A Self-Contained Hypothermic Rewarming System: A Case Study

Hypothermia is a serious medical condition that affects urban and rural populations. An estimated 1,500 patients in the United States die from hypothermia each year.¹

Hypothermia (defined by core temperature below 35°C) occurs when heat loss exceeds heat production.¹ Humans can adapt to heat exposure, but compensatory measures are limited in cold exposures.² Hypothermia is classified into four categories based on core body temperature: mild (35°C-32°C), moderate (32°C-28°C), severe (<28°C), and profound (<24°C)^1,3 with acuity increasing as temperature decreases.

Mild hypothermia results in dehydration due to diuresis caused by a central volume shift.² Moderate hypothermia can precipitate cardiac conduction abnormalities, including bradycardia, atrial fibrillation, premature atrial and ventricular beats, and electrocardiogram changes such as QT prolongation and Osborn waves.² Severe hypothermia leads to bradycardia resulting from decreased function of the sinoatrial node, shifts in oxygen and electrolyte concentrations, and pH changes of the tissues.²  Bradycardia can exacerbate hypotension, which increases the risk of coma, cardiac dysrhythmias, and resultant cardiac arrest.⁴ Cardiac arrest secondary to profound hypothermia can be uniquely challenging as guidelines recommend rewarming to a near-normal core body temperature prior to ceasing resuscitative efforts.

Rewarming techniques include active internal warming measures such as warmed and humidified oxygen therapy via endotracheal tube, thoracic lavage via chest tubes, peritoneal and/or bladder lavage, warmed IV fluids, and external warming measures such as heated blankets or external targeted temperature management devices. Resuscitation of the severely hypothermic patient is often prolonged and inefficient, requiring a significant amount of dedicated personnel with time to achieve desired core temperatures of 33°C-34°C.^5,6 Resuscitations can be quite burdensome on the limited staff in community EDs, and prolonged resuscitation time can lead to poor patient outcomes. This leaves a need for a more efficient rewarming method for these hypothermic cardiac arrest patients in hospitals without extracorporeal membrane oxygenation (ECMO) capability and limited staff.  

The most efficacious and rapid rewarming technique for severe or profound hypothermia is ECMO.⁷ However, ECMO is resource-draining and limited in availability, requiring trained personnel, blood product transfusion, ICU monitoring, and frequent laboratory monitoring.⁸ Due to the limited availability of ECMO-capable centers and challenges associated with transferring a patient in cardiac arrest, ECMO is often not realistic. More commonly utilized methods of resuscitation include modified ACLS protocol with continuous CPR until the patient has been rewarmed to 30°C prior to continuation of ACLS medications and defibrillation.

Studies have shown that using intravascular rewarming catheters could be more effective and less invasive than traditional rewarming measures.^9,10,11 Other studies have shown that rewarming rates are comparable between traditional rewarming measures and endovascular rewarming, with no increased risk of complications in patients with endovascular rewarming.¹² In addition, the use of endovascular rewarming simultaneously provides physicians with the capability to give vasoactive medications and rapidly correct hypovolemia.¹²

While this is a novel technique that requires more investigation into its efficacy, preliminary data suggest these catheters are highly effective in hypothermic rewarming.¹¹ It has been shown that the more hypothermic a patient is, the faster this modality can rewarm them, but as the patient approaches normal body temperature, the warming rate decreases because of peripheral vasoconstriction on heat distribution.¹¹ The use of intravascular rewarming catheters is also less invasive than other measures such as peritoneal lavage, thoracic lavage, and ECMO.^9,10,11 This system also has the potential to alleviate the personnel burden.¹¹

Some concern has been raised about the incidence of thromboembolism when rewarming hypothermic patients with targeted temperature management catheters.^13,14 However, this is a risk of any central venous catheter, and studies have shown that the placement of IVC filters prior to removal of these catheters later in the patient’s care can alleviate this risk.^13,14 Other studies have shown that these endovascular rewarming catheters are very safe and do not significantly increase complication rates in patients at all.¹²

Case Presentation 

Between December 2022 and December 2023, 2 patients presented to affiliated local EDs in hypothermic cardiac arrest, during which intravascular warming devices were utilized in the resuscitation.

Patient A was a 30-year-old male who presented via EMS after being found down. He was initially noted to have a weak pulse and agonal respirations, unresponsive to naloxone, but lost pulse when transferred to the EMS stretcher. Cardiac rhythms en route included initial ventricular fibrillation followed by pulseless electrical activity that persisted until arrival at the emergency department. Upon arrival at the ED, the patient had a core body temperature of 26.5°C by temperature-sensing urinary catheter.

Patient B was a 38-year-old male who presented via EMS after being found down. He was found outside of a gas station and had requested help from an employee shortly before EMS arrival. Upon EMS arrival, the patient was pulseless, apneic, and unresponsive to naloxone. EMS detected ventricular fibrillation, asystole, and then pulseless electrical activity, which persisted until arrival at the emergency department. Upon arrival, his core temperature was 29.1°C by temperature sensing urinary catheter.

