ULTRASOUND AS A SUPPORT TOOL FOR CAUDAL EPIDURAL INJECTION IN THE HORSE

The aim of the study was to describe the sonoanatomy of the epidural space at first, second and third coccygeal space in horses. Phase 1: two tails, obtained from a slaughterhouse, were used to perform the ultrasound anatomical study of the epidural space at the coccygeal level. One tail was first used to obtain CT images and then was used to make anatomical sections. The second tail was dissected to individualize the ligaments and the muscular planes, then the tail was completely stripped to bone in order to obtain the coccygeal bones to make a water immersion ultrasound study. Phase 2: Fifteen standardbreed female horses, undergoing perineal surgical procedures, were enrolled in the study. After individuation of anatomical landmarks done in phase 1, images of the sacro-coccygeal zone were first collected from the horses always by the same operator in order to acquire the technique. Than each horse was sedated with xylazine 0.5 mg/kg IV and the registration of data started; one expert operator and different inexpert operators individuated the needle insertion point for the epidural space with the classical method described by Skarda et al., 2009. The insertion point was marked with a specific dot for inexpert and expert operators. Then ultrasound images of the coccygeal (Co) spaces were taken and the most appropriate insertion point was detected. The distance between the expert and the inexpert points, the expert and the ultrasound technique points and between the inexpert and the ultrasound technique points were measured with a caliber. After the measurements were acquired, a surgical scrub of the area was done and an epidural needle insertion was performed at the ultrasound individuated point. The depth of the epidural space was individuated by ultrasound. The Thouy needle was then inserted with a 90° angle respect to the skin and the right positioning of the tip needle was confirmed by the hanging drop technique. Stage 1: CT and ultrasound images of the tails confirmed that the spinous processes of coccygeal vertebrae are incomplete. Specific ultrasound images can be individuated and the depth of the epidural space can be measured. Stage 2: mean depths of epidural space recorded at the spaces between Co1 and Co2 and between Co2 and Co3 were 3.069 ± 0.36 and 2.63 ± 0.29 respectively. Mean distance between the expert and inexpert points was 1.18 ± 0.94 cm, between the inexpert and ultrasound points was 2.16 ± 1.77 cm and between the expert and ultrasound points was 1.26 ± 1.46 cm. The hanging drop technique confirmed the right positioning of the needle in all horses. Ultrasound evaluation of the epidural space at coccygeal level is feasible and quite easy. This study puts in evidence that the ultrasound technique can be more accurate than both inexpert and expert operators in individuating the epidural injection point. This technique can also be used to know the depth of the epidural space. The technique may be a support tool and not a guide because the 90° angle of the needle does not allow the direct visualisation under the ultrasound probe during the procedure. Further studies are to be performed to evaluate the possibility to make the procedure under the ultrasound direct visualization. Skarda RT, Muir WW, Hubbel JAE, Local Anesthetic Drugs and Technique in Muir WW, Hubbel JAE “Equine Anesthesia Monitoring and Emergency Therapy Second Edition, St Louis, Saunders Elsevier, 2009. Anaesthesiology and pain therapy epidural anesthesia, horse, ultrasound