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PEDIATRIC ANESTHESIOLOGY

Ilioinguinal/Iliohypogastric Blocks in Children: Where Do We Administer the Local Anesthetic Without Direct Visualization?

Marion Weintraud, MD^*, Peter Marhofer, MD^*, Adrian Bösenberg, MBChB, FFA (SA), Stephan Kapral, MD^*, Harald Willschke, MD^*, Michael Felfernig, MD, and Stephan Kettner, MD^*

From the *Department of Anaesthesia and Intensive Care Medicine, Medical University of Vienna, 1090 Vienna, Austria; Department of Anaesthesia, University Cape Town, Red Cross Children Hospital, Rondebosch, South Africa; and Department of Anaesthesia and Intensive Care, Royal Naval Hospital, Gibraltar, United Kingdom.

Address correspondence and reprint requests to Peter Marhofer, MD, Department of Anaesthesia and Intensive Care Medicine, Medical University Vienna, Waehringer Guertel 18–20, 1090 Vienna, Austria. Address e-mail to peter.marhofer{at}meduniwien.ac.at or web site www.sono-nerve.com.

Abstract

BACKGROUND: Ultrasonographic observation of peripheral nerve blocks enables direct visualization of the spread of local anesthetic around the targeted nerves. Similarly, ultrasonography may be used to determine the site of local anesthetic placement when landmark-based techniques are used. We performed a study to determine the actual location of local anesthetic when ilioinguinal/iliohypogastric nerve blocks are performed using landmark-based techniques in children in an attempt to explain a failed block.

METHODS: After induction of general anesthesia (1 minimum alveolar anesthetic concentration halothane and laryngeal mask airway), 62 children scheduled for inguinal surgery received an ilioinguinal/iliohypogastric nerve block based on standard anatomical landmarks. Ultrasonography was then used to determine the actual location of local anesthetic placement. The anesthesiologist performing the block was blinded to the ultrasonographic investigation. Successful blocks were recorded either when the local anesthetic surrounded the nerves or were based on clinical signs after skin incision.

RESULTS: In 14% of the blocks, the local anesthetic was administered correctly around the nerves resulting in successful blocks. In the remaining 86%, the local anesthetic was administered in adjacent anatomical structures (iliac muscle 18%, transverse abdominal muscle 26%, internal oblique abdominal muscle 29%, external oblique abdominal muscle 9%, subcutaneous 2%, and peritoneum 2%), and 45% of these blocks failed.

CONCLUSION: Accurate placement of local anesthetic around the ilioinguinal/iliohypogastric nerves in children is seldom possible when landmark-based techniques are used. In the majority of patients, the local anesthetic was inaccurately placed in adjacent anatomical structures with unpredictable block results.

The ilioinguinal/iliohypogastric nerve block is a popular regional anesthetic technique for postoperative pain relief after inguinal surgery in children. A success rate of approximately 70% has been reported when "blind," anatomical landmark-based techniques are used.1 In an attempt to improve the success rate, larger volumes of local anesthetic are used but these may be complicated by inadvertent fascia iliaca compartment or femoral nerve blocks.2,3

Significant complications, such as colonic puncture, have also been described when blind techniques are used.4,5 This is not surprising because the peritoneal cavity is millimeters from the ilioinguinal and iliohypogastric nerves in small children.6

An analysis of the exact location of local anesthetic placement during these blind, landmark-based techniques using ultrasound may help to understand the reason for their failure and thereby improve the success rate of these blocks. A prospective blinded study was designed to observe the placement of local anesthetic using ultrasonography during ilioinguinal/iliohypogastric nerve blocks by anesthesiologists in training using the standard technique based on anatomical landmarks.

METHODS

After approval from the local ethics committee and informed parental consent, 62 children scheduled for inguinal surgery were included in this prospective study. Children with infections at the proposed puncture site, known anatomical abnormalities in the inguinal region, blood coagulation disorders, and allergies to amino-amide local anesthetics were excluded.

After oral premedication with midazolam 0.5 mg/kg and standard monitoring (electrocardiogram, pulse oximetry, and noninvasive arterial blood pressure), general anesthesia was induced with sevoflurane via facemask, IV access was established, and anesthesia was maintained with 1 minimum alveolar anesthetic concentration halothane in air/O₂ (fraction of inspired oxygen, 0.3). The children breathed spontaneously via a laryngeal mask airway and, if necessary, respiration was assisted to maintain an end-expired carbon dioxide partial pressure of 35–45 mm Hg throughout the intraoperative period.

