AB4 - Nerve blocks Flashcards
In regional anaesthesia for parturition, what are the advantages for caudal (coccygeal) block?
Reduces straining by blocking sensory input from vulva & vaginal without reducing uterine contraction.
Helpful in cases of dystocia, by providing pain relief + permitting obstetrical manipulation
In coccygeal block, anaesthetic is introduced into the epidural space. Briefly describe what is the epidural space.
Epidural space is a fat-filled virtual space, between the bony vertebrae and the outmost layer of the spinal cord (dura mater)
How many vertebrae are there in each section of the cattle spine?
Thoracic: 13
Lumbar: 6
Sacral: 5 (fused)
Coccygeal: 18-20
Where would you introduce anaesthetic in an epidural nerve block in a cow? And how would you locate the space?
Sacrococcygeal (S5-Co1) OR First coccygeal space (Co1-2)
Locate by moving the tail up and down, palpating for dorsal depression - slight negative pressure indicates needle is correctly placed
What does the epidural nerve block desensitise?
Desensitises Sacral nerves (S2), S3, S4, S5 as they emerge through the dura mater, pass through the epidural fat to reach the intervertebral foramen
Why might this technique be preferred in large animals over a high (lumbosacral) epidural block, or true spinal (intrathecal) where local anaesthetic is introduced into the subarachnoid space?
Subarachnoid space consists of the CSF, between the arachnoid layer (middle layer) & pia mater (innermost layer) that surrounds the spinal cord.
Lumbosacral epidural block would numb the legs, so not ideal if surgery were to perform on a standing cow.
In regional anaesthesia for caesarean section or rumenotomy, briefly which nerves and regions are desensitise?
Nerves to the flank (skin, muscle peritoneum) - dorsal + ventral branches of the spinal nn.
Region innervated by T13, L1, L2, (L3)*
*L3, L4 are not generally blocked
In caesarean regional nerve block, L3 and L4 are generally not blocked unless a procedure requires a particularly caudal approach. What could be the disadvantage of blocking the ventral branch of spinal nerve 4?
Could result in post-operative muscle weakness and ataxia, because L3 and 4 supplies motor fibres to the ischial femoral nerves.
Difficult for cow to stand or move after procedure, increasing risk of pressure sores, pneumonia etc.
What are the different techniques to provide caesarean regional anaesthesia?
1) Line block - LA instilled along the incision line (vertically in the middle of paralumbar fossa)
2) Inverted L block - LA instilled along perpendicular lines cranial/dorsal to incision
3) Paralumbar block - LA instilled at specific sites to block T13, L1 & L2
What are the advantages of paralumbar block over simple infiltration?
- Less distortion of clinical site/tissue irritation
- More precise, reliable regional anaesthesia
- Fuller anaesthesia of peritoneum
(BUT need to know landmarks, and may be more difficult to palpate these in heavy animals)
Describe the placement of paralumbar block.
Transverse process of L1 is difficult to palpate, locate the lateral tip of L2 as initial landmark instead.
Proximal:
LA is instilled around dorsal and ventral branches approximately half way between midline and tip of transverse process. To deposit anaesthetic around ventral branch, needle is directed vertically downwards until it hits bone - then “walks off” edge of transverse process (caudal to L2 for lumbar nerves, cranial to L1 for T13) and through the intertransverse ligament. Further anaesthetic deposited as withdrawn to anaesthetise dorsam branch.
Distal:
Needle directed from lateral tip of transverse process towards midline - LA deposited above and below the process (“fanned out” to ensure coverage) to block both dorsal and ventral branches
Describe how the thoracolumbar spinal nerves exit the vertebral canal via the intervertebral foramen.
Nerves exit caudal to their named vertebra
i.e. T13 emerges caudal to rib 13
Lumbar nerves emerge between bases of the transverse processes
Name the connective tissue structure that lies between dorsal and ventral spinal nerve branches.
Intertransverse ligament
Name the major lumbar nerves for blockage in Caesarian and their locations.
T13 - L1: Costoabdominal nn.
L1 - L2: iliohypogastric nn.
L2 - L3: ilioinguinal nn.
(All have dorsal & ventral branches)
Lumbar nerve L1 is difficult to palpate, how would you pinpoint the location of costoabdominal nerve?
T13 - Spine - L2 as boundaries to form a triangle
