This clinical review feature article is presented in conjunction with the Department of Emergency Medicine Education at the University of Texas Southwestern Medical Center, Dallas.
>> Identify the benefits of therapeutic hypothermia to cardiac arrest victims.
>> Identify the body's physiological response to hypoxemia during cardiac arrest.
>> Identify practical ways to induce hypothermia in the prehospital setting.
>> Discuss the costs and equipment needed for implementing a hypothermia program.
>> Describe the benefits to an EMS system that implements a therapeutic hypothermia program.
Asystole: Absence of ventricular contraction (heart beat) demonstrated as a flat line on an ECG monitor.
BiPAP:Method of delivering air at two different pressures during the respiratory cycle.
CPAP: Continuous positive airway pressure; flow of air delivered at a constant pressure during the respiratory cycle.
Encephalopathy:Literally meaning "disease of the brain"; generally means damage or impairment in brain function.
Hypothermia: Subnormal body temperature, commonly defined as below 35° C (95° F).
Hypoxemia: Condition resulting from inadequate oxygenation in arterial blood, which can lead to hypoxia or inadequate oxygen supply reaching tissues.
Normal sinus rhythm: Pattern of a normal, beating heart demonstrated by a characteristic waveform on an ECG.
Ventricular fibrillation: Fibrillation or ineffective, uncoordinated twitching of the ventricular heart muscles demonstrated as a wavy (regularly irregular) line on an ECG monitor.
In 1894, when Thoreau wrote, "To affect the quality of the day, that is the highest of arts," he certainly wasn't describing EMS, then or now.(1) But if Thoreau were around today and unexpectedly went into cardiopulmonary arrest, was resuscitated by EMS, experienced post-resuscitation therapeutic hypothermia (TH) started in the field, and subsequently awoke neurologically intact, we think he would be more than happy to let EMS borrow his line.
TH started by EMS is more than just "putting the bill chill on the recently clinically dead patient in the field; it's the latest example of sophisticated EMS systems broadly impacting the quality of emergency care far beyond our sandbox of medicine in the streets.
All Signs Point to TH
If you've been in EMS any time at all, you've likely encountered a cardiac arrest in a patient you judged simply too young and otherwise too healthy to unexpectedly die. If several variables aligned right, you restored spontaneous circulation, stabilized the patient and transferred care at an emergency department (ED) with understandable hope that the patient would come see you at your station for a celebratory "second birthday."
Sadly, and more often than not, this date of rebirth is a date that marks transient and non-meaningful survival or survival only with dense neurologic deficit. Clearly, there's a lot more pathophysiology-based treatment involved than just getting a flat line (asystole) or chaotically wavy line (ventricular fibrillation)back to a standard looking ECG (normal sinus rhythm).
TH is a classic, but relatively recent, example of how a better understanding of what actually transpires in sudden nontraumatic cardiac arrest leads to better treatment. (As an aside, the phrase "sudden nontraumatic cardiac arrest" reminds us of a quote from a famous Jack Nicholson character, Col. Nathan Jessep: "Is there any other kind?").(2) Classically, we all think it's the transient oxygen deprivation accompanying cardiac arrest that causes permanent neurologic disability in survivors. This is at least partially the case the longer cardiac arrest continues. But what about the cardiac arrest patient who drops in public (witnessed), gets prompt assistance (bystander CPR), benefits from a short EMS response time (timely defibrillation) and is stabilized prior to hospital arrival (timely ALS care) and yet still experiences profound loss of awareness and other neurologic capabilities? It must not be just the lack of oxygen. Turns out, it's our bodies' well-intentioned compensatory responses to the lack of oxygen more than the hypoxemia itself.
In an April 2009 JEMS webcast, Brent Myers, MD, director and medical director for the Wake County (N.C.) EMS System, discussed the unfortunate but powerful post-resuscitation encephalopathy(PRE) that we humans have in response to cerebral hypoxemia followed by hyperperfusion with higher than normal oxygen levels.(3) (If you haven't seen this compelling one-hour presentation, go to JEMS.com/webcasts and make it your educational priority when you finish this article.) In short, applied hypothermia that's started in a timely manner after return of spontaneous circulation (ROSC) can decrease metabolic demand and blunt the inflammatory cascade response, thereby decreasing the neurologic impact of the cardiac arrest.
