New Minimally-Invasive Bed-Ridden Patient Weighing SystemAmy Rosenthal, Nicole Typaldos, Emily Jaeger

Mentor: Dr. Frank CP Yin

BackgroundPatient’s weight is critical to care

Uncomfortable for patients to be weighedDifficult and time consuming for nurses to

move patientsNurses often estimate weight to avoid the

hassle May become unsafe to weigh certain patients

Obesity has increased to over 35% of the population1

1. United States. Center for Disease Control and Prevention. Department of Health and Human Services. Prevalence of Obesity in the United States, 2009-2010. By Cynthia L. Ogden, Margaret D. Carroll, Brian K. Kit, and Katherine M. Flegal. Vol. 83. Hyattsville, MD: National Center for Health and Statistics, 2012. CDC. Web. 23 Sept. 2012.

ProblemPatients can be lifted

UncomfortableUnsafe for patient and nurseDifficultComplicated

Scale built into bedNurses forget to tarePoor repeatabilityNurses are expected to do calculation

Bed can be weighedDifficult to move the bedUncomfortable for patient to moveLarge weight of the bed must be subtracted off causing

less accuracy

ScopeDesign a device for weighing bedridden patients within 0.23 kg

(0.5 lbs) and with minimal movement of patient to avoid the discomfort for patients and hassle for nurses.

A single user with no additional training will be able to operate the device and determine the weight of the patient within 5 minutes of seeking the information so weighing can be done efficiently without taking the current 15-20 minute standard.

The device design will not interfere with normal patient care. Adults and obese patients weighing 22.7 kg to 453.6 kg (50 lbs to

1000 lbs) should be able to remain comfortable while weight is monitored.

Some automatic capabilities will be added to ease continual patient weight monitoring including an automatic readout for use in hospitals.

The device will cost a maximum of $10,000.

Current PatentsAttached to the bed

Design raises bed on a leg attached to a force transducer that takes weight1

1. Neuman, Eli. Weighting Device for Bedridden Patients. Tedea-Huntleigh Intl. Ltd., assaignee Patent 5747745. 05 May 1998

Current PatentsMobile scale

Design slides under hospital bed and then weighs both bed and patient and then the bed weight is subtracted1

Design has scale wheeled against patient bed, but still requires moving patient2

Design goes under bed mattress to give reading3

1. Ashpes, Adam T., Rynd, Richard. Mobile Hospital Bed Scale. EZE Weigh, LLC., assignee. Patent 5990423. 23 Nov. 1999

2. Stultz, Frederick L., and Clark, George C. Scale for Weighing Hospital Patients in their Horizontal Position. Acme Sclae Company, assignee. Patent 4006789. 08 Feb 1997

3. Hasty, Byron E. and Carbona, John A. Portable Scale. CH Administration Inc., assginee. Patent 5393935. 28 Feb. 1995.

Current PatentsVeterinary scales

Design pulls cables taught when table is in lowest position, letting force transducer measure weight1

Design has a platform suspended at four corners with tensile load cells that give signal proportional to force2

1.Rosenberg, Philip M., and Rosenberg, Alexander J. Veterinary Examination Table. Animal Veterinary Products, Inc.,

assignee. Patent RE32052. 24 Dec. 1985. 2. Schneider, H. Allen. Animal Scale. Weigh Right Electronic Systems, Inc., assignee. Patent

4286679. 01 Sept. 1981

Stryker Hospital BedsBariatric Hospital Beds

Model: Bari 10A In bed scale standard with 453.6 kg (1000lb) range

Critical Care BedsModels: InTouch, Epic II

Integrated scale only comes standard in InTouch model Maximum weight capacity of only 228 kg (500lb)

Med/Surge BedsModels: S3, GoBed II

Integrated one-touch scale optional in both models Ability to weigh patient in any position

Stryker. http://www.stryker.com/en-us/products/PatientHandlingEMSandEvacuationEquipment/Beds/index.htm

