Non-invasive accurate measurement of arterial PCO2 in a pediatric animal model

<p>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 (PetCO(2)), as a noninvasive surrogate for PaCO2. Studies have revealed that, unfortunately, the differences between PetCO(2) and PaCO2 are too variable to be clinically useful. We hypothesized that end-inspiratory rebreathing, previously shown to equalize PetCO(2) 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 PetCO(2) and PaCO2 (Pet-aCO(2)). The Pet-aCO(2) 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-aCO(2) 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.</p>