Local Anesthetics: Clinical Application as Epidural Anesthesia

Epidural anesthetics are administered in the fat-filled epidural space around the thoracic, lumbar, or sacral regions of the spine during surgeries of the lower abdomen and pelvis or labor and delivery.

They can be injected into the epidural space or infused through catheters that allow continuous or repeated administration of the drugs. Usually, short-acting local anesthetics or LAs are repeatedly administered via catheters to work for a more extended period.

Epidural LAs primarily act on spinal nerve roots. The concentration of LAs determines which type of nerve fiber will be blocked.

High LA concentrations can block sympathetic, somatic sensory and somatic motor fibers. In contrast, intermediate concentrations of LA only block the somatic sensory fibers, while low concentrations block the sympathetic nerves alone.

This is particularly important during labor. High concentrations of LAs can pass through the amniotic sac into the placenta, entering the fetal blood and affecting the infants' respiration during birth. Repeated administration of LA at low concentrations only blocks the sympathetic nerves to relieve pain without affecting motor neurons to help the baby's delivery.