The introduction of an esophageal heat transfer device into a therapeutic hypothermia protocol: A prospective evaluation

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.

A Systematic Literature Review to Assess Fever Management and the Quality of Targeted Temperature Management in Critically Ill Patients

Targeted temperature management (TTM) has been proposed to reduce mortality and improve neurological outcomes in postcardiac arrest and other critically ill patients. TTM implementation may vary considerably among hospitals, and "high-quality TTM" definitions are inconsistent. This systematic literature review in relevant critical care conditions evaluated the approaches to and definitions of TTM quality with respect to fever prevention and the maintenance of precise temperature control. Current evidence on the quality of fever management associated with TTM in cardiac arrest, traumatic brain injury, stroke, sepsis, and critical care more generally was examined. Searches were conducted in Embase and PubMed (2016 to 2021) following PRISMA guidelines. In total, 37 studies were identified and included, with 35 focusing on postarrest care. Frequently-reported TTM quality outcomes included the number of patients with rebound hyperthermia, deviation from target temperature, post-TTM body temperatures, and number of patients achieving target temperature. Surface and intravascular cooling were used in 13 studies, while one study used surface and extracorporeal cooling and one study used surface cooling and antipyretics. Surface and intravascular methods had comparable rates of achieving target temperature and maintaining temperature. A single study showed that patients with surface cooling had a lower incidence of rebound hyperthermia. This systematic literature review largely identified cardiac arrest literature demonstrating fever prevention with multiple TTM approaches. There was substantial heterogeneity in the definitions and delivery of quality TTM. Further research is required to define quality TTM across multiple elements, including achieving target temperature, maintaining target temperature, and preventing rebound hyperthermia.

Perioperative targeted temperature management of severely burned patients by means of an oesophageal temperature probe

BACKGROUND

Hypothermia in severely burned patients is associated with a significant increase in morbidity and mortality. The use of an oesophageal heat exchanger tube (EHT) can improve perioperative body temperatures in severely burned patients. The aim of this study was to investigate the intraoperative warming effect of oesophageal heat transfer in severe burn patients.

METHODS

Single-centre retrospective study performed at the Burns Centre of the University Hospital Zurich. Between January 2020 and May 2021 perioperative temperature management with EHT was explored in burned patients with a total body surface area (TBSA) larger than 30%. Data from patients, who received perioperative temperature management by EHT, were compared to data from the same patients during interventions performed under standard temperature management matching for length and type of intervention.

RESULTS

A total of 30 interventions (15 with and 15 without EHT) in 10 patients were analysed. Patient were 38 [26-48] years of age, presented with severe burns covering a median of 50 [42-64] % TBSA and were characterized by an ABSI of 10 [8-12] points. When receiving EHT management patients experienced warming at 0.07 °C per minute (4.2 °C/h) compared to a temperature loss of - 0.03 °C per minute (1.8 °C/h) when only receiving standard temperature management (p < 0.0001). No adverse or serious adverse events were reported.

CONCLUSION

The use of an oesophageal heat transfer device was effective and safe in providing perioperative warming to severely burned patients when compared to a standard temperature management protocol. By employing an EHT as primary temperature management device perioperative hypothermia in severely burned patients can possibly be averted, potentially leading to reduced hypothermia-associated complications.

Computational modeling of targeted temperature management in post-cardiac arrest patients

Our core body temperature is held around [Formula: see text]C by an effective internal thermoregulatory system. However, various clinical scenarios have a more favorable outcome under external temperature regulation. Therapeutic hypothermia, for example, was found beneficial for the outcome of resuscitated cardiac arrest patients due to its protection against cerebral ischemia. Nonetheless, practice shows that outcomes of targeted temperature management vary considerably in dependence on individual tissue damage levels and differences in therapeutic strategies and protocols. Here, we address these differences in detail by means of computational modeling. We develop a multi-segment and multi-node thermoregulatory model that takes into account details related to specific post-cardiac arrest-related conditions, such as thermal imbalances due to sedation and anesthesia, increased metabolic rates induced by inflammatory processes, and various external cooling techniques. In our simulations, we track the evolution of the body temperature in patients subjected to post-resuscitation care, with particular emphasis on temperature regulation via an esophageal heat transfer device, on the examination of the alternative gastric cooling with ice slurry, and on how anesthesia and the level of inflammatory response influence thermal behavior. Our research provides a better understanding of the heat transfer processes and therapies used in post-cardiac arrest patients.