Before placement of the ilioinguinal/iliohypogastric nerve block, an initial ultrasound exploration of the area of the proposed injection site was performed by an experienced ultrasonographer using a SonoSite 180plus transportable ultrasound unit and a 5–10 MHz linear "hockey stick" probe with an active area of 25 mm (SonoSite, Bothell, WA). The proposed site of injection was then prepared with chlorhexidine. The blocks were performed by anesthesiologists in training with experience performing ilioinguinal/iliohypogastric blocks guided by the landmarks described by van Schoor et al.7 All blocks were conducted with a 22-gauge facette needle (Pajunk ^TM, Geisingen, Germany) using a "single pop" technique.

After careful aspiration, 0.3 mL/kg bupivacaine 0.5% was injected under real-time ultrasound imaging to detect both the position of the needle tip and the spread of local anesthetic. The position of the ultrasound probe relative to the needle is illustrated in Figure 1. The position of the needle tip in a particular anatomical structure (adjacent to the nerves; within the iliac muscle, transverse abdominal muscle, internal oblique abdominal muscle, external oblique abdominal muscle; within the peritoneal cavity or subcutaneous) was recorded. The anesthesiologist performing the block was blinded to the ultrasound image. However, if, in the opinion of the ultrasonographer, the needle was in a potentially dangerous position, the anesthesiologist was alerted. After injection of the local anesthetic, the shortest distance from the local anesthetic bolus to the nerves was measured on the ultrasound image.

View larger version (44K): [in this window] [in a new window]   Figure 1. Position of the ultrasound probe relative to the needle ("out of plane" technique).

A successful block was defined as either confirmation of the correct placement of the local anesthetic around the ilioinguinal/iliohypogastric nerves by the ultrasonographer, or clinically by the response to skin incision that was performed at least 15 min after placement of the block. An increase in heart rate or arterial blood pressure of >10%, tachypnea or spontaneous movements defined a failed or inadequate block. Rescue analgesia was provided with fentanyl 1 mcg/kg. Because the focus of the study was the ultrasound investigation of the position of the needle tip and the spread of local anesthetic, postoperative pain scores were not assessed. However, additional analgesia was provided if required.

Four hours postoperatively all children were examined for block-related complications such as leg weakness or hematoma.

The difference between the failed blocks and successful blocks was assessed by t-test for independent samples. Thereby, those cases in which the local anesthetic was administered exactly around the nerves were excluded from statistical analysis. The success rates relative to the site of injection of local anesthetic were compared by Fisher’s exact test. Statistical significance was considered for P < 0.05. All values are expressed as mean (sd).

RESULTS

Sixty-two children, mean age 51 (range, 2–96) mo and weight of 18 (range, 3.8–44) kg, were included in the study. Pertinent demographic data are shown in Table 1. The ultrasonographer considered that the local anesthetic was administered in the correct place, i.e., between the internal oblique abdominal and transverse abdominal muscles in only nine (14%) of the blocks. All these blocks were clinically successful. Conversely, in the remaining 53 (86%) blocks, the local anesthetic was placed in surrounding tissues and, of these, 24 (45%) blocks did not meet the clinical criteria of success. Eighty-four percent of blocks that were placed more than one anatomical layer from the nerves were unsuccessful. The overall clinical success rate including all sites of local anesthetic administration was 61% (38 of the 62). The distribution of the local anesthetic in the adjacent structures, as judged by the ultrasonographer, is shown in Figure 2. The relationship between the site of injection and a successful block is also shown.

View larger version (7K): [in this window] [in a new window]   Figure 2. Ratio of successful and failed blocks at different adjacent anatomical structures (*P < 0.05 compared with iliac muscle and external oblique abdominal muscle).

The distance of the local anesthetic to the nerve structures is shown in Table 2. In those cases in which the local anesthetic was administered around the nerves, successful block was achieved.

Clinical successful blocks were closer to the targeted nerves than failed blocks (P = 0.002). However, there was a large overlap of the measured distances, as shown in Figure 3. Therefore, we found no cut-off point for the distance between local anesthetics and nerves that led to block failure.

View larger version (8K): [in this window] [in a new window]   Figure 3. Box plot of the distance of the local anesthetic to the nerves for successful and failed blocks. The box solid line represents the median value, the boxes are the interquartile range, and the whiskers are the 10th and 90th percentile range. *Difference between failed and successful blocks; P = 0.002.

No block-related complications such as leg weakness or hematoma were noted.

DISCUSSION

"Regional anesthesia always works provided you put the right dose of the right drug in the right place." This adage from an editorial by Denny and Harrop-Griffith8 sounds simple but reflects the reality of regional anesthesia. The success rate for ilioinguinal/iliohypogastric nerve block has been reported to be approximately 70%.1 In modern anesthesia, most would consider a failure rate of 30% to be unacceptably high. This study adds further support to the argument that "blind" techniques based purely on anatomical landmarks have a high failure rate. In this study, most of the anesthesiologists placed the local anesthetic in adjacent structures.

