely Hypothermic Patient. JETem 2018. 3(2):V34-35. https://doi.org/10.21980/J8H34S
6. Walpoth BH, Walpoth-Aslan BN, Mattle HP, Radanov BP, Schroth G, Schaeffler L, Fischer AP, von Segesser L, Althaus U. Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming. N Engl J Med. 1997 Nov 20;337(21):1500-5. doi: 10.1056/NEJM199711203372103. PMID: 9366581.
7. Bjertnæs LJ, Hindberg K, Næsheim TO, Suborov EV, Reierth E, Kirov MY, Lebedinskii KM, Tveita T. Rewarming From Hypothermic Cardiac Arrest Applying Extracorporeal Life Support: A Systematic Review and Meta-Analysis. Front Med (Lausanne). 2021 May 13;8:641633. doi: 10.3389/fmed.2021.641633. PMID: 34055829; PMCID: PMC8155640.
8. Savage RD, Fowler RA, Rishu AH, Bagshaw SM, Cook D, Dodek P, Hall R, Kumar A, Lamontagne F, Lauzier F, Marshall J, Martin CM, McIntyre L, Muscedere J, Reynolds S, Stelfox HT, Daneman N. Pathogens and antimicrobial susceptibility profiles in critically ill patients with bloodstream infections: a descriptive study. CMAJ Open. 2016 Oct 13;4(4):E569-E577. doi: 10.9778/cmajo.20160074. PMID: 28018869; PMCID: PMC5173462.