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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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If catheters can be avoided during epidural anesthesia (i.e., by selecting an appropriate local anesthetic), a potential source of difficulty with the technique can also be avoided. Epidural catheters can be malpositioned in a number of ways. If a catheter is inserted too far into the epidural space, it can be routed out of the foramina, resulting in a patchy epidural block. The catheter can also be inserted into the subdural or subarachnoid space or into an epidural vein. Similarly, the use of epidural catheters may be complicated by a prominent dorsomedian connective tissue band (epidural septum or fat pad) that is found in some patients.

Another means of facilitating the success of epidural anesthesia is to allow the block enough “soak time” prior to beginning the surgical procedure. This is most effectively accomplished if the block is carried out in an induction room separate from the operating room. The anesthesiologist should be aware that there appears to be a plateau effect in the doses of epidural local anesthetics. That is, once a certain quantity of local anesthetic has been injected, more of the same agent does not significantly increase the block height but, rather, may make the block denser, perhaps improving its quality.

One observation about epidural anesthesia through a catheter that needs to be reemphasized is the often faulty “clinical logic” that by giving incremental doses through a catheter the level of sensory anesthesia can be slowly developed, thereby allowing frail and physiologically compromised patients to undergo epidural anesthesia. I believe that often the logic behind this concept is flawed. Usually when this approach is taken, anesthesiologists do not allow enough time between injections because of the reality of time pressures in the normal operating room. They inject small doses through the catheter but then do not allow sufficient time to pass before they perform the next incremental injection. Often the clinical result is high block levels in just those patients in whom lower levels were the goal. Furthermore, this approach to epidural anesthesia unnecessarily delays making the patient ready for the operation and makes surgical and nursing colleagues less accepting of the technique.

Epidural catheters are indicated in some situations, especially when the technique is used for postoperative analgesia. To place a known length of catheter into the epidural space, the catheter must be marked, and either a way must be found to maintain the catheter’s position once the needle has been withdrawn over the catheter, or else both the needle and the catheter must have distance markings. Because many epidural needles do not have distance markers, a method for maintaining catheter position while the needle is withdrawn over the catheter is required. One technique for positioning the catheter is illustrated in Figure 49-14 . An object of known length, such as a syringe or the anesthesiologist’s finger, is selected, and that object is placed next to the needle catheter assembly after the catheter has been inserted 3 cm into the epidural space. Because the catheter is marked, a known point on the catheter can be conceptually related to a known point on either the finger or the syringe. As shown in Figure 49-14 A , the 15-cm mark is opposite the plunger on the syringe or the anesthesiologist’s knuckle. Once this relation has been noted, the needle is removed while the catheter position is maintained. The measurement object is then placed next to the catheter (as illustrated in Fig. 49-14 B ), and the catheter is withdrawn to the point at which the distance marker on the catheter relates to the previously identified point. In this example, the 15-cm mark on the catheter is placed opposite the plunger of the syringe or the anesthesiologist’s knuckle. Using this technique, the epidural catheter can be accurately placed without the need for either a marked needle or a ruler.

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Figure 49-14  Epidural block: catheter measurement technique.

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