Ultrasound-guided thoracic epidural block is utilized in a variety of clinical scenarios as a diagnostic, prognostic, and therapeutic maneuver as well as to provide surgical anesthesia for thoracic and upper abdominal surgeries. As a diagnostic tool, ultrasound-guided thoracic epidural block allows accurate placement of the epidural needle tip within a specific area of the epidural space when performing differential neural blockade on an anatomic basis in the evaluation of chest wall and intra-abdominal pain. As a prognostic tool, ultrasound-guided thoracic epidural block can be utilized as a prognostic indicator of the degree of motor and sensory impairment that the patient may experience if thoracic nerve roots are going to be destroyed in an effort to palliate intractable pain in patients too sick to undergo neurosurgical destructive procedures. In the acute pain setting, ultrasound-guided thoracic epidural block with local anesthetics and/or opioids may be used to palliate acute pain emergencies while waiting for pharmacologic, surgical, and/or antiblastic methods to become effective. This technique has great clinical utility in both children and adults when managing acute postoperative and posttrauma pain. Sympathetically mediated pain syndromes including the pain of acute herpes zoster of the thoracic dermatomes, intractable angina, phantom breast syndrome, and the pain of acute pancreatitis can also be effectively managed with epidurally administered local anesthetics, steroids, and/or opioids. Pain of malignant origin of the chest wall, flank, and abdomen as well as spinal metastatic disease (especially from breast and prostate primary cancers) is also amenable to treatment with epidurally administered local anesthetics, steroids, and/or opioids (Fig. 87.1).

The cephalad boundary of the epidural space is the fused periosteal and spinal layers of dura at the level of the foramen magnum. The caudad border of the epidural space is the fused layers of connective tissue that make up the sacrococcygeal membrane. Anteriorly, the thoracic epidural space is bounded by the posterior longitudinal ligament. Posteriorly, the thoracic epidural space is bounded by the vertebral laminae and the ligamentum flavum (Fig. 87.2). The vertebral pedicles and intervertebral foramina form the lateral limits of the epidural space. The thoracic epidural space is 3 to 4 mm at the C7-T1 interspace with the cervical spine flexed and ˜5 mm at the T11-T12 interspace. The thoracic epidural space contains fat, veins, arteries, lymphatics, and connective tissue.

From the standpoint of performing ultrasound-guided epidural blocks, the upper thoracic vertebral interspaces from T1-T2 and the lower thoracic vertebral interspaces from T10-T12 are functionally equivalent insofar as the technique of epidural block is concerned, being most analogous to performing a lumbar epidural block. The thoracic vertebral interspaces between T3 and T9 are morphologically and functionally unique when compared with the T1-T2 and T10-T12 segments because of the acute downward angle of the spinous processes (Fig. 87.3). Blockade of these middle thoracic interspaces requires use of the paramedian oblique or transforaminal approach to the thoracic epidural space, and the close proximity of the spinous processes limits the size of the acoustic window, thus decreasing the utility of ultrasound guidance (Fig. 87.4).

Ultrasound-guided thoracic epidural block can be carried out by placing the patient in the sitting position with the head resting comfortably on a padded bedside table and the arms resting comfortably on the patient’s lap (Fig. 87.5). A total of 5 to 7 mL of local anesthetic is drawn up in a 10-mL sterile syringe. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic. If performing ultrasound-guided epidural block in the upper thoracic or lower thoracic levels, the technique is more analogous to that used for ultrasound cervical or thoracic epidural block, and a transverse interlaminar ultrasound view is easily obtained. Because of the more
sharply angled spinous processes of the midthoracic spine, a clinically usable interlaminar view is more elusive. In the midthoracic region, a parasagittal oblique view will offer the greatest clinical utility.

To perform ultrasound-guided thoracic epidural block, a three-step process is used. Although this may seem cumbersome, the three-step process allows the clinician to quickly identify critical anatomic structures while at the same time maintaining a transducer position that allows a safe and easy placement of needles into the thoracic epidural space.

Step one is to obtain a paramedian sagittal transverse process view by placing the 2- to 5-MHz low-frequency curvilinear probe in the longitudinal plane 3 to 4 cm lateral to the right side of the middle of the spinous processes at the level to be blocked for the right-handed clinician and 3 to 4 cm to the lateral to the left side of the middle of the spinous processes at the level to be blocked for the left-handed clinician (Figs. 87.6 and 87.7). An initial depth setting of 7 to 8 cm will work for most patients. An ultrasound survey is taken, and the transducer is slowly moved medially and laterally until successive transverse processes are visualized. The transverse processes of the thoracic spine will appear as hyperechoic domes with sausage-like acoustic shadows beneath them (Fig. 87.8). This classic appearance of successive transverse processes viewed in the longitudinal plane has been named the “trident sign” after Neptune’s trident (Fig. 87.9).

After the transverse processes are identified in the paramedian sagittal transverse process view, the ultrasound transducer is slowly slid toward the midline until the superior and inferior articular facets are visualized (Step Two) (Figs. 87.10 and 87.11).
In longitudinal paramedian ultrasound articular process view, the superior and inferior articular facets will appear as successive hyperechoic hills and valleys, with each hill representing a facet joint (Fig. 87.12).