Wireless Infusion System with Liquid Flow Rate Self-Measuring Module

Xiang Zheng Tu

   

A large volume infusion can be done using gravity driving method. In this method, a spit need inserts into an infusion bottle containing a drug liquid. The spit need has two side channels, one channel connecting the bottle to atmosphere and the other connecting the bottle to the infusion line. In operation, air enters into the bottle and drives the liquid into the infusion line. The driving force is provided by the height of the liquid of the bottle. Although this method is manual and labor intensive, it offers some significant advantages. First, the use of gravity for a driving force is energy efficient. Second, the force is low, so the dangers of large volume infusions can be avoided. Third, the gravity infusions are allowed to use a low cost and readily available pressure cuff. Forth, a gravity administration is not capable of infusing much air into the infusion tube line, because the driving force goes to zero as the liquid empties. 

In order to keep the advantages of the gravity driving method and reduce its labor independence, a liquid flow rate self measuring module has been developed by POSIFA.

The module comprises a house with an inlet and an outlet tubes, a print circuit board, a thermal flow sensor, an amplifier, a microcontroller, a wireless communication IC, and a lithium battery. When air flows through the house the thermal flow sensor will measure the flow rate of the air and produce a corresponding electronic signal. After conditioning and processing, the signal will be further send to a wireless infusion monitor.

The thermal flow sensor is fabricated using MEMS technology based on silicon micromachining processes. It is well known that silicon and other materials adapted for MEMS are bio-compatibility. Many MEMS devices are implantable for medical applications. For example, MEMS implantable pressure sensors have been used for continuous monitoring in Glaucoma patients. MEMS accelerometers have been used in defibrillators and pacemakers. An implantable drug delivery system based on MEMS technology also has been designed as a platform for treatment in ambulatory emergency care.  Generally, the thermal flow sensor based liquid flow rate self measuring module can be not used only for gravity driving infusion, but also for pump driving infusion. It means that the thermal flow sensor is allowed to measure drug liquid flow rate without worry about cross contamination.

As shown in the above picture, a bottle filled with a drug liquid is hung up and inserted with a split needle. The module is installed on the air suction side of the split needle. The liquid flow out side of the split needle is connected to an infusion line. When the liquid flows into the infusion line, a similar volume air will flow into the bottle. According the laws of physics, the flow rate of the liquid is equal to the flow rate of the air. So the module has a liquid flow rate self-measuring function.

In the picture, the wireless infusion monitor locates at the central region of an infusion room. It receives the signals from all modules arranged in the room and then displays graphically them. Through the monitor, a nurse in charge of the infusion room can see the liquid volume, battery level and all the other infusion parameters online and can be instantly notified for clinical issues. Physicians can supervise the infusion progress and therapy related events like the requested and given bolus. The physicians also can view the patient’s infusion history, make decision on the evolution of the therapy, and change protocol online. Indeed with the module everything can be done in real time through the web.