No Abstract. Southern African Journal of Anaesthesia and Analgesia Vol. 12(1) 2006: 37-3

Bosenberg, A

Johnson, S

Kapra, S

Marhofer, P

Willschke, H

English

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Southern African Journal of Anaesthesia & Analgesia • March 2006 37TRAVEL FELLOWSHIPIntroductionAlthough Ilio-inguinal nerve blocks are commonly used, thedose advocated varies between 0.3-0.5ml/kg. Despite thesedoses a failure rate of up to 20-30% has been described usingthe standard technique. These failures may be due toinadequate understanding of the anatomy, faulty technique, orincorrect placement of local anaesthetic. Ultrasound guidednerve blocks permit the precise placement of localanaesthetic. In a previous study an ultrasound-guided ilio-inguinal block was found to be more effective than thestandard “fascial click” method. In that study the injection oflocal anaesthetic was stopped when the target nerve was seento be surrounded by local anaesthetic. Significantly lowervolumes of 0.25% levobupivacaine were required in theultrasound-guided group than in the “fascial click” group(0.19± 0.05ml/kg vs. 0.3ml/kg; p<0.0001). Despite these lowervolumes of 0.25% levobupivacaine, a better quality ofanalgesia was achieved. These findings stimulated a furtherstudy using an ultrasound-guided technique to determinewhether a further reduction in the volume of 0.25%levobupivacaine was possible without loss of efficacy.ObjectiveTo determine the lowest effective dose of local anaesthetic forilio-inguinal block using ultrasound guidance.MethodsFollowing ethical approval, 40 consecutive ASA I childrenaged 1-8 years scheduled for elective unilateral inguinalsurgery were enrolled in this prospective study. Informedconsent was obtained from the parents of all children andwhere appropriate, assent was obtained from the child.Exclusion criteria included any contraindication to ilio-inguinalblock, parental or patient refusal, or allergy to amide localanaesthetics.After oral premedication with midazolam 0,5mg/kg,general anaesthesia was induced with sevoflurane. Afterestablishing venous access, a laryngeal mask was placed andanaesthesia was maintained with 1 MAC halothane in nitrousoxide: oxygen 40:60 and spontaneous ventilation.Intraoperative monitoring included ECG, heart rate, pulseoximetry, non-invasive blood pressure and end-tidal carbondioxide concentration.A SonoSite 180+ portable ultrasound unit (SonoSiteô,Bothell, WA, USA) and a 5-10 MHz linear hockey stick probewere used to identify the target nerves. Adjustments (depth,probe frequency, low and far gain) were made to obtainIlio inguinal block: do we know the correctdose?A Bosenberg, H Willschke, S Johnson, P Marhofer, S KapralDepartment of Anaesthesia, University of Cape Townoptimal ultrasonographic images of the nerves and thesurrounding anatomical structures (muscles layers,peritoneum). Following aseptic preparation of the puncturesite and the ultrasound probe, the nerve block was performedusing an insulated 22-gauge 40mm needle (Pajunkô,Geisingen, Germany) under ultrasound guidance Afteridentifying the target nerves (ilio-inguinal and ilio-hypogastricnerve), the needle was positioned using real time ultrasoundimaging. Once the needle was correctly positioned, andfollowing a negative aspiration test, a predetermined volumeof 0.25% levobupivacaine was injected.Using a step down approach, with 10 children in eachstudy group, 0,2ml/kg levobupivacaine 0.25% was used as thestarting dose. Results were analysed after each group of 10patients. If all blocks were successful and satisfactoryanalgesia was achieved, the volume of local anaesthetic washalved and a further 10 patients were enrolled into the study.After each group of 10 patients, the results were analysed. Afurther 50% reduction was planned if all blocks weresuccessful. Failure to achieve a 100% success in the wholegroup instigated an increase of half the previous volumereduction to be used in the subsequent group. For example, ifafter reducing the dose from 0.2ml/kg to 0.1ml/kg, and any ofthe 10 blocks failed, the next group would receive 0.15ml/kg0.25% levobupivacaine.In all patients skin incision was performed at least 15minafter placement of the ilio-inguinal nerve block. An increase inheart rate of more than 15% during operation was defined as afailed block and rescue analgesia using fentanyl 1µg/kg wasgiven. The efficacy of postoperative analgesia was documentedusing the objective pain score (OPS). If OPS score was <11, theblock was also considered a failure and the child receivedrescue analgesia and 30mg/kg paracetamol. The children weremonitored hourly for four hours postoperatively, i.e. the usuallength of stay before discharge from the outpatient surgical unit.The children were discharged home after 4 hours, when theywere pain free and when there was no other medical reason toadmit them to a surgical ward. The children were dischargedwith an oral paracetamol suspension (30mg/kg) for subsequentanalgesia, to be administered by their parents or careproviders, who were also asked to report immediately to RedCross Childrenís Hospital in the event of difficulty in painmanagement.Demographic data were compared by ANOVA. Theincidence of failed or inadequate block was compared by chi-square test between the four groups. P < 0.05 was consideredstatistically significant.Southern African Journal of Anaesthesia & Analgesia • March 2006 38TRAVEL FELLOWSHIPResultsPatient demographics were similar in all groups (gender,weight and height). In the 0.1ml/kg group there was adifference in the median age of the children compared to theother groups, but this difference was not significant. The samesurgeon performed all surgical procedures and all blockswere performed by anaesthetists experienced in ultrasound-guided regional anaesthesia in children. The ilio-inguinal andthe iliohypogastric nerve could be visualized in all cases.There were no surgical or anaesthetic complications.There was no significant difference in heart rate at skinincision in the 0.2ml/kg or 0.1ml/kg or 0. 