Effects of constant rate infusion of lidocaine and ketamine, with or without morphine, on isoflurane MAC in horses.

The research studies the impact of administering lidocaine and ketamine, with or without morphine, on the minimum alveolar concentration (MAC) of isoflurane in horses. It finds that administering lidocaine and ketamine can decrease isoflurane requirements, but the addition of morphine does not significantly improve this effect or impact recovery.

Research Methodology

• The sample used in this study consisted of six healthy adult horses. These horses underwent three anaesthesia procedures with xylazine, ketamine and isoflurane.
• For the first treatment group, a constant rate infusion (CRI) of lidocaine-ketamine (LK) was administered. For the second group, a CRI of morphine-lidocaine-ketamine (MLK) was given, and the third group received saline (CTL) as a control.
• The loading doses for morphine and lidocaine were 0.15 mg/kg bwt i.v and 2 mg/kg bwt i.v, respectively. These were followed by a CRI of 0.1 mg/kg bwt/h for morphine and 3 mg/kg bwt/h for lidocaine. Ketamine was delivered via CRI at 3 mg/kg bwt/h.
• The anaesthetic-sparing effect of the drug infusions was primarily monitored by changes in MAC. This is considered the standard measure for analgesia in anaesthetic evaluation.
• Furthermore, the quality of the horses’ recovery was assessed using a scoring system, to monitor the effect of the drug combinations on the recovery process.

Research Findings

• Results showed that the mean isoflurane MAC in controls was 1.25 ± 0.14%, while in the LK and MLK groups it was significantly reduced to 0.64 ± 0.20% and 0.59 ± 0.14% respectively. This is a 49% and 53% reduction, respectively. This indicates that lidocaine and ketamine administered via CRI effectively decreases isoflurane requirements in horses.
• Observations also revealed no significant difference in recovery from anaesthesia across the three groups. This suggests that whether administered alone, or in combination with morphine, lidocaine and ketamine do not affect horse recovery negatively.
• Interestingly, the addition of morphine to the lidocaine-ketamine infusion did not provide an additional reduction in isoflurane requirements. This contests the general belief that morphine decreases the MAC in domestic animals.

Conclusion

• This research concludes that the administration of lidocaine and ketamine via a CRI effectively decreases the isoflurane requirements in horses, making the anaesthesia process more efficient.
• However, adding morphine to this combination does not further enhance this anaesthetic-sparing effect nor does it impair the horse’s recovery process.