Regional Nerve Blocks in Anesthesia and Pain Therapy

Metadata

• Author: Danilo Jankovic
• Full Title: Regional Nerve Blocks in Anesthesia and Pain Therapy
• Category: #books
• Document Tags: pain regional textbook

Highlights

• There is evidence that tourniquet application may be tolerated better, which is attributed to local anesthetic spread to the intercostobrachial nerve (View Highlight)
  • Note: (infraclavicular BPB)
• the intercostobrachial nerve runs along the inferior aspect of the brachial plexus sheath in the infraclavicular-axillary fossa and is often blocked by anesthetic spread following infraclavicular injection (View Highlight)
• 
  Fig. 25.3
  Course of the infraclavicular brachial plexus with the arm abducted at the shoulder. Note that all the cords of the brachial plexus are clustered superolateral to the axillary artery in the medial portion of the infraclavicular fossa. Lateral cord (white), posterior cord (blue), medial cord (green), axillary artery (red). (View Highlight)
• There is a fascial sheath around the neurovascular bundle that contains and directs the spread of local anesthetic. There is usually a fascial septum that separates the lateral cord from posterior and medial cord; piercing this septum is necessary to achieve the U-shaped local anesthetic spread posterior to the artery that is associated with block success (View Highlight)
• The injection site for posterior TAP blocks is posterior to the midaxillary line. As discussed in Carney’s radiological study, posterior deposition may offer access to the paravertebral space, thus providing additional sympathetic blockade which may in turn prolong analgesia (View Highlight)
• The original approach to the TAP block was a landmark-based technique, using the lumbar triangle of Petit to identify the insertion point (Fig. 32.1). In this method, a needle is inserted posterior to the midaxillary line within the triangle, until two ‘pops’ are appreciated. The first positions the needle in the fascial plane between the external and internal oblique muscles, the second in the desired position between the internal oblique and transversus abdominis muscles.
  
