Figure 3. Individual MACISOvalues obtained at individual plasma fentanyl concentrations for all pigs receiving fentanyl. Zero plasma fentanyl concentrations correspond to the baseline MACISOdeterminations for these pigs. Regression equation was y = 2.0 - 0.01x, r sup 2 = -0.59, and was statistically significant (P less or equal to 0.01).