What are the advantages of adding a vasoconstrictor to the spinal anesthetic solution?

What are the advantages of adding a vasoconstrictor to the spinal anesthetic solution?

The goal of adding vasoconstrictors to local anesthetics is usually to decrease local anesthetic uptake secondary to diminished blood flow. Nerves are bathed in the local anes-thetic longer, and the duration of blockade is frequently prolonged. Although 0.2–0.4 mg of epinephrine prolongs the effects of isobaric solutions and hyperbaric tetracaine, it does not increase the duration of blockade produced by hyperbaric bupivacaine. Nevertheless, vasoconstrictors do seem to provide other beneficial effects for spinal anesthe-sia. α-Agonists such as epinephrine and phenylephrine, when applied to the spinal cord, demonstrate analgesic properties. It is postulated that the vasoconstrictors’ inde-pendent spinal cord actions add to those of the local anes-thetics to improve intensity of anesthesia.

Fear that vasoconstrictors might impair spinal cord blood flow to the point of neuronal damage has been dispelled. Lidocaine and tetracaine increase spinal cord blood flow, which is minimally offset by the addition of epinephrine. The addition of vasoconstrictors to subarach-noid local anesthetics has not proven to be deleterious.

Clonidine, a centrally acting α₂-agonist, has also been shown to prolong the duration of action of spinal tetra-caine. This has been achieved with intrathecal injection and oral premedication administration.