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Intravenous Pump – Alarm Monitor

The client is a mother of one living a with young son estimated at 10-12 years old. She is deaf but can hear well with the aid of hearing aids during daytime. At night she does not wear the hearing aids. Her son is wheelchair-bound, also deaf and requires regular, almost continuous intravenous (IV) nutrition and fluids (day and night). Two portable intravenous pumps (IV pumps: Bodyguard 323) are used to facilitate this, which are carried on his wheelchair during daytime and then placed in a charging cradle on a pole stand at night.

The pumps are not owned by the client. Occasionally one of the pumps may have a problem and sound an alarm.  If the problem is not fixed quickly the infusion may need to be restarted (inconvenient) or lead to a medical condition requiring treatment by doctors or at hospital. If one of the pumps fails at night the client needs to be woken up to attend the alert. She was seeking a solution to be woken in a next door room if one of the pumps alarms during the night.

Over time different pumps have been used some of which had external alarm circuits. However the current pumps do not have any alarm interface;  just an intermittent audible alarm and flashing screen. The current solution is a baby sound alarm in her son’s room with a pager vibrating alert worn on her arm. However the baby monitor triggers on any reasonable sound, so creates many false calls.

Since the pumps are lifted in and out of their charging cradle daily it would be difficult to attach anything to the pumps. Any modification to the pumps may be difficult since the client doesn’t own them and the American manufacturer is not responsive to information requests or correspondence.

The solution

On receipt of one of the Bodyguard 323 pumps the alarm sound was found to be a ~2Khz frequency that pulses on-off with a precise 2 second pulse repetition rate (PPR). The signal is not clean enough to measure the ~2kHz directly.  The 2 sec PRR is very stable however.

A microphone held close to the body of the pump was used to detect the audio signal. The mount for the microphone clips over the charger cradle and allows the pump to be removed for day time use. The microphone signal is processed by an audio amplifier and then used to trigger a 1.2sec mono-stable pulse. This pulse is monitored by an Aurdino micro-controller. Code was written to filter pulses that arrive with a PPR of of 2 ±5% seconds. Two separate independent monitor channels are provided one per pump used.

If 30 consecutive pulses with the correct PPR are detected the controller triggers a relay to activate the pager. The relay contacts are connected to a Connevans RF pager unit (the client has several) which in turn activates the pager worn by the client in an adjacent room. The connection is such that if power fails or the pager connection is removed the pager activates. The monitor is powered by a small 12V dc supply and has an internal battery for short duration mains supply failure.

The filters of 2 ±5% seconds and  30 consecutive pulses means the monitor will not generate an alarm output from random tapping or knocking of the unit. The extended period of 30 consecutive pulses was chosen as the client has said that sometimes her son rolls onto the IV tube and that then triggers the Bodyguard alarm, but he normally rolls off again quite quickly. So the client will not be alerted before the alarm has been running for at least one minute.

As well as simply running the unit with the Bodyguard in alarm mode some ambient noise testing was carried out as well. An MP3 file of traffic noise played through speakers. At a level of to 70-75 dBA  the system still reliably detected the pump alarm. This is roughly equivalent to a vacuum cleaner running in the room. It seems highly unlikely that the ambient noise in a bedroom would be anywhere close to these levels.

The monitor has a clamp that allows it to be mounted on standard IV pole below the pump unit(s). A small metal bracket holds the pager transmitter.

09/11/21 Update Mk2 Unit

A second unit has been supplied (the client is based in two locations that both require this type of monitor) and the design has been refined. The electronics and software have been modified to reduce the component count and allow a single pcb to be used. The controls have been simplified with one button acting as test and reset. The test function also allows a ‘walk round’ test for the pager unit. The LED indicators are now hidden-till-lit and have been muted. The yellow LED will flash when ambient sounds are picked up as this was found to be disturbing at times.

The benefit

The client can be reliably alerted to a pump alarm condition and attend to the situation with out excessive false alarms. The son’s intravenous treatment can be maintained without significant interruption and reduce the chance of further medical intervention.

The monitor has been with the client for circa 4 weeks now (early October ’21) and she has just reported that it did wake her to a pump failure during the night and she was able to deal with the situation in good time. She says that she can now sleep soundly with out having to worry about the pumps(s) failing.

Update 27.11.21 the following email was received from the client after receipt of the 2nd unit.

Just a quick email to say the new system is working perfectly. It’s attached to the IV pole above the pumps, mainly because the pumps are in (my son’s) reach so he can turn them off (when told!) in the morning. I had the alarm go off this morning because one of the IV fluid bags ran out, so I was able to go in to turn the pump off. The 15 beeps is definitely much better for us, as (my son) will fiddle if it’s any longer, and I’ll not be alerted. It all looks rather stream line, and I’ve also seen what happens when the power gets disconnected by mistake!

I can’t thank you enough, …, it looks really good and is really helping me sleep, knowing that I’ll be woken in an emergency.

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