Esophageal Cooling for Hypoxic Ischemic Encephalopathy: A Feasibility Study

Targeted temperature management (TTM) is a recognized treatment to decrease mortality and improve neurological function in hypoxic ischemic encephalopathy. An esophageal cooling device (ECD) has been studied in animal models, but human data are limited. An ECD appears to offer similar benefits to intravascular cooling catheters, with potentially less risk to the patient. We studied whether the ECD could act as a substitute for intravascular cooling catheters in delivering adequate TTM after cardiac arrest. Nine patients admitted to the intensive care unit after cardiac arrest who required TTM were enrolled prospectively. The primary outcome measures were timeliness of insertion, ease of insertion, user Likert ratings, time to achieve a target temperature of 36°C, and time during which target temperature was maintained within 1°C of the 36°C goal for 24 hours by using an ECD. Time to reach target temperature was 0 to 540 minutes (mean: 113.33 minutes, median: 0 minute, standard deviation [SD]: 179.22). Maintenance of a target temperature of 36°C over 24 hours had a range of 58.33% to 100% (mean: 91.67%, median: 95.83%, SD: 13.34). Ease of insertion related to Likert ratings with a range of 1-9 (mean: 5.38, median: 5.5, SD: 3.43) and a simplicity of ECD uses a range of 4-10 (mean: 7.63, median: 8.0, SD: 1.65). Overall, there was preference for the ECD over intravascular cooling methods (mean: 6.71, mean: 6, SD: 3.01) and external cooling methods (mean: 8.0, median: 9.0, SD: 2.33). For patients requiring TTM, use of an ECD adequately allowed for TTM goals to be achieved and maintained. Overall, user evaluation was positive.

Core warming of coronavirus disease 2019 (COVID-19) patients undergoing mechanical ventilation-A protocol for a randomized controlled pilot study

BACKGROUND

Coronavirus disease 2019 (COVID-19), caused by the virus SARS-CoV-2, is spreading rapidly across the globe, with little proven effective therapy. Fever is seen in most cases of COVID-19, at least at the initial stages of illness. Although fever is typically treated (with antipyretics or directly with ice or other mechanical means), increasing data suggest that fever is a protective adaptive response that facilitates recovery from infectious illness.

OBJECTIVE

To describe a randomized controlled pilot study of core warming patients with COVID-19 undergoing mechanical ventilation.

METHODS

This prospective single-site randomized controlled pilot study will enroll 20 patients undergoing mechanical ventilation for respiratory failure due to COVID-19. Patients will be randomized 1:1 to standard-of-care or to receive core warming via an esophageal heat exchanger commonly utilized in critical care and surgical patients. The primary outcome is patient viral load measured by lower respiratory tract sample. Secondary outcomes include severity of acute respiratory distress syndrome (as measured by PaO2/FiO2 ratio) 24, 48, and 72 hours after initiation of treatment, hospital and intensive care unit length of stay, duration of mechanical ventilation, and 30-day mortality.

RESULTS

Resulting data will provide effect size estimates to guide a definitive multi-center randomized clinical trial. ClinicalTrials.gov registration number: NCT04426344.

CONCLUSIONS

With growing data to support clinical benefits of elevated temperature in infectious illness, this study will provide data to guide further understanding of the role of active temperature management in COVID-19 treatment and provide effect size estimates to power larger studies.

Using Esophageal Temperature Management to Treat Severe Heat Stroke: A Case Report

BACKGROUND: Exertional heat stroke (EHS) is defined by a core body temperature that exceeds 40°C with associated central nervous system dysfunction, skeletal muscle injury, and multiple organ damage. The most important initial focus of treatment involves reduction of patient temperature. First approaches to achieve temperature reduction often include ice packs, water blankets, and cold intravenous fluid administration. When these measures fail, more advanced temperature management methods may be deployed but often require surgical expertise. Esophageal temperature management (ETM) has recently emerged as a new temperature management modality in which an esophageal heat transfer device replaces the standard orogastric tube routinely placed after endotracheal intubation and adds a temperature modulation capability. The objective of this case study is to report the first known use of ETM driven by bedside nursing staff in the treatment of EHS. METHOD: An ETM device was placed after endotracheal intubation in a 28-year-old man experiencing EHS over a 5-day course of treatment. RESULTS: Because the ETM device was left in place, when the patient experienced episodes of increasing temperature as high as 39.1°C, which required active cooling, nursing staff were able to immediately adjust the external heat exchange unit settings to achieve aggressive cooling at bedside. CONCLUSION: This nurse-driven technology offers a new means to rapidly deploy cooling to critically ill patients without needing to implement advanced surgical approaches or obstruct access to the patient, freeing the provider to continue optimal care in high-morbidity conditions.

