2. Ausgabe 1995

Thoracic epidural anesthesia

T. T. Horlocker

Introduction

Thoracic epidural anesthesia was introduced fifty years ago to provide anesthesia to awake unintubated patients during intrathoracic surgical procedures (Crawford, 1952). Subsequently, thoracic epidural anesthesia and postoperative analgesia have been utilized in the intraoperative and postoperative anesthetic management of patients undergoing thoracic and upper abdominal surgery (Stanton-Hicks, 1988; Zwarts, 1989). Although lumbar spinal and epidural blockade are often preferred by the anesthesist, primarily because of the technically less difficult needle placement and decreased probability of dural puncture and neural injury, thoracic epidural anesthesia provides selective blockade of the surgical site, with diminished requirements of opioids and local anesthetics. In addition, thoracic epidural techniques have recently been utilized in the management of acute and chronic pain syndromes, such as postoperative thoracotomy pain and pain due to cancer (de Leon-Casasola, 1952). In patients with coronary artery disease, thoracic epidural anesthesia relieves anginal pain, decreases preload and afterload, and improves left ventricular wall motion and coronary artery blood flow (Blomberg, 1989 and 1990).

Anatomy

The vertebral column is made up of 7 cervical, 12 thoracic, and 5 lumbar vertebra, in addition to the sacrum and coccyx. All of the vertebrae have common features. A typical vertebrae consists of a body, an arch made up of two pedicles anteriorly and two laminae posteriorly. The transverse processes emanate from the junction of the pedicles and laminae, while the spinous process projects posteriorly from the junction of the laminae. The angle of projection of the spinous process varies depending on the region. The spinous processes change cephalocaudal angle from almost perpendicular at T1, to strongly caudal at T7 (with the tip of the process overlying the bottom of the T8 lamina), and again perpendicular at T11-12. This makes midline access to the epidural space almost impossible from T5 to T9. Therefore, a paramedian approach for epidural needle placement is recommended at these levels.

The ligaments in the thoracic region are similar to those in the lumbar region. However, the ligamentum flavum is thickest and strongest in the lumbar region, and progressively weakens with ascending levels. The ligamentum flavum is thinnest in the midline, and becomes thicker laterally. The depth of the epidural space (distance from ligamentum flavum to dura) is 5 to 6 mm at L2, 3 to 4 mm in the midthoracic region, and only 1 to 2 mm in the cervical region.

Topographical landmarks are helpful in determining needle insertion site. The spinous process of C7 is the most prominent process, and may be readily palpated in most individually. The spine of the scapula is at the level of T3. Also, the lower pole of the scapula lies at approximately T7, although scapular motion is independent of the spine. The twelfth rib, if palpable, can help determine T2 spinous process; the angle of the rib to the spine is usually fairly acute (approximately 45o ), but increases with "barrel chests" and emphysema. This acute angle should be considered in tracing the rib back to the spine to avoid estimating too low. Often, each interspace between spinous processes is palpable, allowing accurate determination of the thoracic spinous processes.

Thoracic epidural technique

Midline thoracic epidural approach is similar to lumbar needle placement, and only requires proficiency with the technique, since the spinal cord is present at thoracic levels. However, in the mid-thoracic region, midline access is almost impossible because of the bony fortification of the spinal cord, and the epidural space must be approached laterally. One method of achieving the three dimensional visualization required for thoracic epidural techniques is to initially practice the paramedian approach to lumbar epidural anesthesia.

The level of needle insertion is typically one level below the midpoint of the surgical site, for example, a T10 insertion site for an open cholecystectomy. The midline approach may be used in the upper and lower thoracic regions. However, the paramedian approach is preferable between T2 and T10 (Bromage, 1978). Paramedian needle insertion site is 1-1,5 centimeters lateral to the spinous process of the cephalad vertebra of the interspace. After local infiltration, the epidural needle is advanced perpendicular to the back (not medial or cephalad), advancing to the lamina and walked cephalad to the interlaminar grove. The needle should be minimally advanced, since it often can pass directly into the epidural and subarachnoid space without further redirection. At this point, a glass or low resistance syringe is attached and the needle advanced using loss of resistance technique. If the upper lamina is encountered during needle advancement, the needle should be redirected medially without withdrawing the needle. If the needle is withdrawn, the position is easily lost and difficult to relocate. After redirecting medially, the needle is advanced into the epidural space through ligamentum flavum. If bone is still contacted, the needle should be walked along the interlaminar grove medially until advancement is possible. It should be noted that with the paramedian approach, there may be no resistance to injection until the ligamentum flavum is encountered. If in doubt, withdraw the needle 5 millimeters and readvance, seeking resistance to injection, then loss of resistance. Indwelling epidural catheters typically advance easily into the thoracic epidural space. Only 3 to 4 cm of catheter is inserted.

