The pleural space extends from the apex of the lung to the inferior reflection of the pleura at approximately L1. It also relates to the posterior and anterior mediastinal structures, as illustrated in
The pleural space extends from the apex of the lung to the inferior reflection of the pleura at approximately L1. It also relates to the posterior and anterior mediastinal structures, as illustrated in Figure 34-1 .
The patient is most often turned to an oblique position with the side to be blocked uppermost, as illustrated in Figure 34-2 . The anesthesiologist stands facing the patient’s back.
Once the patient is positioned properly and supported by a pillow, a skin wheal is raised immediately superior to the eighth rib in the seventh intercostal space, approximately 10 cm lateral to the midline. If a continuous technique is selected, a needle allowing passage of a catheter (often epidural) is selected. If a single injection technique is to be utilized, a short, beveled needle of sufficient length to reach the pleural space can be used. (The proponents of this technique most often advocate intermittent injections via catheter; thus, a single-injection technique is unusual.) Before inserting the needle, a syringe containing approximately 2 mL of saline solution is inserted immediately superior to the eighth rib, utilizing a loss-of-resistance technique much like that used during epidural anesthesia. When the needle tip is in the pleural space, it is easy to inject local anesthetic solution.
Conversely, some clinicians are proponents of a modified “hanging drop” technique to identify entry into the pleural space. These anesthesiologists have suggested a new term, “falling column,” as descriptive of this technique. If the syringe plunger shown in Figure 34-2 were to be removed and the column of solution in the syringe barrel observed, entry of the needle tip into the pleural space would be identified by a falling column of saline solution. The needle is then secured, and the procedure continues as it does with the loss-of-resistance method.
Once the needle is in position, either the local anesthetic is injected (if it is to be a single-shot technique) or a catheter is threaded through the needle. If a catheter is used, it should be threaded approximately 10 cm into the pleural space, taking care to minimize the volume of air entrained through the needle. The catheter is then taped in a position that does not interfere with the surgical procedure, and local anesthetic is injected. Typically, 20 to 30 mL of local anesthetic is injected, and the patient is rolled into the supine position to allow distribution of the local anesthetic.Potential Problems.
Although pneumothorax might seem to be associated with any technique that violates the pleural space, it is apparently an infrequent problem with interpleural anesthesia. Despite this observation, as time passes the true incidence of pneumothorax associated with this technique will become clearer. A second problem with interpleural anesthesia is the unpredictable nature of the analgesia accompanying what seems to be an otherwise acceptable technique. This may be a result of anesthesiologists’ gaining experience with the technique, or perhaps it is the result of overzealous promotion of the technique.