Modeling esophageal protection from radiofrequency ablation via a cooling device: an analysis of the effects of ablation power and heart wall dimensions

BACKGROUND

Esophageal thermal injury can occur after radiofrequency (RF) ablation in the left atrium to treat atrial fibrillation. Existing methods to prevent esophageal injury have various limitations in deployment and uncertainty in efficacy. A new esophageal heat transfer device currently available for whole-body cooling or warming may offer an additional option to prevent esophageal injury. We sought to develop a mathematical model of this process to guide further studies and clinical investigations and compare results to real-world clinical data.

RESULTS

The model predicts that the esophageal cooling device, even with body-temperature water flow (37 °C) provides a reduction in esophageal thermal injury compared to the case of the non-protected esophagus, with a non-linear direct relationship between lesion depth and the cooling water temperature. Ablation power and cooling water temperature have a significant influence on the peak temperature and the esophageal lesion depth, but even at high RF power up to 50 W, over durations up to 20 s, the cooling device can reduce thermal impact on the esophagus. The model concurs with recent clinical data showing an 83% reduction in transmural thermal injury when using typical operating parameters.

CONCLUSIONS

An esophageal cooling device appears effective for esophageal protection during atrial fibrillation, with model output supporting clinical data. Analysis of the impact of ablation power and heart wall dimensions suggests that cooling water temperature can be adjusted for specific ablation parameters to assure the desired myocardial tissue ablation while keeping the esophagus protected.

The Use of Core Warming as a Treatment for Coronavirus Disease 2019 (COVID-19): an Initial Mathematical Model

Background: Increasing data suggest that elevated body temperature may be helpful in resolving a variety of diseases, including sepsis, acute respiratory distress syndrome (ARDS), and viral illnesses. SARS-CoV-2, which causes coronavirus disease 2019 (COVID-19), may be more temperature sensitive than other coronaviruses, particularly with respect to the binding affinity of its viral entry via the ACE2 receptor. A mechanical provision of elevated temperature focused in a body region of high viral activity in patients undergoing mechanical ventilation may offer a therapeutic option that avoids arrhythmias seen with some pharmaceutical treatments. We investigated the potential to actively provide core warming to the lungs of patients with a commercially available heat transfer device via mathematical modeling, and examine the influence of blood perfusion on temperature using this approach. Methods: Using the software Comsol Multiphysics, we modeled and simulated heat transfer in the body from an intraesophageal warming device, taking into account the airflow from patient ventilation. The simulation was focused on heat transfer and warming of the lungs and performed on a simplified geometry of an adult human body and airway from the pharynx to the lungs. Results: The simulations were run over a range of values for blood perfusion rate, which was a parameter expected to have high influence in overall heat transfer, since the heat capacity and density remain almost constant. The simulation results show a temperature distribution which agrees with the expected clinical experience, with the skin surface at a lower temperature than the rest of the body due to convective cooling in a typical hospital environment. The highest temperature in this case is the device warming water temperature, and that heat diffuses by conduction to the nearby tissues, including the air flowing in the airways. At the range of blood perfusion investigated, maximum lung temperature ranged from 37.6°C to 38.6°C. Conclusions: The provision of core warming via commercially available technology currently utilized in the intensive care unit, emergency department, and operating room can increase regional temperature of lung tissue and airway passages. This warming may offer an innovative approach to treating infectious diseases from viral illnesses such as COVID-19, while avoiding the arrhythmogenic complications of currently used pharmaceutical treatments.

Effects of High-Flow Transesophageal Dry Air on Core Temperature: A Novel Method of Therapeutic Hypothermia

Therapeutic hypothermia (TH) is one of the few proven neuroprotective modalities in clinical practice. However, current methods to achieve TH are suboptimal. We investigated a novel esophageal device that utilizes high-flow transesophageal dry air to achieve TH via evaporating cooling. Seven Yorkshire pigs (n = 7) underwent hypothermia therapy using a novel esophageal device that compartmentalizes a segment of esophagus through which high-flow dry air freely circulates in and out of the esophagus. Efficacy (primary objective) and safety (secondary objective) were evaluated in all animals. Safety assessment was divided into two sequential phases: (1) acute safety assessment (n = 5; terminal studies) to evaluate adverse events occurring during therapy, and (2) chronic safety assessment (n = 2; survival studies) to evaluate adverse events associated with therapy within 1 week of follow-up. After 1 hour of esophageal cooling (mean airflow rate = 64.2 ± 3.5 L/min), a significant reduction in rectal temperature was observed (37.3 ± 0.2°C → 36.3 ± 0.4°C, p = 0.002). The mean rectal temperature reduction was 1 ± 0.4°C. In none of the seven animals was oral or pharyngeal mucosa injury identified at postprocedural visual examination. In the two animals that survived, no reduction of food ingestion, signs of swallowing dysfunction or discomfort, or evidence of gastrointestinal bleeding was observed during the 1-week follow-up period. Open-chest visual inspection in those two animals did not show damage to the esophageal mucosa or surrounding structures. A novel esophageal device, utilizing high-flow transesophageal dry air, was able to efficiently induce hypothermia despite external heating. Therapy was well-tolerated, and no acute or chronic complications were found.

