Anesthetic Recovery Following a Midazolam-Containing Co-Induction Protocol in Horses Undergoing Total Intravenous Anesthesia.

Overview

• This study compared two anesthetic induction protocols in horses undergoing total intravenous anesthesia to assess their effects on anesthetic induction quality, recovery quality, total recovery time, and the number of attempts required for the horse to stand up after anesthesia.
• One protocol included midazolam combined with xylazine and ketamine (XCM), while the other used xylazine and ketamine alone (XC).

Introduction and Research Objective

• Anesthetic recovery in horses, especially under field conditions, is a critical and potentially risky period where quality of recovery is vital to avoid injuries or complications.
• Different anesthetic induction protocols could influence the horse’s recovery, affecting how smoothly and quickly the animal wakes and stands up post-anesthesia.
• The study aimed to compare two induction protocols:
  • XC: Xylazine (1 mg/kg) + Ketamine (2 mg/kg)
  • XCM: Xylazine (0.5 mg/kg) + Ketamine (2 mg/kg) + Midazolam (0.1 mg/kg)
• They specifically looked at the following outcomes during total intravenous anesthesia (TIVA):
  • Quality of anesthetic induction
  • Quality of recovery
  • Total recovery time
  • Number of attempts to successfully stand

Methods

• Subjects: Twelve healthy male horses older than two years.
• Random assignment to one of two groups:
  • XC group received xylazine and ketamine only.
  • XCM group received a lower dose of xylazine, the same ketamine dose, plus midazolam.
• Anesthesia maintenance involved continuous infusions of guaifenesin, ketamine, and xylazine for both groups.
• Measurements:
  • Induction quality scored on a defined scale.
  • Recovery quality evaluated both descriptively and with a quantitative scoring system.
  • Total recovery time measured (in minutes).
  • Count of attempts the horse made before successfully standing.

Results

• Induction Quality:
  • Median induction scores were similar between XC (3.5; range 1-4) and XCM (3.5; range 2-5) protocols (P=0.61), indicating no significant difference in how smoothly anesthesia was induced.
• Total Recovery Time:
  • No significant difference was observed in recovery duration:
    • XC: 80.3 ± 15.5 minutes
    • XCM: 80.2 ± 20.5 minutes
    • (P=0.98)
• Recovery Quality:
  • XCM group showed significantly poorer recovery compared to XC:
    • Descriptive scale median values: 2.5 (range 2-4) for XCM vs. 1 (range 1-1) for XC (P=0.003)
    • Quantitative scale means: 40.3 ± 11.5 for XCM vs. 19.0 ± 3.2 for XC (P=0.002)
• Attempts to Stand:
  • Horses in the XCM group required more attempts to successfully stand:
    • Median attempts: 2 (range 1-4) for XCM vs. 1 (range 1-1) for XC (P=0.03)

Conclusions and Implications

• The inclusion of midazolam in the anesthetic induction protocol (XCM) led to poorer quality recovery and increased difficulty for horses to stand after anesthesia, even though induction quality and total recovery time did not differ from the non-midazolam protocol (XC).
• This suggests that midazolam, at the dose tested, may negatively impact recovery quality in horses undergoing TIVA under field conditions.
• Practitioners should be cautious when using midazolam as part of co-induction in horses due to the potential for poorer recovery outcomes and the need for more assistance during recovery.
• Further studies may be warranted to explore different dosing strategies or alternatives to improve recovery quality without compromising induction smoothness.