Effect of different surgical procedures on the accuracy of prediction of the plasma concentration of fentanyl: comparison between mastectomy and laparoscopic prostatectomy

Background The accuracy of simulation-predicted fentanyl concentration in different types of surgical procedure is not fully understood. We wished to estimate the effect of different types of surgical procedure on the accuracy of such simulations. Findings Fifty patients who had undergone elective mastectomy or laparoscopic prostatectomy (American Society of Anesthesiologists physical status = I-II) were enrolled. Anesthesia was maintained throughout surgery with sevoflurane and a bolus infusion of fentanyl. A maintenance infusion was administered with 8 mL/kg/h Ringer's acetate solution from the start of anesthesia to completion of blood sampling. An infusion to compensate for blood loss was administered (one to two volumes of hydroxyethyl starch). A blood sample was drawn every 30 min during anesthesia.We measured the plasma concentration of fentanyl in 358 samples from 50 patients. The plasma concentration of fentanyl was correlated significantly with the simulated predicted fentanyl concentration (r = 0.734, P < 0.01) but 36.0% of all samples had a difference greater than ±0.5 ng/mL. Approximately 0.3 ng/mL of a fixed bias was shown throughout mastectomy. During laparoscopic prostatectomy, the fixed bias gradually became negative from ≈0.3 to -0.3 ng/mL as the sampling stage proceeded. Conclusions The predicted concentration of fentanyl was significantly correlated with the plasma concentration of fentanyl (r = 0.734). However, there were different patterns of a fixed bias between mastectomy and laparoscopic prostatectomy groups. We should pay attention to this tendency among different surgical procedures. Trial registration UMIN000005110.