The extent of anesthesia after selective blocks of the peripheral nerves originating
from the lumbar and lumbosacral plexi is often assessed before surgery can begin. This
assessment may be deceptively difficult if
one has incomplete understanding of lower extremity innervation or if the
evaluation is hindered by slow onset of sensory block. Conversely, timely
evaluation of the block allows the anesthesiologist to identify inadequately
anesthetized nerves, thus providing the opportunity to modify the block
A simple system for assessing the adequacy of upper extremity nerve
block has been described and enjoys acceptance by anesthesiologists
worldwide. The four P's (push, pull, pinch, punt) concept was likely
developed during World War II as a straightforward method for medics to
determine the extent of battlefield injury. The concept was later formalized
and popularized by Thompson and Brown.1 Herein is
described a methodology for assessing lower extremity anesthesia that is a
variation of the four P's concept. For lower extremity evaluation, the P's
are modified slightly to become push, pull, pinch, punt.
Several minutes after depositing local anesthetic near a peripheral nerve,
the following individual assessments are undertaken to determine blockade of
the four major nerves of the lower extremity.
The sciatic nerve is derived from the lumbosacral plexus and provides
motor control to the posterior thigh and the entire lower leg and foot. Its
sensory distribution includes the posterior thigh, the posterior knee joint,
and all the lower leg except for the saphenous nerve distribution (medial
lower leg and ankle). Because plantar flexion of the foot is controlled by
the sciatic nerve, its function is evaluated by asking the patient to
push the foot against the resistance of the examiner's hand or “step on the gas” (Figure 32–1). Anesthesia within the sciatic nerve distribution
is indicated by weakness during the performance of this maneuver. Because
the evaluation is performed distally, it is applicable to all sciatic nerve
block approaches, including the blocks at the popliteal fossa.
Push. Patients with successful sciatic or popliteal
fossa block are unable to push the target with their foot.
A: Tibial nerve or dorsiflex the foot;
B: Common peroneal nerve.
The obturator nerve, a component of the lumbar plexus, provides motor
innervation to the adductors of the thigh and variable sensory innervation to the
proximal medial thigh. It also has small branches to the knee and hip
joints. To assess obturator nerve function, the anesthesiologist abducts the
patient's leg and then requests that the patient pull the leg toward the midline
against resistance (Figure 32–2). The obturator nerve has been
successfully blocked if the patient exhibits adductor weakness during this
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