• After emerging from the foraminae of the spinal column, the spinal nerves divide immediately into a small dorsal branch, which supplies skin and muscle of the loins, with some supply cutaneously down the flank, and a ventral branch which runs obliquely down and back between the muscles, providing the main nerve supply to the flank (skin, muscles and peritoneum). (J15.23.w2)
• The 13th thoracic nerve passes cranially to the transverse process of the first lumbar vertebra (L1); the ventral branches of the lumbar nerves each run obliquely, just below the intertransverse ligament, across the space between the transverse processes. (J15.23.w2)

The paravertebral block involves perineural injection of local anaesthetic solution around the spinal nerves as they emerge, through the intervertebral foramina, from the vertebral canal. (B205.12.w12)

In all versions:

• Clip and surgically scrub and disinfect the skin over the area where the needles will be introduced. (J15.23.w2)

SHEEP AND GOATS

For operations through the flank the thirteenth thoracic nerve and the first, second and third lumbar nerves are blocked. (B205.13.w13, J15.22.w1); T13, L1 and L2 are blocked. (J234.6.w1) 

• Inject 0.5 to 1.0 mL of local anaesthetic into the skin over the midpoint of each of the first, second and third lumbar processes. (B359.App8.w30)
  • Wait a few minutes to allow this to take effect. (B359.App8.w30)
  • The subsequent injections are made through the areas desensitized by these injections. (B359.App8.w30)
• To block T13 and L1: 
  • Place a 6 cm spinal needle 2.5 to 3 cm from the midline. (J234.6.w1, J234.12.w2) half way between the midline and the tip of the transverse process. (J15.22.w1)
    • A 6 cm 19 gauge needle is adequate. (B359.App8.w30)
  • "Walk" the needle off the cranial and caudal edges of the transverse process of the first lumbar vertebra to block T13 and L1 respectively. (B359.App8.w30, J234.6.w1)
    • This is about 2 cm deep. (J215.7.w1)
  • Inject 4-5 mL 1% lidocaine or mepivacaine to block the ventral nerve roots and 2 mL to block the dorsal nerve roots, at each site. (J234.6.w1)
• To block L2: 
  • Place a 6 cm spinal needle 2.5 to 3 cm from the midline. (J234.6.w1) 
  • "Walk" the needle off the cranial edge of the transverse process of the third lumbar vertebra.(J234.6.w1)
    • Or: off the caudal edge of the transverse process of the second lumbar vertebra. (J215.7.w1)
  • Inject local anaesthetic solution below the transverse ligament to block the ventral nerve root and, as the needle is withdrawn, above it to block the dorsal nerve root. (B205.13.w13, J15.22.w1, J234.6.w1)
    • Suggested quantities of local anaesthetic are: 4 to 5 mL 1% lidocaine or mepivacaine to block the ventral nerve root and 2 mL to block the dorsal nerve root. (J234.6.w1); about 3 to 5 mL of 2% lidocaine after the needle has passed through the intertransverse ligament and a further 1 to 2 mL above the transverse ligament. (J15.22.w1); Up to 5 mL of 1% or 2% lidocaine is injected for each nerve, divided between above and below the transverse ligament. (B205.13.w13)
    • Note: The total dose injected may be up to a maximum of 6 mg/kg bodyweight. (B205.13.w13)
• To block L3, if required.
  • Place the needle (16 gauge 6 cm long) over the midpoint of the transverse process of the third lumbar vertebra and insert 4-5 cm deep to contact the transverse process. (B359.App8.w30)
  • Withdraw slightly and direct the needle forwards to "walk" the needle off the caudal edge of the transverse process. (B359.App8.w30)
  • Inject 2-3 mL of local anaesthetic solution just below the transverse process. (B359.App8.w30)
  • Withdraw the needle to above the transverse process and inject another 2 to 3 mL local anaesthetic. (B359.App8.w30)
• Alternative options: 
  • The needle may be "walked" off the cranial edges of L1, L2 and L3 to block T13, L1 and L2 respectively. (J234.12.w2)
• Onset of analgesia may occur as soon as five minutes after injection. (B205.13.w13, J234.6.w1); the flank should be anaesthetised after about 10 minutes. (B359.App8.w30)
• Duration of analgesia is approximately one hour with plain lidocaine solution, longer if lidocaine solution with adrenaline is used. (B205.13.w13)

Distal paravertebral block:

