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Pediatric Anesthesia: Research Report

Ultrasonographic-Guided Ilioinguinal/Iliohypogastric Nerve Block in Pediatric Anesthesia: What is the Optimal Volume?

Willschke, H, MD*; Bösenberg, A, MBChB, FFA(SA); Marhofer, P, MD*; Johnston, S, MBChB, FCA(SA); Kettner, S, MD*; Eichenberger, U, MD§; Wanzel, O, MD; Kapral, S, MD*

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doi: 10.1213/01.ane.0000217196.34354.5a
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Although pediatric regional anesthesia is gaining popularity for providing postoperative analgesia, the volume of local anesthetic required for peripheral nerve blocks in children is not clearly defined. For example, ilioinguinal/iliohypogastric nerve blocks have been described for perioperative pain management in pediatric day-case surgery patients. However, previous studies using the so-called “fascial click” method for ilioinguinal/iliohypogastric nerve blocks have shown a requirement for additional analgesia in up to 35%–75% of children (1–3).

The recommended dose for ilioinguinal/iliohypogastric nerve block in children, according to textbooks on regional anesthesia, is between 0.3 and 0.5 mL/kg local anesthetic (4–7). Although adequate, long lasting analgesia is essential for patients' happiness and parents' satisfaction, long lasting analgesia in lower extremity blocks can also cause motor blocks and urinary retention. The unpredictable spread of a large volume of local anesthetic is one reason for these side effects. In a recent editorial, Denny and Harrop-Griffiths (8) quoted Morton's “Regional anesthesia always works—provided you put the right dose of the right drug in the right place.” With this idea in mind, ultrasonographic guidance may allow the precise placement of local anesthetic and thereby the key finding of Morton's “right place.”

Previously, our study group demonstrated that an ultrasonographic-guided ilioinguinal/iliohypogastric block technique was more effective than the conventional fascial click method (9), and the unpredictable anatomy of children might explain the poor success rate of this regional anesthetic technique in children. In addition, significantly smaller volumes of levobupivacaine were used in the ultrasonographic-guided group, where the injection of local anesthetic was stopped when the target nerves were seen to be surrounded by local anesthetic, when compared with the fascial click group (0.19 ± 0.05 mL/kg versus 0.3 mL/kg; P < 0.0001). These results are similar to adult regional anesthesia studies using a smaller amount of local anesthetic (10,11). This study was designed to determine the minimum volume of 0.25% levobupivacaine required for an effective blockade of the ilioinguinal/iliohypogastric nerves using ultrasonographic guidance in children undergoing unilateral inguinal surgery.

Methods

After IRB approval, 40 consecutive ASA physical status I children aged 1–8 yr old, scheduled for elective unilateral inguinal surgery in the outpatient theater, were enrolled in this prospective study. Informed consent was obtained from the parents of all children, and when appropriate, assent was obtained from the child. Exclusion criteria included any contraindication to ilioinguinal block, parental or patient refusal, allergy to amide local anesthetics, and the inability to visualize the ilioinguinal and iliohypogastric nerve with ultrasound.

Children were premedicated with oral midazolam 0.5 mg/kg. General anesthesia was induced with sevoflurane via facemask. After establishing venous access, a laryngeal mask was placed, and anesthesia was maintained with 1 minimum alveolar anesthetic concentration of halothane in oxygen/nitrous oxide 40:60 and spontaneous ventilation. Intraoperative monitoring included electrocardiogram, heart rate, pulse oximetry, automatic noninvasive arterial blood pressure, end-tidal carbon dioxide concentration, and end-expiratory measurement of the halothane concentration. All surgical procedures were performed by the same surgeon, and all blocks were performed by the same anesthesiologist, who has experience in ultrasound-guided regional anesthetic techniques in children.

A SonoSite 180 plus portable ultrasound unit (SonoSite, Bothell, WA) and a 5- to 10-MHz linear hockey stick probe were used to identify the targeted nerves (ilioinguinal and iliohypogastric nerve). Adjustments (depth, probe frequency, and low and far gain) were made to achieve optimal ultrasonographic figures of the nerves and the surrounding anatomical structures (Fig. 1). After aseptic preparation of the puncture site and the ultrasonographic probe, the nerve block was performed under continuous ultrasound guidance using an insulated 22-gauge 40-mm needle with a facette tip and an injection line (Pajunk, Geisingen, Germany). Once the tip of the needle was correctly positioned between the ilioinguinal and the iliohypogastric nerve by using a cross-sectional ultrasonographic puncture technique (Fig. 2), and after a negative aspiration test, a predetermined volume of 0.25% levobupivacaine (Chirocaine; Abbott, Roscrea, Ireland) was injected. The distribution of local anesthetic was monitored under real-time ultrasonography, and in the case of a misdistribution of the local anesthetic, the needle would have been repositioned. Misdistribution was defined as when the local anesthetic did not surround the nerve structures.

