The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

COMPARISON OF MICROSTREAM AND MAINSTREAM CAPNOGRAPHY WITH ARTERIAL CO2 IN NEONATES

Kathleen Deakins RRT-NPS, John Dickson RRT-NPS, Ricardo Rodriguez MD, Michael Anderson MD, Robert L. Chatburn RRT-NPS, FAARC, University Hospitals of Cleveland, OH

Introduction: End-tidal carbon dioxide (PETCO2) is commonly monitored as an indicator of ventilation. Some published studies have shown good correlation between PETCO2 and PaCO2 in low birthweight infants with Respiratory Distress Syndrome [An Esp Pediatr 1997 (2): 171-180]. Microstream sampling technology has been marketed as requiring smaller, lower dead space adaptors and smaller sampling sizes when compared to conventional mainstream sampling. The purpose of this study was to test the hypothesis that microstream sampling of PET CO2 is a more accurate estimate of PaCO2 than mainstream sampling in low birthweight infants and that the end tidal-arterial PCO2 difference is related to respiratory rate and/or weight.

Methods: A convenience sample of infants in the NICU or PICU weighing 559-3000 grams with artificial airways and arterial lines participated in this study. A microstream sampling adapter (Microcap, Oridion Capnography) was connected to the endotracheal tube for a minimum period of five minutes prior to sampling an arterial blood gas. A PETCO2 reading was obtained and the respiratory rate was counted while an arterial blood gas was drawn. The procedure was repeated on the same patient using a mainstream sampling adapter (Spacelabs) when a subsequent blood gas was indicated. The order of adapter type usage was randomized. Data collected included age, weight, diagnosis, respiratory rate and PETCO2 and PaCO2 values using both technologies. The Mann-Whitney Rank Sum Test was used to compare median values for PETCO2 - PaCO2 difference. The correlation between PETCO2 - PaCO2 difference and either weight or respiratory rate was evaluated with Pearson's Product Moment Correlation Coefficient. Significance was set at p = 0.05.

Results: 55 infants entered the study. Both end tidal sampling techniques underestimated arterial PCO2. The median PETCO2 - PaCO2 difference for the Spacelabs mainstream sampling adapter was significantly less than the difference for the Microcap microstream sampling adapter (-8 torr versus -13 torr, p = 0.001). There was no significant correlation between PETCO2 - PaCO2 difference and either birth weight or respiratory rate for either sampling technology. This finding held true even when the data were restricted to infants weighing less than 1,100 grams.



Conclusions: Mainstream PETCO2 sampling was a more accurate estimator of PaCO2 than microstream sampling in this population of neonates. Errors in estimating PaCO2 do not appear to be related to either birth weight or respiratory rate.

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