THE lumbar plexus is derived from rami from the first through the fourth lumbar nerves and is primarily responsible for innervation of the extensor and adductor compartments of the thigh. Blockade of the lumbar plexus using a posterior approach, via  either a single injection or continuous technique using an indwelling catheter, is an attractive alternative for postoperative pain management in patients undergoing surgery of the hip and above the knee. This technique may enable blockade of all branches of the lumbar plexus, most notably the lateral femoral cutaneous, femoral, and obturator nerves. The genitofemoral and ilioinguinal nerves, also formed from contributions of ventral rami of the first and second lumbar nerves, are generally not considered incorporated in the block of the plexus. Also referred to as the continuous psoas compartment block, it is considered reliably safe with few complications. 1,2 

We report the case of a total spinal anesthetic after a posterior lumbar plexus blockade performed during general anesthesia.

A 45-yr-old woman (weight, 68 kg), American Society of Anesthesiology (ASA) class III, presented for left total hip arthroplasty for traumatic arthritis following a past motor vehicle collision. General endotracheal anesthesia with postoperative continuous lumbar plexus blockade to facilitate postoperative pain control was discussed and planned with the patient preoperatively. Appropriate ASA monitors were used with the addition of a right radial arterial pressure monitor.

Intravenous induction was performed with propofol and vecuronium. The patient was positioned right decubitus. Maintenance was accomplished with isoflurane, oxygen, nitrous oxide, and supplemented with fentanyl. The operative procedure was uneventful. No residual neuromuscular blockade was confirmed with a peripheral nerve stimulator and the patient was spontaneously breathing at the end of surgery.

With the patient remaining in the right decubitus position, she was prepped for insertion of a continuous lumbar plexus catheter using a posterior approach by the regional anesthesia attending as previously described. 3Landmarks included the superior border of the iliac crest of the operative hip, the third through fifth lumbar spinous processes to identify the midline, and a 3- to 5-cm perpendicular line from the midline at approximately the level of the posterior superior iliac spine. The intersection of these two lines represents the point of needle insertion. A 4-in insulated Contiplex Touhy needle (B.Braun Medical, Bethlehem, PA) was inserted perpendicular to all planes using a peripheral nerve stimulator. The needle was advanced until contact with the transverse process of the fifth lumbar vertebrae was met then angled in a caudal direction. A myotonic response of the quadriceps muscles was observed, consistent with femoral nerve distribution. This was elicited at 1.5 mA and decreased to 0.5 mA at a depth of approximately 9 cm. A 40-ml mixture of 1.5% mepivacaine and 0.75% ropivacaine was injected after a negative aspiration for blood, air, and cerebral spinal fluid. A catheter was then inserted to 14 cm at the skin and secured with tape and benzoin.

The patient was then positioned supine and isoflurane was discontinued, at which time it was noted she was hypotensive with systolic blood pressure of 80 mmHg, confirmed by both arterial trace and cuff pressure. This was immediately treated with fluids and vasoactive agents consisting of intermittent boluses of ephedrine and phenylephrine, which improved blood pressure. It was also noted the patient had become apneic. Her pupils were dilated at 6 mm bilaterally and sluggish to light reaction. A suspicion of intrathecal injection with total spinal anesthesia was considered. All extremities of the patient were flaccid and did not react to painful stimuli. The patient was transferred to the postanesthesia recovery unit for postoperative ventilation, intubated, and placed on a ventilator. She was given propofol and midazolam to maintain her sedation and hypnosis.

After approximately 140 min, the patient was awake and opening her eyes upon command. The patient recovered spontaneous respirations after 180 min. After 260 min, she was moving all extremities with head lift, at which time she was extubated uneventfully and transferred to an intermediate monitoring unit for postoperative care.

The lumbar plexus catheter was left in situ , but not infused. The catheter was assessed postoperative day 1 by aspiration and clear fluid was withdrawn. Laboratory analysis showed a glucose level of 84 g/dl. Intrathecal placement was confirmed, and the catheter was removed. The patient recovered without further sequelae. There were no motor or sensory deficits appreciated prior to discharge. When the patient was questioned regarding recall of the event, she stated that she “remembers being numb to her ears.”

The lumbar plexus blockade, using a posterior approach, is a relatively safe alternative for postoperative pain management in patients undergoing surgery above the knee. Combined with a sciatic nerve block, anesthesia to the leg can be accomplished. Continuous techniques using indwelling catheters for peripheral nerve blocks have been used widely in Europe and are becoming more popular in the United States. Despite infrequent occurrence of complications with these procedures, subcapsular renal hematoma, 4psoas hematoma and plexopathy, 5and even inadvertent coagulation of the catheter tip at the surgical site impeding catheter removal 6have been reported.

We report a case of inadvertent total spinal anesthesia after lumbar plexus block. Although this complication has been reported in the French literature, 7to our knowledge, it has not been reported in the United States. Our case presents critical points both of our technique and of the procedure as a whole.

The lumbar plexus originates from the ventral rami of the first four lumbar nerves and lies within the psoas muscle and anterior to the transverse processes of the corresponding lumbar vertebrae. Care must be taken to maintain perpendicular needle insertion, and the direction should be in a cranial or caudal fashion with regard to the transverse processes. A more medial direction may result in intrathecal puncture or dural sleeve contact similar to a paramedian approach to the epidural space.

The exact mechanism behind this complication in our case is unknown. Perhaps a more medial approach was not appreciated or use of improper landmarks was used because our patient was obese.

Hypotension after lumbar plexus block can occur due to epidural spread of local anesthetic, especially with volumes greater than 20 ml, 8,9and it should be suspected as a side effect rather than a complication of the procedure. We considered this as well as an etiology for the hypotension encountered. However, apnea and dilated bilateral pupils are more consistent with intrathecal injection and total spinal anesthesia. We used a large volume (40 ml), which we have amended to 20 ml in our practice, not to avoid inadvertent intrathecal injection but to decrease the likelihood of epidural spread. Also, we do not routinely perform peripheral nerve blocks in anesthetized patients, although time constraints created difficulty with preoperative placement. Having the patient anesthetized removes the patient as a monitor of this complication because the patient is unable to communicate any unusual symptoms, such as complete motor block or dyspnea. Further, a test dose was not used, because it would not have been detected in our patient who was anesthetized. However, in our opinion, a test dose should be performed in the awake patient and thorough aspiration for cerebral spinal fluid should be routine for all patients. Intrathecal placement of either the needle and/or catheter is difficult to determine. A loss of resistance technique, along with the use a nerve stimulator, would help determine this since cerebral spinal fluid should be apparent from the hub of the needle. Our needle was connected to injection tubing. Spinal fluid may have been overlooked when we aspirated because it was mixed with the local anesthetic in the small caliber tubing.

Use of peripheral nerve blockade either for regional anesthesia or postoperative pain management is gaining popularity in the United States. Although this type of blockade is considered relatively safe, especially in experienced hands, the operator must maintain constant vigilance for potential complications.

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