Figure 31-16 Plasma concentration of fentanyl at the time of certain clinical stimuli, along with the presence or absence of hypertension. During sternotomy and aortic dissection, even high plasma concentrations of fentanyl (>15 ng/mL) do not always prevent hypertension. (Redrawn with modification from Wynands JE, Wong P, Townsend GE, et al: Narcotic requirements for intravenous anesthesia. Anesth Analg 63:101, 1984.)