1 Department of Paediatric Anaesthesia, Children CHU Timone Hospital, 13385 Marseille Cedex 5, France. 2 Medical and Clinical Pharmacology Department, CHU Timone, 13385 Marseille Cedex 5 France
*Corresponding author. E-mail: olivier.paut@mail.ap-hm.fr
Accepted for publication: September 9, 2003
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Abstract |
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Methods. In this prospective, double-blind study, children received an FIC block as a part of their anaesthetic management during elective orthopaedic surgery on the thigh. They were randomized to receive ropivacaine 0.7 ml kg1 using either a 0.375% or 0.5% solution. Venous blood samples were drawn up to 6 h after injection. Plasma concentrations of ropivacaine were measured by gasliquid chromatography.
Results. Six children (10.2 (range 515) yr, 35.6 (SD 10) kg were included. FIC block provided satisfactory peroperative pain relief. No signs of toxicity were observed, but high maximal plasma concentrations (Cmax 4.335.6 µg ml1), were observed for three of four patients in the ropivacaine 0.5% group. The two patients in the 0.375% group showed values within the safe range (Cmax 0.66 and 0.98 µg ml1 respectively). Even though no toxic effects were observed, these results led us to discontinue the study.
Conclusions. The administration of ropivacaine 3.5 mg kg1 can be associated with sustained high plasma concentrations of ropivacaine, outside the tolerable range. In view of these results, we recommend the use of lower ropivacaine dosage during FIC block in children.
Br J Anaesth 2004: 92: 41618
Keywords: anaesthesia, paediatrics; anaesthetic techniques, fascia iliaca compartment block; anaesthetics local, ropivacaine; pharmacokinetics; pharmacology
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Introduction |
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The aim of this study was to compare the pharmacokinetic characteristics of two doses of ropivacaine in FIC block in children undergoing orthopaedic surgery.
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Methods and results |
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The FIC block was performed at least 15 min before surgery in anaesthetized patients. FIC block was performed using the technique of Dalens and colleagues.4 The puncture point was 0.51 cm below the inguinal ligament, at the union of the lateral one-third and medial two-thirds of the line between the pubic tubercle and anterior superior iliac spine. The needle was introduced at a 4560° angle with the skin, until the perception of two losses of resistance corresponding to the crossing of the fascia lata and then the fascia iliaca. The children were randomly assigned to receive either ropivacaine 0.7 ml kg1, 0.5% (0.5% group) or 0.375% (0.375% group). Venous blood samples (1 ml) were collected from a peripheral venous catheter dedicated to blood sampling, before and 5, 10, 20, 30, 45, 60, 90, 120, 240 and 360 min after completion of the block. After centrifugation, plasma samples were stored at 20°C. Total plasma concentrations of ropivacaine were measured by gasliquid chromatography using nitrogen/phosphorus detection according to a method previously reported for bupivacaine analysis,5 and modified for ropivacaine determination. The limit of quantification was 15 ng ml1. The area under the ropivacaine concentration curve (AUC) was determined by the trapezoidal rule.
At the end of the procedure, the anaesthetist evaluated the quality of analgesia provided by the FIC block during surgery using a four-point scale (excellent, good, moderate, poor). Postoperative pain at rest and on mobilization was assessed using a visual analogue scale (children >6 yr) or the Objective Pain Scale (children <6 yr), at each sampling time and then every 4 h during the first postoperative day. In case of insufficient analgesia, i.v. morphine 50 µg kg1 and/or i.v. propacetamol 30 mg kg1 was administered. Every side-effect was recorded in the protocol chart.
Four patients were included in the 0.5% group and two in the 0.375% group. Median duration of surgery was 92 min. The time course of plasma ropivacaine concentrations is reported in Figure 1 and the individual pharmacokinetic values are listed in Table 1. In the 0.5% group, high Cmax (4.335.6 µg ml1) was observed for three patients, and one patient had ropivacaine plasma concentrations within the expected range (Cmax=1.85 µg ml1). In the 0.375% group, both patients showed Cmax values within the safety range (1.05 and 0.86 µg ml1, respectively). These Cmax concentrations were reached after a time (tmax) ranging between 20 and 90 min.
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Comment |
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The pharmacokinetics of ropivacaine administered for a peripheral block has been studied in two recent paediatric series.3 6 After using ropivacaine 3 mg kg1 for an ilioinguinal nerve block, providing effective post-operative analgesia, Dalens and colleagues reported a mean Cmax of 1.5 µg ml1 and tmax between 15 and 64 min.3 Two children developed a high ropivacaine Cmax (3.1 and 4.8 µg ml1). The corresponding fu was 3.5 and 0.6% respectively, providing plasma concentrations of free ropivacaine below the threshold concentrations for toxicity (0.15 (0.08) µg ml1). In another study, ropivacaine 0.75% 2 mg kg1 was administered in children during ilioinguinaliliohypogastric nerve block.6 Mean Cmax was 1.5 µg ml1 and tmax was 35 min.6
How can we explain such high ropivacaine plasma concentrations in our patients? Intravenous absorption of local anaesthetics is one complication that may be encountered during regional anaesthesia.7 This has not been previously described during FIC block and seems unlikely in our patients as the injection point is distant from a vessel.4 Furthermore, the occurrence of blood reflux within the needle and tube was checked frequently during injection. Obviously, in the case of i.v. administration, the Cmax should have been reached early, yielding a tmax shorter than those in our study (between 20 and 45 min). A second possible cause for these high plasma concentrations is that it is possible to administer a local anaesthetic intramuscularly while performing an FIC block. The close relationship between the lumbar plexus and the psoas major can explain this possibility.8 A third explanation could be an inappropriate ropivacaine dosage. In this study, we used a maximal dose of ropivacaine 3.5 mg kg1 to achieve an FIC block. This dose is close to that used by Dalens and colleagues during ilioinguinal block3 and by others during caudal block in children.9 Due to the presence of many richly vascularized muscles within the fascia iliaca compartment, rapid absorption during an FIC block may occur, leading to high ropivacaine plasma concentrations.4 We speculate that the ropivacaine 3.5 mg kg1 dose used in three children, combined with the rapid resorption of local anaesthetics during FIC block, could explain the high ropivacaine concentrations. In this case, the use of lower doses of ropivacaine during an FIC block should be safer. This is supported by the acceptable Cmax we found in the two children receiving ropivacaine 2.6 mg kg1. However, the safety of ropivacaine 0.7 ml kg1 0.375% has to be demonstrated, since only two patients were included in this study group.
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Acknowledgement |
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References |
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