Minimum effective volume of local anesthetic for shoulder analgesia by ultrasound-guided block at root C7 with assessment of pulmonary function.
OBJECTIVE
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%.
Renes
Steven H
SH
Department of Anesthesiology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands. s.renes@anes.umcn.nl
van Geffen
Geert J
GJ
Rettig
Harald C
HC
Gielen
Mathieu J
MJ
Scheffer
Gert J
GJ
D000328:Adult; D000368:Aged; D000577:Amides / Q000008:administration & dosage*; D000698:Analgesia / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage*; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging; D003964:Diaphragm / Q000000981:diagnostic imaging / Q000187:drug effects*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007263:Infusions, Parenteral; D008297:Male; D008875:Middle Aged; D009407:Nerve Block; D009426:Netherlands; D010147:Pain Measurement; D010149:Postoperative Pain / Q000209:etiology / Q000517:prevention & control*; D011446:Prospective Studies; D012123:Pulmonary Ventilation / Q000187:drug effects*; D000077212:Ropivacaine; D012782:Shoulder / Q000294:innervation* / Q000601:surgery; D020069:Shoulder Pain / Q000209:etiology / Q000517:prevention & control*; D013147:Spirometry; D013997:Time Factors; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional
D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine