Sonographic evaluation of epidural and intrathecal injections in cats.

OBJECTIVES: To describe the ultrasonographic anatomy of the caudal lumbar spine in cats and to detect ultrasound (US) signs associated with epidural or intrathecal injection. STUDY DESIGN: Prospective, clinical study. ANIMALS: Twenty-six client-owned cats. METHODS: Transverse (position 1) and parasagittal (position 2) two-dimensional US scanning was performed over the caudal lumbar spine in all cats. Midline distances between the identified structures were measured. Cats assigned to epidural injection (group E, n = 16) were administered a bupivacaine-morphine combination confirmed by electrical stimulation. Cats assigned to intrathecal injection (group I, n = 10) were administered a morphine-iohexol combination injected at the lumbosacral level and confirmed by lateral radiography. The total volume injected (0.3 mL kg-1 ) was divided into two equal aliquots that were injected without needle repositioning, with the US probe in positions 1 and 2, respectively. The presence or absence of a burst of color [color flow Doppler test (CFDT)], dural sac collapse and epidural space enlargement were registered during and after both injections. RESULTS: US scanning allowed measurement of the distances between the highly visible structures inside the spinal canal. CFDT was positive for all animals in group E. In group I, intrathecal injection was confirmed in only two animals, for which the CFDT was negative; seven cats inadvertently and simultaneously were administered an epidural injection and showed a positive CFDT during the second aliquot injection, and the remaining animal was administered epidural anesthesia and was excluded from the CFDT data analysis. Dural sac collapse and epidural space enlargement were present in all animals in which an epidural injection was confirmed. CONCLUSIONS AND CLINICAL RELEVANCE: US examination allowed an anatomical description of the caudal lumbar spine and real-time confirmation of epidural injection by observation of a positive CFDT, dural sac collapse and epidural space enlargement.

Anatomical and radiological study of the thoracic paravertebral space in dogs: iohexol distribution pattern and use of the nerve stimulator.

OBJECTIVE: To describe the landmarks and methodology to approach the thoracic paravertebral space in dogs; to evaluate if intercostal muscular response could be evoked by a nerve-stimulator; to radiographically assess the distribution pattern of a radio-opaque contrast medium after thoracic paravertebral injections. STUDY DESIGN: Randomized, controlled, experimental trial. ANIMALS: Two mongrel dog cadavers (anatomical study) and 24 mongrel dogs (experimental study). METHODS: For the anatomic study 0.2 mL kg(-1) of new methylene blue (NMB) was injected at the 5th thoracic paravertebral space; for the experimental study dogs were divided into three groups and received 1 (T(5)), 2 (T(4) and T(6)) or 4 (T(4), T(5), T(6) and T(7)) paravertebral injections of iohexol. The paravertebral approach was performed with insulated needles using landmarks and a blind technique. When the needle tip reached the respective thoracic paravertebral space, the nerve-stimulator was switched-on and the presence/absence of intercostal muscular twitch was registered, thus a total volume of 0.2 mL kg(-1) of iohexol, divided into equal parts for each injection point, was administered. Radiological studies were performed with two orthogonal projections at different times. Positive injection was confirmed when the paravertebral space was occupied by iohexol in both projections. RESULTS: NMB was distributed in the T(5) paraverterbal space. In the experimental study, when the needle tip reached the respective paravertebral space, intercostal twitching was obtained in 80% of the total injections with a stimulating current of 0.5 mA. The incidence of positive cases when the intercostal twitch was obtained with 0.5 mA was 83.3%. The main distribution pattern observed was cloud like without longitudinal diffusion. CONCLUSION AND CLINICAL RELEVANCE: Intercostal muscular responses obtained with a stimulating current of 0.5 mA could be useful to locate thoracic spinal nerves in dogs and in our study the injected solution was confined to one thoracic paravertebral space.