Development Of A Nutritional Assessment System For Ventilated Pediatric Patients

Development Of A Nutritional Assessment System For Ventilated

Pediatric Patients

David Walding,1 Yadin David,1 Jorge Coss Bu,2 Larry Jefferson,2

Department of Biomedical Engineering,1 & Critical Care Section,2 Texas Children’s Hospital

Development Of A Nutritional Assessment System

• Clinical Engineering Role

– Clinical Protocol Specifications– Research Available Technologies– System Design and Integration– System Testing and Validation– Ongoing Support and Upgrades


• Why Nutritional Assessment ?

– To Prevent Over/Underfeeding, one must measure the metabolic rate.

– Malnutrition is developed early after admission– Prediction formulas to calculate energy needs are

inaccurate for patients individually– Many Factors alter metabolic rate in critically ill

patients in the ICU.


• Metabolic Measurements

– Metabolic response to stress: Metabolic rate– How is measured: Indirect calorimetry– Energy Expenditure: From measured oxygen

consumption and CO2 production– Methodology:

» Fick Method: Pulmonary artery catheter; invasive» Gas Exchange Method: Metabolic cart; noninvasive


• Available Technologies

– Flow & Volume Measurements» Pneumotach, Turbine, & Heated Wire

– Gas Concentration Measurements» Mass Spec., IR, Paramagnetic & Zirconium

– Mixing Chamber & Breath-by-Breath


• Complications with Ventilated Patients

– Compressible Volumes and Leaks– Partial Pressure and Water Vapor– Fluctuating and High FiO2

– Measurement Response Time– PEEP and Flow-By changes– Small erratic Tidal Volumes


• Selected Technologies

– Mass Spectrometer (Perkin Elmer MGA-1100– Multi-Screen Pneumotac (Hans Rudolph)– Laptop PC (Inspiron 7500)– A/D Card (Computer Boards PCM-DAS16D)– Configurable Software (Consentius Technologies)

TCH Nutritional Assessment System


Why Use a Mass Spec. (MGA 1100)

• Response Time (70 msec) Multi-gas• Partial Pressure (Ratio Summing PCB)• Water Vapor Content (Disregarded, Sum PCB)• Not affected for Pressure Fluctuations

Magnetic-Sector Mass Spectrometry


• Error Reducing Techniques

– Develop Auto-Calibration PCB– Filter Data with Excel Macro– Digital Replay of Data– For Volume & Flow Measurements

» Use Pneumotac Viscosity Correction» STPD Volume Correction» Flow Non-Linearity Auto-Correlation

Auto-Calibration Modification for TCH Metabolic Cart


• Design Phase

– Review Clinical Needs– Outline Measurement Complications– Obtain System Components– Design Cart, Interface Components to PC– Design Modifications & Specifications– Data Report and Spreadsheet Conversion


• System Testing and Validation

– Room Air Spontaneous Breathing» Tissot Gasometer (p < 0.05)» Douglas Bag ( p < 0.005)» Room Calorimeter (p < 0.05)

– High FiO2 and PEEP (With Ventilator)» Infusion Gas Technique


• Room Air Spontaneous Breathing Validation

• Tissot Bag Calorimeter

VO2 -0.9 +/- 1.5 -0.4 +/- 1.5 -0.3 +/- 2.3

VCO2 -0.6 +/- 1.7 -1.1 +/- 1.1 0.8 +/- 2.4

RQ 0.3 +/- 0.9 -0.6 +/- 0.8 1.1 +/- 1.1

Volume -1.3 +/- 0.8 1 +/- 1.8


– High FiO2 and PEEP (With Ventilator)

•

FiO2 VO2 VCO2 RQ PEEP

0.4 1.25 +/- 2 -1.6 +/- 1.2 -2.6 +/- 1.8 50.4 2.02 +/- 1.8 0.81 +/- 0.9 -2.3 +/- 1.7 150.6 0.03 +/- 3.4 -3.8 +/- 1.2 -4.8 +/- 3.3 50.6 0.9 +/- 3 -2.4 +/- 1.1 -4.2 +/- 3 15


• Clinical Engineering Plays an Important Role in the Clinical Setting

• The Validation and Custom Design of Metabolic System Demonstrate it’s Usefulness for Clinical Assessment


•The ICU is a rapidly changing environment. The resources of clinical engineering should not be overlooked when using technology in this area.

Wilder DK, MSEE, CCE. Critical Care Clinics 1995; 9:501

Other Clinical Projects

Remote Metabolic MeasurementRespiratory MechanicsExhaled Nitric OxideBypass Surgery Temperature ChangesBrain Death Assessment

Magnetic-Sector Mass Spectrometry Theory

• The ion optics in the ion-source chamber of a mass spectrometer extract and accelerate ions to a kinetic energy given by:

K.E. = 0.5 mv2 = eV • m = mass of the ion, v = velocity, e = charge of the ion, & V = applied

voltage of the ion optics. • The ions enter the flight tube between the poles of a magnet and are

deflected by the magnetic field, H. Only ions of mass-to-charge ratio that have equal centrifugal and centripetal forces pass through the flight tube:

• mv2 / r = Hev centrifugal = centripetal forces. • Where r is the radius of curvature of the ion path: r= mv / eH

Health & Medicine

Development Of A Nutritional Assessment System For Ventilated Pediatric Patients