Intravascular Cooling Device Versus Esophageal Heat Exchanger for Mild Therapeutic Hypothermia in an Experimental Setting

BACKGROUND

Targeted temperature management is a standard therapy for unconscious survivors of cardiac arrest. To date, multiple cooling methods are available including invasive intravascular cooling devices (IVDs), which are widely used in the clinical setting. Recently, esophageal heat exchangers (EHEs) have been developed providing cooling via the esophagus that is located close to the aorta and inferior vena cava. The objective was to compare mean cooling rates, as well as differences, to target temperature during maintenance and the rewarming period of IVD and EHE.

METHODS

The study was conducted in 16 female domestic pigs. After randomization to either IVD or EHE (n = 8/group), core body temperature was reduced to 33°C. After 24 hours of maintenance (33°C), animals were rewarmed using a target rate of 0.25°C/h for 10 hours. All cooling phases were steered by a closed-loop feedback system between the internal jugular vein and the chiller. After euthanasia, laryngeal and esophageal tissue was harvested for histopathological examination.

RESULTS

Mean cooling rates (4.0°C/h ± 0.4°C/h for IVD and 2.4°C/h ± 0.3°C/h for EHE; P < .0008) and time to target temperature (85.1 ± 9.2 minutes for IVD and 142.0 ± 21.2 minutes for EHE; P = .0008) were different. Mean difference to target temperature during maintenance (0.07°C ± 0.05°C for IVD and 0.08°C ± 0.10°C for EHE; P = .496) and mean rewarming rates (0.2°C/h ± 0.1°C/h for IVD and 0.3°C/h ± 0.2°C/h for EHE; P = .226) were similar. Relevant laryngeal or esophageal tissue damage could not be detected. There were no significant differences in undesired side effects (eg, bradycardia or tachycardia, hypokalemia or hyperkalemia, hypoglycemia or hyperglycemia, hypotension, overcooling, or shivering).

CONCLUSIONS

After insertion, target temperatures could be reached faster by IVD compared to EHE. Cooling performance of IVD and EHE did not significantly differ in maintaining target temperature during a targeted temperature management process and in active rewarming protocols according to intensive care unit guidelines in this experimental setting.

Faster Hypothermia Induced by Esophageal Cooling Improves Early Markers of Cardiac and Neurological Injury After Cardiac Arrest in Swine

Background

After cardiopulmonary resuscitation, the protective effects of therapeutic hypothermia induced by conventional cooling are limited. Recently, esophageal cooling (EC) has been shown to be an effective, easily performed approach to induce therapeutic hypothermia. In this study we investigated the efficacy of EC and its effects on early markers of postresuscitation cardiac and neurological injury in a porcine model of cardiac arrest.

Methods and Results

Thirty‐two male domestic swine were randomized into 4 groups: sham control, normothermia, surface cooling, and EC. Sham animals underwent the surgical preparation only. Ventricular fibrillation was induced and untreated for 8 minutes while defibrillation was attempted after 5 minutes of cardiopulmonary resuscitation. At 5 minutes after resuscitation, therapeutic hypothermia was induced by either EC or surface cooling to reach a target temperature of 33°C until 24 hours postresuscitation, followed by a rewarming rate of 1°C/h for 5 hours. The temperature was normally maintained in the control and normothermia groups. After resuscitation, a significantly faster decrease in blood temperature was observed in the EC group than in the surface cooling group (2.8±0.7°C/h versus 1.5±0.4°C/h; P<0.05). During the maintenance and rewarming phases the temperature was maintained at an even level between the 2 groups. Postresuscitation cardiac and neurological damage was significantly improved in the 2 hypothermic groups compared with the normothermia group; however, the protective effects were significantly greater in the EC group.

Conclusions

In a porcine model of cardiac arrest, faster hypothermia successfully induced by EC was significantly better than conventional cooling in improving early markers of postresuscitation cardiac and neurological injury.

