Cheap and simple, could it get even cooler? Mild hypothermia and COVID-19

Targeted Temperature Management After Cardiac Arrest in COVID-19 Patients

There is a paucity of evidence regarding the utility of targeted temperature management (TTM) in COVID-19 patients who suffer cardiac arrest. This systematic review and meta-analysis aimed to use the available data of how temperature predicts outcomes in COVID-19 patients and the association between active cooling and outcomes in non-COVID-19 cardiac arrest patients to give recommendations for the utility of TTM in COVID-19 survivors of cardiac arrest. The PubMed, Embase, and Web of Science databases were queried in August 2022 for two separate searches: (1) temperature as a predictor of clinical outcomes in COVID-19 and (2) active cooling after return of spontaneous circulation (ROSC) in non-COVID-19. Forest plots were generated to summarize the results. Of the 4209 abstracts screened, none assessed the target population of TTM in COVID-19 victims of cardiac arrest. One retrospective cohort study evaluated hyperthermia in critically ill COVID-19 patients, two retrospective cohort studies evaluated hypothermia in septic COVID-19 patients, and 20 randomized controlled trials evaluated active cooling in non-COVID-19 patients after ROSC. Risk of death was higher in COVID-19 patients who presented with hyperthermia (risk ratio [RR] = 1.87) or hypothermia (RR = 1.77; p < 0.001). In non-COVID-19 victims of cardiac arrest, there was no significant difference in mortality (RR = 0.94; p = 0.098) or favorable neurological outcome (RR = 1.05; p = 0.41) with active cooling after ROSC. Further studies are needed to evaluate TTM in COVID-19 victims of cardiac arrest. However, given the available evidence that hyperthermia or hypothermia in COVID-19 patients is associated with increased mortality as well as our findings suggesting limited utility for active cooling in non-COVID-19 cardiac arrest patients, we posit that TTM to normothermia (core body temperature ∼37°C) would most likely be optimal for the best outcomes in COVID-19 survivors of cardiac arrest.

Improving oxygenation in severe ARDS treated with VV-ECMO: comparative efficacy of moderate hypothermia and landiolol in a swine ARDS model

BACKGROUND

Acute respiratory distress syndrome (ARDS) remains a significant challenge in critical care, with high mortality rates despite advancements in treatment. Venovenous extracorporeal membrane oxygenation (VV-ECMO) is employed as salvage therapy for refractory cases. However, some patients may continue to experience persistent severe hypoxemia despite being treated with VV-ECMO. To achieve this, moderate hypothermia and short-acting selective β1-blockers have been proposed.

METHODS

Using a swine model of severe ARDS treated with VV-ECMO, this study investigated the efficacy of moderate hypothermia or β-blockade in improving arterial oxygen saturation (SaO2) three hours after VV-ECMO initiation. Primary endpoints included the ratio of VV-ECMO flow to cardiac output and arterial oxygen saturation before VV-ECMO start (H0) and three hours after ECMO start (H3). Secondary safety criteria encompassed hemodynamics and oxygenation parameters.

RESULTS

Twenty-two male pigs were randomized into three groups: control (n = 6), hypothermia (n = 9) and β-blockade (n = 7). At H0, all groups demonstrated similar hemodynamic and respiratory parameters. Both moderate hypothermia and β-blockade groups exhibited a significant increase in the ratio of VV-ECMO flow to cardiac output at H3, resulting in improved SaO2. At H3, despite a decrease in oxygen delivery and consumption in the intervention groups compared to the control group, oxygen extraction ratios across groups remained unchanged and lactate levels were normal.

CONCLUSIONS

In a swine model of severe ARDS treated with VV-ECMO, both moderate hypothermia and β-blockade led to an increase in the ratio of VV-ECMO flow to cardiac output resulting in improved arterial oxygen saturation without any impact on tissue perfusion.