  Fig. 32.1 (View Highlight)
• The TA muscle is a bilateral paired muscle sheet, the innermost of the abdominal wall muscles. Laterally, the internal and external oblique muscles lie superficially, whilst medially, the rectus abdominis and pyramidalis muscles form the corresponding outer layers. In its lateral course, the TA muscle tapers off along with the internal oblique, back into its origin from the thoracolumbar fascia. (View Highlight)
• Medially, it blends with the aponeuroses of the internal and external oblique muscles to form the rectus sheath. The TA muscle also inserts into the anterior two-thirds of the iliac crest (View Highlight)
• Superiorly, the TA muscle attaches to the 7th–12th costal cartilages, as well as the xiphoid process. Inferiorly, the aponeurosis of the TA inserts into the pubic crest and pectineal line via the conjoint tendon. (View Highlight)
• The TA plane offers access to all of the nerves supplying the anterior and lateral abdominal wall. The innervation is derived from the anterior primary rami of the lower seven thoracic spinal nerves (the thoracoabdominal nerves, T6–T12), as well as the ilioinguinal and iliohypogastric nerves (L1). (View Highlight)
• Each of the thoracoabdominal nerves gives off a lateral cutaneous branch in the midaxillary line, supplying the lateral abdominal wall. The anterior divisions progress medially, emerging in the costal margin between the TA and the IO muscle to travel in the TA plane. The four uppermost of these, T6–T9, only enter the TAP medial to the anterior axillary line. (View Highlight)
• The anterior branch of T6 enters just proximal to the linea alba, with the anterior branch of each subsequent lower nerve entering the TAP incrementally more lateral. This has important implications for the pattern of nerve blockade seen at different injection sites whilst performing TAP blocks. (View Highlight)
• The lower segmental nerves (T9–L1) give off multiple communicating branches, forming a longitudinal TAP plexus from which the terminal anterior divisions arise. (View Highlight)
• Subcostal TAP Block
  This approach offers more reliable coverage of the upper thoracoabdominal nerves T6–T9 and is suitable for use in procedures where supraumbilical analgesia is desired (View Highlight)
• Injectate spread and resultant block may vary with insertion site. If the injection is made lateral to the linea semilunaris (at the lateral border of the RA muscle), the block will centre around the T10 and T11 dermatomes. However, if the desired area of blockade is T9 and above, the chosen site should be medial to the linea semilunaris, as close as possible to the xiphoid process (View Highlight)
• 
  Fig. 32.11
  Image from Carney, McDonnell et al. 2011 study on injectate spread within the TAP for a posterior TAP block. View of QL with posterior probe placement (View Highlight)
• Collectively, the IIN, IHN, and GFN are called the “border nerves,” and the chronic pain originating from these nerves is called “border nerve syndrome.” These nerves show very high rate of anatomical variability from the spinal nerve root origin, divisions, communication between the nerves, fascial plane penetration, and sensory contributions. Performing these nerve blocks using blind landmark techniques or nerve stimulating techniques has been used for many years with a high rate of failure and complications which is highly understandable due to the anatomical variability and location (View Highlight)
• (View Highlight)
• 
  Fig. 36.2
  The anterior abdominal wall muscles showing the relationship of “border nerves” and GFN (View Highlight)
• The II and IH nerves originate from the anterior rami of L1 nerve roots with contributions from T12 or L2, emerging near the lateral border of the psoas major muscle. These two nerves extend diagonally toward the crest of the ilium (View Highlight)
• The GFN tends to originate predominantly from L1 and L2, and after the intrapelvic course, it enters the abdominal wall at the level of the deep inguinal ring. (View Highlight)
• The IHN pierces the transversus abdominis muscle above the iliac crest, midway between the iliac crest and the 12th rib. The IIN runs caudally and parallel to the IHN. Here, both nerves can be found consistently (90%) between the transversus abdominis and internal oblique muscles (View Highlight)
• Terminal branches of the IH nerve perforate the external oblique muscle aponeurosis approximately 4 cm lateral to the midline to supply the skin over the lower portion of the rectus abdominis. The IH nerve also provides sensory innervation to the skin above the tensor fasciae latae through a lateral cutaneous branch (View Highlight)
• Terminal branches of the II nerve enter the inguinal canal through the deep inguinal ring; it may lie upon the cremaster muscle and fascial layer of the spermatic cord in men or the round ligament in women. Here, the II nerve is often accompanied by the genital branch of the GF nerve, and wide variations in the course of these nerves within the inguinal canal have been documented. The terminal sensory branches may innervate the skin of the mons pubis, inner thigh, inguinal crease, and anterior surface of the scrotum or anterior one-third of the labia (View Highlight)
• the main concept to remind when dealing with the “border nerves” is the high rate of variability they are associated with. Anatomic studies highlight this variability, which have been reported with respect to their origin and spinal contribution, communication between nerves, penetration of fascial layers, branching patterns, and dominance patterns; in some cases, one of the nerves may be entirely absent. (View Highlight)
• The most consistent anatomical location for the II and IH nerves to perforate the abdominal muscular layers is lateral and superior to the anterior superior iliac spine, where they run between the transversus abdominis and internal oblique muscular layers, even though the distance from the ASIS to the point the nerves enter the fascial layer can widely vary (View Highlight)
• Special considerations are needed for pediatric patients. Anatomically, pediatric patients have varying II and IH nerves compared with adults; anatomical results from adults cannot be downscaled to infants and children, in whom the iliohypogastric and ilioinguinal nerves lie closer to the ASIS than originally thought, and differences have been noted according to different age groups (View Highlight)
• Most of clinical studies or reports used ASIS as landmark, and the position of the probe was above ASIS and moved along the line joining the ASIS and umbilicus. This approach carries some limitation: when the probe is placed too near to ASIS, the external oblique muscle layer may be missed; when the probe is too far away from the ASIS (the “bone shadow of the iliac crest” not in the scan), the nerve seen in between the transversus abdominis and internal oblique muscular layers is likely to be the 12th intercostal nerve or subcostal nerve instead. (View Highlight)
• The recommended area for ultrasound scanning of II and IH nerves is lateral and superior to the anterior superior iliac spine (Fig. 36.5), because the two nerves are detectable in this area in 90% of cases (View Highlight)
• The IIN and IHN will be found in the split fascial plane between the internal oblique and transversus abdominis muscle layers. Both nerves should be within 1.5 cm of the iliac crest at this site, located on the “upsloping” split fascia close to the iliac crest, with the IIN closer to the iliac crest. In some cases, the nerves may run approximately 1 cm apart, and in many cases, they are so close together so that it is visualized as single neurovascular bundle. The deep circumflex iliac artery which is close to the two nerves in the same fascial layer can be revealed with the use of color Doppler (View Highlight)
• 
  Fig. 36.5
  The probe position for the ilioinguinal and iliohypogastric nerves (View Highlight)