I worked in a biomedical equipment service department for a large university hospital, where a new building had just been finished, and all nursing units were moved in. Shortly after the move, our central sterile processing department started sending us IV pumps that were returned from new nursing units because of discharged backup batteries. The batteries are normally only used during patient transports or power outages. The standard nursing practice was to keep devices with rechargeable batteries plugged in while in use or in storage.
At first it was just a couple pumps a week from one model of a manufacturer’s pump. All of the returned pumps did indeed have depleted batteries. When we tested the charge/discharge characteristics of the sealed lead-acid batteries in the returned pumps, they indicated normal operation of the charging circuits and normal battery run times. The pump manufacturer did not have any suggestions beyond what we had tried.
As a precaution, we replaced the batteries and the pumps and returned them to service. We kept an eye out for these particular pumps, but other pumps with discharged batteries started showing up, and were not coming from the same serial numbers. Pretty soon, a variety of IV and syringe pumps from different manufacturers started coming in with the same problem. We compared our service records with central sterile processing’s equipment assignment records. Those records indicated almost all problem pumps were returned from the new neonatal Intensive Care Unit.
Since this was a new building, we now suspected that there might be outlets that were intermittent or not powered. Again, we coordinated problem pumps with bed assignment histories. We checked all the outlets but found no anomalies. We even installed a power line monitor on suspected locations, but to no avail. Nothing connected the dots. We asked the nursing staff to immediately report any questionable pump battery failures to us, so we could do an onsite investigation.
With a report of another pump battery failure, I had a facilities electrician accompany me to the patient room. The pump was indeed in “low battery” mode, even though it was plugged into an outlet. While standing around rehashing possible failure scenarios, the electrician noticed that the plug of the offending pump was plugged into the power outlet at a slight upward angle. I reached up about six feet and reseated the plug, with some difficulty, into the outlet. The pump immediately went into the “battery charging” mode.
The problem? The hospital had new “hospital-grade” outlets with very strong contact retention-force that required more than normal pressure to insert the power plugs. If the plugs were not inserted far enough, any movement of the cord could eventually cause loss of contact and force the pumps into an unintended “battery mode.”
This entry was submitted by Ken Moffett and edited by Rob Spiegel.
Ken Moffett holds a BS in industrial arts education from Iowa State University. He is currently employed as a scientific instrumentation technician for the science division at Macalester College in St Paul, Minn.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
Yes, this was a problem with no pat solution...and no one you could point a finger at. In my opinion the design of the high placement of some of the outlets was the biggest factor.
And, yes there are a lot of the short nurses, aids, pump techs, RTs, ....
Only "Hospital Grade" plugs are used in these environments. I'm not sure that "loosening up" the contacts by plugging and unplugging a plug would work in a reasonable amount of time...although they do get less tight after a few years. Messing around with lubricants is not a solution in an environment where vast amounts of medical equipment cord sets are cleaned within an inch of their lives after every use...and no guarantee that any single device will go back to a location were it's a problem. The fact is that in most hospital beds, though the headwalls have high outlets, they are never used...they're there "just in case". Our NICU was a special case. I had seen as many as 18 devices on one tiny baby.
On many devices there may be no "battery charging" indication during use, it's just on. There are "battery operation" indicators though. The problem was that they would initially work OK, but we suspected that cord movement caused the disconnects. Going into battery operation is usually just one beep. With loads of devices at one bed, this could be missed.
Staff training in those areas, especially the supervisors, pretty much ended the problem.
Good point, Warren. But perhaps the manufacturer was OK with the idea of the user modulating speed by partial engagement. How else is the user going to slow down the power to the wheels?
Good point, Paul-c. Since this was happening multiple times, you can hardly blame the users. There was something intrinsically flawed in the design if plug after plug failed to insert correctly.
Warren: I think you've already hit upon the solution, but haven't realized it. It's true that these "hospital grade" receptacles have extremely strong springs. The cure may simply be to use a "hospital grade" plug (which usually have quite thick prongs) to break-in each and every new receptacle. This, plus a bit of contact lubricant on the plug's prongs to lube the socket, should make it easier for the user.
I think part of the problem is that these receptacles were installed quite high up, makings it harder for the user to apply sufficient insertion force. By the way, were the staff members short?
I think the line was supposed to be "if the plugs were NOT inserted far enough".
The article mentions 'battery charging mode' which I think would be an indicator lamp. I know this will sound ridiculous, but a 'plug inserted fully to get AC power' lamp would confirm the plug is seated. Or a more obvious 'running on battery' indicator or alarm might bring attention to the plug being loose.
Unfortunately, I see no solution for this problem. You can't train everyone to "push hard on the plug when you plug it into the wall." There is no guarantee that they will always to that. Maybe over time the sockets will loosen up a little and it won't be such a problem. Maybe a little or not so little sign warning them. But technically, this is a problem with no or limited solutions. You're dealing with "people," the weakest link in the chain.
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