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Correspondence  |   August 2010
Different Injectate Volumes in Cervical Medial Branch Blocks: Does Increased Diagnostic Accuracy with Smaller Injectate Volume Lead to Changes in Outcome?
Author Affiliations & Notes
  • Steven P. Cohen, M.D.
    *
  • *The Johns Hopkins Medical Institutions, Baltimore, Maryland, and Walter Reed Army Medical Center, Washington, D.C.
Article Information
Correspondence
Correspondence   |   August 2010
Different Injectate Volumes in Cervical Medial Branch Blocks: Does Increased Diagnostic Accuracy with Smaller Injectate Volume Lead to Changes in Outcome?
Anesthesiology 8 2010, Vol.113, 499. doi:10.1097/ALN.0b013e3181e6a7f3
Anesthesiology 8 2010, Vol.113, 499. doi:10.1097/ALN.0b013e3181e6a7f3
In Reply:
We would like to thank Drs. Datta and Manchikanti for their astute comments regarding our article.1 The authors correctly point out that patients who received the higher volume of injectate in our study1 actually experienced—somewhat paradoxically—a smaller decrease in pain scores. However, we believe it is imperative to point out that this association in no way implies a causative relationship. Specifically, this study was neither designed nor powered to detect a difference in postblock pain scores. Achieving this goal would ideally employ an enriched enrollment design, in which patients with facetogenic pain were preidentified in a “run-in” phase by postblock pain relief, akin to the methodology sometimes used in clinical trials evaluating medications.2,3 Furthermore, it cannot be determined from this study whether this positive response was clinically meaningful or truly therapeutic (i.e.  , provided long-term benefit), as Manchikanti et al.  4 themselves suggested.
Instead, the sole purpose of this study was to compare accuracy rates between two different approaches, using two different volumes (i.e.  , four techniques). The decision to use postblock CT scans in patients with chronic neck pain was one of convenience, but we could have just as easily chosen to substitute asymptomatic volunteers for patients with pain, as Dreyfuss et al.  5 did for lumbar medial branch blocks, or perform injections with colored dye in cadavers, as is often done to gauge accuracy for ultrasound-guided nerve blocks.6 The operative question we believe needs to be answered now is whether this enhanced specificity translates to improved outcomes.
*The Johns Hopkins Medical Institutions, Baltimore, Maryland, and Walter Reed Army Medical Center, Washington, D.C.
References
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