Cardiopulmonary responses during the cooling and the extracorporeal life support rewarming phases in a porcine model of accidental deep hypothermic cardiac arrest

Therapeutic Hypothermia for Refractory Hypoxemia on Venovenous Extracorporeal Membrane Oxygenation: An In Silico Study

Patients with respiratory failure may remain hypoxemic despite treatment with venovenous extracorporeal membrane oxygenation (VV-ECMO). Therapeutic hypothermia is a potential treatment for such hypoxia as it reduces cardiac output ( ) and oxygen consumption. We modified a previously published mathematical model of gas exchange to investigate the effects of hypothermia during VV-ECMO. Partial pressures were expressed as measured at 37°C (α-stat). The effect of hypothermia on gas exchange was examined in four clinical scenarios of hypoxemia on VV-ECMO, each with different physiological derangements. All scenarios had arterial partial pressure of oxygen (PaO 2 ) ≤ 46 mm Hg and arterial oxygen saturation of hemoglobin (SaO 2 ) ≤ 81%. Three had high with low extracorporeal blood flow to ratio ( ). The problem in the fourth scenario was recirculation, with normal . Cooling to 33°C increased SaO 2 to > 89% and PaO 2 to > 50 mm Hg in all scenarios. Mixed venous oxygen saturation of hemoglobin as % ( ) increased to > 70% and mixed venous partial pressure of oxygen in mm Hg ( ) increased to > 34 mm Hg in scenarios with low . In the scenario with high recirculation, and increased, but to < 50% and < 27 mm Hg, respectively. This in silico study predicted cooling to 33°C will improve oxygenation in refractory hypoxemia on VV-ECMO, but the improvement will be less when the problem is recirculation.

On the footsteps of Hippocrates, Sanctorius and Harvey to better understand the influence of cold on the occurrence of COVID-19 in European countries in 2020

COVID-19 pandemic has been characterized by a pattern of consecutive declines and regrowth in European countries in 2020. After being partially regressed during the summer, the reappearance of the infection during fall 2020 in many temperate countries strongly suggests that temperature and cold may play a role in influencing the infectivity and virulence of SARS-CoV-2. While promoting medicine as an art, Hippocrates interpreted with logical reasoning the occurrence of diseases such as epidemics, as a consequence of environmental factors, in particular climatic variations. During the Renaissance, Sanctorius was one of the first to perform quantitative measurements, and Harvey discovered the circulation of blood by performing experimental procedures in animals. We think that a reasoning mixing various observations, measurements and experiments is fundamental to understand how cold increases infectivity and virulence of SARS-CoV-2. By this review, we provide evidence linking cold, angiotensin-II, vasoconstriction, hypoxia and aerobic glycolysis (the Warburg effect) to explain how cold affects the epidemiology of COVID-19. Also, a low humidity increases virus transmissibility, while a warm atmosphere, a moderate airway humidity, and the production of vasodilator angiotensin 1-7 by ACE2 are less favorable to the virus entry and/or its development. The meteorological and environmental parameters impacting COVID-19 pandemic should be reintegrated into a whole perspective by taking into account the different factors influencing transmissibility, infectivity and virulence of SARS-CoV-2. To understand the modern enigma represented by COVID-19, an interdisciplinary approach is surely essential.

Use of Extracorporeal Membrane Oxygenation in Patients with Refractory Cardiac Arrest due to Severe Persistent Hypothermia: About 2 Case Reports and a Review of the Literature

We report the cases of two patients experiencing persistent severe hypothermia. They were 45 and 30 years old and had a witnessed cardiac arrest managed with mechanized cardiopulmonary resuscitation (CPR) for 4 and 2.5 hours, respectively. Extracorporeal membrane oxygenation was used in both patients who fully recovered without any neurological sequelae. These two cases illustrate the important role of extracorporeal CPR (eCPR) in persistent severe hypothermia leading to cardiac arrest.

Extracorporeal membrane oxygenation for accidental deep hypothermia-current challenges and future perspectives

The incidence of accidental hypothermia (core temperature ≤35 °C) is difficult to estimate, as the affected population is heterogeneous. Both temperature and clinical presentation should be considered while determining severity, which is difficult in a prehospital setting. Extracorporeal rewarming is advocated for all Swiss Staging System class IV (hypothermic cardiac arrest) and class III (hypothermic cardiac instability) patients. Veno-arterial extracorporeal membrane oxygenation (ECMO) is the method of choice, as it not only allows a gradual, controlled increase of core body temperature, but also provides respiratory and hemodynamic support during the unstable period of rewarming and reperfusion. This poses difficulties with the coordination of patient management, as usually only cardiac referral centers can deliver such advanced treatment. Further special considerations apply to subgroups of patients, including drowning or avalanche victims. The principle of ECMO implantation in severely hypothermic patients is no different from any other indication, although establishing vascular access in a timely manner during ongoing resuscitation and maintaining adequate flow may require modification of the operating technique, as well as aggressive fluid resuscitation. Further studies are needed in order to determine the optimal rewarming rate and flow that would favor brain and lung protection. Recent analysis shows an overall survival rate of 40.3%, while additional prognostic factors are being sought for determining those patients in whom the treatment is futile. New cannulas, along with ready-to-use ECMO sets, are being developed that would enable easy, safe and efficient out-reach ECMO implantation, thus shortening resuscitation times. Moreover, national guidelines for the management of accidental hypothermia are needed in order that all patients that would benefit from extracorporeal rewarming would be provided with such treatment. In this perspective article, we discuss burning problems in ECMO therapy in hypothermic patients, outlining the important research goals to improve the outcomes.