• Identify the distal ends of the transverse processes of lumbar vertebrae L1, L2 and L4. (B342.16.w16, J234.12.w2)
• Clip and disinfect the skin over the ends of the transverse processes. (B342.16.w16)
• For each transverse process:
  • Use about 1 to 3 mL of 2% lidocaine at each site. (J234.12.w2)
  • Using a 7.5 cm 18 gauge needle and approaching laterally, inject in a fan pattern ventral to each transverse process (L1, L2 and L4), then partially withdraw the needle and reinsert slightly dorsal and caudal to the transverse process to inject at this site. (J234.12.w2) The depth to which the needle must be inserted will vary depending on the body condition of the animal. (V.w69)

CATTLE

• Proximal paravertebral block:

a) Using the cranial borders of the lumbar processes:

• The nerve is blocked at the cranial border of the transverse process of the vertebra behind (caudal to) the nerve to be blocked; for T13 to L3. (B205.12.w12); for T13, L1 and L2; L3 and L4 may also be blocked using this technique however this may result in ataxia. (J234.12.w2)
• Identify the most obvious parts of the transverse processes of the first, second, third and fourth lumbar vertebrae. (B205.12.w12)
  • At the site of injection, 5 to 6 cm from the midline, the cranial borders of the transverse processes are in the same cross sectional plane of the animal's body as the most prominent parts of the lateral borders of the same processes. (B205.12.w12); about 5 cm from the midline, at the most obvious covering of the transverse processes. (J234.12.w2)
  • If identification of the first lumbar vertebra is difficult (e.g. in well-muscled or obese individuals), estimate from the distance between the second and third transverse processes. (B205.12.w12, J234.12.w2)
• Raise a skin wheal at 5 to 6 cm from the midline over each transverse process. (B205.12.w12)
  • Inject 2-3 mL of 2% lidocaine using a 2.5 cm 22 gauge needle at each site. (J234.12.w2)
• To reach the injection sites:
  • Either: Insert a stout, 7 cm long 3 mm bore needle through each skin wheal and through the underlying longissimus dorsi muscle to a depth of about 4 cm, infiltrating with local anaesthetic (2 to 3 mL 1% lidocaine) as the needle is advanced. (B205.12.w12)
    • This reduces spasm of the longissimus dorsi muscles. (B205.12.w12)
  • After a pause, introduce a 10 cm long, 2 mm bore needle, though the hole made by the first needle. (B205.12.w12)
    • This must be vertical when it first contacts the cranial border of the transverse process or redirection over the edge of the process may bring the needle to a position away from the nerve. (B205.12.w12)
  • Or: Insert a 1.25 cm 14 gauge needle through the skin then use this as a cannula and insert through it a 12.5 to 15 cm long 18 gauge needle, at 90 degrees to the spinal cord. As the needle is advanced inject small amounts of local anaesthetic solution into the longissimus dorsi muscle to reduce spasm. (J234.12.w2) 
• Once the transverse process is reached:
  • Advance the needle until it reaches the anterior border of the transverse process. (B205.12.w12)
  • Redirect the needle cranially ("walk" it off the cranial edge (J234.12.w2)), over the cranial edge of the transverse process, and advance until the needle penetrates the intertransverse ligament (this can be felt). (B205.12.w12); 
    • It is easier to feel this if a needle with a short bevel is used. (B205.12.w12)
  • Inject 15 mL of local anaesthetic solution immediately below the transverse ligament. (B205.12.w12, J234.12.w2); there should be minimal resistance to this injection. (J234.12.w2)
  • Withdraw the needle to just above the ligament (1.0 to 1.5 cm above (J234.12.w2)) and inject a further 5 mL of local anaesthetic solution; there will be slight resistance to this injection. (B205.12.w12, J234.12.w2)
• While withdrawing the needle fully from the animal, press down on the skin to prevent separation of the connective tissue and possible aspiration of air through the needle. (B205.12.w12)
• If the nerve has been infiltrated successfully a belt of hyperaemia will develop causing an appreciable rise in skin surface temperature. (B205.12.w12)
• Analgesia develops in about 10 minutes. (B205.12.w12)
• Unilateral block results in development of lateral curvature of the spine towards the injected side. (B205.12.w12)
• Using lidocaine with 1:400,000 adrenaline analgesia persists for about 90 minutes. (B205.12.w12)

b) Using the caudal borders of the lumbar processes (J15.23.w2):

