Use of this content is subject to the Terms and Conditions of the MD Consult web site.
Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
< Previous Next >

Chapter 49 – Epidural Block

PERSPECTIVE

Epidural anesthesia is the second primary method for 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 48 , 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, thereby allowing reinjection and prolongation of the 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 can be produced that does not block the lower extremities.

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 intra-abdominal procedures involving the upper abdomen, it is advisable to combine this technique with light general anesthesia because diaphragmatic irritation can make the patient, surgeon, and anesthesiologist uncomfortable. Other candidates for epidural anesthesia are patients in whom a continuous technique has been found to be increasingly helpful for providing epidural local anesthetic and/or opioid analgesia postoperatively following major surgical procedures. This application alone probably explains the increased interest in epidural block.

Pharmacologic Choice.

To utilize 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-, intermediate-, and long-acting agents; when epinephrine is added to these agents, surgical anesthesia ranging from 45 to 240 minutes following 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 is preferred for techniques that do not require muscle relaxation.

Lidocaine, the prototypical amino amide local anesthetic, 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 15 to 30 minutes longer at equivalent dosages. Epinephrine significantly prolongs (i.e., by approximately 50%) the duration of surgical anesthesia with 2-chloroprocaine and both lidocaine and mepivacaine. Plain lidocaine produces surgical anesthesia that lasts 60 to 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% to 0.25%. Its duration of action is not prolonged as consistently as by 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. Analgesic techniques can be performed 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 purposes. Nevertheless, the clinical advisability of routinely adding bicarbonate to local anesthetic solutions should be determined by the local practice settings.

< Previous Next >

About MD Consult Contact Us Terms and Conditions Privacy Policy Registered User Agreement
Copyright © 2007 Elsevier Inc. All rights reserved. www.mdconsult.com 
Bookmark URL: /das/book/0/view/1353/140.html/top