Retrospective Analysis of Esophageal Heat Transfer for Active Temperature Management in Post-cardiac Arrest, Refractory Fever, and Burn Patients

Core temperature management is an important aspect of critical care; preventing unintentional hypothermia, reducing fever, and inducing therapeutic hypothermia when appropriate are each tied to positive health outcomes. The purpose of this study is to evaluate the performance of a new temperature management device that uses the esophageal environment to conduct heat transfer. De-identified patient data were aggregated from three clinical sites where an esophageal heat transfer device (EHTD) was used to provide temperature management. The device was evaluated against temperature management guidelines and best practice recommendations, including performance during induction, maintenance, and cessation of therapy. Across all active cooling protocols, the average time-to-target was 2.37 h and the average maintenance phase was 22.4 h. Patients spent 94.9% of the maintenance phase within ±1.0°C and 67.2% within ±0.5°C (574 and 407 measurements, respectively, out of 605 total). For warming protocols, all of the patient temperature readings remained above 36°C throughout the surgical procedure (average 4.66 h). The esophageal heat transfer device met performance expectations across a range of temperature management applications in intensive care and burn units. Patients met and maintained temperature goals without any reported adverse events.

Esophageal Heat Exchanger Versus Water-Circulating Cooling Blanket for Targeted Temperature Management

To date, the optimal cooling device for targeted temperature management (TTM) remains unclear. Water-circulating cooling blankets are broadly available and quickly applied but reveal inaccuracy during maintenance and rewarming period. Recently, esophageal heat exchangers (EHEs) have been shown to be easily inserted, revealed effective cooling rates (0.26-1.12°C/h), acceptable deviations from target core temperature (<0.5°C), and rewarming rates between 0.2 and 0.4°C/h. The aim of this study was to compare cooling rates, accuracy during maintenance, and rewarming period as well as side effects of EHEs with water-circulating cooling blankets in a porcine TTM model. Mean core temperature of domestic pigs (n = 16) weighing 83.2 ± 3.6 kg was decreased to a target core temperature of 33°C by either using EHEs or water-circulating cooling blankets. After 8 hours of maintenance, rewarming was started at a goal rate of 0.25°C/h. Mean cooling rates were 1.3 ± 0.1°C/h (EHE) and 3.2 ± 0.5°C/h (blanket, p < 0.0002). Mean difference to target core temperature during maintenance ranged between ±1°C. Mean rewarming rates were 0.21 ± 0.01°C/h (EHE) and 0.22 ± 0.02°C/h (blanket, n.s.). There were no differences with regard to side effects such as brady- or tachycardia, hypo- or hyperkalemia, hypo- or hyperglycemia, hypotension, shivering, or esophageal tissue damage. Target temperature can be achieved faster by water-circulating cooling blankets. EHEs and water-circulating cooling blankets were demonstrated to be reliable and safe cooling devices in a prolonged porcine TTM model with more variability in EHE group.

Protecting the esophagus from thermal injury during radiofrequency ablation with an esophageal cooling device

PURPOSE

We sought to quantify the capabilities of a commercially available cooling device to protect the esophagus from RF injury in an animal model and develop a mathematical model to describe the system and provide a framework from which to advance this technology.

METHODS

A series of ablations (10 W, duration 30-45 seconds) were performed directly on exposed swine esophagus. Control ablations were performed with static 37°C water, and treatment ablations were performed with water (range 5°C-37°C) circulating within the device. Mucosal lesions were evaluated visually and with target tissue histology. A mathematical model was then developed and compared against the experimental data.

RESULTS

All 23 ablations (100%) performed under control conditions produced visible external esophageal lesions; 12 of these (52%) were transmural. Under treatment conditions, only 5 of 23 ablations (22%) produced visible external lesions; none (0%) were transmural. Transmurality of lesions decreased as circulating water temperature decreased, with absolute reduction ranging from 5.1% with the use of 37°C water (p=0.7) to 44.5% with the use of 5°C water (p<0.001). Comparison to the mathematical model showed an R^2 of 0.75, representing good agreement.

CONCLUSION

Under worst-case conditions, with RF energy applied directly to the adventitial side of the esophagus, internal esophageal cooling with an esophageal cooling device provides significant protective effect from thermal injury. A mathematical model of the process provides a means to further investigate this approach to preventing esophageal injury during RF ablation and can serve to guide ongoing clinical investigations currently in progress.

Esophageal Temperature Management in Patients Suffering from Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death in the United States, and represents 2.5 million Emergency Department attendances, admissions into hospital, and deaths. A range of temperature modulating devices have been used to proactively cool TBI patients; however, there are currently no uniform targeted temperature management (TTM) guidelines in this patient population. Esophageal temperature management (ETM) is a relatively new TTM modality and the purpose of this study is to determine whether ETM is effective in controlling core temperature in TBI cases. This prospective interventional trial was a single-site study that enrolled 12 patients who received a TTM protocol using ETM. Eleven out of 12 patients reached target temperature during the first 10 hours of treatment. A total of 480 temperature measurements were recorded; 85% of the total measurements were within ±1°C of target temperature (408 measurements) and 75% were within ±0.5°C of target temperature (360 measurements). The average time to target was 5.83 ± 5.01 hours (range 1–20), with an average cooling rate of 0.58°C/h (range 0.15–1.5°C/h). This prospective interventional trial supports that ETM is a feasible TTM modality for severe TBI cases. The esophageal heat transfer device used in this study demonstrated comparable or superior performance to other commercially available TTM modalities, and the low adverse event rate may offer advantages over more invasive methods with reported higher complication rates.