Hill-Rom Hospital BedsBariatric Beds

TriFlex II-Optional In-bed scale Maximum capacity 453.6 kg (1000 lb) capacity

Excel Care ES – In-bed scale standard Accuracy of 1% of patient weight when sleep deck in

supine position Maximum capacity of 453.6 kg (1000 lb) capacity

TotalCare Bariatric Plus – Integrated scale standard Accuracy of 1% of patient weight up to 181.4 kg (400

lb) Functional up to 227 kg (500 lb)

Hill-Rom. http://www2.hill-rom.com/usa/index.asp

Hill-Rom Hospital BedsNon-Bariatric Beds

VersaCare – In-bed scale standard Accuracy of 1% of patient’s weight, even with head

elevatedCareAssist ES – optional integrated scale

Accuracy within 1 kg (2.2 lb) or 1.1% of patient’s weight, whichever is greater

Repeatability is within 2% of patient’s weight Functional up to 227 kg (500 lb)

Hill-Rom. http://www2.hill-rom.com/usa/index.asp

Hoyer Lift ScalesVariety of models with capacities ranging

around 500 to 700 lbsNeed to buy the lift and the scale separatelyLift slings can be either a chair or a stretcher

liftCommonly usedPortable

Design Specifications: ForceRange: 22.68 kg 453.59 kg (50 lbs to 1000

lbs)Sensitivity: 0.23 kg (0.5 lbs)Repeatability: Variance of less than 0.25 kgForce transducers linear over 44 N to 5000 N

Design Specification: SafetyShockproofWaterproofCan be sterilizedCurrent leakage of less that 100 microamp

Design Specifications: DeviceSize: fit within normal bed dimensions (91 x 213 cm)Portable: May be carried by a single nurse, less than 35lbsDigital readout of weightOption to remove or add the object’s weight (i.e. to

account for removal or addition blankets)Interface with computer or standalone deviceDisplay output in units of kg or lbsEfficient: less than 5 minutes to operate and single output

for easy readingMade for adults and obese patientsPower source: 120 V AC or convert to DCTemperature range: Perform in 10°C to 37°C (50°F to 100°F)

Design SpecificationsMinimal movement of patientNo change to patient’s comfort

Load Cell EquationsConverts force into an electrical signal.

Force deforms a strain gauge which measures the strain as an electrical signal, as a strain causes a change in the electrical resistance

Strain gauge in form of Wheatstone bridge

€

Rx =R2

R1

⋅ R3

Load Cell Equation Electrical signal output must be amplified by

instrumentation amplifier

€

VoutV2 −V1

= 1+2R1

Rgain

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟R3

Rgain

Mass EquationWeight = mass x acceleration due to gravityg = 9.81 m/s2 = acceleration due to gravity

€

750N

9.81ms2

= 76.4kg

Freitag, Elke, et al. "Determination of body weight and height for critically ill patients admitted to the intensive care unit: A quality improvement project." Australian Critical Care 23 (2010): 197-207.

Current Nurse Calculations for Weight by Bed

Team OrganizationAmy Nicole Emily

First Presentation Second Presentation Third Presentation

Computer Programming

Hospital Contact Client Contact

Designs Electrical Component Mechanical Aspect

      1 2 3 4 5 6 7 8 9 10 11 12 13 14Initial Process                              

 Background Research                            

    Literature                                Patents                            

   Social Impact                            

    Interviews                              Problem Definition                            

   Project Scope                            

   Specifications                            

    Metrics                            Concept Generation                              

   Brainstorming                            

   Comination Table                            

   Design Alternatives                            

Project Choice                              

   

Design Requirements                            

    DesignSafe                            

   

Project Development                            

  Draft Due  Timeline to

work on project

  

Course Assignments 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th

12th

13th 14th 15th

Preliminary Report    

Preliminary Presentation    

Progress Report    Progress

Presentation    Final Report    

Final Presentation    Design Webpage          

Poster Presentation          Final Due Date

  Initial Draft 

Timeline to work on project 

 

Due Dates

Questions?