title: Non-invasive accurate measurement of arterial PCO2 in a pediatric animal model.
abstract: The PCO2 in arterial blood (PaCO2) is a good parameter for monitoring ventilation and acid-base changes in ventilated patients, but its measurement is invasive and difficult to obtain in small children. Attempts have been made to use the partial pressure of CO2 in end-tidal gas (PETCO2), as a noninvasive surrogate for PaCO2. Studies have revealed that, unfortunately, the differences between PETCO2 and PaCO2 are too variable to be clinically useful. We hypothesized that end-inspiratory rebreathing, previously shown to equalize PETCO2 and PaCO2 in spontaneously breathing humans, would also be effective with positive pressure ventilation. Eight newborn Yorkshire pigs were mechanically ventilated via a partial rebreathing circuit to implement end-inspiratory rebreathing. Arterial blood was sampled and tested for PaCO2. A variety of alveolar ventilations resulting in different combinations of end-tidal PCO2 (30-50 mmHg) and PO2 (35-500 mmHg) were tested for differences between PETCO2 and PaCO2 (PET-aCO2). The PET-aCO2 of all samples was (mean ± 1.96 SD) 0.4 ± 2.7 mmHg. Our study demonstrates that, in ventilated juvenile animals, end-inspiratory rebreathing maintains PET-aCO2 to what would be a clinically useful range. If verified clinically, this approach could open the way for non-invasive monitoring of arterial PCO2 in critically ill patients.
authors.affiliation: Division of Neurosurgery, University Health Network, Toronto, ON, Canada. jornfierstra@gmail.com
authors.forename: Jorn
authors.initials: J
authors.lastname: Fierstra
authors.forename: Jeff D
authors.initials: JD
authors.lastname: Winter
authors.forename: Matthew
authors.initials: M
authors.lastname: Machina
authors.forename: Jelena
authors.initials: J
authors.lastname: Lukovic
authors.forename: James
authors.initials: J
authors.lastname: Duffin
authors.forename: Andrea
authors.initials: A
authors.lastname: Kassner
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fisher
mesh_terms: D000758:Anesthesia / Q000379:methods; D000818:Animals; D000831:Animals, Newborn; D062186:Arterial Pressure; D001158:Arteries / Q000502:physiology; D001784:Blood Gas Analysis / Q000295:instrumentation / Q000379:methods*; D002245:Carbon Dioxide / Q000097:blood / Q000737:chemistry*; D023421:Models, Animal; D016343:Monitoring, Intraoperative / Q000379:methods; D010313:Partial Pressure; D010372:Pediatrics / Q000379:methods; D011312:Pressure; D012119:Respiration; D012121:Respiration, Artificial / Q000379:methods*; D012815:Signal Processing, Computer-Assisted; D013552:Swine
chemical_list: D002245:Carbon Dioxide