Targeted Temperature Management in Brain Injured Patients

Evidence from animal models indicates that lowering temperature by a few degrees can produce substantial neuroprotection. In humans, hypothermia has been found to be neuroprotective with a significant impact on mortality and long-term functional outcome only in cardiac arrest and neonatal hypoxic-ischemic encephalopathy. Clinical trials have explored the potential role of maintaining normothermia and treating fever in critically ill brain injured patients. This review concentrates on basic concepts to understand the physiologic interactions of thermoregulation, effects of thermal modulation in critically ill patients, proposed mechanisms of action of temperature modulation, and practical aspects of targeted temperature management.

Targeted Temperature Management in Brain Injured Patients

Evidence from animal models indicates that lowering temperature by a few degrees can produce substantial neuroprotection. In humans, hypothermia has been found to be neuroprotective with a significant impact on mortality and long-term functional outcome only in cardiac arrest and neonatal hypoxic-ischemic encephalopathy. Clinical trials have explored the potential role of maintaining normothermia and treating fever in critically ill brain injured patients. This review concentrates on basic concepts to understand the physiologic interactions of thermoregulation, effects of thermal modulation in critically ill patients, proposed mechanisms of action of temperature modulation, and practical aspects of targeted temperature management.

Esophageal Cooling Device Versus Other Temperature Modulation Devices for Therapeutic Normothermia in Subarachnoid and Intracranial Hemorrhage

Achieving and maintaining normothermia (NT) after subarachnoid hemorrhage (SAH) or intracerebral hemorrhage (ICH) often require temperature modulating devices (TMD). Shivering is a common adverse effect of TMDs that can lead to further costs and complications. We evaluated an esophageal TMD, the EnsoETM (Attune Medical, Chicago, IL), to compare NT performance, shiver burden, and cost of shivering interventions with existing TMDs. Patients with SAH or ICH and refractory fever were treated with the EnsoETM. Patient demographics, temperature data, shiver severity, and amounts and costs of medications used for shiver management were prospectively collected. Controls who received other TMDs were matched for age, gender, and body surface area to EnsoETM recipients, and similar retrospective data were collected. All patients were mechanically ventilated. Fever burden was calculated as areas of curves of time spent above 37.5°C or 38°C. Demographics, temperature data, and costs of EnsoETM recipients were compared with recipients of other TMDs. Eight EnsoETM recipients and 24 controls between October 2015 and November 2016 were analyzed. There were no differences between the two groups in demographics or patient characteristics. No difference was found in temperature at initiation (38.7°C vs. 38.5°C, p = 0.4) and fever burden above 38°C (-0.44°C × hours vs. -0.53°C × hours, p = 0.47). EnsoETM recipients showed a nonsignificant trend in taking longer to achieve NT than other TMDs (5.4 hours vs. 2.9 hours, p = 0.07). EnsoETM recipients required fewer shiver interventions than controls (14 vs. 30, p = 0.02). EnsoETM recipients incurred fewer daily costs than controls ($124.27 vs. $232.76, p = 0.001). The EnsoETM achieved and maintained NT in SAH and ICH patients and was associated with less shivering and lower pharmaceutical costs than other TMDs. Further studies in larger populations are needed to determine the EnsoETM's efficacy in comparison to other TMDs.

Esophageal Heat Transfer for Patient Temperature Control and Targeted Temperature Management

Controlling patient temperature is important for a wide variety of clinical conditions. Cooling to normal or below normal body temperature is often performed for neuroprotection after ischemic insult (e.g. hemorrhagic stroke, subarachnoid hemorrhage, cardiac arrest, or other hypoxic injury). Cooling from febrile states treats fever and reduces the negative effects of hyperthermia on injured neurons. Patients are warmed in the operating room to prevent inadvertent perioperative hypothermia, which is known to cause increased blood loss, wound infections, and myocardial injury, while also prolonging recovery time. There are many reported approaches for temperature management, including improvised methods that repurpose standard supplies (e.g., ice, chilled saline, fans, blankets) but more sophisticated technologies designed for temperature management are typically more successful in delivering an optimized protocol. Over the last decade, advanced technologies have developed around two heat transfer methods: surface devices (water blankets, forced-air warmers) or intravascular devices (sterile catheters requiring vascular placement). Recently, a novel device became available that is placed in the esophagus, analogous to a standard orogastric tube, that provides efficient heat transfer through the patient's core. The device connects to existing heat exchange units to allow automatic patient temperature management via a servo mechanism, using patient temperature from standard temperature sensors (rectal, Foley, or other core temperature sensors) as the input variable. This approach eliminates vascular placement complications (deep venous thrombosis, central line associated bloodstream infection), reduces obstruction to patient access, and causes less shivering when compared to surface approaches. Published data have also shown a high degree of accuracy and maintenance of target temperature using the esophageal approach to temperature management. Therefore, the purpose of this method is to provide a low-risk alternative method for controlling patient temperature in critical care settings.