Unfortunately, the description of many peripheral blocks in children is based on adult studies. Ilioinguinal/iliohypogastric nerve blocks are one of the most popular nerve blocks in children, in part because inguinal surgery is common and because peripheral nerve blocks are frequently used for ambulatory surgery. An anatomical study on neonatal cadavers showed a high inter-individual variability of the nerve location.7 In addition, large discrepancies between the puncture sites as described by different authors and the nerve location were noted. The depth of the nerve is also variable, particularly in children of different ages or different body habitus.6 Techniques relying on a single- or double "pop" technique require experience but, even then, there is a finite distance between accurate placement and failure or potential abdominal complications.4,5

Needle placement and spread of local anesthetic is easily seen with high-resolution ultrasonography. Using ultrasound guidance, greater success can be achieved by more accurate placement of reduced volumes of local anesthetics closer to the targeted nerves. This has been shown for both ilioinguinal/iliohypogastric nerve blocks6,9 and rectus sheath blocks10 in children. Reduced onset times, longer duration of blocks, and improved postoperative pain scores have also been achieved for various regional anesthetic techniques using ultrasound guidance.6,9–13

Alternatively, ultrasonography could be used to determine the local anesthetic placement. The aim of this study was to ascertain where the local anesthetic was placed when the standard landmark-based technique was used in an attempt to explain the reasons for success or failure. With this information it may be possible to improve the success rate of blind, landmark-based techniques.

In this study, local anesthetic was administered correctly between the internal oblique abdominal and the transverse abdominal muscles and around the targeted nerves in only 14% of cases. These blocks were as successful as expected. In the majority of the remaining cases, the local anesthetic was administered within the transverse and internal oblique abdominal muscles. Three-quarters of these were defined as clinically successful suggesting that diffusion of the local anesthetic from the initial placement within the muscle to the nerves occurred. However, there was a large overlap of distances in failed and successful blocks (e.g., a distance of 3.0 mm from the administration of local anesthetic inside the transverse abdominal muscle to the nerves resulted in a failed block and a distance of 6 mm resulted in a successful block). Eighty percent of blocks that were placed deeper than the transverse abdominal muscle and all blocks more superficial than the internal oblique abdominal muscle failed. In those cases in which there was more than one anatomical layer between the local anesthetic and the nerve, the block failed.

The block also failed when the local anesthetic was injected into the peritoneal cavity. The short bevel needle did not damage the bowel. Apart from anecdotal reports,5 there are no data on the incidence of intraperitoneal injection during ilioinguinal/iliohypogastric block. This may occur more frequently than realized in small children judging by the close proximity of the peritoneal cavity to these nerves as we have shown.6

The limitations of this study are twofold. First, the measurement of the local anesthetic-nerve distance by ultrasonography was not validated. To validate this technique, it would probably be necessary to compare it with high resolution magnetic resonance imaging. This was not feasible in our institution. Second, the detection of hypo-echogenic fluids in soft tissues, in this case, the local anesthetic by ultrasound, is relatively easy but is only two-dimensional. The lateral spread of local anesthetic was not measured. It could also be argued that the spread of local anesthetic was only observed immediately after the placement. Monitoring the spread without delaying the surgery was not feasible. Furthermore, it is clearly not possible to observe the subsequent diffusion of local anesthetic through the tissues. However, the dissipation of local anesthetic may be worthy of further investigation.

CONCLUSION

Accurate placement of local anesthetic using the standard anatomical landmark-based technique for ilioinguinal/iliohypogastric nerve blocks is difficult. In this study, successful block was achieved in only 62% of cases. Based on the ultrasound findings, only 9 of 62 block had accurate placement of the local anesthetic. The rest were placed in the surrounding tissues. Only some of these were successful with the proviso that the local anesthetic was less than one tissue plane away from the nerves. In comparison, previous studies using ultrasound-guided techniques have achieved 100% success, even with reduced doses.6,9 This, we believe, is a strong argument for the use of ultrasound guidance for ilioinguinal/iliohypogastric nerve blocks in children.

ACKNOWLEDGMENTS

The authors thank the EVN (Energieversorger Niederösterreich) company for providing a SonoSite 180plus portable ultrasound unit for the conduct of this study.

Footnotes

Accepted for publication August 23, 2007.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Weintraud, M. Articles by Kettner, S. Search for Related Content PubMed PubMed Citation Articles by Weintraud, M. Articles by Kettner, S. Related Collections Pediatrics Regional Anesthesia