• Identify the second transverse lumbar process. The transverse process cranial to the external angle of the ileum is the fifth transverse process; counting forward from this identifies the second transverse process. Each process is directed laterally and slightly cranially. (J15.23.w2)
• For L2:
• About 6 cm from the dorsal midline of the animal, using a 2 cm 23 gauge needle, inject a 2-3 mL bleb of local anaesthetic under the skin towards the caudal edge of the second lumbar transverse process. (J15.23.w2)
• Extend the subcutaneous injection a few millimetres into the muscle (longissimus dorsi) to reduce the risk of this muscle spasming and bending the longer needle used for the main injection. (J15.23.w2)
• Insert a 10 or 15 cm long, 16 gauge or 18 gauge spinal needle through the desensitised skin and down until it strikes the lumbar transverse process. (J15.23.w2)
• Slightly withdraw the needle and "walk" the needle off the caudal edge of the process. (J15.23.w2)
• Advance the needle about 1 cm to pass beneath the intertransverse ligament; loss of resistance will be felt as the needle penetrates this ligament. (J15.23.w2)
• By slightly withdrawing and then redirecting the needle, slowly injecting local anaesthetic solution all the time, inject 12 to 14 mL of 2% lidocaine at slightly varying depths and with slightly varying direction, to block the ventral branch of the nerve. (J15.23.w2)
• Start to withdraw the needle and inject the last 6 to 8 mL of local anaesthetic solution as the needle is withdrawn, to ensure that the dorsal branch of the nerve is desensitised. (J15.23.w2)
• For L1 and T13: If the transverse process of the first lumbar vertebra is not palpable, which is the case in many heavily muscled or obese animals, calculate the distance forward from the second lumber vertebrae: it is the same as the distance between the second and third lumbar vertebrae. (J15.23.w2)
• About 6 cm from the dorsal midline of the animal, using a 2 cm, 23 gauge needle, inject a 2 to 3 mL bleb of local anaesthetic under the skin at the distance cranial to the bleb over the transverse process of L2 calculated to be over the transverse process of L1. This should be over the midpoint of the transverse process of L1. (J15.23.w2)
• Introduce the spinal needle through this bleb and down until it strikes the transverse process of L1, withdraw slightly and redirect off the caudal edge of the process. Inject 12 to 14 mL of lidocaine to block the ventral branch of L1, as described above for L2, and 6 to 8 mL to block the dorsal branch. (J15.23.w2)
• Withdraw slightly again and redirect the needle off the cranial edge of the process. Inject 12 to 14 mL of lidocaine to block the ventral branch of T13, as described above for L2, and 6 to 8 mL to block the dorsal branch. (J15.23.w2)
• Block L3 and L4, if required, by positioning the needle of the caudal edge of the respective lumbar vertebral transverse processes (of vertebrae L3 and L4, respectively) as described for L2. (J15.23.w2)
• Note: Prior to the first injection the approximate depth of the muscle should be calculated. If this depth is passed without hitting bone, partly withdraw the needle and let go; if muscle contraction has caused the needle to deviate from its intended path this will be seen in movement of the visible portion of the needle. Withdraw the needle to just under the skin and advance again perpendicularly to strike the transverse process. (J15.23.w2)
• Signs of successful block (J15.23.w2): 
  • Anaesthesia of the skin;
  • Increased skin temperature. This occurs due to hyperaemia resulting from paralysis of cutaneous vasomotor nerves;
  • Relaxation of flank muscles;
  • Scoliosis (curving of the spine) towards the desensitised side. 

  (J15.23.w2)

c) Lateral or distal paravertebral block:

• Identify each transverse process (L1, L2, L3, L4). (B205.12.w12) Identify the distal ends of the transverse processes of lumbar vertebrae L1, L2 and L4. (B342.16.w16, J234.12.w2)
• Clip and disinfect the skin over the ends of the transverse processes. (B205.12.w12)(B342.16.w16)
• For each transverse process:
  • Use a total of about 20 mL local anaesthetic per transverse process. (B205.12.w12, J234.12.w2) Use 15-25 mL 2% lidocaine solution per transverse process. (B342.16.w16) 
  • Using a 7.5 cm 18 gauge needle and approaching laterally, insert the needle about 5 cm (J234.12.w2) and inject 10 to 20 mL in a fan pattern (15 mL (J234.12.w2)) ventral to each transverse process (L1, L2 and L4), then partially withdraw the needle and reinsert slightly dorsal and caudal to the transverse process; inject a further 5 mL 2% lidocaine. (B342.16.w16, J234.12.w2)
    • Approach laterally and inject about 10 mL local anaesthetic below the transverse process towards the midline. (B205.12.w12) 
    • Partially withdraw the needle, redirect cranially and inject along the new line of insertion. (B205.12.w12)
    • Partially withdraw the needle, redirect caudally and inject along the new line of insertion. (B205.12.w12)
    • Inject the last of the anaesthetic solution slightly dorsal and caudal to the transverse process. This blocks the dorsolateral branches of the nerves (B205.12.w12) 

