Fig. 1.  The cumulative fentanyl dose (μg/kg) for 3 days after surgery. F group = fentanyl group; F–P group = fentanyl–acetaminophen group. The cumulative dose of fentanyl at 1, 6, 12, 24, 36, 48, 60, and 72 h after surgery was significantly lower in the F–P group than in the fentanyl group. *P < 0.05 compared with the F–P group.