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Korean Journal of Anesthesiology 2002;42(6):715-721.
DOI: https://doi.org/10.4097/kjae.2002.42.6.715   
Equianalgesic Concentration of Fentanyl Comparable to 67% N2O during Propofol Based General Anesthesia.
Ho Yeong Kil, Hong Seong Yoo, Hyun Hee Ahn, Yoon Sook Lee, Hyun Hwa Lee
Department of Anesthesiology, College of Medicine, Hallym University, Seoul, Korea. kilhy@www.hallym.or.kr
When using a target controlled infusion (TCI) of propofol, combination with N2O or fentanyl as an analgesic adjuvant is common in clinical practice. In a previous study, a minimal steady state plasma concentration necessary to prevent a response in 50% of the patients following a skin incision (Cp50i) for propofol was reduced from 6ng/ml to 4.5ng/ml with 67% nitrous oxide/oxygen compared to air/oxygen. The goal of this study was to quantify the effect site concentration of fentanyl required to replace 67% N2O at a propofol effect site target concentration of 4.5ng/ml.
Forty six ASA class I or II adult patients scheduled for lower extremity surgery were randomly allocated to one of three groups according to assigned effect site concentration of fentanyl. Group 1, n = 15; 0.5 ng/ml, Group 2, n = 15; 1.0 ng/ml, Group 3, n = 15; 1.5 ng/ml. Patients received propofol with target concentration 4.5ng/ml and predetermined target concentration of fentanyl in three groups. A laryngeal mask airway was placed after anesthesia induction and all patients were controlled ventilation with 67% air/33% oxygen. The response to the skin incision was observed and the patients categorized as movers or non-movers according to Eger's criteria. Cp50i for fentanyl was evaluated using nonlinear regression analysis.
Non-movers to skin incision was 20%, 43.7%, 73.7% in groups 1 3 respectively. Cp50i for fentanyl combined with propofol 4.5ng/ml was 1.08 ng/ml.
We concluded that the MAC for 67% N2O is equivalent to an effect site target fentanyl concentration of 1.08 ng/ml in terms of no movement to skin incision.
Key Words: Equianalgesic concentration; fentanyl; N2O


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