Lateral thoracolumbar interfascial plane block is utilized as an alternative to paravertebral nerve block and lower thoracic and lumbar epidural block to provide surgical anesthesia for surgeries involving the lower posterior thorax, lower back, lower thoracic spine, and lumbar spine (Fig. 104.1). This technique has great clinical utility in both children and adults when managing acute postoperative and posttrauma pain in the area subserved by dorsal rami of the thoracolumbar nerves including back, lower thoracic, and lumbar spine surgeries pain. Continuous lateral thoracolumbar interfascial plane block techniques have been utilized to provide prolonged analgesia following back and lumbar spine surgery. The area of anesthesia following lateral thoracolumbar interfascial plane block is determined in part by the volume of local anesthetic injected and the level at which the block is performed. Clinical experience suggests that it will require between 3 and 5 mL of local anesthetic to block a dermatome and that if a catheter is being used for continuous blockade, the use of a curved-tip epidural needle to direct the catheter either cephalad or caudad can also influence the area of anesthesia.

The primary targets of the lateral thoracolumbar interfascial plane block are the dorsal and possibly the ventral rami of the spinal nerves, which are blocked when local anesthetic is placed between the interfascial plane between the longissimus and iliocostalis muscles (Fig. 104.2).

The anatomic basis for the lateral thoracolumbar interfascial plane block is the fact that the fascia surrounding the muscles of posture creates potential compartments than can contain local anesthetics when injected within the facial compartments. Because the nerves contained within or in proximity to these fascial compartments traverse these fascial compartments, they are amenable to neural blockade at various points along their paths. Since these fascial compartments can potentially prevent the spread of local anesthetic to block other nerves, repositioning of the needle tip into adjacent fascial compartments may be required in order to provide complete anesthesia and analgesia for the area desired.

To perform ultrasound-guided lateral thoracolumbar interfascial plane block, place the patient in the sitting position, lateral, or prone position as the clinical situation dictates. If a bilateral block is required for incisions involving the midline, the sitting or prone positions have the advantage over the lateral position of not having to reposition the patient to block the contralateral side. If the lateral position is used, the side to be blocked should be superior. A total of 20 mL of local anesthetic is drawn up in a 20-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. A high-frequency linear transducer is placed in the transverse orientation at the midline at the level of the iliac crest and is slowly moved laterally until the longissimus and iliocostalis muscles are identified (Fig. 104.3). Under continuous ultrasound imaging, the transducer position is fine-tuned to identify the fascial plane between the longissimus and iliocostalis muscles (Fig. 104.4). Intentional identification of the transverse process should be carried out prior to needle placement to avoid inadvertent injury to neuroaxial structure. Color Doppler will aid in the identification of vasculature within the operative field. When these anatomic structures are clearly identified on ultrasound scan, the skin is prepped with anesthetic solution and a 3½-inch, 22-gauge needle is advanced from the medial aspect of the ultrasound transducer using an in-plane approach with the trajectory being adjusted under real-time ultrasound guidance from a medial to lateral direction until the needle tip is resting within longissimus muscle. At that point, after careful aspiration, a small amount of solution is injected under

real-time ultrasound imaging to utilize hydrodissection to confirm the position of the needle tip within the substance of the longissimus muscle. Once the position of the needle tip is reconfirmed, the needle is carefully advanced into the interfascial plane between the longissimus and iliocostalis muscles. After careful aspiration, a small amount of solution is again injected to aid in identification of the exact position of the needle tip. If the needle tip is intramuscular, the hydrodissection of either the longissimus or iliocostalis muscles will appear globular in nature, while if the needle tip is within the fascial
plane, the solution will be seen to open the space between the two muscles (see Fig. 104.2). After careful aspiration, the remainder of the solution is slowly injected under ultrasound guidance, which will demonstrate a further spreading of the interfascial plane. There should be minimal resistance to injection. The needle is then removed, and a sterile pressure dressing and ice pack are placed at the injection site. Should continuous blockade be desired for postoperative or posttrauma pain relief, a blunt Hustead or Tuohy needle may be used, and the curved tip should be oriented toward the anatomic area to be blocked prior to catheter placement.