075ml.kg 0.25%levobupivacaine groups (p< 0.05). In the 0,05ml/kg group, 3 outof 10 children (30%) received rescue analgesia (fentanyl) inresponse to an increase in heart rate of more than 15% onincision. The rest of the group showed no increase in heart rateon skin incision. With regard to postoperative pain, there was nosignificant difference in the OPS levels in the 0.2ml/kg, 0.1ml/kgand 0.075ml.kg 0.25% levobupivacaine groups. No parent orchild from these groups requested additional analgesia.However there was a significant increase in OPS levels after onehour in the 0.05ml/kg group compared to the 0.2ml/kg and0.1ml/kg groups. Four children in the 0.05ml/kg group who hadan OPS Score <11 were treated with paracetamol. Three ofthese had received fentanyl intra-operativelyIn accordance with the protocol, in view of the 30% failurein the 0.05ml/kg group, a volume of 0.075ml/kg was used inthe subsequent group. There were no failures in the 0.075ml/kg 0.25% levo-bupivacaine group; No statistically significantdifference in the heart rate at skin incision or in thepostoperative OPS pain scores could be detected when the0.75ml.kg and the 0.2ml/kg or 0.1ml/kg groups werecompared. No additional analgesia was required in the0.075ml/kg group.DiscussionThe major advantage of ultrasound guided nerve blocks isthat the nerves can be “visualised” using real time imaging.The local anaesthetic solution can be seen as it is injected intothe correct tissue plane and seen to surround the nerve. If not,the position of the needle can be adjusted. With experiencethe exact location of the needle in relation to the nerve can bedetermined.Reducing the volume of local anaesthetic has severaladvantages. Firstly the risk of toxicity is diminished. This isparticularly relevant after ilio-inguinal nerve blocks in infantsand small children. In a recent pharmacokinetic study, Ala-Kokko et al demonstrated high plasma concentrations ofbupivacaine following ilioinguinal nerve blocks that wereperformed using the traditional “fascial click” method inchildren aged 2-10years. The median venous plasmaconcentration was 2.2µg/ml bupivacaine (0.9-4.9), a levelconsidered by some to be close to the maximum tolerated.Smith et al also reported unexpected high bupivacaineplasma levels (up to 4mg.L) in children between 10-15kg(1.5± 0.9mg.L range 0.43-4.0mg.L) compared with a group ofchildren with 15-30kg (0.9± 0.3mg.L range 0.35-1.34mg.L)Secondly a reduction in volume potentially reducesunwanted side effects. Transient femoral nerve palsy is a welldescribed side effect of ilio-inguinal nerve block in childrenwhich may delay ambulation and be disturbing to the childand parents. The femoral nerve palsy is thought to be volumerelated and occurs as a result of spread of local anaestheticbetween the muscle layers to the femoral nerve, or whenincorrect landmarks are used.Conversely the volume of local anaesthetic should not bereduced to such an extent that efficacy is lost. Studies usingultrasound guidance have suggested that more accurateplacement of smaller amounts of local anaesthetic does notreduce the efficacy. However, there must be a point at whichthe reduction of local anaesthetic volume, for a givenconcentration, is no longer as effective In this study successfulblocks were achieved using 0.2ml/kg, 0.1ml/kg and 0.075ml/kg of 0.25% levo-bupivacaine without compromising thequality of analgesia Stated differently the quality of analgesiadoes not improve when larger volumes of local anaesthetic areadministered.Four of the 10 children in the 0.05ml/kg group requiredadditional analgesia; either fentanyl (3) intra-operatively inresponse to the increase in heart rate, or paracetamol (4 ofwhich 3 had previously received fentanyl) postoperatively inresponse to inadequate analgesia based on the OPS score.Some initial analgesia was provided for the children in the first60 min in the 0.05ml.kg group since they had similar OPSscores as the other groups. After 60 min the OPS levels weresignificantly higher than those in the other groups. Thissuggests that some of the ilio-inguinal blocks may have beeneffective initially, or that the rescue analgesia (fentanyl 1ug.kg)had some initial analgesic effect.ConclusionThis study demonstrates that much lower volumes of localanaesthetic can be used to perform successful ilioinguinalnerve blocks in children than previously recommended. Thelowest effective dose was 0.075 ml/kg 0.25% levo-bupivacainewhen performed under ultrasound guidance. This volume wasas effective as 0.1ml/kg or 0.2ml/kg although pain assessmentwas limited to first 4 postoperative hours.

Ilio inguinal block: do we know the correct dose?

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Ilio inguinal block: do we know the correct dose?

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