Sciatic Nerve Block

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Tiffany Tavernier

L4-S3 spinal nerve roots

Largest nerve trunk in the
human body

Distribution = hamstrings,
long head of biceps
femoris, adductor magnus;
part of hip and knee joint

Blocks skin of posterior
aspect of thigh and entire
leg below knee
exception of skin of medial
aspect of lower leg

Classical Posterior
Approach
› Pt lies in lateral
decubitus position
› Landmarks: greater
throchanter and
posterior-superior iliac
spine
› Needle is inserted 4-5
cm distal to midpoint
btw the two
landmarks
perpendicular to skin
in all planes

Parasacral Approach
› Pt lies in lateral
decubitis position
› Landmarks: posterior
superior iliac spine
and ischial tuberosity
› Needle is inserted
6cm caudal to line
btw the 2 in sagittal
plane

Lithotomy
› Pt is supine with hip
flexed and upper leg
perpendicular to torso
› Landmarks: greater
trochanter of femur
and ischial tuberosity
› Needle is inserted 4
cm in claudal
direction midway
between the 2
› Needle is advanced
parallel to horizontal
plane

Anterior approach
› Pt is supine with legs
extended
› Landmarks: femoral
crease and femoral
arterial pulse
› Needle inserted 405
cm distal from pulse
of femoral artery and
perpendicular to line
of femoral crease
100 pts undergoing
minor knee surgery
 Randomly divided by
envelope to receive
anterior or posterior
approaches combined
with femoral and lateral
femoral cutaneous
nerve blocks using US
 1% mepivacaine with
short 1100m, 21 gauge
 Block: 20mL of 1.5%
mepivacaine with
1:400,000 epinephrine

Anterior Approach
 Nerve stimulator was
used @ 2Hz to elicit foot
plantar- or dorsiflexion
Posterior Approach
 Same as anterior, but
without nerve stimulator.
both then placed in supine position with
legs extended and femoral and lateral
femoral cutaneous blocks were performed
 Measurements of depth and size of sciatic
nerve, needle depth, block execution time
for sciatic nerve block, block execution
time for all 3 blocks, time required for onset
of sensory and motor blocks of sciatic nerve
and duration of blockade of sciatic nerve
were measured






Sciatic nerve was located deeper in anterior
approach
Both had similar block execution time for
sciatic nerve block, but anterior approach took
less time to complete all 3 blocks
Onset of sensory block for superficial peroneal,
sural and tibial nerves was similar
Sensory block of posterior femoral cutaneous
nerve was achieved less often with the
anterior approach - less block of posterior
area of thigh
Onset of motor block was similar with both
approaches

Although posterior femoral cutaneous
nerve was rarely blocked with anterior
approach, can still be used in knee
surgery where thigh tourniquet is used 
pts who required fentanyl was similar btw
groups  tourniquet pain is not affected
by presence of posterior femoral
cutaneous nerve block
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