Use of test dose allows early detection of subdural local anesthetic injection with lumbar plexus block

A 56 year-old woman underwent a lumbar plexus block for a revision of a left total hip arthroplasty. During the block procedure, the needle was advanced over the transverse process and isolated quadriceps twitches were elicited. After administering a test dose of 3 ml of 1.5% lidocaine, the patient developed loss of sensation in the L3–4 dermatomal distribution that progressed caudally to involve both legs followed by inability to move the left leg. The patient shortly thereafter became hypotensive and sensory block spread cephalad and peaked at C7 bilaterally suggesting possible subdural spread of local anesthetic. The patient was resuscitated with normalization of blood pressure and eventually had full resolution of motor and sensory block. Subdural spread of local anesthetic is a potential complication of lumbar plexus block related perhaps to injection of local anesthetic near dural sleeves of nerve roots. The use of a test dose allows early recognition of subdural injection and may limit consequences of inadvertent subdural spread of local anesthetic.