+++
Intertendinous (Posterior) Approach
++
The patient is in the prone position.15 The foot on
the side to be blocked should be positioned so that even the slightest
movement of the foot or toes can be easily observed. This is best achieved
by allowing the foot to protrude off the bed.
++
A standard regional anesthesia tray is prepared with the following
equipment:
++
- Sterile towels and 4-in. × 4-in. gauze packs
- Three 20-mL syringes with local anesthetic
- Sterile gloves, marking pen, and surface electrode
- One 1½-in., 25-gauge needle for skin infiltration
- A 5-cm long, short-bevel, insulated stimulating needle
- Peripheral nerve stimulator
++
Landmarks for the intertendinous approach to popliteal block are easily
recognizable even in obese patients (Figure 38–3). The landmarks
should be routinely outlined by a marking pen: (1) popliteal fossa crease,
(2) tendon of biceps femoris (laterally), and (3) tendons of semitendinosus
and semimembranosus (medially).
++
++
The needle insertion point is marked at 7 above the popliteal fossa
crease at the midpoint between the tendons. This point is just above the
sciatic nerve in the popliteal fossa in nearly two thirds of patients
(Figure 38–4).
++
++
++
++
After application of an antiseptic solution, local anesthetic is
infiltrated subcutaneously at the site of the block needle entry. The
practitioner is best positioned on the side of the patient with the
palpating hand on the biceps femoris muscle while observing the motor
response of the foot and toes (Figure 38–6). The needle is
introduced at the midpoint between the tendons. The nerve stimulator should
be initially set to deliver 1.5 mA current (2 Hz, 100 μsec). When
the needle is inserted in a correct plane, advancement of the needle should
not result in local muscular twitches; the first response to nerve
stimulation is typically that of the sciatic nerve (foot twitch). After the
initial stimulation of the sciatic nerve is obtained, the stimulating
current is gradually decreased until twitches are still seen or felt at
0.2–0.5 mA. This typically occurs at a depth of 3–5 cm from the skin.
After negative aspiration for blood, 35–45 mL of local anesthetic is slowly
injected.
++
++
++
There are two basic types of motor responses that can be elicited with
sciatic nerve stimulation at the level of the popliteal fossa. Stimulation of the common
peroneal nerve results in dorsiflexion and eversion of the foot,
whereas stimulation of the tibial nerve results in plantar flexion and
inversion (Figure 38–7). As the stimulating current is being
decreased, the twitch of the great toe often remains the only motor response
seen with currents of <0.5 mA. Either response is adequate when
the response is still present with current intensity of 0.2–0.4 mA (0.1
msec) as long as a large volume of local anesthetic is used. However, when the stimulation can not be accomplished with current <0.5 mA,
stimulation of the tibial nerve may result in a higher success rate. Some common
responses to nerve stimulation and the course of action to obtain the proper
response are shown in Table 38–2.16
++
++
+++
Block Dynamics and Perioperative Management
++
The intertendinous approach to popliteal block is associated with
relatively minor patient discomfort because the needle passes only through
the adipose tissue of the popliteal fossa. Regardless, adequate sedation and
analgesia are always important to ensure a still and tranquil patient.
Midazolam 1–2 mg after the patient is positioned and alfentanil 250–500
mcg just before block placement suffices for most patients. A typical onset
time for this block is 10–25 minutes, depending on the type, concentration,
and volume of local anesthetic used. The first signs of the onset of
blockade are usually spontaneously reported by the patient who reports that
the foot “feels different” or that he or she is unable to wiggle the toes.
Sensory anesthesia of the skin with this block is often the last to develop.
Inadequate skin anesthesia despite the apparent timely onset of the blockade
is common because it may take up to 30 minutes for full blockade to develop.
However, local infiltration at the site of the incision by the surgeon is
often all that is needed to allow the surgery to proceed until the block
fully sets in.
+++
Continuous Popliteal Block
++
Continuous popliteal block is an advanced regional anesthesia
technique, and adequate experience with the single-shot technique is
necessary to ensure its efficacy. The technique is similar to the
single-shot injection; however, slight angulation of the needle cephalad is
necessary to facilitate insertion of the catheter. Securing and maintaining
of the catheter are easy and convenient. This technique can be used for
surgery and postoperative pain management in patients undergoing a wide
variety of lower leg, foot, and ankle surgeries.
++
Catheters may be inserted through a variety of approaches and
equipment/infusion-specific techniques. There are also a variety of infusion
systems, such as simple elastomeric pumps, which are easy for the patient to
use. These infusion systems are disposable, deliver a fixed rate, and are
generally inexpensive. Mechanical, battery-operated pumps offer more
flexibility of programming and bolus dosing, but tend to be more
costly.10 Souron et al.17 reported the use
of the continuous catheter technique to provide high-quality postoperative
analgesia after oncologic orthopedic surgery of the leg.
