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Minimum Effective Volume of Local Anesthetic for Shoulder Analgesia by Ultrasound-Guided Block at Root C7 With Assessment of Pulmonary Function
  1. Steven H. Renes, MD*,
  2. Geert J. van Geffen, MD, PhD*,
  3. Harald C. Rettig, MD, PhD,
  4. Mathieu J. Gielen, MD, PhD* and
  5. Gert J. Scheffer, MD, PhD*
  1. From the *Department of Anesthesiology, Radboud University Nijmegen Medical Centre; and
  2. Department of Anesthesiology, Ikazia Hospital, Rotterdam, the Netherlands.
  1. Address correspondence to: Steven H. Renes, MD, Department of Anesthesiology, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, the Netherlands (e-mail: s.renes{at}anes.umcn.nl).

Abstract

Background and Objectives: This study was performed to determine the minimum effective volume of ropivacaine 0.75% required to produce effective shoulder analgesia for an ultrasound (US)-guided block at the C7 root level with assessment of pulmonary function.

Methods: Using the Dixon and Massey up-and-down method study design, 20 patients scheduled for elective open shoulder surgery under combined general anesthesia and continuous interscalene brachial plexus block were included. Initial volume of ropivacaine 0.75% was 6 mL; block success or failure determined a 1-mL decrease or increase for the subsequent patient, respectively. General anesthesia was standardized. A continuous infusion of ropivacaine 0.2% was started at a rate of 6 mL/hr at 2 hrs after completion of surgery. Ventilatory function was assessed using spirometry, and movement of the hemidiaphragm was assessed by US.

Results: The minimum effective volume of local anesthetic in 50% and 95% of the patients was 2.9 mL (95% confidence interval, 2.4-3.5 mL) and 3.6 mL (95% confidence interval, 3.3-6.2 mL), respectively. Ventilatory function and hemidiaphragmatic movement was not reduced up to and including 2 hrs after completion of surgery, but 22 hrs after start of the continuous infusion of ropivacaine 0.2%, ventilatory function and hemidiaphragmatic movement were significantly reduced (P < 0.001).

Conclusions: The minimum effective volume of local anesthetic for shoulder analgesia for a US-guided block at the C7 root level in 50% and 95% of the patients was 2.9 and 3.6 mL, respectively. Pulmonary function was unchanged until 2 hrs after completion surgery, but reduced 22 hrs after start of a continuous infusion of ropivacaine 0.2%.

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Footnotes

  • This work was sponsored by an ESRA Research Grant and supported by departmental funding.

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