Figure 7. (A) Increasing concentrations of fentanyl reduced the propofol concentration at which 50% of patients did not respond somatically to abdominal wall retraction (Cp50ret). [white circle]= negative somatic response;[black circle]= positive somatic response. The solid line shows the interaction of propofol and fentanyl concentration at which 50% of patients did not respond somatically. (B) Increasing concentrations of fentanyl reduced the propofol concentration at which 50% of patients did not respond hemodynamically to abdominal wall retraction. [white circle]= negative hemodynamic response (<15% sBP increase from the presurgical baselines);[black circle]= positive hemodynamic response (> 15% systolic blood pressure [sBP] increase from the presurgical baseline). The dashed lines show the interaction of propofol and fentanyl concentrations at which 50% of patients did not respond hemodynamically at 10%, 15%, and 30% sBP increases from presurgical baseline values.