New York School Of Regional Anesthesia - Continuous Lumbar Plexus Block

Indications: Hip, anterior thigh, and knee surgery
Landmarks: Iliac crest, spinous processes (midline)
Nerve stimulation: Twitch of the quadriceps muscle at 0.5-1.0 mA current
Local anesthetic: 25-35 mL

Continuous lumbar plexus blockade is an advanced regional anesthesia technique and adequate experience with the single-shot technique is a prerequisite to ensure its efficacy and safety. Otherwise, the technique is quite similar to the single-shot injection, except that the Tuohy-style tip needle is preferable. The needle opening should be directed cephalad to facilitate threading of the catheter. This technique can be used for postoperative pain management in patients undergoing hip, femur, and knee surgery.

Refer to Lumbar Plexus Block - Anatomy

Refer to Lumbar Plexus Block - Distribution of Anesthesia

Refer to Lumbar Plexus Block - Patient Positioning

A standard regional anesthesia tray is prepared with the following equipment:

Sterile towels and 4"x4" gauze packs
20-mL syringe with local anesthetic
Sterile gloves, marking pen, and surface electrode
One 1½" 25-gauge needle for skin infiltration
A 10-cm long, insulated stimulating needle (preferably Tuohy-style tip)
Catheter
Peripheral nerve stimulator

The landmarks for continuous lumbar plexus block are the same as in the single-shot technique:

Iliac crest
Midline (spinous processes)
Needle insertion site 4-cm lateral to the midline

The skin and subcutaneous tissues are anesthetized with local anesthetic. The needle is attached to the nerve stimulator (1.5 mA, 2 Hz, 100 µsec) and to a syringe with local anesthetic. The palpating hand should be firmly pressed and anchored against the paraspinal muscles to facilitate the needle insertion and redirection of the needle when necessary (Fig. 20.14). A 10-cm, Tuohystyle tip, continuous block needle is inserted at a perpendicular angle and advanced until the quadriceps twitch response is obtained at 0.5 to 1.0 mA current. At this point, the initial volume of local anesthetic is injected (e.g., 15-25 mL) and the catheter is inserted approximately 8-10 cm beyond the needle tip. The needle is then withdrawn back to the skin level, while the catheter is simultaneously advanced. This method prevents inadvertent removal of the catheter.

Before administering local anesthetic, the catheter is checked for inadvertent intravascular and intrathecal placement by negative aspiration test. The radiograph shows dispersion of the dye within the sheath of the psoas muscle.

TIPS:

It is useful to inject some local anesthetic intramuscularly to prevent pain on advancement of a larger gauge or blunt tipped needles used for continuous block.
The opening of the needle tip should be oriented cephalad before threading the catheter.
The skin in the lumber area is very movable, thus insertion, of the catheter to a depth of 8-10 cm is necessary to help prevent its removal during patient repositioning, etc.

Continuous infusion is always initiated after an initial bolus of dilute local anesthetic through the catheter. For this purpose, we routinely use 0.2% ropivacaine (15-20 mL). Diluted bupivacaine or l-bupivacaine are also suitable, but can result in more motor blockade. The infusion is maintained at 10 mL/hr or 5 mL/hr when a PCA dose is planned (5 mL/q30 minutes). Figure 20.15 shows the dispersion of 20 mL of a contrast solution within the psoas sheath.

TIPS:

Breakthrough pain in patients on continuous infusion is always managed by administering a bolus of local anesthetic. Simply increasing the rate of infusion is rarely adequate. With patients on the ward, a higher concentration of a shorter acting local anesthetic (e.g., 1% mepivacaine) is useful to both manage the pain and test the position of the catheter.
When the bolus injection through the catheter fails to result in blockade after 30 minutes, the catheter should be considered dislodged and it should be removed.
Every patient receiving lumbar plexus block infusion should be prescribed an alternative pain management protocol because incomplete analgesia and catheter dislodgment can occur. For inpatients, this is probably best done using a back-up IV PCA.

Visible or palpable twitches of the quadriceps muscle at 0.5-1.0 mA current.

TIPS:

Successful lumbar plexus blockade depends on the dispersion of the local anesthetic in the fascial plane (psoas muscle) where the roots of the plexus are situated. Thus, the goal of the nerve stimulation is to identify this plane by eliciting stimulation of one of the roots.
Stimulation at currents less than 0.5 mA should not be sought when using this technique. Dural sleeves thickly envelop the roots of the lumbar plexus. Motor stimulation with a low current may indicate placement of the needle inside a dural sleeve. An injection inside this sheath can result in tracking of the local anesthetic toward the epidural or subarachnoid space, with consequent epidural or spinal anesthesia.

Failure to obtain quadriceps twitch on first needle pass

When insertion of the needle does not result in quadriceps muscle stimulation, the following maneuvers should be performed:

Withdraw the needle to the skin level, redirect 5º-10º cranially, and repeat the procedure.
Withdraw the needle to the skin level, redirect 5º-10º caudally, and repeat the procedure.
Withdraw the needle to the skin level, redirect 5º-10º medially, and repeat the procedure.
Withdraw the needle to the skin level and reinsert 2-cm caudally or cranially and repeat the procedure.

TIPS:

Failure to obtain a quadriceps muscle twitch on the first needle insertion is common, even with proper needle placement, simply because the needle tip may pass between the two roots and thus stimulation is not obtained.
Using a higher stimulating current (e.g., 4 mA) to decrease the chance of missing the roots is only marginally beneficial. In addition, there is a drawback that such stimulation is very uncomfortable for the patient (burning) and much deeper sedation/analgesia is required.

Some common responses to nerve stimulation and the course of action to take to obtain the proper response:

Response Obtained	Interpretation	Problem	Action
Local twitch of the paraspinal muscle	Direct stimulation of the paraspinal nerve	Too shallow placement of the needle	Continue advancing the needle
Needle contacts bone at 4-6 cm depth; no twitches are seen	The needle advancement is stopped by the transverse process	This indicates proper needle placement, but requires redirection of the needle	Withdraw the needle to the skin level and redirect 5^o cranially or caudally
Twitches of the hamstring muscles are seen; needle inserted 6-8 cm	This is the result of stimulation of the roots of the sciatic plexus (sciatic nerve)	The needle is inserted too caudally	Withdraw the needle and reinsert 3-5 cm cranially
Flexion of the thigh at the depth of > 6-8 cm	This subtle and often missed response is caused by direct stimulation of the psoas muscle	The needle is inserted too deep (missed the lumbar plexus roots); further advancement may place the needle intraperitoneally	Stop advancing the needle; withdraw the needle and reinsert using the protocol outlined in the technique description
The needle is placed deep (10 cm) but twitches were not elicited and bone is not contacted	The needle missed the transverse process and roots of the lumbar plexus	Too deep placement of the needle	Withdraw the needle and reinsert using the protocol outlined in the technique description

Refer to Lumbar Plexus Block - Choice of Local Anesthetics

Refer to Lumbar Plexus Block - Block Dynamics and Perioperative Management

Refer to Lumbar Plexus Block - Complications and How to Avoid Them

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