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Infraclavicular Catheter Dosing

Title
The effects of local anesthetic concentration and dose on continuous infraclavicular nerve blocks: a multicenter, randomized, observer-masked, controlled study
Authors
Ilfeld BM, Le LT, Ramjohn J et al.
Journal
Anesthesia and Analgesia 2009 Jan; 108: 345-350.

 

Study Summary

 

Study design
  • Multi-center, randomized controlled trial with observer blinding
Patient population
  • 50 adult patients undergoing ambulatory orthopaedic surgery of the lower arm.
  • A stimulating infraclavicular catheter was inserted using a coracoid approach and neurostimulation-guidance.
    • The endpoint was a motor response in the digits (distribution not specified) at 0.3-0.5mA.
    • Efficacy of the catheter was determined by motor and sensory block of the index finger after injection of 50mls of 1.5% mepivacaine through the catheter.
    • The catheter was removed on the afternoon of POD 2.
Intervention
  • 0.4% ropivacaine at 4ml/h with a 2ml bolus q30min
Comparator(s)
  • 0.2% ropivacaine at 8 ml/h with a 4ml bolus q30min
Main findings
  • The 0.4% group had more episodes of an insensate limb (mean of 1.8 vs 0.6 times, p = 0.001) than the 0.2% group
  • There were no clinically significant differences between groups in reported pain scores on POD 1-3.
  • The 0.4% group had inferior postoperative analgesia, reflected by
    • higher opioid consumption (100% and 50% more on POD 1 & 2 respectively),
    • more awakenings due to pain on the first postop night (median of 2 vs 0)
    • less satisfaction with analgesia (7 vs 10 on a 0-10 scale).

 

Comments on the study

  • The most significant result of this study is that the effect of varying dose and concentration in continuous infraclavicular blockade was completely opposite to that observed in a similar study of continuous popliteal blockade by the same authors [1]. With popliteal catheters, a higher infusion rate of more dilute ropivacaine resulted in a higher incidence of insensate limbs; although quality of analgesia was similar between groups.
  • This difference is likely to be due to the anatomical differences between the 2 sites: the sciatic nerve is compact and a smaller volume of local anesthetic is more likely to distribute to all areas of the nerve; whereas the brachial plexus in the infraclavicular region is composed of 3 separate cords, which are more spread out and separated by the axillary artery.
  • However the optimal dosing regime for infraclavicular catheters remains unclear. The authors did not assess the distribution of sensory loss nor its correlation with the site of surgical pain. It may well have been that in the 0.4% ropivacaine group, only part of the hand was insensate, but that part was not the site of surgical pain. There is also no data on the number of boluses delivered and the total volume infused, which would have also influenced the extent and density of sensory block.
  • It should also be noted that the authors did not specify the motor response endpoint that was used for catheter placement, nor if there was any attempt to match this to the likely site of surgical pain. Recent studies [2-4] suggest the optimal endpoint for a single-shot infraclavicular block is a motor response in the radial distribution, as this is most likely to be associated with circumferential spread around all 3 cords. However it is uncertain if this applies to catheter placement as well.

References

  1. Ilfeld BM et al. Effects of varying local anesthetic concentration and volume on continuous popliteal sciatic nerve blocks: dual center, randomized, controlled study. A&A 2008;107:701-7.
  2. Bloc S, et al. Spread of injectate associated with radial or median nerve-type motor response during infraclavicular brachial-plexus block: an ultrasound evaluation. Reg Anesth Pain Med 2007;32:130-5.
  3. Bloc S et al. Single-stimulation, low-volume infraclavicular plexus block: influence of the evoked distal motor response on success rate. Reg Anesth Pain Med 2006;31:433-7.