Figure 1.
Figure 1.:
Ultrasonographic picture of the inguinal region (left side = lateral; arrow indicates the nerve structures).
Figure 2.
Figure 2.:
The needle position relative to the linear ultrasound probe for the ilioinguinal/iliohypogastric nerve block (cross-sectional technique).

Using a modified step-up-step-down approach, with 10 children in each study group, 0.2 mL/kg of 0.25% levobupivacaine was used as the initial dose. Results were analyzed after each group of 10 patients. If all blocks were successful and satisfactory analgesia was achieved (see below), the volume of local anesthetic was halved, and a further 10 patients were investigated until a group of insufficient blocks was observed. The study was designed such that if 100% were not obtained with the designated volume, a 50% increase in volume followed, and a further 10 patients were enrolled. For example, if after reducing the dose from 0.2 mL/kg to 0.1 mL/kg, and any of the 10 blocks failed, the next group would receive 0.15 mL/kg of 0.25% levobupivacaine.

In all patients, skin incision was performed at least 15 min after placement of the ilioinguinal/iliohypogastric nerve block. An increase in heart rate of more than 15% and or arterial blood pressure at skin incision was defined as a failed block, and rescue analgesia using fentanyl 1 μg/kg was given. Intraoperatively, an increase in heart rate or arterial blood pressure was also treated with fentanyl 1 μg/kg because it was not related to traction on the peritoneum. The efficacy of postoperative analgesia was documented using the objective pain score (OPS), where objective behavioral variables (crying, facial expression, position of torso and legs, and motor restlessness) are assessed (12,13). Each pain variable is scored on a 3-point scale (1 = none, 2 = moderate, and 3 = severe) to give a maximum cumulative score of 15. If the OPS score was ≥11, the child received 30 mg/kg of acetaminophen rectally. Postoperatively, the children were monitored every 15 min during the first hour and every 30 min for the next 3 h until discharge. Intra- and postoperative pain evaluation were performed by an anesthesiologist who was not involved in the study protocol and who was blinded to the volume of local anesthetic used. The data were collected by a research nurse, who was also blinded to the volume of local anesthetic used.

The children were discharged home after 4 h, when they were pain free and there was no other medical reason to admit them to a surgical ward. The children were discharged with an oral acetaminophen suspension (30 mg/kg) for therapy of subsequent analgesia to be administered by their parents or care providers, who were also asked to report immediately to Red Cross Children's Hospital in the event of difficulty in pain management.

Demographic data were compared by analysis of variance. Data are presented as mean ± sd or as median (range) for ordinal data.

Results

Patient demographics were similar in all groups with regard to sex, weight, and height (Table 1). The ilioinguinal and the iliohypogastric nerve could be visualized in all cases, and no needle reposition caused by misdistribution of local anesthetic was required. There were no surgical or anesthetic complications. Children were discharged home after 4 h. No parent reported any pain management concerns after discharge.

Table 1
Table 1:
Demographic Data

There was no increase in heart rate at skin incision in the 0.2-mL/kg, 0.1-mL/kg, or 0.075-mL/kg groups. In the 0.05-mL/kg group, 3 of 10 children (30%) received rescue analgesia (fentanyl 15.3 μg [95% confidence interval (CI), 11.3–19.3]) because of an increase in heart rate at skin incision of more than 15%. The cumulative increase in heart rate in the 0.05-mL/kg group caused by skin incision was 5.3% from baseline.

Regarding postoperative pain, there was no difference in the OPS levels in the 0.2-mL/kg and 0.1-mL/kg groups. In these groups, no child received acetaminophen within the first 4 h. Four children (40%) in the 0.05-mL/kg group who had an OPS score ≥11 were treated with acetaminophen. Three of these children had previously received fentanyl.

In accordance with the protocol, in view of the 40% failure in the 0.05-mL/kg group, a volume of 0.075 mL/kg was used for the subsequent group. There were no failures in the 0.075-mL/kg group, and therefore, no additional analgesia was required. Changes in heart rate at skin incision are presented in Table 2. There was no change in arterial blood pressure.