To date, there has yet to be a published study indicating harm, or even an equivalent effect of TH post-nontraumatic cardiac arrest. In fact, two of the most commonly referenced TH studies of cooling started in-hospital show striking benefit. In 2002, Bernard and others in Australia reported marked improvements in survival (32% with normothermia compared to 49% with TH of 12 hours) as well as particularly meaningful neurologically intact survival (26% with normothermia in contrast to 49% with TH of 12 hours).(4) If you're keeping close mathematical score, all the survivors who received hypothermia also survived neurologically intact -- your kind of survivor, right?
Contemporaneously, the Hypothermia After Cardiac Arrest (HACA) Study Group from Europe presented similarly impressive findings. Following the survivors of cardiac arrest in this study out to six months post arrest revealed notable increases in survival (45% normothermia compared to 59% with TH of 24 hours) and the ever-important neurologically intact outcome (39% normothermia in contrast to 55% with TH of 24 hours). Of the HACA study survivors, the results equated to 75 out of the 80 survivors being neurologically able to resume a previous high quality life.
To Be Considered
The positive outcomes of these two landmark studies can certainly diffuse the argument that all EMS is accomplishing by cooling ROSC patients is to fill up extended-care facilities with occupants in persistent vegetative states. So why would an EMS agency or hospital be resistant to implementing this practice? And if this describes your local emergency medical community, how can you work positively toward bringing TH to your hometown?
Costs: Like all additional therapies, even evidence-based and promising ones, initial costs of equipment and training must be determined, as well as anticipated maintenance costs of the program. Fortunately for EMS, the equipment costs can be reasonably controlled. In Oklahoma City and Tulsa, like most EMS systems providing TH, our method involves placing chemical cool packs in the axilla and groin while infusing up to 2 L of normal saline cooled to 4° C (39.2° F).
Multiple devices are available for stocking and cooling IV fluids. At startup, we utilized portable temperature-controlled coolers that cost a few hundred dollars apiece. As with any portable device in the patient compartment of our ambulances, careful consideration was given to its location and we ensured it could be fixated to avoid potential projectile concerns. Long range, new ambulances in our system are arriving with integrated refrigeration compartments that offer even tighter temperature control and ruggedness. We will still be able to utilize the portable coolers should an infrequent refrigeration malfunction arise, thereby keeping the ambulance in service until scheduled maintenance can occur.
Obviously, there's also extra expense involved in stocking an additional 4–6 L of normal saline per ambulance. But there's no additional expense for other IV supplies because we use the vascular access established during cardiac arrest, IV or intraosseous (IO).
We chose to place TH cooling devices and fluids on all ambulances in our system due to the large land mass we cover. (Oklahoma City alone is over 660 square miles.) Our emergency medical responders in affiliated fire departments play essential roles in cardiac arrest resuscitations, and some patients achieve ROSC prior to ambulance arrival. Even in these cases, however, ambulance arrival is three to five minutes or less after pulsatile circulation restoration. Looking at the logistics and cost of having a cooling device on all ALS fire apparatus would dramatically increase the cost of our TH program.
Making careful cost comparisons in your system will most likely allow for a post-cardiac arrest cooling program to be financially feasible. Further cost containment can be possible if the program is based from rapidly arriving supervisor vehicles only, if your coverage area and staffing models make this logistically possible in clinically reasonable timeframes.
We controlled training costs by incorporating the TH education into our regularly scheduled protocol update classes. No additional training sessions or educators were required.
Hospitals: EMS equipment and training concerns can typically be surmounted, but what about for your hospital partners? Consensus indicates that once hypothermia is started, it must be continued for at least 12 hours to have meaningful impact, so it's not enough to cool your patient in the field only to see rapid re-warming occur in the ED. Hospital participation was an absolute prerequisite to beginning TH in Oklahoma City and Tulsa; at least one hospital in each city had to reliably provide 24/7 cooling availability before we could start the therapy ourselves.
Just as there's a multitude of cooling devices and even methods for consideration by EMS, hospital clinicians can choose from a variety of proprietary cooling systems. Although the actual cooling machine or pump may involve a one-time cost of $10,000Ï$15,000, the average individual patient costs (cooling pads, wraps or blankets) are limited to a few hundred dollars or less. One system we know of utilizes a central vascular line catheter that can cost just north of $1,000 per patient. Our system works with numerous hospitals, and we endorse any clinically appropriate method that can produce the goal of appropriately cooling a patient and sustaining evidence-based effective temperatures for 12-plus hours.
