AbstractAbstractThe metabolic rates of critically ill patients The metabolic rates of critically ill patients

can vary drastically from typical metabolic rates. can vary drastically from typical metabolic rates. This can cause problems for health care This can cause problems for health care providers when determining the correct amount providers when determining the correct amount to feed the patient. Matt O’Brien, RRT, performs to feed the patient. Matt O’Brien, RRT, performs metabolic tests on these critically ill patients to metabolic tests on these critically ill patients to determine their metabolic rate and food intake determine their metabolic rate and food intake needs. This is done with indirect calorimetry, needs. This is done with indirect calorimetry, measuring the concentration of oxygen of the measuring the concentration of oxygen of the inspired and exhaled air of the patient. In order inspired and exhaled air of the patient. In order to stabilize the inspired oxygen level produced to stabilize the inspired oxygen level produced by the ventilator, our final design is an air by the ventilator, our final design is an air mixing chamber placed within the series of air mixing chamber placed within the series of air flow from the ventilator to the patient.flow from the ventilator to the patient.

Problem StatementProblem Statement

To develop a mixing chamber to To develop a mixing chamber to help stabilize oxygen help stabilize oxygen percentage delivered from percentage delivered from mechanical ventilators to mechanical ventilators to critically ill patients; this critically ill patients; this chamber would allow for chamber would allow for increased accuracy of increased accuracy of metabolic measurements.metabolic measurements.

ResearchResearchGreater metabolic rate of critically ill patients and malnutrition can lead to longer hospital stays and worsened conditions. Indirect calorimetry measures the dimensionless respiratory quotient, RQ, which is the CO2 produced divided by the O2 consumed (1)

RQ depends on the amount and type of food consumed, therefore indicates if patient is receiving too few or too many calories (2)

Two factors can cause inconsistent RQ values or values outside normal range (1.3- 0.67) : inadequate mixing of the gasses or changes in gas pressure between ports (3)

FIO2 must be measured on a breath-to-breath basis during these metabolic tests and the inconsistencies from gas concentration and pressure must be made as small as possible in order to have appropriate RQ values (3)

MotivationMotivation

Our client, Matt O’Brien, is a Registered Our client, Matt O’Brien, is a Registered Respiratory Technician at the UW Hospital who Respiratory Technician at the UW Hospital who performs metabolic measurements and is performs metabolic measurements and is interested in having more accurate and reliable interested in having more accurate and reliable data in the tests he performs. He believes that data in the tests he performs. He believes that the inadequate mixing of oxygen and air could be the inadequate mixing of oxygen and air could be to blame for some inconsistent RQ measurements to blame for some inconsistent RQ measurements he has made. Thus, he has requested our team to he has made. Thus, he has requested our team to design and build him a small mixing chamber to design and build him a small mixing chamber to sufficiently mix the gas in hopes for a more stable sufficiently mix the gas in hopes for a more stable FIOFIO22 value and thus logical RQ data. This will aid value and thus logical RQ data. This will aid in a more accurate nutritional assessment of in a more accurate nutritional assessment of mechanical ventilator-dependent patients and mechanical ventilator-dependent patients and help prevent over and underfeeding of these help prevent over and underfeeding of these critically ill patients.critically ill patients.

Design SpecificationsDesign Specifications

Stabilize FIOStabilize FIO22 measurements through measurements through improved mixing of gases improved mixing of gases Reduced size than existing chamber Reduced size than existing chamber dimensions: 15.9 x 5.1 x 8.3 cm dimensions: 15.9 x 5.1 x 8.3 cm The inlet and outlet ports: outer diameter of The inlet and outlet ports: outer diameter of 22 mm and inner diameter of 15 mm 22 mm and inner diameter of 15 mm Easily sanitized yet maintain an airtight Easily sanitized yet maintain an airtight sealsealChamber constructed of a transparent Chamber constructed of a transparent materialmaterialTo withstand use approximately once a To withstand use approximately once a week week

Design Alternative - 1Design Alternative - 1A grid or filter to create turbulent A grid or filter to create turbulent flowflow

Tube and filter dimensions Tube and filter dimensions dependent on theory of Reynolds's dependent on theory of Reynolds's number, predict behavior of air number, predict behavior of air flow, laminar or turbulent (4)flow, laminar or turbulent (4)

Advantages: Design simplicity, ease of manufacture, low Advantages: Design simplicity, ease of manufacture, low cost cost

Disadvantages: Mixing completely dependent on the grid Disadvantages: Mixing completely dependent on the grid turbulence created, induced turbulence can quickly die outturbulence created, induced turbulence can quickly die out

Design Alternative - 2Design Alternative - 2Turbulence created by air flow obstacles: Turbulence created by air flow obstacles: holes, wall heights, etc. and small pressure holes, wall heights, etc. and small pressure difference between the entrance and exit difference between the entrance and exit

Have same effect as electrically powered fanHave same effect as electrically powered fan

Advantages: Simplicity, easily cleaned, deals Advantages: Simplicity, easily cleaned, deals with large and small scale mixing problemswith large and small scale mixing problems

Disadvantages: Disadvantages: Pressure differences Pressure differences could affect could affect ventilation, difficulty ventilation, difficulty of constructionof construction

Design Alternative - 3Design Alternative - 3Three stationary turbines each oriented in Three stationary turbines each oriented in opposite rotation direction to the one opposite rotation direction to the one preceding itpreceding it

