Segmental epidural and subarachnoid analgesia in conscious horses: a comparative study.

The study investigates and compares the effect of two methods of administering pain relief to horses – segmental epidural analgesia (SEA) and segmental subarachnoid analgesia (SSA). The findings suggest that SSA has a quicker onset, but SEA has a longer-lasting effect and some additional physiological effects, such as changes in temperature and respiratory rate.

Methods

• Two types of analgesia procedures – segmental epidural analgesia (SEA) and segmental subarachnoid analgesia (SSA) – were performed on six adult horses. A 17-gauge Huber point directional needle was used to place a catheter into the epidural or subarachnoid space.
• The placement of the catheter was confirmed using radiographic techniques, ensuring it was accurately placed at the lumbosacral intervertebral junction to catheterize the thoracolumbar epidural or subarachnoid space.
• Both SEA and SSA procedures were carried out using a 2% solution of mepivacaine hydrochloride. However, the dose concentration varied – with 80 mg (4 ml) being used to induce SEA and 30 mg (1.5 ml) for SSA.

Findings

• The onset of analgesia, calculated from the response to superficial and deep muscular pinprick stimulations, was quicker in horses treated with SSA compared to SEA (8.0 +/- 1.9 minutes vs 15.8 +/- 3.8 minutes).
• Maximum thoracolumbar analgesia extended from spinal cord segments T14 to L3 in horses with SSA and from T12 to L2 in horses treated with SEA, suggesting a slightly broader coverage area for SSA.
• However, the duration of analgesia was significantly longer in horses treated using SEA, nearly double that of SSA (80.8 +/- 16.9 minutes vs 44.8 +/- 14.5 minutes).
• Additional physiological effects were observed on horses administered with SEA. This includes a significant increase in subcutaneous temperature at the T18 dermatomes and decreases in respiratory rate and rectal temperatures. SSA did not effect significant changes in respiratory rate and rectal temperature.

Implications

• The research presents insights on the effect of SEA and SSA procedures in pain management in horses, providing valuable information for veterinary anaesthesia.
• It also suggests that when the onset of analgesia needs to be rapid, SSA is more efficient, but for longer-lasting effects, SEA should be considered.
• The study also indicates that SEA has additional physiological effects, which could be useful in certain clinical scenarios, but need to be taken into account when choosing an analgesic procedure.