Fig. 5. Respiratory system compliance (mean ± SD) at time after initiation of retraction and packing of abdominal contents. Baseline measurements decreased to time 0, i.e. , with insertion of retractor and abdominal packs. Covariate analysis − slope of the line for respiratory system compliance over time from time 0 was compared within and between groups. A positive slope with a group × time interaction (G × T) of P = 0.0001 was seen for the variable ventilation (VV) group. The G × T for slope with conventional ventilation (CV) was P = 0.09. Comparison of slopes had a P value of 0.0001.