Reassessment of a meta-analysis of intraoperative cerebral oximetry-based management studies
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CORRESPONDENCE
Reassessment of a meta-analysis of intraoperative cerebral oximetry-based management studies Jason A. Davis, DPhil
. Rhodri Saunders, DPhil
Received: 4 October 2018 / Revised: 13 October 2018 / Accepted: 15 October 2018 Ó Canadian Anesthesiologists’ Society 2019
To the Editor, We read with interest the meta-analysis regarding intraoperative cerebral oximetry-based monitoring for maximizing perioperative outcomes by Zorrilla-Vaca et al.1 We note, however, some important discrepancies between the original source literature and the data that are used in the current analysis, which raise concerns. While conclusions regarding the primary outcome of cognitive impairment are not impacted, the means to reach that conclusion are at times not as accurate as they could be, and some of the secondary outcome conclusions differ in significance. A primary example of discrepancy is in the studies used for the postoperative delirium outcome (Fig. 6). Of the six studies analyzed, three of them actually make no mention of ‘‘postoperative delirium’’, ‘‘POD’’, or ‘‘delirium’’ in the text or supplementary materials.2–4 Nor is there any mention of instruments typically used to assess POD in patients, such as the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU). Of the remaining studies, the event counts used for Deschamps et al. appear to be for those receiving transfusions, not the delirium cases.5 A further example of data extraction concerns comes in the transfusion analysis in their Fig. 5. Values used for the study by Colak et al. (18 of 94 in the near-infrared This letter is accompanied by a reply. Please see Can J Anesth 2019; 66: this issue.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12630-019-01469-7) contains supplementary material, which is available to authorized users. J. A. Davis, DPhil (&) R. Saunders, DPhil Coreva Scientific, Baden Wu¨rttemberg, Germany e-mail: [email protected]
spectroscopy (NIRS) group vs 24 of 96 in the control) are partly derived from values found in Fig. 1 of the source publication.6 Nevertheless, in Table 1 of the subsequent text, these values are noted to be percentages of patients (not absolute numbers of patients) who did not receive transfusions, meaning that the real numbers were 77 of 94 for NIRS and 73 of 96 for control, and thus change the direction of the effect. The inclusion of the 2010 study by Cohn et al.7 represents a case where discrepancies in both data extraction and application of study inclusion criteria occur. The data extracted for length of hospital stay were described in the source paper as hospital-free days of the first 30 post-surgical days. Most importantly, Cohn et al. describe thenar placement of the oximetry probes, and we would therefore question inclusion of this study in a metaanalysis of cerebral NIRS-based management. Following good practice, Zorrilla-Vaca et al. published their meta-analysis protocol (PROSPERO: CRD42017057293), but there were some deviations from
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