Fig. 3. Respiratory rate, arterial carbon dioxide partial pressure (Paco2), tidal volume, and respiratory system compliance in the 3 groups over the course of the study. Paco2(P < 0.0001), tidal volume (P < 0.02), and respiratory system compliance (P < 0.0001) had significant group-versus -time interactions:P < 0.05 versus *control, ‡Pflex, #RM, and †30 min.