Advantages include simplicity, small size, Advantages include simplicity, small size, ease of dismantling and sanitationease of dismantling and sanitation

Design also minimizes areas of leakage due Design also minimizes areas of leakage due to airtight cylinder being purchasedto airtight cylinder being purchased

Final DesignFinal Design

Plexiglas box with Plexiglas box with air path air path obstructions - obstructions - variation of design 2variation of design 2

Air ports placed on Air ports placed on opposite sides of opposite sides of chamberchamber

12.0 x 12.0 cm 12.0 x 12.0 cm length and width, length and width, 2.0 cm deep2.0 cm deep

Further ResearchFurther Research

Gathered new information from Mayo Gathered new information from Mayo Clinic about behavior of air and mixing in Clinic about behavior of air and mixing in a ventilatora ventilator

Using filter as mixing chamber could Using filter as mixing chamber could interfere with ventilation functioninterfere with ventilation function

Air heater and humidifier could be source Air heater and humidifier could be source of leaks causing fluctuationsof leaks causing fluctuations

Given a prototype design of mixing Given a prototype design of mixing chamber found to be most effective by chamber found to be most effective by Mayo ClinicMayo Clinic

TestingTestingTested Mayo Clinic chamber, filter Tested Mayo Clinic chamber, filter attachments and client’s chamberattachments and client’s chamberSeveral variables were testedSeveral variables were tested

-Ventilators – Servo 300a vs. Servo-I-Ventilators – Servo 300a vs. Servo-I-Several ventilation modes-Several ventilation modes-Artificial lung vs. test patient (group -Artificial lung vs. test patient (group

member)member)-With or without humidifier-With or without humidifier-Position of chamber within line of -Position of chamber within line of

ventilation ventilation tubing tubing Tested interference of chamber with Tested interference of chamber with ventilation functionventilation function

ResultsResultsNone of chambers affected ventilation functionNone of chambers affected ventilation function

Mayo Clinic mixing chamber most effective, FIOMayo Clinic mixing chamber most effective, FIO22 fluctuation <0.1%fluctuation <0.1%Client’s mixing chamber second most effective (+-0.2%)Client’s mixing chamber second most effective (+-0.2%)Filter least effective (+-1.0%)Filter least effective (+-1.0%)Newer ventilator, Servo-i, produced smaller Newer ventilator, Servo-i, produced smaller fluctuations in FIOfluctuations in FIO22 Pressure regulated ventilation modes created the most Pressure regulated ventilation modes created the most fluctuation in FIOfluctuation in FIO22 values for all chambers values for all chambers

Humidifier had little to no affect on consistency of FIOHumidifier had little to no affect on consistency of FIO22, , not causing leaks in systemnot causing leaks in systemPosition of chamber made little to no differencePosition of chamber made little to no difference

Final Design SpecificationsFinal Design Specifications

Modeled in proportion to Mayo Clinic Modeled in proportion to Mayo Clinic prototype, scaled down to meet client’s prototype, scaled down to meet client’s requestrequest

Input and outlet ports placed on opposite Input and outlet ports placed on opposite sides of chamber for easier attachment sides of chamber for easier attachment and integration into tubing circuitand integration into tubing circuit

Chamber lid clamps down, creating Chamber lid clamps down, creating airtight seal against rest of chamber airtight seal against rest of chamber with siliconewith silicone

System DiagramSystem Diagram

Ethical IssuesEthical Issues

Effective testing should be done with Effective testing should be done with critically ill patientscritically ill patients

Can be tested on several healthy Can be tested on several healthy people before use on the critically illpeople before use on the critically ill

If risks to patient found, must be If risks to patient found, must be weighed against benefits to patientweighed against benefits to patient

Protocol need for review prior to Protocol need for review prior to testing on patientstesting on patients

Future WorksFuture Works

Test effectiveness of various lid Test effectiveness of various lid clamps and other air tight sealsclamps and other air tight sealsTesting our 1/3 scale model with the Testing our 1/3 scale model with the client’s ventilator and equipmentclient’s ventilator and equipmentContacting client’s company to Contacting client’s company to manufacture our designmanufacture our designResearching other techniques and Researching other techniques and materials for manufacturing to create materials for manufacturing to create most durable and air tight junctions most durable and air tight junctions of Plexiglasof Plexiglas

ReferencesReferences

1.1. Disease Management with Gas Exchange Disease Management with Gas Exchange. . Medical Graphics Medical Graphics Corporation. 2002.Corporation. 2002.

2. Harris, C.L. “Weaning With Indirect 2. Harris, C.L. “Weaning With Indirect Calorimetry.” Calorimetry.” Clinical WindowClinical Window. 2003(12).. 2003(12).

3. “American Association of Respiratory Care 3. “American Association of Respiratory Care Clinical Clinical Practice Guideline.” Practice Guideline.”

Respiratory Care Journal.Respiratory Care Journal. 1994:39(12):1170-75. 1994:39(12):1170-75.

4. Smart Measurement. 2002. Fluid 4. Smart Measurement. 2002. Fluid Mechanics: Overview Mechanics: Overview [Online] [Online] http://www.efunda.com/formulae/smc_fluidhttp://www.efunda.com/formulae/smc_fluids/ovs/ov erview.cfm.erview.cfm.