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LETTER TO THE EDITOR

Correlation of the Depth of Anesthesia with POCD (Postoperative Cognitive Dysfunction)

Department of General Anesthesiology, Cleveland Clinic, Cleveland, OH, schubea{at}ccf.org

In Response:

We appreciate Dr. Gaba’s (1) interest in and compliment about our work (2) on anesthetic level and remote postoperative cognitive dysfunction (POCD). Dr. Gaba points out that we failed to use a control group in our study to correct for the practice learning effect inherent sequential to test-retest practice cognitive function paradigms. We did not incorporate a concurrent nonsurgical, nonanesthetic control group because the test–retest effect of the WAIS III and WMS III subscores utilized in our study is well known from the standardization of these testing instruments. Our assessment of reliable change did use historical controls, though. As mentioned in our paper, we used standardized regression-based formulas for change derived from the test–retest samples obtained during the standardization of the WAIS III and the WMS III to derive equations for retest WAIS III and WMS III subscores. These equations were applied to our randomized groups to determine whether the observed retest scores differed from the known norms in our reliable change analysis. Table 6 shows that with test–retest effects taken into account, only PSI was different in the LOBIS versus HIBIS groups. This effect was confirmed in our analysis of covariance adjusting for baseline score where we again found a difference in PSI between LOBIS and HIBIS patients. We contest therefore that the contemporaneous study of a nonsurgical control group was not necessary as practice effect could be adequately controlled through the use of historical controls and the known test–retest related norms for the cognitive function tests our patients completed.

Dr. Gaba further mentions that we did not describe blinding in our report. All cognitive function testing was performed by appropriately trained and certified personnel who were unaware of the patients’ randomized status. Lastly, we would like to comment on our claim that ours is the first report to link intraoperative anesthetic level to remote, postoperative cognitive performance, which Dr. Gaba disputes by citing the work of Wong et al. (3) and his own (4). We readily acknowledge previous reports of anesthetic level and early POCD, including that of Wong et al. who assessed POCD up to 72 h postoperatively. We applaud Dr. Gaba’s work assessing for POCD at 90 days in elderly patients undergoing major thoracic, orthopedic, or vascular surgery (3). We note, however, that the abstract he mentions concentrates on delirium as an end point and does not mention his findings with regard to POCD.

REFERENCES

1. Gaba V. Correlation of the depth of anesthesia with POCD (postoperative cognitive dysfunction). Anesth Analg 2007; 104:1298.[Free Full Text]
2. Farag E, Chelune GJ, Schubert A, Mascha EJ. Is depth of anesthesia, as assessed by the Bispectral Index, related to postoperative cognitive dysfunction and recovery? Anesth Analg 2006;103:633–40.[Abstract/Free Full Text]
3. Wong J, Song D, Blanshard H, et al. Titration of isoflurane using BIS index improves early recovery of elderly patients undergoing orthopedic surgeries. Can J Anaesth 2002;49:13–18.[Web of Science][Medline]
4. Gaba VK, Mathews DM, Zhaku B, Neuman GG. Correlation of the intraoperative bispectral index score (BIS) with incidence of postoperative cognitive disorders (POCD) in the geriatric population. Anesth Analg 2004;98:S-71.

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