A New Minimally-Invasive Bedridden Patient Weighing System

1. Group 16 Emily Jaeger Amy Rosenthal Nicole Typaldos A New Minimally-Invasive Bedridden Patient Weighing System

2. Current weighing techniques are inadequate and often dangerous • Lifts require suspension of patient over the bed • Uncomfortable for patient and time consuming and difficult for nurses • Built-in scales have low accuracy (1% of patient weight) • Beds with built in scales are expensive, causing a low adoption rate The Problem

3. Weigh bedridden patients within 0.23 kg (0.5 lb) and with minimal movement of patient. A single user with no additional training to operate the device and obtain patient weight in less than 5 minutes. Device will not interfere with normal patient care. Adult and obese patient weighing 22.7 kg to 453.6 kg (50 lb to 1000 lb) should remain comfortable. Automatic readout to display screen. The device will cost a maximum of $10,000. Design Requirements

4. The Bladder • Location of the weight sensing • The Controller • Allows the user to interact with the device and stores all important data • The Cart • Contains a pump and reservoir to fill, drain, and store the fluid when not in use A compartmentalized Fluid Filled Bladder

5. Smallest bed deck size: 90.2 cm x 203.2 cm • Bladder dimensions selected to be 90 cm x 200 cm to accommodate all bed sizes • The bladder had to be thick enough to fit the sensor while also minimizing the volume of water • The internal thickness is 3 cm in order to accommodate the sensor Analysis – The Bladder

6. Maximum weight to be held is 453.6 kg (1000 lb) • Given the area, this translates to a maximum internal pressure of 8.0 kPa Analysis – The Bladder

7. Power Requirements for Each Component Analysis – The Controller

8. Pump Selection • Needed to be able to overcome the maximum pressure within the bladder to refill if patient is present • Needed to fill within our set goal of 5 minutes • To pump up to 53 L (14 gallons) in 5 minutes, or 2.8 gallons per minute minimum Analysis – the Cart

9. Material: PVC Tarpaulin (5 mm thick) Dividers: High Density Polyurethane (HDPE) (2 mm thick) Overall dimensions: 90 cm x 200 cm x 3 cm 4 compartments each with a pressure sensor Details – The Bladder

10. Pressure to Weight • Each compartment contains a pressure sensor • The tare value of each sensor is stored in the controller • Using the area of the specific compartment, the weight on that compartment is obtained • These pressures are then summed by the controller to output the patient’s weight Details – The Bladder

11. Internal Components • LCD Display • High contrast • Displays desired 40 characters • Minimizes glare in the hospital setting • MCU • Takes at least 10 inputs • Can store information and still obtain new information • 16-key keypad • Numbers: 0 through 9 • Function keys: Tare, Get weight, Adjust, Units, Cancel, Yes Details – The Controller

12. External Components • 4 Pressure Sensors (140PC Series, Honeywell) • Gauge input • Linear within desired range • Fluid Level Sensor (eTape, Milone Technologies) • Varies resistance based on fluid level Details – The Controller

13. Cart Frame • Constructed from alloy 6061 aluminum • 2.5” and 2.0” extruded square tubing (1/4” thick) • 3/64” thick sheets for platforms • 1.25” extruded circular tubing (1/16” thick) • Tiered design to minimize dimensions Details – The Cart

14. Water Reservoir • Material: HDPE (1/16” thick) • Volume • Maximum: 66.8 L • To fill line: 57.4 L • Opening near base with fitting for connection to pump • Design allows for higher fill accuracy as volume lowers Details – The Cart

15. The Pump • Rotary vane pump (McMaster-Carr) • 19.7 L per minute (5.2 gallons per minute) • Maximum pressure of 1.66 Mpa (241 psi) Details – The Cart

16. Cords and tubing pose a tripping risk High pressure produced by the pump, requires safety labeling and careful usage Water spill risk due to the tubing Controller displays warnings and confirmation screens when certain functions are called Training required for nurses to ensure proper usage Details – Safety Concerns

17. Production – The Bladder • In order to seal the bladder, high frequency welding is used. • Production cost ~$100

18. Production – The Controller

19. OKW provides free prototype creation with the purchase of controller housing products. • The PCB printing and customization would cost $30.58. (Sunstone Circuits) • Circuit assembly and soldering could be done by team members • For mass production • Circuitry assembly would cost $158 • Milling of the enclosure would cost $14 Production – The Controller

20. Production – The Cart

21. Aluminum components are welded together • Rate of ~$60 per hour • For 2 hours of welding: $120 • For prototyping, the tank is created through plastic welding of sheets of HDPE: ~$50 for fabrication • Mass production would utilize injection molding Production – The Cart

22. Total cost of materials: $2,412.69 Total cost of manufacturing: $300.58 Total cost for a single prototype: $2713.27 Production Overall

23. Attempted to solve the problem, but many unforeseeable complications arose throughout the design process Due to these complications, a patent was not pursued Conclusions

24. Communication and clear explanation is critical when working in a team Even the smallest parts play a critical role In preliminary design, all possible calculations, even trivial ones, should be completed to avoid surprises later on Lessons

25. Questions?