Epidural block

Perspective

Epidural anesthesia is the second primary method of neuraxial block. In contrast to spinal anesthesia, epidural block requires pharmacologic doses of local anesthetics, making systemic toxicity a concern. In skilled hands, the incidence of postdural puncture headache should be lower with epidural anesthesia than with spinal anesthesia. Nevertheless, as outlined in Chapter 40 , Spinal Block, I do not believe this should be the major differentiating point between the two techniques. Spinal anesthesia is typically a single-shot technique, whereas frequently intermittent injections are given through an epidural catheter, thus allowing reinjection and prolongation of epidural block. Another difference is that epidural block allows production of segmental anesthesia. Thus if a thoracic injection is made and an appropriate amount of local anesthetic is injected, a band of anesthesia that does not block the lower extremities can be produced.

Patient Selection. Epidural block is appropriate for virtually the same patients who are candidates for spinal anesthesia, except that epidural anesthesia can be used in the cervical and thoracic areas as well—levels at which spinal anesthesia is not advised. As with spinal anesthesia, if epidural block is to be used for intraabdominal procedures involving the upper abdomen, it is advisable to combine this technique with a light general anesthetic because diaphragmatic irritation can make the patient, surgeon, and anesthesiologist uncomfortable. Other candidates for epidural anesthesia are patients in whom a continuous technique has increasingly been found to be helpful in providing epidural local anesthesia or opioid analgesia after major surgical procedures. This clinical application likely explains the increased interest in epidural block over the last 20 years.

Pharmacologic Choice. To use epidural local anesthetics effectively, one must combine an understanding of the potency and duration of local anesthetics with estimates of the length of the operation and the postoperative analgesia requirements. Drugs available for epidural use can be categorized as short-acting, intermediate-acting, and long-acting agents; with the addition of epinephrine to these agents, surgical anesthesia ranging from 45–240 minutes after a single injection is possible.

Chloroprocaine, an amino ester local anesthetic, is a short-acting agent that allows efficient matching of the length of the surgical procedure and the duration of epidural analgesia, even in outpatients. 2-Chloroprocaine is available in 2% and 3% concentrations; the latter is preferable for surgical anesthesia and the former for techniques not requiring muscle relaxation.

Lidocaine is the prototypical amino amide local anesthetic and is used in 1.5% and 2% concentrations epidurally. Concentrations of mepivacaine necessary for epidural anesthesia are similar to those of lidocaine; however, mepivacaine lasts from 15–30 minutes longer at equivalent dosages. Epinephrine significantly prolongs (i.e., by approximately 50%) the duration of surgical anesthesia with 2-chloroprocaine and either lidocaine and mepivacaine. Plain lidocaine produces surgical anesthesia that lasts from 60–100 minutes.

Bupivacaine, an amino amide, is a widely used long-acting local anesthetic for epidural anesthesia. It is used in 0.5% and 0.75% concentrations, but analgesic techniques can be performed with concentrations ranging from 0.125%–0.25%. Its duration of action is not prolonged as consistently by the addition of epinephrine, although up to 240 minutes of surgical anesthesia can be obtained when epinephrine is added.

Ropivacaine, another long-acting amino amide, is also used for regional and epidural anesthesia. For surgical anesthesia, it is used in 0.5%, 0.75%, and 1% concentrations. Analgesia can be obtained with concentrations of 0.2%. Its duration of action is slightly less than that of bupivacaine in the epidural technique, and it appears to produce slightly less motor blockade than a comparable concentration of bupivacaine.

In addition to the use of epinephrine as an epidural additive, some anesthesiologists recommend modifying epidural local anesthetic solutions to increase both the speed of onset and the quality of the block produced. One recommendation is to alkalinize the local anesthetic solution by adding bicarbonate to it to achieve both these purposes. Nevertheless, the clinical advisability of routinely adding bicarbonate to local anesthetic solutions should be determined by local practice protocols.