Continuous Posterior Lumbar Plexus Block for Acute Postoperative Pain Control in Young Children

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IT is well-established that postoperative pain is frequently poorly managed in children and that they receive relatively less analgesic than adults. Side effects associated with the use of opioids 1often limit their administration. Although neuroaxial continuous block techniques represent an interesting alternative, their associated side effects (urinary retention, hypotension, intrathecal infection, post–dural puncture headache, and the poor tolerance of a lasting bilateral sensory and motor block in children) limit these continuous techniques. 2Although it was shown that complications of central blockade are rare, 3,4bilateral blockade is unnecessary for a unilateral operation. We present two cases of the use of continuous lumbar plexus block as a main postoperative orthopedic analgesia in young children.

A 4-yr-old, 20-kg boy was admitted at the Memorial-Hermann Children Hospital (Houston, Texas) after an automobile–pedestrian accident. At the time of arrival, he was diagnosed with a skull fracture, a scalp avulsion, and a right femur fracture. The femur fracture consisted of a proximal transverse subtrochanteric fracture and was placed on traction. The open reduction and fixation of the femur was performed 7 days later during general anesthesia. At the end of surgery, the child was placed in a left lateral position for the placement of a posterior lumbar plexus catheter during general anesthesia (See video on the Anesthesiology Web site).

First, a vertical line was drawn at the level of the highest point of the right iliac crest. Second, a horizontal line parallel to the spine process line was drawn at the level of the right posterior iliac spine. The site of the introduction of the needle was defined as the intersection between these two lines. An insulated 18-gauge, 50-mm introducer Sprotte needle (Pajunk, Albany, NY) was connected to a nerve stimulator (Stimuplex HNS 11; B-Braun Medical, Bethlehem, PA) set up to deliver a current of 1.5 mA, two times per second (2 Hz), with an impulse duration of 0.1 ms with the neutral electrode placed on the opposite leg.

The needle was introduced perpendicular through the skin in search of the transverse process of L5 and then oriented slightly cranially. At a depth of 3 cm, a quadriceps contraction was elicited, indicating the stimulation of the lumbar plexus. The intensity of the current was progressively decreased, and the position of the needle was adjusted to maintain the same motor response with a current of 0.5 mA. After negative aspiration for blood, a test dose of 2 ml of a 0.2% ropivacaine–1.5% mepivacaine (vol/vol) mixture was slowly injected and followed by 12 ml of the same mixture for a total volume of 14 ml. This was followed by the placement of a 20-gague Stimulong plexus catheter (Pajunk) introduced about 1 cm beyond the tip of the introducer needle (4 cm at the skin). The catheter was secured in place with steri-strip (3M Health Care, St. Paul, MN) and covered with a tegaderm (3M Health Care, St. Paul, MN). The child was placed in a supine position, was awakened, underwent extubation, and was transferred to the postoperative acute care unit. The absence of epidural spread was assessed by hemodynamic stability after the performance of the blocks and by the presence of an adequate reaction to pin prick of the opposite leg after emergence. Standard anesthesia care monitoring was used during the procedure and recovery. In the postoperative acute care unit, a continuous infusion pump (Baxter AP II; Baxter Healthcare, Deerfield, IL) was connected to the lumbar plexus catheter and set up to deliver a continuous infusion of 0.2% ropivacaine at a rate of 4 ml/h. The acute orthopedic pain management team took care of the child until discharge from the hospital.

Postoperatively, the child did not request morphine. He slept the full night after his surgery, for the first time since he arrived in our facility. He received a total of only 450 mg acetaminophen on the first postoperative day, and 5 ml acetaminophen plus codeine elixir on one and two occasions on the first and second postoperative days, respectively. No side effects or complications were observed. The nurses and parents were satisfied with the child’s postoperative pain management.

A 16-month-old, 12-kg boy was involved in a lawnmower accident. He was admitted at the Memorial-Hermann Children Hospital. At the time of arrival, the child had a partial left great toe amputation, a right femur fracture associated with a severe injury of the knee, and multiple lacerations to his right thigh. After proper consent was received, he underwent irrigation and drainage and a free vascularized tissue transfer of the right leg. This was followed by irrigation and drainage of the left foot on the next day and by an open reduction of the right femur and knee during general anesthesia. A continuous posterior lumbar plexus block was performed after induction of general anesthesia and positioning of the child in the left lateral position (fig. 1).