• To provide unilateral analgesia of the paralumbar fossa for flank laparotomy. An alternative to the inverted L block. (B205.12.w12, B205.13.w13, J15.22.w1, J15.23.w2, J234.6.w1)
• Preferable to a line block or an inverted L block in relation to both speed of application and safety. (J234.6.w1)
• This block is more likely to provide uniform desensitisation of the peritoneum than is field infiltration, and also provides relaxation of the abdominal wall. (B205.12.w12)
• For caesarean section, this technique provides good muscle relaxation, does not risk development of haematomas at the operating site and provides for good healing as well as the ewe quickly regaining her feet and mothering her lambs. (J15.21.w4)

Advantages over L-block or line infiltration:

• Wide uniform analgesia from the last rib to the tuber coxae and ventrally to the fold of the flank, through all layers of the abdominal wall. (B359.App8.w30, J15.23.w2, J234.12.w2)
• Faster to carry out. (J15.23.w2)
• Significantly smaller total volume of local anaesthetic solution is required. (B359.App8.w30, J15.23.w2, J234.12.w2)
• No haematoma formation at the proposed incision site. (B359.App8.w30J234.12.w2)
• Produces relaxation of flank muscles and decrease in intra-abdominal pressure. (B359.App8.w30, J15.23.w2)
• Intraoperative increase in the length of the laparotomy incision can be performed if required. (J15.23.w2)
• The peritoneum is desensitised and some abdominal viscera also. (J15.22.w1)

Advantages of the lateral or distal paravertebral block over the proximal block:

• Needle sixes used are more routinely used and available. (B342.16.w16, J234.12.w2)
• Scoliosis is not produced. (B342.16.w16, J234.12.w2)
• No risk of penetrating a major blood vessel such as the aorta or posterior vena cava. (B342.16.w16, J234.12.w2)
• Minimal pelvic limb weakness or ataxia. (B342.16.w16, J234.12.w2)

• The thirteenth thoracic and first and second lumbar nerves supply the area of the flank which is bounded cranially by the last rib, caudally by the angle of the ileum and dorsally by the lumbar transverse processes. (B205.12.w12)

Signs of successful block (B205.12.w12, J15.23.w2): 

• Anaesthesia of the skin;
• Increased skin temperature. This occurs due to hyperaemia resulting from paralysis of cutaneous vasomotor nerves;
• Relaxation of flank muscles;
• Scoliosis (curving of the spine) towards the desensitised side. 

(B205.12.w12, J15.23.w2, J234.12.w2)

General notes for local anaesthesia:

• The analgesic technique chosen should be decided based on the procedure to be undertaken, the facilities available and the skills of the practitioner. (J215.7.w1)
• Epinephrine (adrenalin) at 1 part per 200,000 or norepinephrine (noradrenaline) at 1 part per 100,000 may be added to the local anaesthesia solution to decrease the absorption of the agents and prolong their action. These vasopressors should not be used for analgesia of appendages such as the tail, teats or toes as they may produce sufficient circulatory compromise of the appendage to result in tissue necrosis and sloughing. (J215.7.w1)
• Standard aseptic techniques should be practiced when performing local analgesia, including surgical preparation of the skin, and sterile injection techniques. (J215.7.w1)
• Aspiration to check for blood should be carried out prior to injection, to avoid inadvertent intravenous injection. (J215.7.w1)

• This technique is technically relatively difficult (B354.20.w20), particularly in fat animals. (J15.21.w4)
  • It is difficult to identify the landmarks for injections in animals which are obese or very heavily muscled. (J15.23.w2, J234.12.w2, B359.App8.w30)
• Vasodilatation may increase haemorrhage; this is considered of minor importance. (J15.23.w2)
• Bowing of the flank may make closure of the laparotomy incision more difficult (J234.12.w2); this is considered of minor importance. (J15.23.w2)
• There is a risk of penetrating the aorta or thoracic longitudinal vein on the left side of the spine or the posterior vena cava on the right side. (J234.12.w2)
• Caudal migration of the drug to the femoral nerve may occur with resultant loss of motor control to the hind limb. (J234.12.w2)

Lateral or distal paravertebral block:

• Analgesic solution may be injected below fascial sheets and therefore not bathe the nerves. (B205.12.w12)
• More local anaesthetic is required than for the proximal paravertebral block. (B342.16.w16); larger volumes may be required due to variability in anatomical position of the nerves. (J234.12.w2)

• 2% Lidocaine solution.
• For cattle: 10 cm spinal needle; 12 cm may be required for cattle of the Belgian blue or other very heavily muscled breeds. (J15.23.w2)
• In sheep: 6 cm spinal needle. (J234.6.w1, J234.12.w2) A 6 cm long 19G needle is adequate for paravertebral block. (B359.App8.w30)

• Drugs required are inexpensive.
• Appropriate spinal needles for cattle may not always be readily available.