The Ripple Effect
The coolest part of this whole EMS-initiated treatment is its effect far beyond the immediate patient receiving TH. Back to Thoreau's observation about affecting the quality of the day, EMS-initiated TH is the latest example of how we're truly advancing the overall quality of emergency care. Remember what happened in the early days of CPAP use in EMS? How quickly did your hospitals stop scratching their clinical heads and purchase or add BiPAP devices to continue your therapy in the ED? And did your local emergency physicians, pulmonologists and cardiologists increase their own use of non-invasive positive pressure ventilation for chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF) patients, thereby reducing the need for endotracheal intubation and treatment for ventilator-associated complications, such as barotrauma and pneumonia? Most likely, yes and with very gratifying results for patients and providers alike.
We firmly believe that by treating our patients to the highest available standards in the field, we directly influence the treatment of these patients in the hospital, not to mention countless others who we (or our EMS colleagues) never even directly touched. That's definitely affecting the widespread quality of emergency care! We can also say the same about the EMS adoption of continuous waveform capnography in airway management and IO access in critical vascular access situations.
In reality, when a major metropolitan EMS system adopts TH, it almost certainly creates the burn for additional hospitals and surrounding EMS agencies to follow suit. When we announced that TH was coming to the EMS system in Oklahoma City and Tulsa, several other EMS agencies announced they were going to beat us on the implementation calendar. The only better music to our ears would have been if they could have beaten us even sooner. For the sooner neighboring EMS agencies started TH, even more Oklahomans received evidence-based medicine that worked. The same will hold true wherever you are. The spillover effect is hard to quantify, but it's there.
This particularly gratifying aspect of advancing EMS care isn't confined to North Carolina or more recently, Oklahoma. John Freese, MD, deputy medical director of the Fire Department of New York City, reflects on their TH program this way: "Adopting hypothermia has definitely played an important role in advancing in-hospital care around our city. We see emergency physicians and nurses really geared up for post-cardiac arrest patients now, and there's a whole new level of belief that these patients are going to be walking out the front doors of the hospital and back to a gratifying life." The FDNY program, like ours and several others, restricts EMS transport of post-nontraumatic cardiac arrest patients to hospitals offering multi-disciplinary, coordinated TH programs.
Kathleen Schrank, MD, medical director of Miami Fire Department, agrees. "Starting hypothermia in the ED should be a no-brainer, but hospitals just aren't doing it. It's the right thing for the patient, so EMS may have to drive the system. We begged our hospitals to do it for a long time, but only one was. So we started cooling in the field and announced that as of Oct. 1, 2008, we would not transport to any hospital unless they had a cooling program, and our associate medical director would come help them set one up. Within a couple months, five more hospitals came on board. Now, we're doing QM follow-up to make sure they're actually doing what they promised. Unfortunately, EMS sometimes must police them."
If you're cooling post-nontraumatic cardiac arrest patients now, keep it up and carefully track your results for effectiveness. If you're trying to start a therapeutic hypothermia program—either for EMS, hospital or both—but you're hitting some stumbling blocks, take heart (and hopefully not one in cardiac arrest) in the fact that every one of the programs doing therapeutic hypothermia has encountered obstacles, too. With dedicated effort and some help along the way, your program will be successful. If you're new to the concept of TH, keep reading about it and talking with experienced colleagues, both in the field and in the hospital. You'll soon find even more reasons why the thing heating up in EMS is cooling patients down! JEMS
Jeffrey M. Goodloe, MD, NREMT-P, FACEP, is associate professor and director of the EMS Division of the Department of Emergency Medicine at The University of Oklahoma School of Community Medicine in Tulsa. He has the great privilege of serving as medical director for all Medical Control Board affiliated EMS agencies in metropolitan Oklahoma City and Tulsa, including the Emergency Medical Services Authority (EMSA), the Oklahoma City Fire Department and the Tulsa Fire Department. Contact him at firstname.lastname@example.org.
T. J. Reginald, NREMT-P, is director of research and clinical standards development for the Office of the Medical Director in Oklahoma City and Tulsa. He's a driving force behind the success and continuing advancement of cardiac arrest resuscitation in the major metropolitan areas of Oklahoma. Contact him at email@example.com.
- Thoreau HD: Walden. Ticknor and Fields: Boston (original publisher), 1854.
- A Few Good Men. Columbia Pictures, 1992.
- Myers JB. "Prehospital Hypothermic Resuscitation." JEMS Webcast, April 15, 2009. www.jems.com/webcasts/Prehospital_Hypothermic_Resuscitation.html
- Bernard SA, Gray TW, Buist MD, et al. Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia. N Engl J Med. 2002;346:557–563.
- Hypothermia after Cardiac Arrest Study Group. Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest. N Engl J Med. 2002;346:549–556.