Editors: Chelly, Jacques E.
Title: Peripheral Nerve Blocks: A Color Atlas, 3rd Edition
Copyright ©2009 Lippincott Williams & Wilkins
> Table of Contents > Section
II – Single-Injection Peripheral Blocks > B – Lower Extremity >
10 – General Considerations for Lower Extremity Blocks
II – Single-Injection Peripheral Blocks > B – Lower Extremity >
10 – General Considerations for Lower Extremity Blocks
10
General Considerations for Lower Extremity Blocks
Jacques E. Chelly
Lower extremity blocks, alone or in combination with
general anesthesia, represent an interesting alternative to neuroaxial
blocks and general anesthesia alone. Contrary to common belief, lower
extremity blocks are not difficult to perform. Most lower extremity
blocks are often performed at some distance from the surgical site,
which often produces a more extended motor and sensory block than the
one required for the surgery. In contrast to the endless discussion
about the advantages and disadvantages of using a nerve stimulator,
paresthesia, or a transarterial approach for upper extremity blocks,
there is a clear consensus favoring the use of nerve stimulators for
lower extremity blocks.
general anesthesia, represent an interesting alternative to neuroaxial
blocks and general anesthesia alone. Contrary to common belief, lower
extremity blocks are not difficult to perform. Most lower extremity
blocks are often performed at some distance from the surgical site,
which often produces a more extended motor and sensory block than the
one required for the surgery. In contrast to the endless discussion
about the advantages and disadvantages of using a nerve stimulator,
paresthesia, or a transarterial approach for upper extremity blocks,
there is a clear consensus favoring the use of nerve stimulators for
lower extremity blocks.
Approaches to Lower Extremity Blocks
Lower extremity blocks can be performed with the patient
in various positions (lateral, prone, or supine). Because lower
extremity surgery usually requires at least two blocks (sciatic and
lumbar plexus or a part of it), and because mobilization of the patient
may be difficult or painful (e.g., morbid obesity, arthritis, trauma),
the choice of technique takes into consideration the need to limit the
mobilization of the patient. For surgery at the knee requiring sciatic
and femoral blocks in a trauma patient who cannot be mobilized,
anterior approaches to these two nerves are indicated. In contrast,
when the patient can assume a prone or lateral position, a parasacral,
posterior, or subgluteal approach to the sciatic nerve combined with a
lumbar plexus approach is possible.
in various positions (lateral, prone, or supine). Because lower
extremity surgery usually requires at least two blocks (sciatic and
lumbar plexus or a part of it), and because mobilization of the patient
may be difficult or painful (e.g., morbid obesity, arthritis, trauma),
the choice of technique takes into consideration the need to limit the
mobilization of the patient. For surgery at the knee requiring sciatic
and femoral blocks in a trauma patient who cannot be mobilized,
anterior approaches to these two nerves are indicated. In contrast,
when the patient can assume a prone or lateral position, a parasacral,
posterior, or subgluteal approach to the sciatic nerve combined with a
lumbar plexus approach is possible.
Some consideration should also be given to the choice of
the block according to the associated surgical requirements. For
example, placement of the tourniquet at the thigh or the calf requires
a lumbar plexus block or a saphenous nerve block, respectively.
Although the arthroscopic knee diagnostic procedure may be performed
under a single femoral nerve block, any knee surgery involving the
posterior aspect of the knee also requires a block of the sciatic
nerve. This is accomplished using a parasacral, posterior,
gluteal/subgluteal, anterior, and lateral or popliteal approach to the
sciatic nerve. Although all these approaches are appropriate for
surgery below the knee, it seems that a gluteal/subgluteal or a lateral
or posterior popliteal approach is favored. Finally, it is possible to
obtain a complete block of the foot with an ankle block. However, the
use of a combined sciatic and lumbar plexus/femoral/saphenous provides
better postoperative analgesia.
the block according to the associated surgical requirements. For
example, placement of the tourniquet at the thigh or the calf requires
a lumbar plexus block or a saphenous nerve block, respectively.
