Presently ultrasound guided nerve blocks are very fashionable but vast majority of people around the world cannot practice these techniques mostly due to lack of resources but even in the developed countries there is lack of training which precludes people from using it. Lack of resources does not mean that patient cannot be provided with appropriate pain relief using nerve blocks. There are some nerve blocks that can be done using the loss of resistance (LOR) techniques. These blocks like, tranversus abdominis plane (TAP), rectus sheath, ilio-inguinal and fascia iliaca blocks can be effectively utilized to provide pain relief in the peri-operative period. For these blocks to be effectively delivered it is essential to understand the anatomical basis. It is also important to understand the reasons for failure, which is mostly due to delivery of the local anaesthetic in the wrong plane. The technique for LOR is not only simple and effective but also it can be delivered with minimal resources. This article deals with the techniques used for LOR blocks, the relevant anatomy and the methods used to administer the blocks. The article also describes the various indications where these blocks can be utilized, especially in the post-operative period where the pain management is sub-optimal.
The latest trend in regional anaesthesia is to perform nerve blocks under ultrasound guidance [
Before dwelling into the individual blocks, it is important to understand the loss-of-resistance (LOR) technique and how it can be used to achieve maximum effect and the reasons why it sometimes fails. The LOR technique relies on using blunt or short-bevelled needles, which provide a good feedback (pops or clicks) when they pass through fascial planes. Short-bevelled needles are commercially available (Figure
Commercially available short-bevel needle for LOR block.
Modifying 21 G hypodermic needle for LOR Block.
Using the modified blunt-tip needle for LOR block; change the angle to almost 90° once the sharp end of the tip has pierced the skin.
For deep structures or for big and obese patients either Tuhoy needle or a 22 G pencil point spinal needle can be used. Despite the simplicity of these blocks, they still fail. The reason for this is inability to feel the “clicks/pops” especially in obese patients, where the fascial layers are weak and thinned out, or deposition of the local anaesthetic in the wrong plane. Depositing the local anaesthetic in a wrong plane probably is the commonest reason for failure of these blocks and this can be attributed to something we call the “cushion effect”. What exactly is a cushion effect and why is it important?
The needles used for the LOR are blunt or short bevelled and therefore a considerable amount of force is needed for the tip of the needle to pierce the skin. This large amount of force tends to obliterate the cushion of subcutaneous fat lying under the skin, the “cushion effect”, and as the skin barrier is breached, the needle passes not only though the skin but also through the subcutaneous tissues and the fascia (Figure
The “Cushion effect” caused by short bevel or blunt needles.
How do we prevent this from happening? The trick to preventing this is to pierce the skin and withdraw the needle back till the tip of the needle is just under the skin and then start feeling the loss of resistance. Before feeling the loss of resistance, it is always nice to feel the bounce on the fascia. Some people like to “scratch” the fascia before feeling the “pop”. A small nick in the skin can also be made with a sharper bigger needle, before introducing the LOR needle through the skin. Another technique that has been described by the author is to use “needle-through-needle” technique (Figure
“Singh Technique” using needle through needle to prevent “cushion effect”.
In the human body, on each side of the midline, there are four principle muscles. Three of these are flat muscles, arranged in layers in the lateral part of the abdominal wall. External oblique is the most superficial, internal oblique lies deep to it, and the deepest layer is transversus abdominis [
The abdominal wall muscles and the neurovascular plane.
A recent review “refining the course of the thoracolumbar nerves; a new understanding of the innervation of the anterior abdominal wall” found that the fascial layer between the internal oblique and transversus abdominis muscles was more extensive than previously described [
Dissection of the right anterolateral abdominal wall revealing the nerves of the transversus abdominis plane (TAP) and rectus sheath. White flag (1): level of umbilicus. White flag (2): anterior superior iliac spine. Red flag: pubic symphysis. Pins: purple L1, yellow T12, blue T11, pink T10, orange T9, green T8. RA: rectus abdominis muscle. LS: linea semilunaris. TA: transversus abdominis muscle. IO: internal oblique muscle. EO: external oblique muscle. F: fascial layer deep to internal oblique. (Courtesy Dr. Warren Rozen).
