Fig. 28.1
(a) Surface anatomy for thoracic paravertebral block. (b) Skeletal model showing the L4 transverse process and posterior superior iliac spine (PSIS) landmarks
Transverse processes: At T1, the transverse process is located directly lateral to its corresponding spinous process. Subsequent transverse processes are extended to increasingly cephalad locations (i.e., the T7 transverse process is lateral to T6 spinous process) due to the increasingly inferior angulation of the spinous processes. The inferior borders of the relevant transverse processes are marked on the skin, and a line is drawn through these marks.
Lumbar Paravertebral Block
Spinous processes: Typically, the spinous process of L4 is at the level of the iliac crests (neonates and infants have a proportionally smaller pelvis, and the sacrum is located more cephalad relative to the iliac crests; in neonates and infants, the intercristal line crosses the midline of the vertebral column at the L4–L5 or L5–S1 interspace [3, 4]). A vertical line intersecting the posterior superior iliac spine (S2 level) is drawn (Fig. 28.1b).
Transverse processes: The transverse processes of the lumbar spine are long and slender and are located directly lateral to their corresponding spinous process. The inferior borders of the relevant transverse processes are marked on the skin, and a line is drawn through these marks.
The distance between the spinous process and the corresponding transverse process is variable, depending on the patient’s age. At the thoracic level, the needle puncture site is lateral to the spinous process but may be 1 cm or larger (2.5 cm) (Fig. 28.1a). For the lumbar levels, the puncture site is also 1–2.5 cm lateral to the corresponding spinous process (Fig. 28.2).
Fig. 28.2
Surface anatomy for lumbar paravertebral block
28.3.1.3 Needle Insertion
Thoracic Paravertebral Block
After aseptic skin preparation and patient sedation, local anesthetic skin wheals are raised at the marked transverse processes.
If using nerve stimulation, an insulated needle (5–8 cm, 22G needles are used, depending on the size of the child) is introduced through the skin wheal in the sagittal plane and directed slightly cephalad to contact the transverse process or, sometimes, likely the costotransverse ligament.
Gentle cephalad or caudad exploration may be required to identify the bone.
The depth of the transverse process should be carefully noted on the needle shaft.
The needle is now withdrawn from the transverse process to the skin level and reinserted 10° superiorly (to target the spinal nerve corresponding to the spinous process) or inferiorly (corresponding to the vertebral level below the spinous process) and slightly deeper (usually up to a maximum of 1 cm) than the previously marked point of bone contact.
The needle should be angled slightly medially to avoid causing pneumothorax. There will be a subtle “give” at the midpoint between these landmarks (spinous and transverse processes), indicating entrance into the paravertebral space.
For the loss-of-resistance technique, an epidural set containing an 18G–22G (the latter for children under 6 months of age) Tuohy needle with a syringe is used. After walking off the transverse processes, a “pop” or loss of resistance to air or D5W may be felt when entering the paravertebral space through the costotransverse ligament.
Lonnqvist et al. [1] reported calculations using computed tomography for determining both the depth of the paravertebral space from the skin (S-PVS depth) and the lateral distance of the paravertebral space from the spinous process (SP-PVS distance) since they correlate with the patient’s body weight:
1.
2.
Lumbar Paravertebral Block
After aseptic skin preparation and patient sedation, local anesthetic skin wheals are raised at the marked transverse processes.
If using nerve stimulation, an insulated needle (5–8 cm, 22G needles are used, depending on the size of the child) is introduced through the skin wheal in the sagittal plane, penetrating the fascia surrounding the quadratus lumborum muscle to contact the transverse process.
Gentle cephalad or caudad exploration may be required to identify the bone.
The depth of the transverse process should be noted on the needle shaft.
The needle is now withdrawn from the transverse process to the skin level and reinserted 10° superiorly (to target the spinal nerve corresponding to the spinous process) or inferiorly (corresponding to the vertebral level below the spinous process) and slightly deeper (up to a maximum of 1 cm) than the previously marked point of bone contact, sliding off the superior or inferior edge of the transverse process.
There will be a subtle “give” at the midpoint between these landmarks (spinous and transverse processes), indicating entrance into the paravertebral space.
For the loss-of-resistance technique, an epidural set containing an 18G–22G (the latter for children under 6 months of age) Tuohy needle with a syringe is used. After walking off the transverse processes, a “pop” or loss of resistance to air or D5W may be felt when entering the paravertebral space through the ligament.
Clinical Pearl
For intermittent or continuous blocks, an epidural catheter set is used, and the catheter is advanced 2–3 cm into the paravertebral space. After aspiration of the catheter, a test dose using lidocaine 1 % (0.1 mL/kg) with 1:200,000 epinephrine (0.5 μg/kg), followed by a bolus dose (0.5 mL/kg) of local anesthetic (0.125–0.25 % bupivacaine, depending on age and weight of the child), can be injected over 5–10 min. Note that the heart rate increase can be unreliable, especially under anesthesia [5]. The continuous block may be maintained with hourly injections of 0.1–0.25 mL/kg/h of the same solution.
28.3.1.4 Local Anesthetic Application
Since the paravertebral space is well-vascularized, inadvertent vascular puncture will often occur, highlighting the need for frequent aspiration and injection in small aliquots.
If depending on multi-segmental block at the thoracic level, inject 0.5 mL/kg of local anesthetic solution (e.g., 0.25 % bupivacaine) with or without epinephrine. This volume should cover at least four to five segments of spinal nerves. If using individual blocks for each segment, the volume of local anesthetic will be reduced to 0.1 mL/kg. Vertical spread of local anesthetic is limited at the lumbar level, so reduced volumes injected at each level will be required. The dose of bupivacaine should not exceed 2 mg/kg. Dilution with normal saline can help increase the volume (to more effectively produce the block) while maintaining safe doses of local anesthetic.
28.3.2 Nerve Stimulation Technique
28.3.2.1 Current Application and Appropriate Responses
An initial current of 1.5–3 mA is used, and the needle is advanced until contractions of the appropriate muscles (e.g., abdominal muscles with thoracic paravertebral block and quadriceps muscle twitch with lumbar paravertebral block) are observed. The current intensity is then reduced to localize the nerves at 0.4–0.6 mA.
Until the paravertebral space is entered, the motor response will be from the paraspinal muscles.
A test dose of local anesthetic (0.1 mL/kg of 1 % lidocaine) will confirm nerve localization, and current dissipation at the needle tip by the conducting solution will eliminate the nerve response.
28.3.2.2 Modifications to Inappropriate Responses
Bilateral muscle twitches of the lower extremity may indicate epidural needle placement. Bilateral twitches at low current (<1 mA) may indicate subdural needle placement.
28.3.3 Ultrasound-Guided Technique
Traditionally, ultrasound imaging has been used prior to (i.e., “pre-procedural,” “supported,” or “off-line” imaging) rather than during (i.e., “real-time” or “on-line” imaging) block performance to identify the deep bony landmarks, including the articular and transverse processes. Real-time imaging for paravertebral blocks is now used widely for both single-shot blocks and catheter insertion [6, 7]. Ultrasound guidance can be used to help identify the paravertebral space and needle placement and to monitor the spread of the local anesthetic. The MRI images in Figs. 28.3, 28.4, 28.5, 28.6, 28.7, and 28.8 correlate to the ultrasound images in these figures, allowing the reader to better understand the anatomy of the region.
