Blood concentrations of remifentanil during and after infusion in horses anesthetized with isoflurane and dexmedetomidine.

The research focused on understanding the concentration of remifentanil, a potent synthetic opioid analgesic drug, in the blood of anesthetized horses after an hour-long infusion of remifentanil and dexmedetomidine, another sedative. The study utilized six adult horses and measured their remifentanil concentration using high-performance liquid chromatography and tandem mass spectrometry.

Research Methodology

• The study involved six adult mixed breed horses. Their mean body weight was 507±61kg and the mean age was approximately 14 years.
• The process was initiated with the sedation of horses using xylazine. The anesthesia was induced using a mixture of ketamine and diazepam, while the maintenance of anesthesia was achieved with isoflurane in oxygen.
• After setting up instrumentation, which took 52±7 minutes, an infusion of dexmedetomidine and remifentanil was administered.
• The drug infusions were introduced into the left jugular vein. Blood samples (4 mL) were drawn from the right jugular vein at predetermined intervals before and during remifentanil infusion.
• Post the infusion, while the horse was recovering, blood samples were taken from the left jugular vein. The blood was gathered into tubes, treated with sodium heparin and citric acid, flash frozen in liquid nitrogen, and stored at -80°C for analysis.

Results and Key Findings

• The researchers used high-performance liquid chromatography and tandem mass spectrometry to measure the remifentanil concentration in the blood.
• The average peak concentration of remifentanil was established to be 7.14ηgmL(-1), observed 50 minutes after the start of the infusion.
• The mean volume of distribution was found to be 268±40mLkg(-1), while the mean half-life was determined to be approximately 12.8 minutes.
• The blood concentration decreased to 1ηgmL(-1) roughly 27 minutes after the infusion was terminated.
• The limit of quantification was noted to be 0.2ηgmL(-1).

This study effectively provides key insights on the behaviour of remifentanil in the blood of anesthetized horses, contributing to the existing knowledge around the use of opioids in veterinary anesthesia.