Capnography provides a substitute for monitoring of arterial carbon dioxide tension (PCO2). We performed a prospective study to evaluate a new application of capnography, using quantitative curve analysis in the pediatric ICU. Twenty-five infants and children admitted to the pediatric ICU after cardiovascular surgery for congenital heart diseases were included in the study. Capnographic curves were recorded during 3 phases of mechanical and spontaneous ventilation: phase 1, immediate postoperative period; phase 3, preextubation period; and phase 2, period between phases 1 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 value 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 assisted ventilator breaths. However, an obvious difference existed between spontaneous 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 spontaneous breaths. However, there was no significant difference in phases 2 and 3 from ventilator-assisted breaths. We further calculated the ratio of parameters 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 differences between phase 2 and phase 3. We conclude that quantitative analysis of exhaled end-tidal PCO2 curves revealed significant changes of specific parameters during the transition from the ventilator-dependent state to the spontaneously breathing ventilator-independent state. This new approach provides a new way to estimate respiratory status in infants and children receiving ventilator therapy. Through quantitative capnographic curve analysis, if P, R, and A from spontaneous breaths approached those of ventilator-assisted breaths, patients have resumed reasonable pulmonary mechanics, and extubation may then be considered.
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