Diagnostics and Therapeutics: Hypothermia

View fullsize

Summer is in full swing, so why not take a look at the cold, and how we approach the hypothermic patient differently from their initial presentation

Identification of Cardiac Arrest

Inappropriately initiating CPR in profound hypothermia induced bradycardia can lead to ventricular dysrhythmias due to stimulation of irritable myocardium. Peripheral pulses are difficult to palpate in a vasoconstricted bradycardic patient, so central pulses should be used. Consider placing an arterial line or utilizing pulse-wave Doppler to identify a central pulse for up to a full minute prior to initiation of CPR. If there are enough providers, you should also perform a bedside echocardiogram to evaluate for cardiac activity. Chest compressions should not be initiated if cardiac activity is visualized on ultrasound, or if a pulse is detectable with doppler ultrasound.

All hypothermic patients should be placed on the monitor on arrival. While the evidence is very sparse, many experts believe that CPR should be withheld in patients with an organized rhythm, as this may represent perfusion that could be disrupted with chest compressions. This also pairs with the argument that PEA would likely be transient and quickly transition to fibrillation or asystole, with which CPR should be started immediately. Remember, with any signs of life, assume that some perfusion is occurring and avoid anything that may cause cardiac irritation.

The only real contraindications for initiation of CPR in the severely hypothermic patient is provider safety, the inability to compress a frozen chest wall, or if the nose and mouth are blocked with snow or ice. Other common indications of futility such as fixed and dilated pupils, mandibular rigidity, or apparent rigor mortis can all occur secondary to hypothermia and should not be used to withhold resuscitation in the hypothermic patient (1,13-14).

Intra-arrest Management:

In hypothermic patients in cardiac arrest, ventricular arrhythmias and asystole may be refractory to conventional therapy until the patient has been rewarmed. The definitive management of ventricular arrhythmia is focused on aggressively rewarming the patient in conjunction with standard cardiac life support, including high-quality CPR. There is not a lot of evidence regarding ventricular arrhythmias in hypothermic patients, but it is reasonable to follow ACLS guidelines, including defibrillation. Some studies have shown successful defibrillation below 30°C. Again, there is very little data, but experts recommend defibrillation with a single shock, with repeat attempts every 1 to 2°C increase in core temperature. Above 30°C, follow ACLS guidelines for normothermic patients (2-4).

In terms of pharmacology, animal studies suggest that vasopressor therapy is more beneficial than anti-arrhythmic medications, with no advantage for intermediate- or high-dose epinephrine. There is likely benefit to giving epinephrine, but repeat dosing is likely unnecessary. Follow normal protocols after rewarming (5).

Post-ROSC Care:

The patient will likely become hypotensive during the rewarming process, as fluid shifts and peripheral vasodilation lead to significant volume loss. This should be addressed with warmed isotonic crystalloid through a Level 1 rapid infuser. Keep in mind that room-temperature fluids can worsen hypothermia. Large infusions may be necessary. Vasoconstriction may make IV access difficult; consider an IO if unable to obtain IV access (6-7).

ECMO:

There is a 40-50% survival rate with the use of ECMO across all demographics (about 70% for witnessed arrest and 30% if unwitnessed). In those who survival, approximately 80-90% have normal neurologic function. Rates of ROSC were higher for patients with a non-asphyxiation mechanism of cooling, females, those with PEA as the initial rhythm, shorter CPR time, lower core temperature, and normal serum potassium. No patient with uncomplicated hypothermia and a core temp above 30°C sustained cardiac arrest (8-10).

The HOPE score, or Hypothermia Outcome Prediction after ECLS, can be utilized to estimate recovery chance with ECMO. This tool was derived from a study of about 300 patients with an overall survival rate of 37%. The tool includes the variables already discussed with the addition of age, with higher age increasing survival rate, but this was not consistent with other similar studies (11-12).

Duration of Resuscitation:

Successful ROSC with complete recovery has been documented after many hours of resuscitation (15-16). This can make the decision to stop CPR difficult. In general, follow the rule that the “patient isn’t dead unless they’re warm and dead,” usually considered above 30°C.

There are several laboratory values that have been studied to guide CPR cessation in hypothermic patients, most notably extreme hyperkalemia caused by cell lysis. There are no reported cases of survival with a potassium exceeding 12 mEq/L, although there is no data to suggest a specific cutoff value in most hypothermic patients. One exception to this is avalanche victims, where one study proposed an optimal cutoff of a potassium of 7 mEq/L because the arrest was likely due to asphyxia vs hypothermia (17-18). Fibrinogen below 50 mg/dL (intravascular thrombosis), ammonia concentrations above 420 mcg/dL, and elevated lactate, sodium, or creatinine are also possible indicators of a poor prognosis, but should not be used to guide management in isolation (19).

