Quantitative analysis of end-tidal carbon dioxide during mechanical and spontaneous ventilation in infants and young children

Capnography provides a substitute for monitoring of arterial carbon dioxide tension (PCO2). We performed a prospective study to evaluate a new applica tion of capnography, using quantitative curve analysis in the pediatric ICU . Twenty-five infants and children admitted to the pediatric ICU after card iovascular surgery for congenital heart diseases were included in the study . Capnographic curves were recorded during 3 phases of mechanical and spont aneous ventilation: phase 1, immediate postoperative period; phase 3, preex tubation period; and phase 2, period between phases I and 3. Each recording included 17 sec of capnographic tracings from consecutive spontaneous and/ or ventilator-driven breaths. Quantitative curve analysis was made to define parameters including peak va lue of exhaled PCO2 (P), mean rate of rise Of PCO2 (R), and area under each capnographic curve (A). Qualitative inspection of the wave contour showed no obvious difference in phase 3 during spontaneous and mechanically assist ed ventilator breaths. However, an obvious difference existed between spont aneous and mechanically assisted breaths in phase 2. For each parameter (P, R, and A), there was a significant difference in phases 2 and 3 from spont aneous breaths. However, there was no significant difference in phases 2 an d 3 from ventilator-assisted breaths. We further calculated the ratio of pa rameters of spontaneous breaths (S) and ventilator-assisted breaths (V) in phase 2 and phase 3. The ratio of SN for P, R, and A showed significant dif ferences between phase 2 and phase 3. We conclude that quantitative analysis of exhaled end-tidal PCO2 curves rev ealed significant changes of specific parameters during the transition from the ventilator-dependent state to the spontaneously breathing ventilator-i ndependent state. This new approach provides a new way to estimate respirat ory status in infants and children receiving ventilator therapy. Through qu antitative capnographic curve analysis, if P, R, and A from spontaneous bre aths approached those of ventilator-assisted breaths, patients have resumed reasonable pulmonary mechanics, and extubation may then be considered. (C) 2001 Wiley-Liss,Inc.