++
Ilfeld9 reported excellent postoperative analgesia using a
continuous catheter in the popliteal fossa and a portable infusion pump for
outpatients having moderately painful, lower extremity orthopedic surgery.
Eighty percent of patients receiving ropivacaine infusion did not require
oral opioid therapy and reported an average resting pain score of less
than 1 (on a verbal pain score scale of zero to 10). Seven percent of
patients who received placebo delayed their first dose of oral opioid until
after infusion discontinuation, with an average resting pain score of 3–4
(out of 10). Breakthrough pain resulted in the worst resting pain score,
with the difference between treatment and control groups being even more
pronounced. The patients who received ropivacaine experienced a significant
decrease in sleep disturbances, oral opioid use, and opioid-related adverse
effects. These benefits were attained for ambulatory patients with the use
of a portable, programmable, patient-controlled infusion pump. The degree of
analgesia and the relative simplicity of the catheter pump system led to a
very high rate of satisfaction for all subjects receiving ropivacaine.
++
Klein et al.18 examined the efficacy and complications of
long-acting popliteal nerve block after discharge home. This prospective
study included 1791 patients who had received an upper- or lower-extremity
nerve block with 0.5% ropivacaine and were discharged the day of surgery.
In all, 2382 blocks were placed: 1119 upper-extremity blocks and 1263
lower-extremity blocks. There were 733 interscalene, 193 supraclavicular,
193 axillary, 338 lumbar plexus, 263 femoral, and 662 sciatic blocks. Block
efficacy was demonstrated by a low rate of conversion to general anesthesia
(1–6%) and a low percentage of opioid use in the postanesthesia care
unit (8–11%). The results showed that long-acting popliteal nerve block
may be used in the ambulatory setting with a high degree of efficacy,
safety, and satisfaction. Chelly et al.19 documented the
benefits of a continuous lateral popliteal sciatic nerve block infusion
technique for postoperative analgesia in patients who had undergone open
reduction and internal fixation of the ankle. Continuous infusion of
ropivacaine 0.2% was associated with a significant reduction of morphine
consumption by 29% and 62% during postoperative days 1 and 2,
respectively.
++
A standard regional anesthesia tray is prepared with the following
equipment:
++
- Sterile towels and 4-in. × 4-in. gauze packs
- Three 20-mL syringes with local anesthetic
- Sterile gloves, marking pen, and surface electrode
- One 1½-in., 25-gauge needle for skin infiltration
- A 5-cm long, insulated stimulating needle
- Catheter
- Peripheral nerve stimulator
++
The needle insertion site is marked at 7 cm proximal to the popliteal
fossa crease and between the tendons of the biceps femoris and
semitendinosus muscles.
++
The continuous popliteal block technique is similar to the single-shot
technique. With the patient in the prone position, the skin is infiltrated
with local anesthetic using a 25-gauge needle at the injection site 7 cm
above the popliteal fossa crease and between the tendons of biceps femoris
and semitendinosus muscles. A 5- to 10-cm needle connected to the nerve
stimulator (1.5 mA current) is inserted at the midpoint between the tendons
of the biceps femoris and semitendinosus muscles (Figure 38–8).
The block needle is advanced slowly with a slight cranial direction while
seeking a plantar or dorsiflexion of the foot or toes. After obtaining
appropriate motor response, the needle is manipulated until the desired
response is seen or felt using a current of approximately 0.5 mA. The
catheter should be advanced some 5 cm beyond the needle tip (see Figure 38–8).
The needle is then withdrawn back to the skin while simultaneously advancing
the catheter to prevent its inadvertent removal. Before activating, the
catheter is checked for inadvertent intravascular placement by negative
aspiration test for blood.
++
++
Continuous infusion is initiated after an initial bolus of local
anesthetic through the catheter. For this purpose, we routinely use
ropivacaine 0.2% (15–20 mL). Diluted bupivacaine or
l-bupivacaine is also suitable, but may result in more
motor blockade. The infusion is maintained at 10 mL/h or 5 mL/h when a
patient-controlled analgesia (PCA) dose is planned (5 mL). The dosing
interval for the PCA dose is 20–60 minutes.
++
+++
Popliteal (Lateral) Approach
++
The main advantage of the lateral approach to the popliteal block is
that the patient does not need to be positioned in the prone position as
with all posterior approaches.5,16,20
+++
Regional Anesthesia Anatomy
++
The sciatic nerve is positioned between the biceps and semitendinosus
muscles (see Figure 38–4). During block performance, stimulation of the
common peroneal nerve is usually obtained first (65%) because this nerve
is positioned lateral and more superficial than the tibial nerve.