Although the arthroscopic knee diagnostic procedure may be performed
under a single femoral nerve block, any knee surgery involving the
posterior aspect of the knee also requires a block of the sciatic
nerve. This is accomplished using a parasacral, posterior,
gluteal/subgluteal, anterior, and lateral or popliteal approach to the
sciatic nerve. Although all these approaches are appropriate for
surgery below the knee, it seems that a gluteal/subgluteal or a lateral
or posterior popliteal approach is favored. Finally, it is possible to
obtain a complete block of the foot with an ankle block. However, the
use of a combined sciatic and lumbar plexus/femoral/saphenous provides
better postoperative analgesia.
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Table 10-1. Peripheral Nerve Block Techniques for Common Lower Extremity Surgery
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It is also important to take into consideration the
duration of the expected postoperative pain. Thus, a continuous nerve
block is indicated for postoperative analgesia for lower extremity
surgery associated with over 24 hours of moderate to severe pain. These
continuous nerve blocks are indicated for both hospitalized and
ambulatory patients. Since in most cases a sciatic and lumbar plexus
block is indicated, it is necessary to place either one perineural
catheter (sciatic for major foot surgery, femoral/lumbar plexus for hip
and knee surgery) or two perineural catheters to cover both territories
(sciatic and lumbar plexus/femoral catheter for total knee
replacement). In this latter instance, the lumbar plexus/femoral
catheter is infusing continuously whereas the mode of infusion of the
sciatic catheter is controlled by the patient (Table 10-1).
duration of the expected postoperative pain. Thus, a continuous nerve
block is indicated for postoperative analgesia for lower extremity
surgery associated with over 24 hours of moderate to severe pain. These
continuous nerve blocks are indicated for both hospitalized and
ambulatory patients. Since in most cases a sciatic and lumbar plexus
block is indicated, it is necessary to place either one perineural
catheter (sciatic for major foot surgery, femoral/lumbar plexus for hip
and knee surgery) or two perineural catheters to cover both territories
(sciatic and lumbar plexus/femoral catheter for total knee
replacement). In this latter instance, the lumbar plexus/femoral
catheter is infusing continuously whereas the mode of infusion of the
sciatic catheter is controlled by the patient (Table 10-1).
Surgical Indications for Lower Extremity Nerve Blocks
Trauma
Patients with trauma to the lower extremity may greatly
benefit from blocks for pain control. In this type of situation, the
block often needs to be performed with the patient in a supine position.
benefit from blocks for pain control. In this type of situation, the
block often needs to be performed with the patient in a supine position.
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Vascular Surgery
For surgeries related to vascular diseases involving the
lower extremities (below-the-knee amputation, debridement, and skin
grafting), femoropopliteal and tibial arterial reconstruction, as well
as for the removal of varices, the use of lower extremity blocks is of
special interest because of their lack of effects on the cardiovascular
system. However, their use remains limited. In this regard, it is
important to recognize that a sciatic nerve block is unnecessary for
removing the internal saphenous veins. A femoral block, or preferably,
a lumbar plexus block that includes L2 is adequate. Finally,
anticoagulant therapy is a contraindication to a sciatic nerve block
using either a posterior or an anterior approach.
lower extremities (below-the-knee amputation, debridement, and skin
grafting), femoropopliteal and tibial arterial reconstruction, as well
as for the removal of varices, the use of lower extremity blocks is of
special interest because of their lack of effects on the cardiovascular
system. However, their use remains limited. In this regard, it is
important to recognize that a sciatic nerve block is unnecessary for
removing the internal saphenous veins. A femoral block, or preferably,
a lumbar plexus block that includes L2 is adequate. Finally,
anticoagulant therapy is a contraindication to a sciatic nerve block
using either a posterior or an anterior approach.
Orthopedic Surgery
There are a number of indications for nerve blocks in orthopedic surgery of the lower extremity (Table 10-1).
Hip Surgery
It is unclear whether a peripheral nerve block can
adequately provide anesthesia for hip surgery and whether a single or a
continuous lumbar plexus or a three-in-one block represents the best
approach for postoperative pain control after total hip replacement.
Irrespective of the approach, it is also important to recognize that
the sciatic nerve also provides innervation to the hip. Consequently,
consideration should be given for a combined lumbar plexus and high
sciatic block for hip surgery.
adequately provide anesthesia for hip surgery and whether a single or a
continuous lumbar plexus or a three-in-one block represents the best
approach for postoperative pain control after total hip replacement.
Irrespective of the approach, it is also important to recognize that
the sciatic nerve also provides innervation to the hip. Consequently,
consideration should be given for a combined lumbar plexus and high
sciatic block for hip surgery.
