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Effect of fentanyl and nitrous oxide on the desflurane anesthetic requirement
1Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Abstract:
The minimum alveolar anesthetic concentration (MAC) of desflurane (I-653) was determined when administered with 60% nitrous oxide (N2O) in oxygen after a standardized induction sequence consisting of 0, 3, 6, or 9 micrograms/kg intravenous (IV) fentanyl followed by 3-6 mg/kg IV thiopental and 1.5 mg/kg IV succinylcholine. For comparison, we also determined the isoflurane MAC with 60% N2O in oxygen after an induction dose of 3 micrograms/kg IV fentanyl and similar doses of thiopental and succinylcholine. All patients were undergoing elective surgical procedures. The minimum alveolar anesthetic concentration in patients given isoflurane and 60% N2O with 3 micrograms/kg fentanyl was 0.4%, approximately 20% below previously reported MAC values for isoflurane with 60% N2O alone. The minimum alveolar anesthetic concentration of desflurane with 60% N2O plus 0, 3, 6, and 9 micrograms/kg IV fentanyl was 3.7%, 3.0%, 1.2%, and 0.1%, respectively. Thus, the MAC-lowering effect of 3 micrograms/kg IV fentanyl appears to be similar with both isoflurane and desflurane. Fentanyl, 3-9 micrograms/kg IV, produces dose-dependent decreases in the MAC of desflurane.
Insights
The minimum alveolar anesthetic concentration (MAC) of desflurane and isoflurane was studied with nitrous oxide and varying doses of fentanyl. Fentanyl significantly reduced the MAC of both anesthetics in a dose-dependent manner.
Area of Science:
- Anesthesiology
- Pharmacology
Background:
- The minimum alveolar anesthetic concentration (MAC) quantifies anesthetic potency.
- Nitrous oxide (N2O) is commonly used as an adjunct anesthetic.
- Fentanyl is an opioid analgesic often used during anesthesia.
Purpose of the Study:
- To determine the MAC of desflurane when co-administered with 60% N2O and varying doses of intravenous fentanyl.
- To compare the MAC-lowering effect of fentanyl on desflurane versus isoflurane in the presence of 60% N2O.
Main Methods:
- MAC of desflurane was measured with 60% N2O and 0, 3, 6, or 9 µg/kg IV fentanyl.
- MAC of isoflurane was measured with 60% N2O and 3 µg/kg IV fentanyl.
- Standardized anesthetic induction sequences were used in patients undergoing elective surgery.
Main Results:
- The MAC of isoflurane with 60% N2O and 3 µg/kg fentanyl was 0.4%, lower than previously reported values.
- The MAC of desflurane with 60% N2O decreased from 3.7% (no fentanyl) to 0.1% (9 µg/kg fentanyl).
- Fentanyl demonstrated a dose-dependent MAC-lowering effect for desflurane, similar to its effect on isoflurane.
Conclusions:
- Intravenous fentanyl significantly reduces the MAC of both desflurane and isoflurane when combined with 60% N2O.
- The MAC-lowering effect of 3 µg/kg fentanyl appears comparable between desflurane and isoflurane.
- Higher doses of fentanyl result in greater reductions in desflurane MAC.