Discussion

Aims:
To establish a safe and efficient manner to obtain cerebrospinal fluid (CSF) from the cervical region of ataxic horses.

Methods:
Ultrasound-guided centesis of the CSF between C1 and C2 was performed in 10 clinically ataxic horses was performed. Horses were sedated using 0.01 - 0.02 mg/kg bwt of detomidine hydrochloride intravenously followed approximately 3 min later by 0.06 mg/kg bwt (approximately 30 ml) of morphine sulphate intravenously. A 10 MHz, microconvex, curvilinear ultrasound probe was used to identify the subarachnoid space and spinal cord between C1 and C2 using a lateral approach with the probe oriented dorsal to ventral. With ultrasound guidance, an 18 gauge 3.5 inch (8.9 cm) needle was introduced ventral to the ultrasound probe and directed dorsally into the dorsal aspect of the subarachnoid space in all horses. Approximately 10 ml of CSF was obtained and analysed.

Results:
No adverse reactions were observed. When the sample was obtained, gentle suction was needed since the fluid did not flow freely. Red blood cell (RBC) contamination in all samples was considered minimal with one sample having 25 RBC/ul, one with
11 RBC/ul, 3 samples having less than 4 RBC/ul and 5 samples having < RBC/ul. The total procedure time was less than 2 minutes from the introduction of the needle to removal of the needle after the acquisition of fluid.

Conclusions and practical significance:
Ultrasound-guided centesis between C1 and C2 is a rapid procedure that causes minimal to no reaction in standing, sedated ataxic horse. Although technically challenging, the use of ultrasound to guide a standing cervical centesis provides an alternative route to obtain CSF for analysis in the ataxic equine patient.