++
The patient is in the supine position. The foot on the side to be
blocked should be positioned so that even the slightest movement of the foot
or toes can be easily observed. This is best achieved by placing the foot on
a foot rest. Attention should be paid so that the Achilles tendon is also
protruding off the foot rest. This positioning allows easy visualization of
any foot movement during nerve stimulation.
++
The equipment is identical with that for the posterior intertendinous
approach except that a 10-cm stimulating needle is used.
++
Landmarks for the lateral approach to popliteal block include popliteal
fossa crease, vastus lateralis muscle, and biceps femoris muscle
(Figure 38–9). The needle insertion site is marked in the groove
between the vastus lateralis and biceps femoris muscles (Figure
38–10).
++
++
++
The operator should be seated, facing the side to be blocked. The
height of the bed with the patient is adjusted to allow for an ergonomic
position and a greater precision during block placement. This position also
allows the performer to simultaneously monitor both the patient and the
responses to nerve stimulation. The site of needle insertion is cleaned with
an antiseptic solution and infiltrated with local anesthetic at the site of
estimated needle insertion using a 1½-in., 25-gauge needle.
++
A 10-cm, 22-gauge needle is connected to a nerve stimulator, inserted in
a horizontal plane between the vastus lateralis and biceps femoris muscles,
and advanced to contact the femur (see Figure 38–10). The contact with the
femur is important because it provides information on the depth of the nerve
(typically 1–2 cm beyond the skin–femur distance) as well as on the angle
at which the needle will need to be redirected posterior to stimulate the
nerve. The current intensity is initially set at 1.5 mA. Keeping the fingers
of the palpating hands firmly pressed and immobile in the groove, the needle
is then withdrawn to the skin, redirected 30 degrees posterior to the angle
at which the femur was contacted, and advanced toward the nerve
(Figure 38–11).
++
++
When the sciatic nerve is not localized on the first needle pass, the needle
is withdrawn to the skin level and the following procedure is followed:
++
1. Make sure that the nerve stimulator is functional and properly
connected to the patient and to the needle and that it is set to deliver
current of desired intensity.
2. Make sure that the leg is not externally rotated in the hip joint and
that the foot forms a 90-degree angle to the horizontal plane of the table.
Any deviation from this angle changes the relationship of the sciatic nerve
to the femur and biceps femoris muscle.
3. Mentally visualize the plane of the initial needle insertion and redirect
the needle in a slightly posterior direction (5–10 degrees posterior
angulation).
4. If the above maneuver fails, withdraw the needle and reinsert with an
additional 5–10 degrees posterior redirection.
5. If the above maneuvers fail, withdraw the needle to the skin and reinsert
1 cm inferior to the initial insertion site; then repeat the above steps.
6. Failure to obtain foot response to nerve stimulation should prompt
reassessment of the landmarks and arm position. In addition, the stimulating
current should be increased to 2 mA.
++
After the initial stimulation of the sciatic nerve is obtained, the
stimulating current is gradually decreased until motor response of the foot
or toes is still seen or felt at 0.2–0.5 mA. This typically occurs at a
depth of 5–7 cm. At this point, the needle should be stabilized, and after
negative aspiration for blood, 35–45 mL of local anesthetic are slowly
injected. The hands should be kept as immobile as possible to prevent
injection outside the sheath of the sciatic nerve.
++
++
++
Some common responses during block placement using a nerve stimulator
and the course of proper action to obtain twitches of the foot
(Table 38–3).
++
+++
Continuous Popliteal Block Through the Lateral Approach
++
The continuous popliteal block technique through the lateral approach
is similar to the single-injection technique. With the patient in the prone
position, the skin is infiltrated with local anesthetic at the injection
site 8 cm above the popliteal fossa crease and in the groove between the
biceps femoris and vastus lateralis muscles using a 25-gauge needle. A 10-cm
Tuohy-style tip needle for continuous nerve block is connected to the nerve
stimulator (at 1.5 mA current intensity) and inserted to contact the femur.
Once the femur is contacted, the needle is withdrawn to the skin and
redirected in a slight cranial and posterior direction relative to the plane
in which the femur was contacted (usually 30 degrees to the horizontal
plane) (Figure 38–13).
++
++
The needle is advanced slowly while seeking a plantar flexion or
dorsiflexion of the foot or toes. After obtaining appropriate twitches, the
needle is manipulated until the desired response is seen or felt using a
current of 0.5 mA. The catheter should be advanced some 5–7 cm beyond the
tip of the needle. The management of the catheter is similar to that of the
intertendinous technique.