Measuring End-Tidal CO2 During Intentional Rebreathing

Abstract

In Response: The aim of our study was to assess the effect of CO2 on the lower esophageal sphincter pressure without increasing pulmonary pressures [1]. This was accomplished by the addition of 40 cm of dead space at the Y-piece, and PETCO (2) was used as a measure of PaCO2. Capnography is a noninvasive technique for continuous monitoring of PETCO2. This technique assumes that PETCO2 is equal to PaCO2; the normal gradient in adults is about 1-3 mm Hg [2]. Large PaCO2-PETCO2 differences are commonly observed during pediatric capnography due to low tidal volume-to-equipment dead space ratios, rapid respiratory rates, and high fresh gas flows [3]. These conditions were not present in our study, since pigs were ventilated using a tidal volume of 300-400 mL and a respiratory rate of 14-18 breaths/min. In addition, a special device was positioned at the proximal connector of the endotracheal tube that allowed concomittent recording of pressures and sampling for PETCO2. This device was not removed at the time when dead space was added. Under these conditions, although PaCO2 was not directly measured, we can assume that PETCO2 is a reliable estimation of PaCO2 values [4]. D. Chassard J. P. Tournadre Anesthesie Reanimation Hopital de l'Hotel Dieu Lyon, France