The rectus sheath is the strong, incomplete fibrous compartment of the rectus abdominis and pyramidalis muscles. Also found in the rectus sheath are the superior and inferior epigastric arteries and veins, lymphatic vessels, and distal portions of the thoracoabdominal nerves (abdominal portions of the anterior rami of spinal nerves
Formation of the rectus sheath at 3 different levels of the abdomen.
Beginning at approximately one-third of the distance from the umbilicus to the pubic crest, the aponeuroses of the three flat muscles pass anterior to the rectus abdominis to form the anterior layer of the rectus sheath, leaving only the relatively thin transversalis fascia to cover the rectus abdominis posteriorly. A crescentic line, called the arcuate line, demarcates the transition between the aponeurotic posterior wall of the sheath covering the superior three quarters of the rectus and the transversalis fascia covering the inferior quarter. Throughout the length of the sheath, the fibers of the anterior and posterior layers of the sheath interlace in the anterior median line to form the complex linea alba [
The posterior layer of the rectus sheath is also deficient superior to the costal margin because the transverse abdominal muscle passes internal to the costal cartilages and the internal oblique attaches to the costal margin. Hence, superior to the costal margin, the rectus abdominis lies directly on the thoracic wall.
The first lumbar nerve divides into upper and lower branches, the iliohypogastric and ilioinguinal nerves. The iliohypogastric nerve travels in the transversus abdominis plane and divides into two terminal branches just above the iliac crest; the lateral cutaneous branch supplies the upper lateral part of the gluteal region and the anterior cutaneous branch supplies the suprapubic region.
The ilioinguinal nerve emerges from the lateral border of the psoas major just inferior to the iliohypogastric, passes obliquely across the quadratus lumborum and iliacus, and travels in the transversus abdominis plane (Figure
Iliohypogastric and Ilioinguinal nerves origin from the lumbar plexus.
It then leaves the neurovascular plane by piercing internal oblique above the iliac crest. It continues between the two obliques muscles and accompanies the spermatic cord (or round ligament of the uterus) in the inguinal canal [
Iliohypogastric and Ilioinguinal nerves in the inguinal area.
The fascia iliaca compartment is a potential space with the following limits: anteriorly it is covered by the posterior surface of the fascia iliaca, and posteriorly it is limited by the anterior surface of the iliacus muscle and the psoas major muscle. Medially the compartment is continuous with the space between the quadratus lumborum muscle and its fascia. The compartment spans from the lower thoracic vertebrae to the anterior thigh (Figure
Iliacus and Iliopsoas muscles and the femoral and lateral cutaneous nerve of thigh.
Regional analgesia techniques by blocking the nerves of the abdominal wall should be used as part of a multimodal analgesia technique. Blocks on their own are insufficient as they provide analgesia of the abdominal wall (somatic) and not the abdominal viscera [
TAP block can be used for any surgery involving the lower abdominal wall. This includes bowel surgery, caesarean section, appendicectomy, hernia repair, umbilical surgery, and gynaecological surgery [
The aim of TAP block is to deposit large amount of local anaesthetic in the transversus abdominis plane that lies below the internal oblique muscle and above the transversus abdominis muscle. Even though the literature describes the block to be performed in the so-called lumbar triangle “Petit’s triangle”, we prefer to use the midaxillary line and a point midway between the costal margin and the iliac crest (Figures
Approaches to Rectus sheath (1 & 2) and TAP block (3 & 4).
Landmarks for the Ilio-inguinal, Rectus sheath, and TAP blocks.
