Paediatric regional anaesthesia continues to gain popularity for intraoperative and postoperative pain management, particularly for day-case surgery in order to ensure long-lasting analgesia.1 Regional anaesthetic techniques are commonly used for pain management after inguinal surgery in children. An important component of the pain experienced by children after herniorrhaphy is derived from the abdominal wall incision. The nerves supplying the abdominal wall course through the neurofascial transversus abdominis plane (TAP) between the internal oblique and the transversus abdominis muscles. The TAP block, a compartmental block, was described in 2001 by Rafi2 via a landmark-based, double-pop, blind technique using anatomic identification of the lumbar triangle of Petit. Ultrasound guidance can increase the accuracy and safety of the injection by providing a direct view of the placement of the needle tip and local anaesthetic spread. Several ultrasound-based studies have reported poor accuracy of blind abdominal wall injections in adult and paediatric populations.3,4 However, the recent widespread use of ultrasonography allows accurate localisation and a decrease in the dose of local anaesthetic solution.5,6
As with any regional anaesthetic technique in infants and children, local anaesthetic toxicity is the most likely serious adverse event. Limitation of local anaesthetic doses (volume or concentration) is mandatory. This study was designed to determine the optimal dose of levobupivacaine required for effective perioperative pain management using ultrasound-guided TAP block in children undergoing ambulatory unilateral inguinal surgery.
Materials and methods
Ethical approval for this study (CPP No. 2010.01.03bis) was provided by the CPP Sud Méditerranée III, Nimes, France (Chairperson J. Pellissier) on 18 March 2010. After written informed parental consent, children aged from 1 to 5 years old scheduled for ambulatory elective unilateral herniorrhaphy were included in this prospective study. Exclusion criteria included any contraindication to general anaesthesias or TAP block, intolerance to nonsteroidal anti-inflammatory drugs, parental refusal, known allergy to local anaesthetic amide drugs and concurrent participation in another clinical trial.
A standard anaesthetic technique was used in all children. Premedication consisted of 0.3 mg kg−1 midazolam rectally 30 min before induction. Standard monitoring, including automatic noninvasive arterial blood pressure measurement, electrocardiogram, pulse oximetry, end-tidal carbon dioxide concentration and end-expiratory measurement of the sevoflurane concentration was applied. General anaesthesia was induced in all children using sevoflurane (inspired fraction 6%) in an oxygen/nitrous oxide mixture (50/50). After securing vascular access, the patients received propofol 2 to 3 mg kg−1 to facilitate insertion of a laryngeal mask airway. No opioid was used before assessment of TAP block efficiency on incision. Mechanical ventilation was applied for the duration of surgery, to achieve an ETCO2 of 4 to 4.7 kPa. Anaesthesia was maintained with one minimum alveolar concentration of sevoflurane adjusted to the mixture of gas used (50/50 oxygen/nitrous oxide mixture).
All blocks were performed under general anaesthesia by anaesthesiologists experienced in ultrasound-guided regional anaesthetic techniques in children. Ultrasonographic images were obtained using a portable ultrasound machine (LOGIQ-E; GE Healthcare, Wauwatosa, Wisconsin, USA) and an 8 to 13 MHz linear array probe. Local anaesthetic solutions were prepared by a nurse anaesthesiologist not involved in clinical management and were presented to the anaesthesiologist in a blinded fashion. After aseptic preparation of the puncture site, the TAP block was performed using a 21-gauge 50 mm needle with an injection line (Uniplex Nanoline, Pajunk, Geisingen, Germany). The probe was placed transversely on the vertical mid-axillary line between the iliac crest and 12th rib. The needle was introduced anteriorly and advanced in-plane. Once the tip of the needle was correctly positioned between the internal oblique and transversus abdominis muscles, and after a negative aspiration test, 0.2 ml kg−1 of a levobupivacaine solution (Chirocaine, Abbott, Rungis, France) was slowly injected.
The levobupivacaine dose for a particular patient was determined by the response of the previous patient to a higher or smaller dose (step size of 0.1 mg kg−1) using Dixon's up-and-down sequential method,7 starting at levobupivacaine 0.5 mg kg−1. Unsuccessful block was defined as an increase in either heart rate (HR) or mean arterial blood pressure (MAP) of at least 20% (compared with preoperative reference values) persisting 1 min after skin incision. Then, the dose of levobupivacaine administered to the next patient was increased by one step. In the case of a successful block, the dose of levobupivacaine given to the next patient was decreased by one step. The dilution protocol of levobupivacaine solution is reported in Table 1.
