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Dialysis Machine Alarm

The Renal Dialysis Unit at Sydney’s St Vincent’s Hospital had a patient, ‘John’, who wanted to use APD as he was running a business. However, there was a problem because he had a hearing impairment and was unable to hear the specific frequency of the alarm.

People with chronic kidney failure have a number of treatment options, including Continuous Ambulatory Peritoneal Dialysis (CAPD), Automated Peritoneal Dialysis (APD) and Haemodialysis (HD).

Peritoneal dialysis uses the peritoneal membrane as a filter. Dialysis fluid is drained into the peritoneal cavity through a catheter, and then draws in the water and waste products from the blood. The fluid is drained out and changed every few hours. In CAPD, the person manually changes the fluid bags, usually about 4 times per day. APD uses a machine to perform the fluid exchanges automatically at night, and is therefore often the best option for people who need to be free during the day for work or school, or who need a carer to help them perform the dialysis.

Unlike haemodialysis, APD must be performed completely every day in order to ensure that the person remains healthy. Therefore the machine has an alarm, which gives a loud high pitched tone to wake up the user if the treatment process has stopped for some reason (for example, the person has rolled over on the fluid line and disconnected it).

The Renal Dialysis Unit at Sydney’s St Vincent’s Hospital had a patient, ‘John’, who wanted to use APD as he was running a business. However, there was a problem because he had a hearing impairment and was unable to hear the specific frequency of the alarm.

The hospital’s Occupational Therapist suggested that TAD might be able to assist, and volunteer Colin McDonald made a device that solved the problem. The first stage was to make four metal blocks to raise the machine off the surface it is sitting on, so that the alarm speaker, which is underneath the machine, can be accessed.

Colin then made a metal box containing a microphone and a two-stage amplifier. This sits underneath the machine, fixed in place with hook and fastener strips, and picks up the sound from the alarm. The amplifier works a relay that locks closed to power a motor in a plastic box about the size of a computer mouse, which is attached by a wire to the main box.

Colin screwed an extra piece of metal onto the shaft of the motor which makes it run out of balance, causing the plastic box to vibrate, or as Colin puts it, ‘it jumps all over the place at the speed of the motor.’ John tapes the plastic box to a suitable part of his body when he sets up the machine, and the vibrations wake him up if there is any problem.

The only way John can stop the vibrations is to switch off the device back at the main box, so there is no danger that it will get switched off accidentally before he wakes up. John can now sleep easily, secure in the knowledge that he will wake up if his treatment has been interrupted.

 

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