Narcotic requirements for intravenous anesthesia.

Area of Science:

• Anesthesiology
• Cardiovascular Surgery
• Pharmacology

Background:

• Minimum end-tidal alveolar anesthetic concentration (MAC BAR) quantifies volatile anesthetic potency.
• The study aimed to define a similar metric for intravenous opiates like fentanyl.

Purpose of the Study:

• To determine the minimal intraarterial plasma concentration (MIC BAR) of fentanyl inhibiting hypertensive responses to noxious stimuli in 50% of patients undergoing aortocoronary bypass surgery (ACBP).

Main Methods:

• Forty-three ACBP patients received varying fentanyl anesthesia protocols.
• Plasma fentanyl concentrations (PFC) were monitored.
• A 20% increase in systolic blood pressure from baseline defined a hypertensive response.

Main Results:

• A MIC BAR for fentanyl could not be established due to significant variability in PFC among hypertensive patients.
• Most patients with PFC > 20 ng/ml did not become hypertensive.
• Hypertension occurred at various PFC levels, including >30 ng/ml during skin incision.

Conclusions:

• Fentanyl's plasma concentration required to prevent hypertensive responses in ACBP patients is highly variable.
• A definitive MIC BAR for fentanyl in this context could not be identified.