Clinical Applications

Epidural local anesthetic block will give bilateral localized dermatomal analgesia or anesthesia, avoiding lumbosacral block and vascular dilation in those dermatomes. The even numbered thoracic dermatomes have easily remembered sites to test for sensory blocks; T2 at the axilla anteriorly, T4 at the nipple, T6 at the xiphoid process, T8 at the lower margin of the ribs anteriorly, T10 at the umbilicus, and T12 at the inguinal fold. The number of dermatomes blocked per unit volume of anesthetic is variable and should be titrated.

Extrathoracic and upper abdominal surgery may be performed under thoracic epidural anesthesia alone if indicated. However, epidural anesthesia is commonly combined with general anesthesia for intrathoracic surgery and procedures involving the diaphragm. Inhalational agents provide amnesia and allow endotracheal intubation in patients undergoing a combined anesthetic technique. Minimal expired concentrations of the volatile anesthetics (0.25-0.5 % isoflurane) are required intraoperatively.

Postoperatively, local anesthetic and/or opioid infusions may be utilized for continuous epidural analgesia. A combination of local anesthetics and opioids allows decreased dosages and concentrations of both agents, theoretically reducing the risk of side effects and complications. Epidural solutions of 0.01 % morphine with 0.05-0.1 % bupivacaine or 0.001 % fentanyl with 0.2 % bupivacaine with infusion rates of 3 to 8 mL/h have been successfully and safely utilized.

Complications

Failed block is the most common "complication" for thoracic epidurals. A consistent approach will minimize this. Two pitfalls are important to note, particularly with paramedian approach. A fairly distinct loss of resistance is obtained by passing through the interspinous ligament, and a catheter will often pass along the lamina. Cephalad, rather than medial, needle advancement will avert this occurrence during paramedian epidural placement. In addition, a paresthesia obtained by catheter placement (after the initial exit from the needle tip) often occurs at the intravertebral foramen; further advancement takes the catheter out of the epidural space and results in a unilateral block. Therefore, catheter insertion distance should be limited to 3 to 4 cm and the patient tested for the presence of bilateral block.

Dural puncture is another complication of thoracic epidural anesthesia. In the thoracic region, the dural sac is closer to the ligamentum flavum, and the spinal cord is in close proximity to the dura. A dural puncture carries the risk of direct spinal cord injury. However, persistent paresthesias occur more frequently with lumbar techniques compared to thoracic techniques (Tanaka, 1993).

Keywords
Thorakale Epiduralanaesthesie

Anschrift

Literatur
[1] Bromage P.R. (1978), Identification of the epidural space. In: Bromage P.R. (ed), Epidural Analgesia. W.B. Saunders Company, Philadelphia, pp 176-214

[2] Blomberg S. (1990), Effects of thoracic epidural anesthesia on coronary arteries and arterioles in patients with coronary artery disease. Anesthesiology 73:840

[3] Blomberg S. (1989), Thoracic epidural anesthesia and central hemodynamics in patients with unstable angina pectoris. Anesth Analg 69:558

[4] Crawford O.B. (1952), Peridural anesthesia for thoracic surgery. N Y State J Med 52:2637

[5] de Leon-Casasola O.A. (1992), Experience using epidural bupivacaine-morphine infusions for post-operative analgesia in 2843 cancer surgical patients. Anesthesiology 77:856

[6] Stanton-Hicks M.D. (1988), High thoracic epidural with sufentanil for post-thoracotomy pain. Reg Anesth 13:62

[7] Tanaka K. (1993), Extensive applications of epidural anesthesia and analgesia in a university hospital: Incidence of complications related to technique. Reg Anesth 18:34

[8] Zwarts S.J. (1989), The effect of continuous epidural analgesia with sufentanyl and bupivacaine during and after thoracic surgery on the plasma cortisol concentration and pain relief. Reg Anesth 14:183

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