David Walding

Resting energy expenditure and nitrogen balance in critically ill pediatric patients on mechanical ventilation.

Nutritional support is important in critically ill patients, with variable energy and nitrogen requirements (e.g., sepsis, trauma, postsurgical state) in this population. This study investigates how age, severity of illness, and mechanical ventilation are related to resting energy expenditure (REE) and nitrogen balance. Nineteen critically ill children (mean age, 8 +/- 6 [SD] y and range 0.4-17.0 y) receiving total parenteral nutrition (TPN) were enrolled. We used indirect calorimetry to measure REE. Expected energy requirements (EER) were obtained from Talbot tables. Pediatric Risk of Mortality (PRISM) and Therapeutic Intervention Scoring System (TISS) score were calculated. Total urinary nitrogen was measured using the Kjeldahl method. PRISM and TISS scores were 9 +/- 5 and 31 +/- 6 points, respectively. REE was 62 +/- 25 kcal.kg-1.d-1, EER was 42 +/- 11 kcal.kg-1. d-1, and caloric intake was 49 +/- 22 kcal.kg-1.d-1. Nitrogen intake was 279 +/- 125 mg.kg-1.d-1, total urinary nitrogen was 324 +/- 133 mg.kg-1.d-1, and nitrogen balance was -120 +/- 153 mg.kg-1.d-1. The protein requirement in this population was approximately 2.8 g.kg-1.d-1. These critically ill children were hypermetabolic, with REE 48% higher (20 kcal.kg-1.d-1) than expected. Nitrogen balance significantly correlated with caloric and protein intake, urinary nitrogen, and age, but not with severity of illness scores or ventilatory parameters.

Nutrition Requirements in Patients with Toxic Epidermal Necrolysis

Patients with toxic epidermal necrolysis, a severe, exfoliative skin disorder, have clinical features similar to those of partial-thickness burn patients. The literature suggests that they also have similar nutritional requirements. We report two patients diagnosed with toxic epidermal necrolysis on mechanical ventilation, in whom resting energy expenditure and respiratory quotient were measured by indirect calorimetry. The patients were treated using standard burn protocols. Nitrogen balance was calculated by measuring total urinary nitrogen in urine samples obtained over 24 hours. These measurements were done while the patients were on mechanical ventilation and receiving total parenteral nutrition. As in burn patients, early in their course the two patients had resting energy expenditure values twice that predicted. After 12 days of hospitalization, nitrogen balance was negative in patient 1 and positive in patient 2. Energy and protein requirements appear to have been related to the amount of body surface affected.

Neonatal Transport Incubator: Vibration Identification, Ranking, and Attenuation—A Novel Approach to Patient Tray Stabilization

The Texas Children’s Hospital (TCH) Biomedical Engineering Department, in conjunction with the Kangaroo Crew and Nursing departments, strive to increase the quality of patient care through research and innovation. The TCH has been engaged in a comprehensive research campaign to characterize the type of mechanical forces that the neonate would experience in a transport incubator on a typical neonatal transport. After several years of measuring vibration forces during in-hospital (J Clin Eng. 2008:74-77), ambulance, and air transportation modalities, it was determined that our core need was to conduct forced vibration tests of the transport incubator in a simulated environment using a large shaker table (Space Act Agreement no. SAA-EA-09-006 with TCH Biomedical Engineering, TCH contract no. NAS-04539, National Aeronautics and Space Administration, Washington, DC). Also, to identify the natural frequencies, mode shapes, and damping ratios of the neonatal incubator system, experimental modal analysis (EMA) and operating deflection shape analysis were performed. In 2009, TCH was awarded a Space Act Agreement with National Aeronautics and Space Administration Johnson Space Center to analyze the transport incubator at Johnson Space Center’s Vibration and Acoustic Test Facility (Houston, Texas). Over the next 2 years (during nonpeak operational times), random and sine sweep excitation tests, EMA, and operating deflection shape analysis tests were performed to aid in the understanding of the dynamics of the TCH incubator and its modal properties (Space Act Agreement no. SAA-EA-09-006 with TCH Biomedical Engineering, TCH contract no. NAS-04539, National Aeronautics and Space Administration, Washington, DC). Sine-sweep and EMA test results point to dominant patient tray natural frequencies of 8 to 10 Hz and a vibration magnification factor of 1.60 and 3.75 at patient tray and at neonatal mannequin, respectively. The EMA results showed the tray first mode (drum mode) with maximum deflection at the tray center. Our goal was to look at ways to stabilize the patient tray and measure vibration attenuation using a common inexpensive measurement device (iPhone 5). The model 20H International Biomedical transport incubator was fitted with an accelerometer at patient tray center and the incubator was pushed over several floor transitions during 4 trials for modified and unmodified incubator. When the patient tray was tethered to a rigid frame, vibration attenuation for Z_min, Z_max, and Z_rms was 78%, 193%, and 65%, respectively.