Feasibility of a Miniature Esophageal Heat Exchange Device for Rapid Therapeutic Cooling in Newborns: Preliminary Investigations in a Piglet Model

Therapeutic hypothermia (TH) after neonatal encephalopathy, commonly provided by 72 hours of whole-body cooling using a wrap, limits parents' physical contact with their infants affecting bonding and may not be suitable for encephalopathic preterm infants with fragile skin. Alternative cooling methods are unavailable for this population. We investigated in a neonatal pig model the feasibility of achieving a 3.5°C reduction in rectal temperature (T_rectal) similar to clinical TH protocols from 38.5°C (normothermia for pigs) to a target of 35°C ± 0.2°C, using a novel neonatal esophageal heat exchanger (NEHE), compared its efficacy to passive cooling, and investigated its ability to maintain target T_rectal. Ventilated and anesthetized Landrace/Large white newborn pigs had the NEHE inserted. Water at adjustable temperatures and rates flowed down a central tube, returning up a surrounding distensible blind ending latex tube in a continuous loop. An initial experiment guided four subsequent cycles of passive cooling (30 minutes), rewarming to 38.5°C, active esophageal cooling to 35°C ± 0.2°C, active maintenance of target T_rectal (30 minutes), and rewarming. We compared surface, rectal temperature, and hemodynamic changes among passive, active, and maintenance phases, and esophageal histopathology against control. Compared with passive cooling, esophageal cooling achieved target T_rectal significantly earlier (71.3 minutes vs. 17.25 minutes, p = 0.003) with significantly greater rates of reduction in rectal (p = 0.0002) and surface (p = 0.005) temperatures and heart rate (p = 0.04). A water temperature of 39.1°C-40.2°C at a flow of 108-120 mL/min maintained T_rectal around 35°C ± 0.2°C. The higher peak heart rate and blood pressure within 8 minutes of the maintenance phase (p = 0.04) subsequently stabilized. Histopathology showed congestion, edema, and neutrophil infiltration with increasing cycles. Esophageal cooling is feasible and effective in achieving rapid cooling in newborns. Subsequent maintenance at this temperature required continued circulation of warm water. Esophageal histopathology needs further evaluation after 72 hours servo-control cooling with a narrower range of water temperatures in a larger group of animals.

Targeted temperature management using the "Esophageal Cooling Device" after cardiac arrest (the COOL study): A feasibility and safety study

BACKGROUND

Targeted temperature management (TTM) between 32 and 36°C is recommended after out-of-hospital cardiac arrest (OHCA). We aimed to assess the feasibility and safety of the "Esophageal Cooling Device" (ECD) in performing TTM.

PATIENTS AND METHODS

This single-centre, prospective, interventional study included 17 comatose OHCA patients. Main exclusion criteria were: delay between OHCA and return of spontaneous circulation (ROSC)>60min, delay between sustained ROSC and inclusion >360min, known oesophageal disease. A TTM between 32 and 34°C was performed using the ECD (Advanced Cooling Therapy, USA) connected to a heat exchanger console (Meditherm III^®, Gaymar, France), without cold fluids' use. Primary endpoint was feasibility of inducing, maintaining TTM, and rewarming using the ECD alone. Secondary endpoints were adverse events, focusing on potential digestive damages. Results were expressed as median (interquartiles 25-75).

RESULTS

Cooling rate to reach the Target Temperature (33°C-TT) was 0.26°C/h [0.19-0.36]. All patients reached the 32-34°C range with a time spent within the range of 26h [21-28] (3 patients did not reach 33°C). Temperature deviation outside the TT during TTM-maintenance was 0.10°C [0.03-0.20]. Time with deviation >1°C was 0h. Rewarming rate was 0.20°C/h [0.18-0.22]. Among the 16 gastrointestinal endoscopy procedures performed, 10 (62.5%) were normal. Minor oeso-gastric injuries (37.5% and 19%, respectively) were similar to usual orogastric tube injuries. One patient experienced severe oesophagitis mimicking peptic lesions, not cooling-related. No patient among the 9 alive at 3-month follow-up had gastrointestinal complains.

