Background and Objectives Erector spinae block is an ultrasound-guided interfascial plane block first described in 2016. The objectives of this cadaveric dye injection and dissection study were to simulate an erector spinae block to determine if dye would spread anteriorly to the involve origins of the ventral and dorsal branches of the spinal nerves. Methods In 10 unembalmed human cadavers, 20 mL of 0.25% methylene blue dye was injected bilaterally into the plane between the fifth thoracic transverse process and erector spinae muscle. An in-plane ultrasound-guided technique with the transducer orientated longitudinally was used. During dissection, superficial and deep muscles were identified, and extent of dye spread was documented in cephalocaudal and lateral directions. The ventral and dorsal rami of spinal nerves and dorsal root ganglion at each level were examined to determine if they were stained by dye. Results There was extensive cephalocaudad and lateral spread of dye deep and superficial to the erector spinae muscles. Except for 1 injection (from 20), the ventral rami were not stained by the dye. In only 2 injections did the dye track posteriorly through the costotransverse foramen to the dorsal root ganglion. In all other cases, the dorsal root ganglia were not involved in the dye injection. The dye stained the dorsal rami posterior to the costotransverse foramen. Conclusions There was no spread of dye anteriorly to the paravertebral space to involve origins of the ventral and dorsal branches of the thoracic spinal nerves. Dorsal ramus involvement was posterior to the costotransverse foramen.

The transversus abdominis plane (TAP) block is a new regional anaesthesia technique that provides analgesia after abdominal surgery. It involves injection of local anaesthetic into the plane between the transversus abdominis and the internal oblique muscles. The TAP block can be performed using a landmark technique through the lumbar triangle or with ultrasound guidance. The goal of this anatomical study with dye injection into the TAP and subsequent cadaver dissections was to establish the likely spread of local anaesthesia in vivo and the segmental nerve involvement resulting from ultrasound-guided TAP block. An ultrasound-guided injection of aniline dye into the TAP was performed for each hemi-abdominal wall of 10 unembalmed human cadavers and this was followed by dissection to determine the extent of dye spread and nerve involvement in the dye injection. After excluding one pilot specimen and one with advanced tissue decomposition, 16 hemi-abdominal walls were successfully injected and dissected. The lower thoracic nerves (T10-T12) and first lumbar nerve (L1) were found emerging from posterior to anterior between the costal margin and the iliac crest. Segmental nerves T10, T11, T12, and L1 were involved in the dye in 50%, 100%, 100%, and 93% of cases, respectively. This anatomical study shows that an ultrasound-guided TAP injection cephalad to the iliac crest is likely to involve the T10-L1 nerve roots, and implies that the technique may be limited to use in lower abdominal surgery.

Tructures, and the approaching needle. We compared a single- versus dual-injection technique for ultrasound-guided paravertebral blockade in a cadaver model, evaluating the spread of contrast dye and location of a catheter. METHODS: Thirty paravertebral injections and 20 catheter placements were performed on 10 fresh cadavers. The paravertebral space was identified using an ultrasound probe in the transverse plane using a linear transducer. An in-plane needle approach was used. Using analine contrast dye, a single 20-mL injection at T6-7 on one side and a dual-injection technique of 10 mL at T3-4 and T7-8 on the contralateral side were performed on each cadaver, followed by insertion of a catheter through the needle. The cadaver was then dissected to evaluate spread of contrast dye and catheter location. RESULTS: The paravertebral space was easily identified with ultrasound on each cadaver. Contrast dye was seen to surround somatic and sympathetic nerves in the paravertebral, intercostal, and epidural spaces. Contrast dye was present in 19 of 20 paravertebral spaces over 3 to 4 segments (range, 0–10) with no significant differences between single- and dual-injection techniques. Contrast dye spread more extensively across intercostal segments with 4.5 spaces (range, 2–10) covered with a single injection and 6 spaces (range, 2–8) covered with a dual-injection technique (P = 0.03). There was epidural spread of contrast in 40% of paravertebral injections in both single- and dual-injection techniques. Catheters were located in the paravertebral space (60%), prevertebral space (20%), and epidural space (5%). CONCLUSIONS: Transverse in-plane ultrasound-guided needle insertion into the thoracic paravertebral space is both feasible and reliable. However, paravertebral spread of contrast is highly variable with intercostal and epidural spread likely contributing significantly to the analgesic efficacy. A dual-injection technique at separate levels seems to cover more thoracic dermatomes because of greater segmental intercostal spread (rather than paravertebral spread) than a single-injection approach. Catheters are located in nonideal positions in 40% of cases using this in-plane technique....