Design of a virtual instrument to correlate tagged exhaled nitric oxide breaths and pulmonary mechanics measurements for ventilated pediatric patients

The Biomedical Engineering Department at Texas Childrens Hospital developed a portable virtual instrument using object oriented programming to combine an existing nitric oxide analyzer with a respiratory profile monitor. Pulmonary mechanics and exhaled nitric oxide (eNO) measurements for pre and post cardiopulmonary bypass procedures (CPB) are of primary concern to pediatric physicians. Patients with normal lung function prior to CPB demonstrate a transient gas exchange abnormality and some develop acute lung injury. The relationship of pulmonary mechanics to changes in eNO is described by opposing views (Pearl JM, 2000 and Morita K, 1996). As such, quantification of lung mechanics is important and can lead to better understanding of the mechanism for eNO changes and its clinical management. The goals of this project were twofold. First, to provide portable means for accurate measurements of eNO and pulmonary mechanics in the operating rooms and critical care environments. Second, to synchronize pulmonary mechanics data on a breath-by-breath basis with eNO tagged breaths. Validation procedure for respiratory profile monitor was performed and the average error (±SD) for compliance (ranges 2–8 ml/cm H2O) and volume measurements were 3.49% ± .11 and 1.99% ± .34 respectively. A portable system that met space and environment requirements for eNO is described as well as its ability to capture serial data streams from each device and correlation of nitric oxide analyzer tagged breaths with those of the respiratory profile monitor.

Development of a nutritional assessment system for ventilated pediatric patients

Summary form only given. Accurately measuring nutritional assessment is particularly important in the management of patients at the intensive care setting. The efficacy of mechanical ventilation is dependent upon, physiological conditions and gas flow, volume, inspired oxygen concentration and end expiratory pressure (PEEP). Lung work measurements are critical, thus, the vital role that Clinical Engineering plays in both evaluating existing technology and validation of new one in matching capability with needs. The metabolic system was designed utilizing a mass spectrometer (Perkin Elmer MGA 1100) for gas analysis, a screen type pneumotachograph (Hans-Rudolph) for volume measurements, and a computer (Inspiron 7500) with software (Consentius Technologies) to calculate the metabolic parameters. Validation results for VO/sub 2/ shown as relative error % were: Douglas Bag was -0.4 /spl plusmn/ 1.5 and the in-vitro infusion technique (CO/sub 2/ & N/sub 2/) was 2 /spl plusmn/ 1.8. The accurate measurement of gas exchange in the clinical setting requires consideration of many variables, with in vitro and in vivo validation. The results of these tests demonstrate that the metabolic system developed is useful in measuring metabolic variables in critical care setting.

Substrate utilization in critically ill children |[dagger]| 188

Background:Critically ill patients usually are catabolic, as assessed by nitrogen balance (NB) studies. When indirect calorimetry (IC) and total urinary nitrogen (TUN) are done simultaneously; carbohydrate (CHO), protein (PROT), and fat utilization can be calculated. Methods: This study measured NB and substrate utilization in 20 critically ill children(mean PRISM and TISS scores of 8±5 and 30±7 respectively) on mechanical ventilation (MV), in relation to their resting energy expenditure(REE) and caloric intake (Cal In.). All patients were receiving TPN or enteral nutrition when evaluated. REE was measured by IC (mass spectrometry) and TUN by the Kjeldahl method. Expected energy requirements (EER) were obtained from Talbots tables. REE/EER index > 1.1 defined a hypermetabolic state. Substrate utilization rates were calculated using the Consolazio formulas. Studies were done at the time of the first evaluation and repeated (n=48). The correlation was measured by Pearsons correlation coefficient. Values are mean±SD.

A computerized method for environmental gas analysis in the hospital setting

Due to the obligation to employee health and OSHAs ever decreasing permissible exposure limits (PELS) for hazardous gases, it has become imperative that hospitals institute an effective and accurate method for gas analysis while adhering to time and budget restraints. Some of the most frequently monitored gases in the hospital environment are ethylene oxide (EtO), nitrous oxide, halothane, xylene, and formaldehyde. With toxic gases such as EtO, it is critical to obtain consistent, fast, and accurate gas levels. With little expense, one can interface the analog output of most analyzers with a small computer to not only increase reading accuracy for part per million (p.p.m.) gas levels but also provide multigas analysis and archiving of data for and report documentation.<<ETX>>