Comparison of cervical epidural morphine with intravenous morphine administration on antinociception in adult horses using thermal threshold testing.

The research study compared the effectiveness of pain relief (antinociception) between morphine administered via the neck with a catheter (epidural) and morphine administered through the vein (intravenous) in horses. The results showed that epidurally administered morphine had a longer lasting effect on pain relief than the intravenously administered morphine.

Methods

The researchers applied a methodical approach in the exploration of the effects of morphine. Key elements of their research techniques included:

• Subjects: Six adult horses owned by the university were chosen for the study.
• Protocol: Each horse was fitted with a catheter in the neck (between the first two cervical vertebrae) and a thermal threshold (TT) testing device placed at the withers (the highest point of the back) and the coronary band (part of the horse’s hoof).
• Treatments: The horses were subjected to three treatment cycles: epidural morphine administration, systemic morphine administration, and a control treatment with no morphine.
• Measurements: The researchers ascertained each horse’s baseline thermal threshold before treatments, and then measured TT at multiple time points after treatment.

Results

The research produced significant findings regarding the efficacy of morphine when administered through different methods:

• Both systemic and epidural morphine administration led to increased TT values compared to baseline and control treatment, indicating effective antinociception or absence of pain.
• The duration of the antinociceptive effect was significantly longer in the epidural administration, lasting between 10-12 hours, as compared to the systemic administration, where it lasted only 1.5-2.0 hours.
• The researchers found that the horses in the epidural group had significantly higher TT values at certain time points, further demonstrating the extended duration of pain relief provided by the epidural morphine.

Conclusions

Based on their findings, the researchers concluded that morphine administered epidurally at the cervical level gave a longer lasting and higher level of pain relief, as measured by higher TT values, when compared to morphine administered intravenously. They also found no complications or adverse effects following the placement of the cervical catheter and administration of the morphine. Therefore, they suggested that the use of a cervical epidural catheter can be considered for pain relief in horses suffering from neck and thoracic limb pain.