MEDICINE


tion, whole blood in EDTA for a complete blood count and fibrinogen concentration, whole blood in EDTA for equine herpesvirus-1 (EHV-1) PCR, serum or heparinized whole blood for a full biochemical pro- file, and nasal swabs when EHV-1 is a differential.


3. Results


Twenty-four horses, 16 healthy and eight neurologic horses had CSF collected from both the C1–C2 site and the LS site in immediate succession based on a computer-generated randomized order. In addi- tion, nine horses underwent CSF collection at 2-week intervals. This resulted in a total of 42 procedures each of the C1–C2 and LS centeses. All horses were sedated with an alpha-2 adrenergic agonist as the sole sedative. Fluid was collected from both sites in all cases although total sample volume at an individual site varied between 1.5 and 6 mL. The time from needle puncture to spinal fluid collection was recorded for each site as well as the horse’s reaction. The average collection time for the C1–C2 tap was 6 minutes, whereas the av- erage time for the LS tap was 8 minutes. However, 42% of C1–C2 taps were performed in under 3 min- utes whereas only 20% of LS taps were completed in under 3 minutes. The horse reaction for the C1–C2 tap was minimal with only 2 horses making minor movements (head toss) during the needle advance- ment but prior to needle placement in the subarach- noid space. Reactions occurred more frequently with the LS tap, where 10 horses reacted by buck- ing, lunging forward, or kicking out with one leg. No horse jumped out of the stocks or fell down dur- ing the procedure. The author has, however, per- formed or witnessed over 120 LS taps and has witnessed on rare occasion horses fall in the stocks, jump forward out of the stocks, and put legs through the sides of the stocks. Gross blood contamination occurs occasionally


with both procedures. In one normal horse that underwent a C1–C2 centesis on two separate in- stances 2 weeks apart, the initial CSF was clear; however, minute streams of blood were detected flowing from the needle without any change in nee- dle position or aspiration technique (presumptively from the meningeal capillaries). The third and fourth CSF aliquots were submitted for cytology and titer analysis to reduce the effect of blood contami- nation on analysis. Of the 84 total centeses, 28 were performed in the field. These samples were processed toward the end of the 2-hour cutoff and provided quality samples with no evidence of cellu- lar degradation such as pyknotic nuclei, lysis, or disintegration of nuclear or cytoplasmic membranes. These samples were kept at ambient temperature (between 40°F and 60°F).


4. Discussion


CSF collection is an invasive procedure and should not be pursued without appropriate precautions and informed client consent. Irrespective of the ap-


482 2018  Vol. 64  AAEP PROCEEDINGS


proach, owners should be made aware of the main risks associated with CSF collection, which include introduction of infection, iatrogenic hemorrhage re- sulting in sterile meningitis, iatrogenic spinal cord trauma, or pain or swelling at the site.6 The com- plication rate associated with CSF collection has not been reported. The author examined the horses in the study at 12-hour intervals for 48 hours following the procedure with no evidence of progression or development of neurologic signs, no evidence of cer- vical discomfort, or systemic inflammation based on physical examination. Some horses reacted to deep palpation of the C1–C2 site but this resolved at or prior to 48 hours without intervention. Practitioners that are skilled at placing needles


under ultrasound guidance will find the C1–C2 cen- tesis less intimidating than those less confident with their ultrasound-guided skills. It is recommended that practitioners practice the technique on eutha- nized horses prior to attempting this procedure in a clinical case. In theory the needle could puncture the spinal cord. The risk of this is minimized by using no longer than a 3.5-inch needle, careful ul- trasound guidance of needle placement, and posi- tioning the needle in the dorsal subarachnoid space. In the five (seven) cases that had a post-mortem examination performed, no gross or histopathologic evidence of needle puncture was detected. When deciding which site to attempt to collect fluid from the pros and cons of both sites should be weighed. The main disadvantages of the LS tap include that they require stocks (or other physical barrier) to separate the person performing the tap from the horse. In addition, the handler must be prepared for the horse to jump or rush forward. The land- marks are sometimes difficult to discern on well- muscled or overconditioned individuals. Finally, as discussed previously, it is sometimes not possible to obtain fluid from the LS space. In those cases, it would be reasonable to attempt the C1–C2 tap on the same day. In the study performed by the au- thor, there was no effect of order of the tap on the cytologic analysis. The benefit of performing the tap at the level of the LS space include being at a caudal location to a lesion localized caudal to C2. In addition, at the level of the LS space, the spinal cord is at or caudal to the conus medullaris as it terminates in the cauda equina (a collection of white matter tracts spinal nerves). Needle puncture of this segment is unlikely to result in neurologic def- icits compared with accidental puncture of the spi- nal cord between C1–C2. The benefits of the C1–C2 tap include being posi-


tioned to the side and at the front end of the horse. Little to no horse reaction was experienced with the use of appropriate local anesthetic, sedation, and restraint. In addition, this may be a more optimal site for neurologic lesions localized intracranially. The disadvantage is that it requires ultrasound equipment, moderate eye-hand coordination, and has the potential to traumatize the spinal cord.


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