The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

INFLUENCE OF SAMPLING SITE ON END TIDAL CARBON DIOXIDE LEVELS (PETCO2) DURING NON-INVASIVE POSITIVE PRESSURE VENTILATION (NPPV)

Arthur Taft1, Jonathan Waugh2, Glenn Pippin3; 1Department of Respiratory Therapy, Medical College of Georgia, Augusta, GA; 2Respiratory Therapy Program, University of Alabama at Birmingham, Birmingham, AL; 3Department of Respiratory Therapy, Shelton State Community College, Tuscaloosa, AL

INTRODUCTION: Capnography use in intubated patients is well established. However, NPPV has become a popular method of ventilating selected patients. The variety of patient interfaces available and lack of data for use with capnography make it unclear how to best utilize capnography during NPPV. The purpose of this study was to identify how different sampling sites influence PETCO2 during NPPV. METHODS and MATERIALS: This study was performed at the University of Alabama at Birmingham (UAB) and the Medical College of Georgia (MCG), was approved by each IRB, and informed consent was obtained. Forty healthy volunteers (20 at each site) received NPPV (VIVO 40®, Breas) at three levels of ventilation (CPAP +5 cm H2O, BiPAP +10/+5 cm H2O, and BiPAP +20/+5 cm H2O) using three different masks (FlexiFit 431, Fisher & Paykel (FP); Mirage Quattro, ResMed (RM); and PerformaTrak, Respironics (RP)). The order in which ventilating pressures and mask types were studied was randomly assigned. PETCO2 was measured (Capnostream™ 20, Oridion) simultaneously at the oral/nasal opening (ONO) and at the mask port (MP). PETCO2, was obtained for 6 min prior to initiating NPPV and afterwards at one minute intervals for 6 min for each setting and mask. Statistical analysis used t-tests to compare pooled data from UAB and MCG. Multivariate Repeated-Measures ANOVA was used to compare the effects of 1) level of ventilation, 2) mask type, and 3) sampling site on PETCO2 values. Pair-wise comparisons were made using the Bonferroni-Sidak test. Data was compared to baseline values using Pearson’s Correlation Coefficient and paired t-tests. RESULTS: There were no statistical differences between data obtained at UAB and MCG (p=0.143). PETCO2 values were different depending upon mask type (FP = 18.0±3.07 mmHg [mean±SD], RM = 25.3±4.42 mmHg, RP = 28.7±4.38 mmHg; p<0.001), level of ventilation (CPAP +5 = 24.7±3.98 mmHg, BiPAP 10/5 = 24.3±3.90 mmHg, BiPAP 20/5 = 23.0±3.50 mmHg; p<0.001), and measurement site (ONO = 30.6±5.73 mmHg, MP = 17.4±3.24 mmHg; p<0.001). When comparing outcome data to baseline, for all masks and levels of ventilation, correlations were strongest with measurements made at ONO as opposed to measurements made at MP. CONCLUSIONS: When using capnography to monitor patients receiving NPPV through a full face mask, measurements should be made at the oral-nasal opening rather than the mask port. If using the mask port, caution must be used in interpreting PETCO2. Sponsored Research - This project was supported by unrestricted educational grants from Oridion Capnography Inc. Equipment was either loaned or donated by the individual manufacturer.

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