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Reduction in halothane MAC: comparison of morphine and alfentanil
Abstract:
The anesthetic potency and effectiveness of alfentanil and morphine were established by determining the effects of increasing drug doses on the alveolar anesthetic requirement of halothane to maintain a constant anesthetic (MAC) level. Six selected doses of alfentanil and four of morphine were administered to groups of mechanically ventilated rats anesthetized with halothane. Alfentanil was given as a loading dose followed by an intravenous infusion of 0.01-100 micrograms X kg-1 X min-1, and morphine was administered as a subcutaneous dose of 4-20 mg/kg. The reduction in halothane requirement after morphine was biphasic, with a rapid linear increase occurring up to an 8 mg/kg subcutaneous dose, followed by a further, slower reduction in halothane requirement after doses of 8-20 mg/kg. At a 20 mg/kg dose, the halothane MAC was reduced approximately 84%. With alfentanil, a curvilinear reduction in halothane MAC occurred up to an alfentanil dose of 15 micrograms X kg-1 X min-1, where a 48% reduction was found. Larger doses produced severe truncal, chest wall, and abdominal rigidity, precluding adequate ventilation and the determination of MAC.
Insights
Morphine significantly reduced halothane MAC in rats, with higher doses yielding greater reductions. Alfentanil also reduced halothane MAC but caused rigidity at higher doses, limiting its effectiveness.
Area of Science:
- Anesthesiology
- Pharmacology
- Veterinary Medicine
Background:
- Anesthetic potency is crucial for safe surgical procedures.
- Opioids like morphine and alfentanil are used for pain management and anesthesia.
- Understanding their interaction with other anesthetics is vital for clinical practice.
Purpose of the Study:
- To compare the anesthetic potency of alfentanil and morphine.
- To determine the dose-dependent effects of these opioids on halothane MAC.
- To evaluate their effectiveness in reducing the requirement for a volatile anesthetic.
Main Methods:
- Mechanically ventilated rats anesthetized with halothane were used.
- Six doses of alfentanil (intravenous infusion) and four doses of morphine (subcutaneous) were administered.
- The reduction in the minimum alveolar concentration (MAC) of halothane was measured to assess anesthetic potency.
Main Results:
- Morphine demonstrated a biphasic dose-response, reducing halothane MAC by up to 84% at 20 mg/kg.
- Alfentanil showed a curvilinear reduction in halothane MAC, reaching 48% at 15 µg/kg/min.
- Higher doses of alfentanil induced severe muscle rigidity, preventing further MAC determination.
Conclusions:
- Morphine is a potent agent for reducing halothane MAC in rats.
- Alfentanil's effectiveness is limited by dose-dependent muscle rigidity.
- These findings have implications for opioid selection in anesthesia.