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COLD Care
Wake County (NC) EMS leaders thought they could do better. Adopting the American Heart Association's revised CPR protocols, which emphasize compression, had increased their agency's prehospital cardiac resuscitation rate from 22% to 37%. But department bosses were disappointed that their hospital-to-home patient discharge rate improved only from 10% to 12%.
Medical literature suggests that therapeutic hypothermia improves survival rates and preserves neurologic function in certain cardiac arrest patients. Medical Director Brent Myers, Assistant Medical Director Paul Hinchey and Chief Skip Kirkwood came to believe it could help them send more patients home to their families with neurologic function intact.
"That," says Hinchey, "is where hypothermia started to look so good to us. We saw it was time-dependent, and we said 'This is a perfect fit for EMS.' If it's time-dependent and falls in the scope of resuscitation, that's right up our alley."
Now Wake County EMS is one of a small group of services nationwide that have implemented the 2005 AHA guidelines for inducing mild hypothermia in selected resuscitated cardiac arrest patients.1
"When we can do something that will benefit the community, we don't necessarily wait, for example, for the American Heart Association to change the standard," says Kirkwood. "If the science is there and it's better for the patient, we do it."
Development
The AHA Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care issued in 2000 noted that mild hypothermia may be beneficial but should not be actively induced. This position was revised by a 2003 International Liaison Committee on Resuscitation (ILCOR) advisory recommending induced hypothermia, a position reflected in the AHA's revised guidelines of November 2005.1-3
The 2005 guidelines recommend inducing moderate hypothermia in adult patients who experience out-of-hospital cardiac arrest resulting from ventricular fibrillation (VF) if they experience a return to spontaneous circulation but remain unconscious. The guidelines call for patients to be cooled to between 32°-34°C and maintained at that temperature for 12-24 hours.
Based on these recommendations, Wake County EMS officials designed a protocol that authorizes paramedics to induce hypothermia at the scene of a cardiac arrest when an adult patient (older than 16) experiences a return of spontaneous circulation but remains comatose, and the body temperature is higher than 34°C.4
The patient is intubated, and ice packs are applied to the armpits, neck and groin to begin cooling. Versed (0.15 mg/kg, up to 10 mg) is administered to sedate the patient, and the paralytic vecuronium (0.1mg/kg, up to 10 mg) is used to prevent shivering as the body attempts to warm itself. A saline IV (30 mL/kg, up to two liters), which has been cooled to between 2°-4°C, is started.
If necessary, medics administer dopamine (10-20 mcg/kg/min) to increase the mean arterial blood pressure to between 90-100 (about 150 systolic pressure) to ensure adequate perfusion. End-tidal CO2 is monitored with a target of 40 mmHg, and hyperventilating the patient is avoided. Paramedics do not wait for the patient to achieve the target temperature to begin transport.
In addition to the supervisors automatically dispatched to every cardiac arrest scene, Myers and Hinchey are also paged at this stage of implementation, in case questions arise.
While the AHA guidelines recommend therapeutic hypothermia for patients with VF, they also state that the procedure may benefit patients with non-VF arrest.1 Wake County EMS officials decided to induce hypothermia in all eligible arrest patients, regardless of their rhythms.
Myers says that because a significant number of patients are likely to experience VF at some point, a single directive that covered all rhythms was less confusing. He also says that in his experience, a significant portion of VF cardiac patients regain consciousness by the time they arrive at the hospital. "The people having adverse neurologic outcomes," he says, "are people who have PEA (pulseless electrical activity) and asystole as well. There's no reason to believe that the brain has any different damage because it didn't have blood flow from fib as opposed to not having blood flow from asystole."
Implementation
Because the procedure for inducing hypothermia on cardiac calls relies largely on skills they already possess, certifying paramedics in the new protocol was easily done through a one-day session incorporated into the agency's mandatory monthly CME program.
The introduction of vecuronium and the use of cold saline and ice packs were essentially the only changes to the cardiac resuscitation protocol, so the training focused largely on explaining how induced hypothermia works and use of the vecuronium. Paramedics are required to pass an exam on the information presented during the lesson.
The most difficult problem Wake officials faced was how to store saline at a near-freezing temperature and maintain a consistent temperature during each 24-hour shift medics worked. They tested a variety of devices, but only the compact portable freezing unit Engel 15, commonly used on boats and campers, was found to meet their requirements, Kirkwood says. The units run off a 12-volt power supply, which can quickly drain an automobile battery when the engine is off, but extension cords can connect the units to external power supplies when necessary.
Wake's response vehicles lacked adequate space for the coolers, so the agency had to find an alternate means of transporting the saline to scenes. Because a supervisor must respond to all cardiac calls, the cooling devices were installed in their vehicles, and they deliver the cold saline. The vehicles of five supervisors, the medical director and the clinical affairs officer all carry the coolers. The seven units, cords and miscellaneous supplies cost the agency approximately $3,500.
Integration
EMS and hospital officials had to synchronize their protocols to ensure a seamless state of hypothermia for patients for up to 24 hours, so Wake County EMS could not launch the program without the participation of hospital staff.
EMS officials spent approximately six months meeting with hospital emergency and intensive care staffs, neurologists, cardiologists and nurses, all of whom contributed to the development of protocols that cover patients from the field to their point of entry into the hospitals' emergency departments and through the rewarming period approximately 24 hours later.
Anticipating that a large number of patients would require catheterization lab services, Wake County EMS officials decided to continue to transport patients to the area's two hospitals that offer 24-hour interventional cardiology services.
Tracking the Results
The rollout of the new protocol on October 5 went as smoothly as anticipated, with paramedics achieving temperature drops of about 2°C with no complications. "They've found it to be one of the easier things we've asked them to do," says Myers.
In less than a month, paramedics had seven opportunities to induce hypothermia. Two of these patients-a 35-year-old man for whom resuscitation was delayed until an extrication could be completed and a 70-year-old man-experienced positive outcomes, returning to baseline mental status with good neurologic function, Hinchey says.
The medical literature on induced hypothermia estimates that, based on VF cardiac cases, one of every six patients treated will have a positive outcome. Myers says Wake's numbers could be lower because paramedics treat cardiac arrests resulting from all rhythms, but he estimates the procedure could aid 5-15 patients annually. The agency responds to 750 cardiac calls a year and expects that 50-75 patients will be eligible for therapeutic hypothermia.
While Myers and Hinchey will need two years of data to evaluate the program's success with any statistical significance, they hope to work with other EMS agencies to expand use of the protocol and collect data. Wake County already has a sophisticated patient-tracking procedure in place and recently improved its system to include patient bands with a unique EMS identifying barcode that will permit EMS and hospital officials to follow patients' progress from the field through hospital discharge.
While improved patient care is the goal, Hinchey says the process of implementing the new protocol in cooperation with hospital officials demonstrated the unique role EMS can play in the delivery of emergency medicine.
"I don't know of a lot of things in EMS history where the prehospital side dictated what happened on the in-hospital side," he says. "Traditionally, it's been a top-down trickle-down from the intensive care units to the emergency departments out into the field. Over the course of 10 or 20 years, this is, I think, probably one of the first times we've gone in the other direction.
"EMS is finally starting to be recognized as a different area of practice," he adds, "and things that may not be applicable in the hospital setting may be applicable in the field setting. So we're really starting to develop EMS as a different practice of medicine that has to integrate into the greater healthcare system."
References
Aimee J. Frank is a writer and former New York state-certified EMT with the Woodstock Fire Department.
