VCP 411: Medicine Section

APPROACH TO THE LUMBOSACRAL SITE IN SHEEP

• The approach is made easier if the animal is restrained in sternal recumbency with the hips flexed and the hindlegs held fully extended alongside the abdomen.
• The site used is the midline depression midway between the last palpable lumbar dorsal spinal process (L5) and the first palpable sacral dorsal spinal process (S2). The site is clipped and surgically prepared and 1 ml of local anaesthetic is injected subcutaneously.
• The needle is directed cranially at an angle of 10º to 15º. The tissues penetrated, in order, are: skin and subcutaneous tissue, interarcuate ligament, ligamentum flavum, dura mater and arachnoid mater.
• The interarcuate ligament presents resistance to the passage of the needle. This resistance is followed by a distinct ‘pop’. Mild resentment, exhibited as fine muscle tremors and tail swishing, may occur at this point as the meninges are penetrated.
• Once the tip of the needle has penetrated the dorsal subarachnoid space CSF appears at the needle hub within two to five seconds.
• It is important to recognise the ‘pop’ through the interarcuate ligament and delay advancing the needle for at least five seconds. This delay allows time for the CSF to collect in the needle hub and avoids unnecessary penetration of the spinal cord.