Veterinary Surgery & Radiology

In cattle, distal paravertebral nerve block (Magda's method / Cakala's modification) desensitizes the flank by blocking the dorsal and ventral branches of T13, L1, and L2 spinal nerves at the tips of the transverse processes of the lumbar vertebrae:

• The T13 nerve is blocked at the free extremity of the transverse process of the First lumbar vertebra (L1 - A).
• The L1 nerve is blocked at the free extremity of the transverse process of the Second lumbar vertebra (L2 - B).
• The L2 nerve is blocked at the free extremity of the transverse process of the Fourth lumbar vertebra (L4 - D), bypassing L3 because the L2 nerve traverses obliquely caudal to L3 towards L4.

Pharmacological properties of acepromazine in equine practice:

• Sedation and Anxiolysis: A phenothiazine neuroleptic that blocks central dopamine $D_2$ receptors, producing calm sedation and anxiolysis.
• Hypotension: Antagonism of peripheral vascular $\alpha_1$-adrenergic receptors produces pronounced arterial vasodilation, resulting in arterial hypotension and reflex tachycardia.
• Priapism: Blockade of $\alpha_1$-adrenoceptors in the retractor penis muscle causes persistent penile protrusion and paraphimosis/priapism in stallions and geldings, potentially leading to permanent erectile dysfunction.
• Minimal respiratory depression: Acepromazine causes minimal depression of resting respiration; while mild reductions in respiratory rate may occur, resting respiratory tidal volume and minute ventilation remain well preserved compared to opioids or alpha-2 agonists. Thus, reduction in tidal volume is not a typical effect.
  
  Option analysis:
• Observed therapeutic tranquilizing effect.
• Well-known side effect via alpha-1 vasodilation.
• Classical adverse reaction in stallions and geldings.
• (Reduction in respiratory tidal volume): Correct answer (as the effect not observed). Tidal volume is well preserved.

Pharmacodynamics of local anesthetic agents:

• Assertion (A) is correct: Ropivacaine has intrinsic vasoconstrictive properties at clinical concentrations ($\lt 0.5\%$ and $0.75\%$). Adding epinephrine offers little to no clinical advantage in extending its sensory block duration or delaying systemic absorption, while carrying potential cardiovascular risks.
• Reason (R) is incorrect: Almost ALL clinically used local anesthetics (e.g., lidocaine, procaine, bupivacaine, mepivacaine) cause VASODILATION (not vasoconstriction) at therapeutic concentrations by directly relaxing vascular smooth muscle. The only exceptions are cocaine (which blocks norepinephrine reuptake) and ropivacaine/levobupivacaine (which produce intrinsic vasoconstriction at clinical doses). Statement R inverts this pharmacological rule.