The
motor and sensory innervation of the lower extremities arises from the nerve
roots of the L2-S3 spinal segments.Lumbo-Sacral Plexus Nerve Block including the 3 in 1 Block
Indications
For procedures of the lower extremities
The lumbo-sacral and 3 in 1 blocks can provide adequate anesthesia over a variety of regions with the added benefit of post-op pain control.
Local Anesthetic Drugs and Dosages
Normal dosing volume is 20-40cc. Concentrations of local anesthetics may vary, keeping in mind higher concentrations will provide a denser block. Caution must be taken when calculating the dose not to exceed toxic dosages.
Lidocaine
For fast onset and short duration block
Usually 0.5-1.0% with a max dose of 5mg/kg (7mg/kg with 1:200,000 of epi)
Onset 10-20 mins
Duration 4-8 hours.
Bupivacaine
Used for longer duration and denser blocks
Usually 0.25-0.5% with a max dose of 3mg/kg
Onset 20-30mins
Duration 18hrs, therefore, epi is usually not indicated.
Ropivacaine
Use becoming more widespread in lieu of bupivicaine because higher clearance results in less toxic events
Usually 0.2-0.5% with max dose of 3mg/kg
Onset and duration similar to bupivicaine and epi not indicated.
Anatomy
The
motor and sensory innervation of the lower extremities arises from the nerve
roots of the L2-S3 spinal segments.
The upper branches, L2-L4, form the lumbar plexus which gives rise to the lateral femoral cutaneous, femoral, and obturator nerves. The lateral femoral cutaneous nerve provides sensory to the lateral thigh. The femoral nerve divides into two branches. The anterior, or superficial, branch provides sensory innervation to the anterior thigh. The posterior, or deep, branch is mainly motor and innervates the quadriceps muscle, knee joint and medial ankle/foot. The obturator nerve provides sensory to the medial thigh and motor to the adductor muscles of the hip.
L4-S3 form the lumbosacral plexus which gives rise to the sciatic nerve which supplies sensory innervation to the posterior thigh then branches into the common peroneal and tibial nerves which innervate the entire leg and foot from just below the knee.
Techniques Demonstrated Include:
The lumbar plexus nerve block (psoas compartment block)
Femoral nerve block
The 3 in 1 block
The sciatic nerve block (sacral plexus).
Please note that there are many variations to these techniques and these represent only some of the more reliable approaches.
Lumbar Plexus Block (Psoas Compartment Block)
The psoas compartment
block has a higher likelihood of anesthetizing all three major nerves of the
lumbar plexus because it blocks the lumbar plexus at a more proximal location.
Positioning and Landmarks
The patient is positioned in the prone or lateral decubitus position with the operative side up.
Initially the fourth lumbar spine is identified from its relationship to the iliac crests. Move cephalad to locate the L3 spinous process.
From L3 move 5cm lateral to the midline and mark with “X”
Procedure
Place a skin wheel of local anesthetic at the mark.
A 21g 100mm insulated needle is attached to a nerve stimulator at 2mA.
The needle is advanced perpendicular to all planes until the transverse process is contacted or the lumbar plexus is stimulated (quadriceps muscle twitch).
When the transverse process is contacted, the needle is withdrawn to the skin and reinserted with a slight cephalad or caudad orientation to pass the transverse process. Again, stimulation of the lumbar plexus at this level is recognized by contractions of the quadriceps femoris muscle and rhythmic twitches of the patella.
The needle is manipulated until twitches of the quadriceps muscle are still seen or felt at 0.5 mA or less. Following successful identification of the lumbar plexus, 30-35cc of local anesthetic of choice is injected with intermittent aspirations to rule out intravascular injection
Femoral Nerve Block
Positioning and Landmarks
Supine position
Palpate both the anterior superior iliac spine and the pubic tubercle; it can be helpful to draw a line to represent this area for this line will represent the inguinal ligament.
The femoral artery should lie at the midpoint and slightly lateral of the inguinal ligament and it is necessary to locate this by feeling for the pulse at this point.
A stimulating needle attached to a nerve stimulator (white arrows) is inserted just above the femoral crease and lateral to the femoral artery. Note that the needle insertion is at 45 degree angle cephalad and well bellow the inguinal ligament (red arrows).
Procedure
The site for injection is 1cm lateral (outside) to the femoral artery and 1-2cm below the line of the inguinal ligament where a skin wheel of local anesthetic is applied.
A 21g 100mm insulated needle connected to a nerve stimulator at 1-2mA is inserted at this site.
It is necessary to obtain contraction of the quadriceps muscle group at 0.5 mA or less
Once the nerve is located, the needle is immobilized and an aspiration test performed
15-20mls of local anesthetic solution is injected
3 In 1 Block
The 3 in 1 block aims to block three nerves with one injection
The femoral nerve
Lateral cutaneous nerve
The obturator nerve.
Recent studies have shown that blockade of the obturator nerve with this technique has a high fail rate, so assessment of the block throughout the procedure is indicated.
Positioning and Landmarks
Same as for femoral block
Procedure
Same as the femoral block with one notable difference.
The thumb is placed firmly below the injection site to prevent distal spread of the local. An assistant is required to perform the injection. After an aspiration test to rule out intravascular annulations, 25-40mls of local anesthetic is injected.
Sciatic Nerve Block (sacral plexus)
Positioning and Landmarks
The patient is positioned lateral with block side up.
The lower leg is straight and upper leg flexed at the hip to form a 90-degree angle.
The greater trochanter is palpated and its upper border marked.
The posterior superior iliac crest is palpated and marked.
A line is then drawn between them with a perpendicular line drawn down at the midpoint.
Landmarks for sciatic block. Black arrows point to the greater trochanter (GT) and posterior-superior iliac spine (PSIS). Needle insertion site is marked 5 cm caudad to the midpoint of the GT-PSIL line (white dot).
Procedure
The needle insertion site is 5cm down the perpendicular line and can be checked by drawing a line between the coccyx and the greater trochanter- the needle is inserted where the two lines intersect.
Using a nerve stimulator set at 2mA and a 21g 100mm needle, the insertion is made at a right angle to the skin.
Once contraction of the hamstring is elicited, the current is reduced to 0.5mA or less and the needle is advanced further until contraction of the gastrocnemius is present.
This will usually cause planter flexion of the foot.
Once in position, aspiration test is performed and 20-30mls of local anesthetic is injected.
Complications
Although complications are rare, nerve injury is one of the most important. Intraneural injection or traumatizing the nerve can cause nerve damage. Signs of intraneural injection are severe pain on injection and marked resistance to injection. These signs should prompt the provider to stop injecting and reposition the needle. It is also possible to cause a hematoma by puncturing an artery, most commonly the femoral artery. If bleeding is evident, pressure at site for approx 5mins can minimize the hematoma.