Are You Being Pushed Around?
If you've ever stood, unrestrained, in the back of a moving ambulance to provide CPR compressions or some other care, you know it doesn't take much. Even slight acceleration, braking or turning forces can push you off balance-perhaps not enough to injure you, but enough to force you to throw out a hand or adjust your stance to steady yourself.
While much has been said and written about the enhanced likelihood of injury or death if you're unrestrained in the back in a crash, the specific forces applied by regular operation of the vehicle, and their subsequent effects, have received little consideration. Exactly what forces are unrestrained providers subjected to in transit? What do those forces mean for them and their patients, and how can we reduce them?
An initial attempt to investigate such questions-"Description of the Acceleration Forces Affecting Balance of Prehospital Providers While Delivering Cardiopulmonary Resuscitation"- earned Best Original Resuscitation Science honors in the Moderated Poster Session of the American Heart Association's 2009 Scientific Sessions.
"There's actually very little data on the question of balance loss in the backs of ambulances, and the number and magnitude of forces EMS providers are subjected to there," says coauthor Michael Kurz, MD, director of emergent cardiac care in the Department of Emergency Medicine at Virginia Commonwealth University Medical Center, who presented on the subject at the National Association of EMS Physicians' Ambulance Safety Conference in January. "We'd had a number of incidents involving provider safety that were directly related to those forces being applied, and we teamed up with the Richmond Ambulance Authority, which had the infrastructure in place to research it. That let us collect and analyze the relevant data."
To do this, investigators used a Road Safety onboard monitoring system to record lateral and axial acceleration data during the transports of 50 cardiac arrest patients, then calculated acceleration and acceleration change vectors for every second of drive time. These forces weren't being applied to actual providers-Richmond uses ZOLL AutoPulses to provide automatic compressions, thus allowing its personnel to remain seated and restrained-but could be compared to known critical thresholds to determine how much exposure a standing provider might have to off-balancing forces.
The results: During cardiac arrest transports, personnel could be, due to frequent, large acceleration forces, at significant risk of balance loss 60% of the time. Resulting balance loss, the authors concluded, may result in personal injury or poorer quality CPR.
"I was astounded," says Kurz. "From my experience as a paramedic, I knew providing CPR in the back of a moving ambulance is challenging, and the forces that are applied are significant to your balance. But I wasn't ready for the magnitude of the forces applied in the average call we analyzed, or the amount of time providers are potentially exposed to off-balancing forces."
Specifically, previous research has shown that acceleration greater than 0.6-0.93 m/sec.² leads to loss of balance. The Richmond data showed acceleration exceeded 0.93 m/sec.² 49% of time. With another predictor of balance loss, jerk-the rate of change of acceleration (i.e., meters per second per second)-the critical threshold of 0.6 m/sec.³ was exceeded 26% of the time. Together, one or the other of the thresholds was exceeded 60% of the time.
What might this mean for actual standing providers delivering chest compressions? Start with the loss of patients' coronary perfusion pressure every time a lurching provider has to interrupt their work to keep their balance.
"Presumably, while these off-balance forces take place, a provider cannot provide quality CPR," says Kurz. "We have a second research project coming online soon to specifically answer that question about the quality of CPR. However, if you just take on faith that if you're off balance, you can't provide quality CPR, we know that if you're not providing quality CPR, the coronary perfusion pressure drops off dramatically, and it requires at least two seconds of quality CPR to get back to a level where there's a high probability of ROSC. So it could have a profoundly detrimental effect on the quality of CPR delivered in the back of the ambulance and the potential for restarting the hearts of cardiac arrest patients."
That second project will, rather than using force parameters as a proxy, measure actual forces on the provider in back and the quality of CPR being done.
As the specifics of this issue are being fleshed out, it's not too early to start considering countermeasures. Specifically to patients who get CPR during transport, automated chest compression devices could represent an effective solution. But the questions are really bigger than that.
"We need to examine why we're even transporting patients with CPR in progress," says Kurz. "Recent research on termination-of-resuscitation guidelines raises the question of whether we should transport these patients at all-it may be that we should be terminating some in the field. And if transport is appropriate for some patients, what is the safest way to transport them, keeping in mind the safety of our providers, the safety of the public, and the quality of CPR and clinical care in the back of the moving ambulance?"
Also worth noting are differences between Code 3 and nonemergent driving. The former, for obvious reasons, applies greater forces.
"I think, in addition, this research prompts the question of when it's appropriate to drive lights and siren," Kurz adds. "Lights and siren driving is about the most dangerous thing we do in EMS, and it should be used with great caution and very judiciously."