Once the skin is cleaned and draped, a short bevel or blunt needle is connected to a syringe with 20 mLs of local anaesthetic. The needle is introduced in the midaxillary line, absolutely perpendicular to the skin. Once the skin barrier is breached (requires a large force), the needle is withdrawn back so that the tip lies just under the skin. The needle is then advanced through the external oblique and a first “pop” sensation is felt when the needle enters the plane between the external oblique and internal oblique. We tend to actively look for a “bounce” of the needle on the fascia before feeling the “pop”. Further advancement of the needle results in a second “pop” after it passes through the internal oblique fascia into the TAP (Figures
The rectus sheath block is mostly used for analgesia after umbilical or incisional hernia repairs and supraumbilical surgical incisions. It is also used to supplement TAP block for complete analgesia following large laparotomy incision that extents from the xiphisternum to the symphysis pubis [
The aim of this technique is to block the terminal branches of the upper intercostal nerves (often missed by TAP block) which run in between the internal oblique and transversus abdominis muscles to penetrate the posterior wall of the rectus abdominis muscle and end in an anterior cutaneous branch supplying the skin of the umbilical area. For this block, large amount of local anaesthetic is often required as it is mostly performed bilaterally. The technique is similar to the TAP block. The point of insertion is 2-3 cm lateral to linea alba, midway between the xiphisternum and the umbilicus (Figures
Inguinal herniorrhaphy and orchidopexy remain the most common indications for this block. Bilateral blocks have also been used for obstetrics and gynaecological procedures that utilise lower abdominal incisions (e.g., Pfannenstiel incision) [
There are many approaches to this block; classical approach uses a landmark technique, which blocks the nerves once they have separated into the different fascial layers. Using a short beveled or a blunt needle, an injection is made at a point 2 cm medial and 2 cm cephalad (some go 2 cm caudad) to the anterior superior iliac spine (ASIS). Once the needle is through the skin, as the needle is advance an initial “pop” sensation is felt as it penetrates the external oblique aponeurosis, around 5–10 mL of local anaesthetic is injected. The needle is then inserted deeper until a second “pop” is felt penetrating the internal oblique, and a further 5–10 mL of local anaesthetic is injected to block the iliohypogastric nerve.
A subcutaneous injection of 3–5 mL can also be made at the point of entry, to block any remaining sensory supply from the intercostals and subcostal nerve. The approach we follow is based on a study by Eichenberger, our injection point is about 5 cm cranial and posterior to the ASIS; at this point both the iliohypogastric and the ilioinguinal nerves lie between the internal oblique and transverse abdominal muscle (Figures
Ilioinguinal and iliohypogastric nerves in relation to the landmark. EOM: external oblique muscle, IOM: internal oblique muscle, and TAM: transversus abdominis muscle.
In younger paediatric patients, the landmarks are different from that used in adults. A line joining the ASIS and the umbilicus is drawn and then trisected. The point joining the lateral 1/3rd and medial 2/3rd is used for the nerve block. Even though in most paediatric patients both the nerves tend to lie below the internal oblique, in practice it is better to inject the LA under both external and internal oblique muscles. The optimal volume for the block is 0.1-0.2 mL/kg of 0.25% levobupivacaine [
The fascia iliaca compartment block (FICB) is a simple and inexpensive method to provide perioperative analgesia in patients with painful conditions affecting the thigh, the hip joint, and/or the femur. The commonest indication for this block is analgesia for fracture neck of femurs [
The landmarks for this block are ASIS, the pubic tubercle, and the inguinal ligament. Once the inguinal ligament is marked, it is trisected and then a point-one fingerbreadth (1 cm) below the junction of the medial 2/3rd and the lateral 1/3rd is marked (Figure
Landmarks for fascia iliaca compartment block.
Anatomy of the fascia iliaca compartment block.
Understanding the anatomy and avoiding the “cushion effect” helps to perform the TAP, Rectus sheath, ilioinguinal, and fascia iliaca blocks with greater confidence and excellent results. Simplicity of these blocks allows them to be performed in the theatres but also be used as “rescue analgesics” in situations where pain can be difficult to control in the postoperative period. Loss-of-resistance techniques are not only easy to learn (and teach) but, due to minimal resources required, they are highly cost effective.