In all patients, skin incision was performed at least 15 min after injection of the TAP block. In the case of failure of the block, rescue analgesia with remifentanil infusion (0.05 to 0.25 μg kg−1 min−1) was used. All patients received systemic analgesia 15 min before the end of surgery using paracetamol (Perfalgan; Bristol-Myers Squibb, Rueil-Malmaison, France) 15 mg kg−1 and ketoprofen (Profenid; Sanofi-Aventis, Paris, France) 1 mg kg−1. The efficacy of postoperative analgesia was assessed using the FLACC (face, legs, activity, cry and consolability) scale.8 Postoperatively, the children were monitored every 15 min during the first hour and every 2 h for the next 6 h until discharge. If the FLACC score was greater than 3, the child received 0.2 mg kg−1 of nalbuphine (Nubain; Dupont Pharma, Paris, France) intravenously as rescue analgesia. The anaesthesiologist performing the TAP block and the clinical research assistants collecting intraoperative and postoperative data were all blinded to the dose of local anaesthetic used.
The children were discharged home after 6 h if they were pain free and there were no other medical or surgical reasons to remain in the hospital. Parents were instructed to administer oral paracetamol (15 mg kg−1) four times daily and oral ibuprofen syrup (Advil; Pfizer, Paris, France) 10 mg kg−1 three times per day to ensure effective postoperative analgesia. Parents were contacted by telephone at home 24 h after day-case surgery. The postoperative pain measure for parents (PPMP)9 was used to assess the children's pain. Parents were also asked for a global satisfactory score about their child's analgesic management (very unsatisfied with the pain relief, satisfied with the pain relief, very satisfied with the pain relief).
The results are presented as mean ± SD or median (interquartile range, IQR) as appropriate. Comparison between qualitative variables was performed by the χ2 test or the Fisher exact test. Comparisons of quantitative variables were performed using the Student's t-test or the Mann–Whitney Wilcoxon test, as appropriate. The mean effective dose of levobupivacaine resulting in efficient analgesic TAP block in 50% of cases (ED50) was obtained by using Dixon's up-and-down sequential method. The data were further analysed: the ED50 and ED95 were estimated and the 95% confidence intervals (CIs) were obtained by bootstrapping and assuming a logistic dose–response relationship; 1000 bootstrap replicates of the original dataset were generated. Statistical analysis was performed using SAS software version 8.02 (SAS Institute, Cary, North Carolina, USA) and R version 2.15.1 (The R Foundation for Statistical Computing ISBN 3-900051-07-0).
A total of 27 consecutive children were enrolled in the study. Patient data in the success and failure groups were similar with regard to sex, weight, age, duration of surgery and clinical details (Table 2). The TAP was visualised and the TAP block was performed in all cases.
The sequences of effective and ineffective TAP block 1 min after skin incision are shown in Fig. 1. The mean effective dose of levobupivacaine resulting in efficient analgesic TAP block in 50% of cases (ED50), according to the up-and-down staircase method, was 0.22 mg kg−1 (95% CI 0.19 to 0.25). Curves constructed on the basis of the bootstrap replicates of the original dataset (Fig. 2) and assuming a logistic dose–response model resulted in ED50 and ED95 estimates of 0.16 mg kg−1 (95% CI 0.11 to 0.24) and 0.43 mg kg−1 (95% CI 0.30 to 0.57), respectively.
In the postanaesthetic care unit (PACU), 60% of children in the failure group required rescue analgesia with nalbuphine. Thirty-five percent of children in the success group received additional rescue analgesia. All children were discharged home the same evening, without significant pain (FLACC < 4). At home, score on the PPMP was 0 in 89% of children and less than 5 in all patients. There was no difference in PPMP score between the success and failure patient groups 24 h after surgery. Parental satisfaction concerning pain management was excellent in all cases. No local or systemic complications related to the technique of regional anaesthesia or surgery were reported.
In paediatric regional anaesthesia, the use of lower total doses of local anaesthetic may improve safety, reducing the potential side effects and the risk of local and systemic toxicity. The current study is the first to investigate the minimal effective dose of local anaesthetic after ultrasound-guided TAP block in children. We report a dose of levobupivacaine close to 0.4 mg kg−1 (0.2 ml kg−1 of 0.2% levobupivacaine solution) to obtain 95% probability of providing adequate surgical analgesia during herniorrhaphy in children.
Ultrasound-guided abdominal wall blocks using real-time imaging have shown a greater probability of block success and require a lower amount of local anaesthetic. These techniques allow for identification of the needle tip and spread of the local anaesthetic solution within the correct fascial plane. As reported by Weintraud et al.,4 the landmark-based technique for ilioinguinal/iliohypogastric nerve blocks resulted in intramuscular, subcutaneous or intra-peritoneal injection in more than 80% of cases. Similar results were published in a recent adult TAP block study3 in which an unexpectedly high number of inaccurate needle placements led to early termination of the study. Of the 72 injections performed on 36 adult patients included in this study, the needle tip and local anaesthetic spread were in the correct plane (TAP) in only 23.6% of the injections. In the remaining cases, the local anaesthetic was administered in the subcutaneous tissue, adjacent muscle structures or peritoneum. In addition, an ultrasound-guided injection technique has been shown to be associated with faster resorption and higher plasma concentrations of ropivacaine than a landmark-based technique for ilioinguinal/iliohypogastric nerve blocks in children.10 Thus, the dose of local anaesthetic should be carefully selected and a dose reduction should be considered when ultrasound guidance is used.