Unlike in normothermic patients with cardiac arrest, low end-tidal CO2 should not be used to terminate resuscitation, as this may reflect a low metabolic rate rather than poor perfusion (20).

---

POST BY Lucas Boyer, MD

Dr. Boyer is a PGY-1 in Emergency Medicine at the University of Cincinnati.

EDITING BY Bailee Stark, MD AND Arthur Broadstock, MD FAWM

Dr. Stark is a PGY-4 and Chief Resident in Emergency Medicine at the University of Cincinnati.

Dr. Broadstock is an Clinical Instructor and Ultrasound Fellow in Emergency Medicine at the University of Cincinnati and an Assistant Editor of TamingtheSRU.

---

References

1.     Bunya N, Sawamoto K, Kakizaki R, Wada K, Katayama Y, Mizuno H, Inoue H, Uemura S, Harada K, Narimatsu E. Successful resuscitation for cardiac arrest due to severe accidental hypothermia accompanied by mandibular rigidity: a case of cold stiffening mimicking rigor mortis. Int J Emerg Med. 2018 Nov 14;11(1):46. doi: 10.1186/s12245-018-0205-8. PMID: 31179929; PMCID: PMC6326142.

2.     Koller R, Schnider TW, Neidhart P. Deep accidental hypothermia and cardiac arrest--rewarming with forced air. Acta Anaesthesiol Scand. 1997 Nov;41(10):1359-64. doi: 10.1111/j.1399-6576.1997.tb04658.x. PMID: 9422306.

3.     Thomas R, Cahill CJ. Successful defibrillation in profound hypothermia (core body temperature 25.6 degrees C). Resuscitation. 2000 Nov;47(3):317-20. doi: 10.1016/s0300-9572(00)00254-9. PMID: 11114463.

4.     Mair P, Gasteiger L, Mair B, Stroehle M, Walpoth B. Successful Defibrillation of Four Hypothermic Patients with Witnessed Cardiac Arrest. High Alt Med Biol. 2019 Mar;20(1):71-77. doi: 10.1089/ham.2018.0084. Epub 2019 Feb 25. PMID: 30801202.

5.     Wira CR, Becker JU, Martin G, Donnino MW. Anti-arrhythmic and vasopressor medications for the treatment of ventricular fibrillation in severe hypothermia: a systematic review of the literature. Resuscitation. 2008 Jul;78(1):21-9. doi: 10.1016/j.resuscitation.2008.01.025. Epub 2008 Apr 10. PMID: 18406039.

6.     Jolly BT, Ghezzi KT. Accidental hypothermia. Emerg Med Clin North Am. 1992 May;10(2):311-27. PMID: 1559471.

7.     Danzl DF, Pozos RS. Accidental hypothermia. N Engl J Med. 1994 Dec 29;331(26):1756-60. doi: 10.1056/NEJM199412293312607. PMID: 7984198.

8.     Saczkowski RS, Brown DJA, Abu-Laban RB, Fradet G, Schulze CJ, Kuzak ND. Prediction and risk stratification of survival in accidental hypothermia requiring extracorporeal life support: An individual patient data meta-analysis. Resuscitation. 2018 Jun;127:51-57. doi: 10.1016/j.resuscitation.2018.03.028. Epub 2018 Mar 23. PMID: 29580960.

9.     Podsiadło P, Darocha T, Svendsen ØS, Kosiński S, Silfvast T, Blancher M, Sawamoto K, Pasquier M. Outcomes of patients suffering unwitnessed hypothermic cardiac arrest rewarmed with extracorporeal life support: A systematic review. Artif Organs. 2021 Mar;45(3):222-229. doi: 10.1111/aor.13818. Epub 2020 Oct 8. PMID: 32920881.

10.  Frei C, Darocha T, Debaty G, Dami F, Blancher M, Carron PN, Oddo M, Pasquier M. Clinical characteristics and outcomes of witnessed hypothermic cardiac arrest: A systematic review on rescue collapse. Resuscitation. 2019 Apr;137:41-48. doi: 10.1016/j.resuscitation.2019.02.001. Epub 2019 Feb 13. PMID: 30771451.

