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.
It sounds like staff training was the only reasonable solution, Ken. Why is this situation unique? Apparently this was not a problem in the older building.
We have similar problems with loose charging plugs of battery operated equipment on ambulances...and of course the battery is always dead when you need it most. Maybe its time we created a new "standard" outlet for medical equipment....something easy to use but with better retention...and then create a simple adapter that allows the device to be used in a standard outlet, of course the adapter needs to be somehow mounted to the plug so its never lost...medical equipment typically doesn't have the same price pressures as consumer electronics...when you buy a $30,000 EKG monitor, you don't mind paying a few extra $ for a plug that works! One simple solution that we have tried that seems to work is switching to plugs with small LED power indicators in them, with a quick look you can tell if there is power being supplied to the power cord.
Twist-loc connectors might solve that particular problem, but would cause greater ones.
First, 120VAC medical equipment with attached cord sets (in the US) come with "standard" hospital-grade 3-prong plugs. And, all standard outlets accommodate these. The cost of switching all outlets where a device might be used and all device plugs to compensate for this one problem would be prohibitive.
Second, medical devices running in battery-mode frequently accompany transported patients. That would mean that any area or vehicle where the patient might be held for any significant length of time would also have to accomodate these plugs for recharging to maintain operation. That would include ambulances, clinics, waiting rooms, hallways....even homes.
That problem, in that hospital was resolved economically through staff awareness.
As an aside, a large percentage of medical devices are now using wall-plug power supplies...for two reasons. The medical devices could be made smaller. And, maybe more practically, the UL approval is now entirely on the power supply manufacturer, not on the medical devise manufacturer. The "wall-warts" compounded our outlet problem. I'm sure you've experienced the situation of a wall-plug supply, plugged into one outlet of a duplex, blocking the second outlet. Each such device occupies two outlets.
I like the twist lock suggestion. Nice trick, Mr. Hat.
This may not be the only application where a critical circuit could come unplugged. The twist-lock would solve those problems, as well. And think of the electricians that could be put to work!
Warren, a twist-lock plug and receptacle would fix this problem. The important outlets in a hospital SHOULD be different from a conventional outlet, so mundane things like a fan or radio cannot be plugged into them.
Twist-locks would keep the receptacles dedicated to hospital equipment, be easy to use, prevent accidental unplugging.
"Maybe the alarm on the devices used should sound until the power is secured. And loud!"
Warren, can you imagine a power failure, and having a hundred-plus devices going into battery-mode and continuously, loudly alarming. The manufacturers make choices based on real world user input...hopefully.
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