Surgery of the Knee and Below the Knee
Sciatic and femoral or saphenous blocks are required to
satisfy surgical requirements in this area. Sciatic nerve blocks using
single injection or continuous infusions are also appropriate for pain
control of tibial fractures (rods, placement of external or internal
fixation).
satisfy surgical requirements in this area. Sciatic nerve blocks using
single injection or continuous infusions are also appropriate for pain
control of tibial fractures (rods, placement of external or internal
fixation).
Foot Surgery
Although ankle blocks represent the classic approach to
surgical and postoperative analgesia for foot surgery, gluteal,
subgluteal, and popliteal sciatic nerve blocks associated with
saphenous nerve blocks when necessary are gaining acceptance. Selective
blocks of the sciatic nerve branches also represent an alternative to
limit the extent of motor block.
surgical and postoperative analgesia for foot surgery, gluteal,
subgluteal, and popliteal sciatic nerve blocks associated with
saphenous nerve blocks when necessary are gaining acceptance. Selective
blocks of the sciatic nerve branches also represent an alternative to
limit the extent of motor block.
Characteristics of Lower Extremity Blocks
Doppler ultrasound can be used to facilitate
identification of the femoral artery (morbidly obese patient) and
fluoroscopy has been used to identify the dorsal surface of the ischium
in patients in a prone position. The indications for both methods still
remain limited.
identification of the femoral artery (morbidly obese patient) and
fluoroscopy has been used to identify the dorsal surface of the ischium
in patients in a prone position. The indications for both methods still
remain limited.
Because the sciatic nerve is the largest nerve that we
block, sciatic nerve blocks have the longest onset and duration of
peripheral blocks commonly performed by anesthesiologists. A minimum of
15 to 30 minutes, and even 45 minutes, is required to allow a complete
block. In contrast to upper extremity blocks, neither the addition of
bicarbonates or epinephrine reduces the onset time of lower extremity
blocks. Although a higher concentration of local anesthetic solution
may reduce the onset time of a block, this long onset time needs to be
taken into consideration when defining the anesthesia strategy. This
contrasts with a femoral block that only requires 5 to 10 minutes for
its onset. On the other hand, these blocks often last more than 12 to
16 hours (especially in diabetic patients) when performed with 0.5% to
0.75% of ropivacaine. This duration needs to be taken into
consideration in the follow-up of the patient.
block, sciatic nerve blocks have the longest onset and duration of
peripheral blocks commonly performed by anesthesiologists. A minimum of
15 to 30 minutes, and even 45 minutes, is required to allow a complete
block. In contrast to upper extremity blocks, neither the addition of
bicarbonates or epinephrine reduces the onset time of lower extremity
blocks. Although a higher concentration of local anesthetic solution
may reduce the onset time of a block, this long onset time needs to be
taken into consideration when defining the anesthesia strategy. This
contrasts with a femoral block that only requires 5 to 10 minutes for
its onset. On the other hand, these blocks often last more than 12 to
16 hours (especially in diabetic patients) when performed with 0.5% to
0.75% of ropivacaine. This duration needs to be taken into
consideration in the follow-up of the patient.
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Various local anesthetics in various concentrations have
been used to block the sciatic and femoral nerves. Except for ankle
blocks, we favor the use of 1.5% lidocaine or mepivacaine and 0.5%
ropivacaine. The total volume of local anesthetic solution required to
block a lower extremity is often 40 to 50 mL (sciatic and lumbar plexus
blocks). In this regard, the better safety profile of ropivacaine
compared with bupivacaine or even levobupivacaine makes ropivacaine
especially attractive when multiple lower extremity blocks are
performed. The use of local anesthetics with shorter half-lives may
also be indicated to favor early recovery of motor function.
been used to block the sciatic and femoral nerves. Except for ankle
blocks, we favor the use of 1.5% lidocaine or mepivacaine and 0.5%
ropivacaine. The total volume of local anesthetic solution required to
block a lower extremity is often 40 to 50 mL (sciatic and lumbar plexus
blocks). In this regard, the better safety profile of ropivacaine
compared with bupivacaine or even levobupivacaine makes ropivacaine
especially attractive when multiple lower extremity blocks are
performed. The use of local anesthetics with shorter half-lives may
also be indicated to favor early recovery of motor function.
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