Probe in the transverse plane approximately in the center of the patient’s back
Fig. 13.2
Midline transverse probe placement: spinous view (SP spinous process, AS acoustic shadow behind spinous process and laminae, PM paraspinous muscle, L lamina)
Fig. 13.3
Midline transverse probe placement: interspinous view (IL interspinous ligament, FJ facet joint, LF/DC ligamentum flavum/dura complex, IS intrathecal space)
Fig. 13.4
B-mode image of the ligamentum at L4–L5 interspace (L4 and L5 lumbar vertebrae, LF/DC ligamentum flavum/dura complex)
When utilizing a longitudinal approach, place the transducer in a paramedian sagittal plane 2–3 cm from the midline (Fig. 13.5), and tilt the probe medially to obtain a paramedian sagittal oblique view. The lamina/articular processes of each vertebral level can be visualized as hyperechoic humps, which form a sawtooth pattern. The hyperechoic line of the ligamentum flavum can be visualized in the paramedian interlaminar spaces. It is helpful to identify the L5–S1 junction, and from that point, the provider can count up to the desired level.
Fig. 13.5
Paramedian sagittal probe orientation
First, identify the L5–S1 junction by visualizing the sacrum, which will appear as a hyperechoic curvilinear structure. Scanning in a cephalad direction from the sacrum, the lamina/articular processes of each vertebral level can be visualized as hyperechoic humps which form a sawtooth pattern. Continue to slide the probe until the appropriate level has been identified. Once the chosen level is positioned in the center of the ultrasound image, a mark on the patient’s skin is made in the center of the probe (Fig. 13.6). Obtain a short axis view by rotating the probe 90° at the desired spinal level with the ultrasound probe in a transverse plane on the midline. Slide the probe cephalad or caudad to obtain a transverse interspinous view of the desired interspace. A slight cephalad tilt of the probe may be necessary to visualize the ligamentum flavum, and this angle should be noted as this is the same angle your needle will need to be inserted. Mark on the patient’s skin at the midpoint of the probe’s long and short sides. The needle insertion site should be the intersection of these two marks (Fig. 13.7).
Fig. 13.6
The center of the ultrasound image is aligned over the spinous process, and a mark is made on the patient’s skin in the center of the probe
Fig. 13.7
(a) Marks indicating midline of long and short probe axes. (b) Needle insertion should be at the intersection of these two dots
At this point, it is beneficial to freeze the ultrasound image. The ultrasound machine’s electronic calipers can be used to measure the depth from the skin to the ligamentum flavum to provide the expected depth of needle insertion (Fig. 13.8). Be careful not to use excessive pressure with the ultrasound probe, as this will depress the patient’s skin and subcutaneous tissue, which could predict a falsely lower estimated depth of needle insertion.
Fig. 13.8
The ultrasound machine’s electronic caliper function measures the depth from the skin to the ligamentum flavum to provide the expected depth of needle insertion (IS intrathecal space, LF/DC ligamentum flavum/dura complex)
After the above landmarks have been identified as described above, the area should be prepped and draped in a sterile fashion to comply with facility guidelines and policies. The spinal needle should be inserted at the respective mark on the skin, and the initial angle should attempt to reproduce the cephalad angulation used with the ultrasound probe needed to obtain the interspinous view. When a “pop” is perceived as the spinal needle passes the dura mater, the stylet should be removed to observe the flow of cerebral spinal fluid from the needle hub. Measurement of the skin to ligamentum flavum obtained above will predict the expected depth of needle insertion.
Blood Patch
The epidural space can be identified by the procedure described in detail above with a loss of resistance technique. With a blood patch, a second operator can facilitate the procedure by obtaining approximately 15–20 ml of the patient’s blood from a peripheral site in a sterile fashion. The blood is injected into the epidural space under real-time ultrasound scanning. Post injection, an increase in space between the ligamentum flavum and posterior dura and the posterior longitudinal ligament and anterior dura can be noted on ultrasound. The use of real-time ultrasound-guided placement of a blood patch is limited albeit it can reliably confirm placement of injectate into the epidural space [6].
Epidural Block
An ultrasound-guided epidural block is approached similarly to a lumbar puncture by initially using the midline transverse probe placement to obtain spinous and interspinous views. Again, a mark on the patient’s skin is made at the midpoint of the probe’s long and short sides. The epidural needle should be inserted at the respective mark on the skin, and the initial angle should attempt to reproduce the cephalad angulation used with the ultrasound probe needed to obtain the interspinous view. A loss of resistance to air or saline technique, indicating penetration through the ligamentum flavum, should be employed for epidural procedures to confirm entry into the epidural space and to avoid dural puncture. Once the epidural space is identified by employing a loss of resistance or hanging drop technique, a catheter may be advanced through the Tuohy needle for continuous or re-dosable analgesia through a bolus or a continuous infusion. Typically, 4–5 cm is added to the depth of the Tuohy needle to ensure that the catheter remains in the epidural space. After placement, the catheter should be aspirated for blood or CSF to detect intravascular or intrathecal placement, respectively. A test dose of lidocaine with epinephrine should be administered after a negative aspiration to confirm an extravascular and epidural catheter placement. It should be noted that an intravascular injection of epinephrine would produce clinical signs such as tachycardia, and lidocaine can elicit a metallic taste in the mouth, dizziness, or tinnitus. An intrathecal injection could produce motor blockade of the lower extremities [7]. Once proper placement is confirmed, adequate analgesia can be reached by intermittent bolus or continuous infusion dependent upon the patient’s clinical picture.
Paravertebral Block
Identify the appropriate spinal level by holding the ultrasound probe perpendicular to the ribs (Fig. 13.9) approximately 5 cm lateral to midline. The appropriate level can be located by counting ribs from the 1st rib and counting down or counting up from the 12th rib. After identifying the appropriate spinal level, rotate the ultrasound probe so that it is oriented parallel to the ribs and perpendicular to the spine (Fig. 13.10). Identify the rib by sliding the probe cephalad or caudad. The rib will appear as a bright hyperechoic (white) line with ultrasound dropout below (black). Medially the rib articulates with the transverse process, which is often identified with a slight depression at the point of articulation. While remaining parallel to the rib, slide the probe caudally. The transverse process will remain in view, but the intercostal muscles will come into view and will have a gray appearance. The internal intercostal membrane is contiguous with the costotransverse ligament and may be visualized as a thin hyperechoic (white) line extending from the transverse process. Deep to the intercostal muscles will be a bright hyperechoic line; this is the pleura of the lung. This will appear different to the rib as the ultrasound waves can penetrate to the deeper lung tissue, which can appear to shimmer and move with patient respirations (Fig. 13.11). The needle is inserted in-plane to the ultrasound probe from a lateral to medial direction (Fig. 13.12). It is important to not advance the needle medial to the transverse process, because this will increase the risk of entering the spinal or epidural space. The goal is to advance the needle through the internal intercostal membrane deep to the transverse process just above the pleura (Fig. 13.13). It is essential to be aware of the position of the needle tip at all times to avoid complications such as pneumothorax and spinal or epidural injections. After aspiration of the needle, local anesthetic can be incrementally injected. An anterior displacement of the pleura is typically observed. Hydrodissection with preservative-free normal saline may help accurately identify needle tip position prior to local anesthetic injection. This also assures proper placement of the local anesthetic. This procedure can be repeated at each desired level.
Fig. 13.9
Probe orientation for identifying appropriate spinal level
Fig. 13.10
After identifying the appropriate spinal level, the ultrasound transducer has been rotated so that it is oriented parallel to the ribs and perpendicular to the spine
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