CONCLUSION

ECD seems an interesting, safe, accurate, semi-invasive cooling method in OHCA patients treated with 33°C-TTM, particularly during the maintenance phase.

Rewarming After Severe Accidental Hypothermia Using the Esophageal Heat Transfer Device: A Case Report

Patients with severe accidental hypothermia require active rewarming. External rewarming may not be successful in severe hypothermia, and use of invasive techniques is limited to regional centers and is associated with vascular access site and other complications. We present a patient with severe accidental hypothermia who was successfuly rewarmed using a novel esophageal heat transfer device. A 55-year-old male (175 cm, 71 kg) was admitted with the first recorded temperature 23.3°C. Rewarming using renal replacement therapy circuit was unsuccessful because of severe hypotension. We inserted the esophageal heat transfer device and rewarmed him successfully to target temperature 35-36°C. After rewarming, we maintained his body temperature in the range 35-36°C until accidental removal of the device. We observed no major adverse effects. To conclude, rewarming from severe accidental hypothermia was possible using the esophageal heat transfer device.

The esophageal cooling device: A new temperature control tool in the intensivist's arsenal

BACKGROUND

Therapeutic hypothermia has been demonstrated to improve neurological outcome in comatose survivors of cardiac arrest. Current temperature control modalities however, have several limitations. Exploring innovative methods of temperature management has become a necessity.

METHODS

We describe the first use of a novel esophageal cooling device as a sole modality for hypothermia induction, maintenance and rewarming in a series of four postcardiac arrest patients. The device was inserted in a manner similar to standard orogastric tubes and connected to an external heat exchange unit.

RESULTS

A mean cooling rate of 0.42 °C/hr (SD ± 0.26) was observed. An average of 4 hr 24 min (SD ± 2 hr 6 min) was required to reach target temperature, and this was maintained 90.25% (SD ± 16.20%) of the hypothermia protocol duration. No adverse events related to device use were encountered. Questionnaires administered to ICU nursing staff regarding ease-of-use of the device and its performance were rated as favorable.

CONCLUSIONS

When used as a sole modality, objective performance parameters of the esophageal-cooling device were found to be comparable to standard temperature control methods. More research is required to further quantify efficacy, safety, assess utility in other patient populations, and examine patient outcomes with device use in comparison to standard temperature control modalities.

Oesophageal heat exchangers with a diameter of 11mm or 14.7mm are equally effective and safe for targeted temperature management

BACKGROUND

Targeted temperature management (TTM) is widely used in critical care settings for conditions including hepatic encephalopathy, hypoxic ischemic encephalopathy, meningitis, myocardial infarction, paediatric cardiac arrest, spinal cord injury, traumatic brain injury, ischemic stroke and sepsis. Furthermore, TTM is a key treatment for patients after out-of-hospital cardiac-arrest (OHCA). However, the optimal cooling method, which is quick, safe and cost-effective still remains controversial. Since the oesophagus is adjacent to heart and aorta, fast heat-convection to the central blood-stream could be achieved with a minimally invasive oesophageal heat exchanger (OHE). To date, the optimal diameter of an OHE is still unknown. While larger diameters may cause thermal- or pressure-related tissue damage after long-term exposure to the oesophageal wall, smaller diameter (e.g., gastric tubes, up to 11mm) may not provide effective cooling rates. Thus, the objective of the study was to compare OHE-diameters of 11mm (OHE11) and 14.7mm (OHE14.7) and their effects on tissue and cooling capability.

METHODS

Pigs were randomized to OHE11 (N = 8) or OHE14.7 (N = 8). After cooling, pigs were maintained at 33°C for 1 hour. After 10h rewarming, oesophagi were analyzed by means of histopathology. The oesophagus of four animals from a separate study that underwent exactly the identical preparation and cooling protocol described above but received a maintenance period of 24h were used as histopathological controls.

RESULTS

Mean cooling rates were 2.8±0.4°C°C/h (OHE11) and 3.0±0.3°C °C/h (OHE14.7; p = 0.20). Occasional mild acute inflammatory transepithelial infiltrates were found in the cranial segment of the oesophagus in all groups including controls. Deviations from target temperature were 0.1±0.4°C (OHE11) and 0±0.1°C (OHE14.7; p = 0.91). Rewarming rates were 0.19±0.07°C °C/h (OHE11) and 0.20±0.05°C °C/h (OHE14.7; p = 0.75).

CONCLUSIONS

OHE with diameters of 11 mm and 14.7 mm achieve effective cooling rates for TTM and did not cause any relevant oesophageal tissue damage. Both OHE demonstrated acceptable deviations from target temperature and allowed for an intended rewarming rate (0.25°C/h).