11.  Pasquier M, Hugli O, Paal P, Darocha T, Blancher M, Husby P, Silfvast T, Carron PN, Rousson V. Hypothermia outcome prediction after extracorporeal life support for hypothermic cardiac arrest patients: The HOPE score. Resuscitation. 2018 May;126:58-64. doi: 10.1016/j.resuscitation.2018.02.026. Epub 2018 Mar 2. PMID: 29481910.

12.  Pasquier M, Rousson V, Darocha T, Bouzat P, Kosiński S, Sawamoto K, Champigneulle B, Wiberg S, Wanscher MCJ, Brodmann Maeder M, Paal P, Hugli O. Hypothermia outcome prediction after extracorporeal life support for hypothermic cardiac arrest patients: An external validation of the HOPE score. Resuscitation. 2019 Jun;139:321-328. doi: 10.1016/j.resuscitation.2019.03.017. Epub 2019 Mar 30. PMID: 30940473.

13.  Lott C, Truhlář A, Alfonzo A, Barelli A, González-Salvado V, Hinkelbein J, Nolan JP, Paal P, Perkins GD, Thies KC, Yeung J, Zideman DA, Soar J; ERC Special Circumstances Writing Group Collaborators. European Resuscitation Council Guidelines 2021: Cardiac arrest in special circumstances. Resuscitation. 2021 Apr;161:152-219. doi: 10.1016/j.resuscitation.2021.02.011. Epub 2021 Mar 24. Erratum in: Resuscitation. 2021 Oct;167:91-92. PMID: 33773826.

14.  ECC Committee, Subcommittees and Task Forces of the American Heart Association. 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2005 Dec 13;112(24 Suppl):IV1-203. doi: 10.1161/CIRCULATIONAHA.105.166550. Epub 2005 Nov 28. PMID: 16314375.

15.  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.

16.  Hilmo J, Naesheim T, Gilbert M. "Nobody is dead until warm and dead": prolonged resuscitation is warranted in arrested hypothermic victims also in remote areas--a retrospective study from northern Norway. Resuscitation. 2014 Sep;85(9):1204-11. doi: 10.1016/j.resuscitation.2014.04.029. Epub 2014 Jun 2. PMID: 24882104.

17.  Romlin BS, Winberg H, Janson M, Nilsson B, Björk K, Jeppsson A, Drake G, Claesson A. Excellent Outcome With Extracorporeal Membrane Oxygenation After Accidental Profound Hypothermia (13.8°C) and Drowning. Crit Care Med. 2015 Nov;43(11):e521-5. doi: 10.1097/CCM.0000000000001283. PMID: 26317568.

18.  Brugger H, Bouzat P, Pasquier M, Mair P, Fieler J, Darocha T, Blancher M, de Riedmatten M, Falk M, Paal P, Strapazzon G, Zafren K, Brodmann Maeder M. Cut-off values of serum potassium and core temperature at hospital admission for extracorporeal rewarming of avalanche victims in cardiac arrest: A retrospective multi-centre study. Resuscitation. 2019 Jun;139:222-229. doi: 10.1016/j.resuscitation.2019.04.025. Epub 2019 Apr 22. PMID: 31022496.

19.  Debaty G, Moustapha I, Bouzat P, Maignan M, Blancher M, Rallo A, Brun J, Chavanon O, Danel V, Carpentier F, Payen JF, Briot R. Outcome after severe accidental hypothermia in the French Alps: A 10-year review. Resuscitation. 2015 Aug;93:118-23. doi: 10.1016/j.resuscitation.2015.06.013. Epub 2015 Jun 19. PMID: 26095302.

20.  Darocha T, Debaty G, Ageron FX, Podsiadło P, Hutin A, Hymczak H, Blancher M, Kosiński S, Mendrala K, Carron PN, Lamhaut L, Bouzat P, Pasquier M. Hypothermia is associated with a low ETCO2 and low pH-stat PaCO2 in refractory cardiac arrest. Resuscitation. 2022 May;174:83-90. doi: 10.1016/j.resuscitation.2022.01.022. Epub 2022 Jan 31. PMID: 35101599.

21.  Gordon L, Paal P, Ellerton JA, Brugger H, Peek GJ, Zafren K. Delayed and intermittent CPR for severe accidental hypothermia. Resuscitation. 2015 May;90:46-9. doi: 10.1016/j.resuscitation.2015.02.017. Epub 2015 Feb 25. PMID: 25725297.