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.
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