Table 2
Table 2:
Heart Rate (HR) in beats/min Before and After Skin Incision

Discussion

The use of ultrasonographic guidance in regional anesthesia results in more frequent success, shorter onset times, and longer duration of action with fewer side effects when compared with more conventional techniques (14). This is the second study in a research project that evaluated the impact of ultrasonographic guidance in ilioinguinal/iliohypogastric nerve blocks in children. By using a modified version of the step-up-step-down technique, we demonstrated that ultrasonographic guidance offers the opportunity to perform successful blocks with 0.075 mL/kg of 0.25% levobupivacaine (15,16). The use of ultrasonographic guidance facilitates a success rate of 100% when the targeted nerves are visualized (14). This is in contrast to conventional techniques, which usually have a success rate between 35% and 75%.

The current study is the first to investigate the minimal volume of local anesthetic, with a given concentration, under direct visualization of a peripheral nerve. Previous studies (15), which investigated the minimal concentration of local anesthetics in epidural anesthesia, used a step-up-step-down technique. However, this technique was recently described to be inadequate for other regional anesthetic techniques, such as spinal anesthesia (17,18). Therefore, we decided to modify the technique for the current study. The step-down approach is usually based on the change of concentration between each patient depending on the response of the previous patient. This approach was developed to evaluate the 50% effective dose of a certain drug. However, our aim was a success rate of 100%, and an insufficient volume of local anesthetic was defined by a success rate of <100%. Therefore, we defined a clinically useful volume of local anesthetic when 10 blocks were successful. This approach seems reasonable to us because the blockade of peripheral nerves is dependent on various factors, such as regional blood flow, functional state of the nerve, or pH value of the surrounding tissue.

Reducing the volume of local anesthetic in pediatric regional anesthesia has several advantages. First, the risk of toxicity is diminished. This is particularly relevant after ilioinguinal/iliohypogastric nerve blocks in infants and small children. In recent pharmacokinetic studies, Ala-Kokko et al. (19,20) demonstrated large plasma concentrations of bupivacaine after ilioinguinal/iliohypogastric nerve blocks that were performed with the fascial click method using 0.39 mL/kg of 0.5% bupivacaine in children aged 3–12 years. In these studies, the median venous plasma concentration was 2.2 μg/mL of bupivacaine, a level considered by some to be close to the maximum tolerated concentration of 2.1 μg/mL. Smith et al. (21) also reported unexpectedly high bupivacaine plasma levels in children between 10 and 15 kg (1.5 μg/mL [range, 0.43–4.0]) compared with a group of children who were 15–30 kg (0.9 μg/mL [range, 0.35–1.34]). They only used 0.25 mL/kg of 0.5% bupivacaine.

Second, a reduction in local anesthetic volume potentially reduces unwanted side effects. Transient femoral nerve palsy is a well-described side effect of ilioinguinal nerve block in children. Femoral nerve block may delay ambulation and can be disturbing to the child and parents (22–25). The femoral nerve palsy is thought to be volume-related and occurs as a result of an unnecessary spread of local anesthetic between the muscle layers to the femoral nerve.

Studies using ultrasound guidance have suggested that more accurate placement of smaller amounts of local anesthetic does not reduce the efficacy. Conversely, the volume of local anesthetic should not be reduced to such an extent that efficacy is lost.

In this study, successful blocks were achieved using 0.2, 0.1, and 0.075 mL/kg of 0.25% levobupivacaine without affecting the quality of analgesia within the first 4 hours. The limitation of this study was that, according to our local practice in the outpatient theater, children were discharged home after 4 hours. Therefore, pain assessment was limited to the first 4 postoperative hours, and conceivably, larger volumes may have given patients a longer period of analgesia.

In conclusion, this study demonstrates that much smaller volumes of local anesthetic can be used to perform successful ilioinguinal/iliohypogastric nerve blocks in children than previously recommended. The smallest effective dose was 0.075 mL/kg of 1 0.25% levobupivacaine when the block was performed under ultrasound guidance. This amount of local anesthetic was six- to eightfold smaller compared with dose recommendations in pediatric anesthesia textbooks (4–7). Further studies are intended to determine whether the duration of action beyond 4 hours is affected when the volume of local anesthetic is reduced to this level.

The accuracy attained in this study with ultrasound is borne out by the 100% success rate achieved when 0.2, 0.1, and 0.075 mL/kg of levobupivacaine 0.25% was used for ilioinguinal/iliohypogastric nerve blocks in children. This study supports the use of ultrasonography for pediatric regional anesthesia.

The authors would like to thank the EVN (Energieversorger Niederösterreich) company for providing a SonoSite 180plus transportable Ultrasonographic machine to conduct this study and others without any financial obligation.

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