Continuous caudal epidural and subarachnoid anesthesia in mares: a comparative study.

The research presents a novel method for inducing continuous caudal epidural analgesia (CEA) and caudal subarachnoid analgesia (CSA) in adult horses (mares) without compromising the functionality of the pelvic limb. It involves the use of a modified needle to place a catheter in the appropriate spaces of the lumbosacral intervertebral junction, and the application of a mepivacaine HCl solution; the findings demonstrate differing response times and periods of analgesia.

Introduction to the Method

• A 17-gauge Huber-point directional needle, that has been adapted, is used to position an inbuilt-stylet catheter into either the subarachnoid or epidural space at the crossing point of the lumbar and sacral vertebrae.
• The exact positioning of the catheter differed between individual cases, either being placed in the mid-sacral (S2-3) subarachnoid space or the end region of the sacral (S-3 to S-5) epidural space in the seven mares being observed.
• To confirm accurate placement of the catheter, the researchers utilized radiography.

Analgesia Application and Results

• A 2% mepivacaine HCl solution was used in different average doses to induce CSA and CEA. The average dose for CSA was 0.061 +/- 0.013 mg/kg (1.3 +/- 0.3 ml), while for CEA it was 0.196 +/- 0.034 mg/kg (4.1 +/- 0.7 ml).
• The onset of analgesia, measured against superficial and deep muscular pinprick stimulation, was found to be faster in CSA than in CEA (8.2 +/- 2.4 minutes vs 21.4 +/- 3.8 minutes).
• The highest level of caudal analgesia, extending from spinal cord segments S-1 to the tailbone, was the same during both CSA and CEA trials.
• CSA resulted in shorter periods of analgesia when compared to CEA (70.0 +/- 21.8 minutes vs 102.1 +/- 13.2 minutes).

Other Observations

• Following the epidural and subarachnoid injections of the mepivacaine HCl solution, an increase was observed in the subcutaneous temperature of the perineal (S-4 to S-5) dermatome.
• However, the heart rate, respiratory rate, systolic, diastolic, and mean arterial blood pressures, pulse pressure, rectal temperature, arterial blood gas tensions (PaCO2, PaO2), pHa, hematocrit, and total solid concentrations did not show significant changes (P greater than 0.05) from the base-line values post-injection.

Conclusion

• The study ends by discussing the potential benefits and complications of CSA and CEA in horses, however, these specific points are not mentioned in the abstract.