The landmarks and technique used as well as the follow-up of this patient were the same as those described in the first case, except that (1) an insulated 18-gauge, 25-mm Sprotte needle was used; (2) the lumbar plexus was found at a depth of 25 mm; (3) a test dose of 2 ml was used, followed by the injection of 6 ml of the same mixture for a total volume of 8 ml; (4) the 20-gauge Stimulong plexus catheter was introduced 3.5 cm at the skin; and (5) 0.2% ropivacaine was infused at a rate of 2 ml/h. Also in this case, the child did not require morphine postoperatively. The child only received acetaminophen on one and two occasions on the first and second postoperative days, respectively.

Continuous femoral infusions have been proven to provide effective postoperative pain control in children. 5,6To our knowledge, these cases represent the first report of continuous posterior lumbar infusions for postoperative pain management in orthopedics in young children. The approach used was similar to the one described by Dalens et al.  7in children according to the original landmarks described by Winnie 8in adults. Dalens et al.  9also evaluated the approach of the lumbar plexus block described by Chayen et al.  10and reported that this approach was associated with an epidural spread in 90% of the cases and was therefore less suitable for unilateral lumbar plexus block.

The depths at which the lumbar plexus was found were approximately 2.5 and 3.0 cm for our 17-month-old and 4-yr-old patients, respectively. These findings are within the limits described by Dalens et al. , 7who established a relation between the depth of the lumbar plexus and the age and the weight of the child (2–2.5 cm for a 1-yr-old infant to 6.0 cm for a 16-yr-old adolescent). Because the depth at which the lumbar plexus is found depends on age, it is clear that the introduction of a needle beyond the recommended depth increases the risk of intraabdominal organ damage. It is critical to recognize that in infants and children, the placement of catheters allowing continuous perineural infusions of local anesthetics requires appropriate expertise and understanding of infant anatomy and, especially for this approach, should be performed by experts in pediatric peripheral nerve blocks.

In adults, the posterior approach to the lumbar plexus is recognized to provide a complete block of the femoral, lateral cutaneous femoral, and obturator nerves. In contrast, the anterior approach to the lumbar plexus (three-in-one block) often misses the lateral cutaneous femoral nerve, the obturator nerve, or both. Although it seems that the anterior approach is preferred for pain management of femoral fracture in infants and children, 5,6the posterior approach was chosen as the technique that most likely would also block the lateral cutaneous femoral and obturator nerves. This was necessary to cover the lateral surgical approach in the first case and the associated lateral laceration and the medial lesion of the knee in the second case. Despite the obvious inability to evaluate the extent of a sensory block in young children, the absence of postoperative requirement for morphine in view of the types of surgeries and expected postoperative pain suggests that indeed our choice produced an appropriate sensory block of the femoral, obturator, and lateral femoral cutaneous nerves.

The use of a continuous infusion technique in infants and children raises questions about the choice, concentration, and rate of infusion of local anesthetics. We chose 0.2% ropivacaine rather than lidocaine or bupivacaine. Like other local anesthetics, the use of ropivacaine is not approved in infants. Nevertheless, local anesthetics are used for neuroaxial continuous blocks, including epidural and caudal blocks. 11,12In this respect, 0.2% ropivacaine has been demonstrated to be safe and effective for epidural continuous infusions at rates similar to those we chose in this infant. 11At these rates, 0.2% ropivacaine has been proven to produce plasma concentrations below those considered toxic in adults. Additional studies investigating the plasma concentrations generated by these dosages are required to confirm the safety of this agent. However, the determination of the local plasma concentration of anesthesia in the absence of a relation between plasma concentrations and clinical symptoms of toxicity is of limited value in the infant. It is well-established that the permeability of the brain barrier as well as the sensitivity of the brain and heart varies with age.

These two case reports represent successful postoperative management of orthopedic pain in children using continuous posterior lumbar plexus infusion. This approach is most likely to provide a complete block of the lumbar plexus and consequently minimizes the need for additional opioids during the postoperative period. However, it is important to recognize that lumbar plexus block in infants and children should only be performed by trained anesthesiologists.