To date, there are no data on the pharmacokinetics of local anaesthetic after TAP block in children. Studies on TAP blocks in the adult population11,12 reported a plasma concentration of local anaesthetic exceeding the potential threshold neurotoxic value (2.2 μg ml−1) with high interindividual variability using a dose of ropivacaine that is normally considered well tolerated. In children, Ala-Kokko et al.13,14 demonstrated a high median venous plasma concentration of local anaesthetic that was considered to be close to the maximum tolerated after ilioinguinal/iliohypogastric nerve blocks performed with the fascial click method using 2 mg kg−1 of 0.5% bupivacaine or levobupivacaine. These results provide a strong argument for reducing the dose of local anaesthetic for ultrasound-guided TAP blocks in a paediatric population. The dose of 0.4 mg kg−1 reported in the present study seems to provide efficient perioperative analgesia while remaining much lower than the maximal levobupivacaine dose allowed for paediatric TAP block (1.25 mg kg−1 per side).15
Current experience with TAP block in the paediatric literature suggests the use of 0.2 to 0.3 ml kg−1 per side of either 0.25% bupivacaine or 0.2% ropivacaine.16–18 Willschke et al.19 reported that a volume of only 0.075 ml kg−1 of 0.25% levobupivacaine (0.1875 mg kg−1) provided sufficient intraoperative and immediate postoperative analgesia (for the first 4 h) after ultrasound-guided ilioinguinal/iliohypogastric nerve blocks in children. This dose is lower than the ED95 obtained in our study but appears close to the minimal efficient dose (ED50) obtained using the up-and-down staircase method [0.22 mg kg−1 (95% CI 0.19 to 0.25)] or based on the bootstrapping analysis [0.16 mg kg−1 (95% CI 0.11 to 0.24)].
The TAP block is an anatomical compartment block. The aim is to achieve wide diffusion of local anaesthetic to nerve endings originating from T9 to L1, including the ilioinguinal and iliohypogastric nerves.20 Conversely, ilioinguinal/iliohypogastric nerve block, especially when performed under ultrasound guidance, can be likened to targeted nerve block with direct visualisation of the distribution of local anaesthetic surrounding the nerve structures. This may explain the lower minimal volume required for ultrasound-guided ilioinguinal and iliohypogastric nerve block in Willschke's study.19 Fredrickson et al.21 compared TAP blocks (n = 20) with ilioinguinal/iliohypogastric nerve block (n = 21) in children undergoing elective inguinal surgery. Both ilioinguinal/iliohypogastric nerve blocks and TAP block were ultrasound guided. When compared with the ilioinguinal/iliohypogastric nerve block group, a higher percentage of children in the TAP block group reported pain in the PACU (76 vs. 45%, P = 0.04) and required rescue analgesia (62 vs. 30%, P = 0.037). As reported by the investigators, the course of the ilioinguinal and iliohypogastric nerves has been described on cadavers with significant variation between studies and with great individual variability. The precise level of penetration of the two nerves through the abdominal wall is also variable.21 In addition, for a compartment block such as TAP block, successful block of both the ilioinguinal and iliohypogastric nerves required sufficient volumes of local anaesthetic to spread to a larger number of segmental roots. In logical agreement with these anatomical principles, we have chosen to maintain 0.2 ml kg−1 as a fixed volume of levobupivacaine and to vary the concentration of local anaesthetic solution to allow a decrease in the total dose of local anaesthetic. However, although the reduction in local anaesthetic volume did not seem to modify the onset time of target nerve blocks, an excessively low volume could cause a loss of efficiency or a clinically important decrease in the duration of sensory blockade.22–25
We report use of rescue analgesics in 60% of patients in the failure group and, despite the quality of the perioperative pain relief, in 35% of children with successful intraoperative pain control. Inappropriate use of nalbuphine for its sedative effect is frequently observed in the PACU to treat emergence delirium secondary to intraoperative sevoflurane use or a child's anxiety due to an intravenous cannula access or lack of a parent.
In our study, some limitations deserve comment. In concordance with our usual practice, all children received nonsteroidal anti-inflammatory drugs and paracetamol at the end of the surgery, which could have influenced the assessment of postoperative pain and rescue analgesic requirements. The present study limited the postoperative analgesia assessment to the first 24 h after surgery. However, all children left the hospital pain free and the parents did not report any pain at 24 h postoperatively.
As part of a multimodal analgesia strategy, ultrasound-guided administration of 0.2 ml kg−1 of 0.2% levobupivacaine in the TAP provided efficient perioperative analgesia in 95% of children who underwent herniorrhaphy. Further studies are necessary to specify the optimal volume required to improve pain management and the pharmacokinetic profile of local anaesthetic after ultrasound-guided TAP block in children. This study supports the use of ultrasound guidance for paediatric regional anaesthesia.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: funding support was provided solely from institutional and/or departmental sources.
Conflict of interest: none.
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