To the Editor:
We read with a great interest the recent publication by Deschamps et al.1 for the Canadian Perioperative Anesthesia Clinical Trials Group. While the results of this randomized controlled study are quite encouraging and further highlight both the feasibility and the potential clinical utility of cerebral oximetry in the setting of cardiac surgery, several concerns should be outlined.
First, the authors proposed a well-known algorithm to be used in the operating theater in order to reverse a cerebral desaturation below 10% relative to baseline. This notably low threshold value differs from those previously recommended and used by the same authors and others.2 Interestingly, an extracranial contamination affecting near-infrared spectro scopy measurements of cerebral oxygen saturation beyond 10% has been reported in healthy volunteers for at least two of the three near-infrared spectroscopy devices used in the current study.3 This last point could be of paramount importance and should be cleared up before conducting a large multicenter randomized controlled trial aiming to demonstrate a positive impact of preventing and treating cerebral desaturation on perioperative outcomes in high-risk surgical patients.
Second, the proposed algorithm suggests the early correction of intraoperative hypotension. Besides, the assessment of cardiac function and optimization of cardiac output occur only as a second-line treatment. That seems quite questionable, as low flow states could be significantly correlated with cerebral oxygenation in cardiac surgery, regardless of systemic arterial pressure.4 In contrast, a decrease in pressure could not affect cerebral oxygen saturation.4 Moreover, phenylephrine and norepinephrine administration in order to correct hypotension have been associated with a further decrease in cerebral oxygenation.4,5
Third, no difference was found in adverse events between the intervention and control groups in the study by Deschamps et al.,1 even if cerebral oximetry was far better preserved in patients randomized to intervention than routine care. Of course, we agree that the study was not designed to demonstrate such a positive impact on perioperative outcomes and that a large-scale multicenter randomized study is mandatory to answer that crucial issue. However, it is noteworthy that the current multicenter study including up to 201 patients was unable to confirm previous results reported by Murkin et al.6 in a randomized, prospective, and single-center study also including 200 patients, using a similar algorithm, and showing a significant reduction in major organ dysfunction in the intervention group (P = 0.048). Again, the definition of the targeted threshold value of cerebral oximetry initiating clinical interventions is probably crucial.
In conclusion, we share the same enthusiasm as that of the authors regarding the potential interest of noninvasive cerebral oximetry in cardiac surgery. While waiting for a large, multicenter, randomized controlled trial definitely showing a benefit on meaningful clinical perioperative outcomes, we need to be cautious before recommending a wider use of this kind of monitoring in the setting of cardiac surgery.
The authors declare no competing interests.