Mechanisms of action behind the protective effects of proactive esophageal cooling during radiofrequency catheter ablation in the left atrium

Proactive esophageal cooling for the purpose of reducing the likelihood of ablation-related esophageal injury resulting from radiofrequency (RF) cardiac ablation procedures is increasingly being used and has been Food and Drug Administration cleared as a protective strategy during left atrial RF ablation for the treatment of atrial fibrillation. In this review, we examine the evidence supporting the use of proactive esophageal cooling and the potential mechanisms of action that reduce the likelihood of atrioesophageal fistula (AEF) formation. Although the pathophysiology behind AEF formation after thermal injury from RF ablation is not well studied, a robust literature on fistula formation in other conditions (eg, Crohn disease, cancer, and trauma) exists and the relationship to AEF formation is investigated in this review. Likewise, we examine the abundant data in the surgical literature on burn and thermal injury progression as well as the acute and chronic mitigating effects of cooling. We discuss the relationship of these data and maladaptive healing mechanisms to the well-recognized postablation pathophysiological effects after RF ablation. Finally, we review additional important considerations such as patient selection, clinical workflow, and implementation strategies for proactive esophageal cooling.

Warmer ambient air temperatures reduce nasal turbinate and brain infection, but increase lung inflammation in the K18-hACE2 mouse model of COVID-19

Warmer climatic conditions have been associated with fewer COVID-19 cases. Herein we infected K18-hACE2 mice housed at the standard animal house temperature of ∼22 °C, or at ∼31 °C, which is considered to be thermoneutral for mice. On day 2 post infection, RNA-Seq analyses showed no significant differential gene expression lung in lungs of mice housed at the two temperatures, with almost identical viral loads and type I interferon responses. There was also no significant difference in viral loads in lungs on day 5, but RNA-Seq and histology analyses showed clearly elevated inflammatory signatures and infiltrates. Thermoneutrality thus promoted lung inflammation. On day 2 post infection mice housed at 31 °C showed reduced viral loads in nasal turbinates, consistent with increased mucociliary clearance at the warmer ambient temperature. These mice also had reduced virus levels in the brain, and an ensuing amelioration of weight loss and a delay in mortality. Warmer air temperatures may thus reduce infection of the upper respiratory track and the olfactory epithelium, resulting in reduced brain infection. Potential relevance for anosmia and neurological sequelae in COVID-19 patients is discussed.

Mild Hypothermia via External Cooling Improves Lung Function and Alleviates Pulmonary Inflammatory Response and Damage in Two-Hit Rabbit Model of Acute Lung Injury

OBJECTIVES

Targeted temperature management (TTM) with therapeutic hypothermia (TH) has an organ-protective effect by mainly reducing inflammatory response. Here, our objective was to determine, for the first time, whether mild TH with external cooling, a simple and inexpensive method, could be safe or even beneficial in two-hit rabbit model of acute lung injury/acute respiratory distress syndrome (ALI/ARDS).

METHODS

Twenty-two New Zealand rabbits (6-month-old) were randomly divided into healthy control (HC) with conventional ventilation, but without injury, model group (ALI), and hypothermia group with external cooling (ALI-HT). After induction of ALI/ARDS through mild lung-lavages followed by non-protective ventilation, mild hypothermia was started in ALI-HT group (body temperature of 33-34 °C). All rabbits were conventionally ventilated for an additional 6-h by recording respiratory parameters. Finally, lung histopathology and inflammatory response were evaluated.

RESULTS

Hypothermia was associated with higher oxygen saturation, resulting in partial improvement in the P/F ratio (PaO2/FiO2), oxygenation index, mean airway pressure, and PaCO2, but did not affect lactate levels. The ALI-HT group had lower histopathological injury scores (hyperemia, edema, emphysema, atelectasis, and PMN infiltration). Further, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6 and -8 levels in lung tissue and serum samples markedly reduced due to hypothermia.

CONCLUSION

Mild TH with external cooling reduced lung inflammation and damage, whereas it resulted in partial improvement in gas exchanges. Our findings highlight that body temperature control may be a potentially supportive therapeutic option for regulating cytokine production and respiratory parameters in ALI/ARDS.