Overwhelming Force

   Not all the dangers associated with your ambulance come in the form of crashes and abrupt starts, stops and swerves. Just getting your patient into your rig to be transported can pose physical risks, as countless providers with battered backs can attest.

   Imagine a patient weighing an unremarkable 197 lbs. If you're an average-size provider, male or female, lifting that patient on a stretcher and loading them into your truck can generate forces on your back that not only exceed the threshold of a potential hazard, but approach the level at which NIOSH advises tasks be redesigned.

   What veteran providers have long known was quantified in recent research by an Australian ergonomist specializing in emergency-services operational issues. Working with a pair of New York agencies, Chris Fitzgerald measured the forces required for 50th-percentile male and female providers to lift and load x-frame stretchers loaded to 197 lbs., then used advanced predictive software to analyze the involved strength requirements. His findings, while more indicative than determinative, lend some mathematical legitimacy to long-held concerns about ergonomic design, physical demands and injury risk.

   "These are things you can measure. And unless you're quantifying your problem, you just have an opinion," says Fitzgerald, CPE, director of Risk & Injury Management Services in suburban Melbourne. "There's no pure reference for ergonomics for the ambulance industry, and to some degree that's what I'm trying to develop: a sort of quantified body of work the industry can draw on to help make decisions about its equipment, how it designs things and how it implements change."

   Change it might want to consider includes reducing what turn out to be considerable forces: Lifting that 197-lb. load translated to a mean peak foot-end lift force of more than 146 lbs. Analysis through the University of Michigan's 3D Static Strength Prediction Program found the lifts put both the male and female providers over the defined threshold of concern for L5-S1 disc compression.

   That lower threshold, or BCDL (back compression design limit), is 3,400 newtons. The upper threshold, or BCUL (back compression upper limit), is 6,400 newtons. "Generally, the closer you're getting to that upper threshold, the more concerned you should be about potential damage," says Fitzgerald, who presented the data last October at the EMS Safety Foundation's Ambulance Transport Innovation Workshop. "And remember, that represented only 50th percentile data-those values may change with larger or smaller providers."

   Interestingly, bigger isn't always better with stretcher lifts. Larger providers are typically stronger, but ergonomically speaking, their segment lengths-the distances between joints-are greater, and so require greater movements. With the position of the hands when lifting a stretcher fixed, back compression values are actually greater for taller people.

   That's not necessarily a risk, though. With proper posture, the spine can withstand large compression forces. The danger lies in deviating from that neutral posture and experiencing compression that's not evenly distributed. And, given the often-excessive joint-strength requirements of lifting and loading, that's a real concern.

   Fitzgerald's loading tests measured the force involved in holding the foot end of the stretcher up while a partner collapsed the legs. That was less taxing to the back, but still required peak force exertion exceeding 146 lbs. And it was a task that, according to the 3DSSPP-which also calculates the percentage of the population sufficiently strong at each key joint to perform the task-0% of women had the shoulder strength to do, and 0% of men and women alike had the elbow strength to do.

   "What can occur then is that either they just can't do it, or they'll start to adopt accommodating behavior," says Fitzgerald. "They'll either change the position of that joint to a stronger position, or transfer load to other joints."

   In other words, such a provider won't necessarily drop the stretcher, but they may shift their weight-for instance, leaning back to transfer some of the load to the legs/hips. That kind of compensation can increase slip risk and overload potential elsewhere.

   Fitzgerald's data also highlights a reality facing systems that are increasingly gender-diverse: While their leg strength is comparable, women, on the whole, simply don't have the same upper body strength as men. With the loading forces in particular, fewer women projected to have sufficient ankle (47% vs. 80% of men), knee (53% vs. 85%), hip (47% vs. 81%), torso (13% vs. 42%) and shoulder (0% vs. 38%) strength.

   There are plenty of caveats to this data, so don't go banning female providers from the foot end just yet. First of all, providers come in all sizes, shapes and strengths. Second, patient weights cover an enormous range. Third, the 3DSSPP is a static strength program, and lifting and loading a loaded stretcher is anything but a static activity. Posture and flexion and load forces can change quickly and dramatically during the process.

   And none of the data measured judgment. Another study Fitzgerald was involved in found that taller, stronger paramedics tend to make judgments involving higher levels of risk, indicating that less-strong paramedics, many of whom will be female, are typically more risk averse. These attributes shouldn't be ignored, he notes, and recruiting on the basis of strength alone is likely to be too limiting.

   In sum, snapshots can tell us a lot, but they're not dispositive.

   "You have to be careful about how you extrapolate the data," says Fitzgerald, "but really, there aren't many industries in the western world that routinely require workers to exert forces greater than 50-60 kg (110-132 lbs.). I used an unremarkable patient weight, but very quickly we saw a high force exertion."

   As manufacturers pursue mechanical solutions to reduce these forces, services may look, short-term, to operational strategies to reduce risk.

   Says Fitzgerald: "That might simply involve understanding that, once we get a person whose weight we estimate to be above x, we need a second person at the foot end. Right now, it's a matter of what operational strategies we can put in place."