Both patients were found down in cold environments with initial resuscitation attempts by EMS, including naloxone and ACLS protocol with CPR, defibrillation, and medications. In both cases, supraglottic airways were placed during transport to the emergency department. Patient A was transported to a single attending coverage community department, while Patient B was transported to a university hospital staffed by double coverage residents and attendings.

Upon arrival, Patient A underwent continuation of CPR and resuscitation. The team replaced the supraglottic airway with an 8.0 endotracheal tube (ETT) and utilized a mechanical chest compression device to provide uninterrupted, effective CPR and to reduce the burden on the limited staff. A temperature-sensing urinary catheter monitored progress while external warming measures, including warm blankets and a forced-air patient warming device, were used. Additionally, warm intravenous fluids were infused. Four 28 French chest tubes were placed in an anterior/posterior configuration bilaterally, with the anterior tubes infused with microwaved bags of warmed saline (in the absence of a fluid warmer) connected via IV tubing and the posterior tubes connected to wall suction, eliminating the need for personnel to manually flush the chest tubes. Despite these measures, the core temperature rose 2.9°C in the first 111 minutes. During the initial rewarming process, the team obtained a ZOLL Quattro Intravascular Temperature Management catheter. They inserted the Quattro into the patient’s right femoral vein with a target temperature of 37°C. The patient achieved a core temperature of 34°C, rising an additional 4.6°C 140 minutes after placement of the rewarming catheter. Despite following ACLS protocol (with medications), the patient remained in asystole after two rounds of ACLS and was pronounced dead.

Upon arrival of Patient B, the team continued CPR and resuscitation, noting rhythm changes, including asystole, ventricular fibrillation with two shocks, and pulseless electrical activity, prior to determining the patient’s core temperature to be 29.1°C. The patient’s supraglottic airway was replaced with a 7.5 ETT, and CPR was continued using a mechanical chest compression device. Warm blankets and a forced-air patient warming device were placed, warm intravenous fluids were transfused, and warm humidified air was provided via ETT. A right femoral arterial line and central venous catheter were placed to aid in management. Four chest tubes were placed with a 28 and 32 French placed in an anterior/posterior configuration bilaterally, with the anterior tubes being infused with warm fluids using a massive transfusion warming device and the posterior tubes connected to low wall suction. In the initial 152 minutes, Patient B’s core temperature rose 0.7°C to 29.8°C. At this time, a ZOLL Quattro Intravascular Temperature Management catheter was procured from a neighboring hospital and used to replace the right femoral central line, with a target temperature of 38°C. In the following 133 minutes, the core temperature rose an additional 2.5°C to a temperature of 32.3°C. The team then initiated ACLS protocol for two rounds, but the patient remained in asystole and was pronounced dead. 

Discussion 

These two cases presented to separate facilities, a single-coverage community hospital and a double-coverage resident and attending academic facility. Neither ED stocked the ZOLL Quattro Intravascular Temperature Management catheter. Both cases had rapid improvement in the rate of rewarming after insertion of the temperature management device. Patient A rose 2.9°C in the first 111 minutes (0.026°C/minute) and an additional 4.6°C in the next 140 minutes (0.033°C/minute) after placement of the rewarming catheter. Patient B's temperature rose 0.7°C in the initial 152 minutes (0.005°C/minute) and an additional 2.5°C in the next 133 minutes after the placement of the catheter (0.019°C/minute).

The use of the targeted temperature management devices reduced the number of hospital personnel required at the bedside throughout the prolonged resuscitations. Also, it is placed like a central line. As such, no additional training is needed for emergency physicians to incorporate this system into their practice. Once the intravascular catheter was placed in patient A, the resuscitation required one nurse for monitoring and documentation purposes and one technician who assisted in warming fluid to be used in the intrathoracic lavage through bilateral chest tubes. The attending continued to see other patients, allowing for improvement in the patient care and overall ED flow.

Once the intravascular catheter was placed in patient B, one nurse continued warm fluids intravascularly via massive transfusion warming device for intrathoracic lavage as needed. The use of the intravascular rewarming device has major implications for personnel, including physicians, nurses, and technicians. The resource-sparing component of these catheters could be particularly advantageous in smaller facilities with limited staff.

The impact of this system on personnel burden alone has the potential to improve patient care significantly. It allows physicians and other staff to care for other patients while simultaneously rewarming the hypothermic patient. This could decrease ED wait times, which in turn could decrease poor outcomes related to delays in care. This system serves as a viable option that should be considered, especially in resource-limited community EDs. It is highly effective in rewarming and is a less invasive technique than many traditional warming measures.

Summary

This two-patient case series on the use of intravascular temperature management devices supports prior research on rewarming critically ill patients with moderate to severe hypothermia to improve their outcomes (REFs). An effective ZOLL or similar catheter could obviate the need for nasogastric and thoracostomy tubes while facilitating more rapid rewarming. Because this system can be used with forced-air patient warming devices, warm fluids, and other external warming measures, it shows considerable promise in maximizing the rewarming potential in moderate to severe hypothermia patients. With more research on its efficacy, this endovascular rewarming system could serve as an equally effective yet less invasive method than ECMO while simultaneously decreasing personnel and resource burden in emergency departments all over the country.

References

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