8.9:
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.
8.9:
Local Anesthetics: Clinical Application as Epidural Anesthesia
Epidural anesthetics are administered in the fat-filled epidural space, the outermost part of the spinal canal. This technique is commonly employed for pain management and anesthesia during lower abdomen and pelvis surgeries or labor and delivery.
Since epidural anesthetics can be infused through an epidural catheter, all types of drugs, including short-acting ones, can be administered. Chloroprocaine and lidocaine are examples of short and long-duration anesthetics, respectively. Bupivacaine is the drug of choice if prolonged anesthesia is required for surgeries. Lower concentrations of bupivacaine are used to provide analgesia during labor. Adding vasoconstrictors like epinephrine reduces systemic toxicity while prolonging the anesthesia duration. A significant difference between spinal and epidural anesthesia is that no differential sympathetic blockade is observed in epidural anesthesia.
Potential risks and complications associated with epidural anesthesia include dural puncture, infection, nerve damage, and systemic toxicity from local anesthetics (LA). High concentrations of LA in plasma during labor can result in the LAs crossing the placenta and entering fetal circulation. This results in neonatal depression during delivery.