Near-infrared spectroscopy for neuromonitoring of unilateral cerebral perfusion

There is neither consensus regarding which methods of neuromonitoring are adequate and reliable for assessing cerebral cross-perfusion during unilateral cerebral perfusion (UCP) nor are any threshold values defined. The aim of the study was to evaluate the usefulness of near-infrared spectroscopy (NIRS) for the neuromonitoring of right-sided UCP, which is increasingly used for cerebral protection as a consequence of the recent rise in supra-aortic cannulation methods.

For the purpose of the study, 122 patients (mean age 67 ± 12 years) who underwent open aortic arch surgery between August 2007 and July 2011 using right-sided UCP with a duration time exceeding 20 min were evaluated. The neuromonitoring consisted of NIRS and pressure measurement in both radial arteries in all patients. Forty-four (36%) patients suffered acute aortic dissection (3 having cerebral malperfusion), and 89 (73%) underwent total or subtotal arch replacement. Logistic regression analysis was used to model neurological adverse outcome (permanent and temporary neurological dysfunctions) as a function of cerebral oxygen saturation and other covariates.

During UCP (mean duration 38 ± 18 min) performed at a constant blood temperature of 28°C, the mean brain oxygen saturation dropped on the non-direct perfused side from 66 to 61% on average, corresponding to 92% of the baseline. In only 1 patient, an insufficient cross-over perfusion was presumed due to an intense drop of the saturation to 15% and was treated by employment of bilateral perfusion. In all remaining patients, the drop was not below 40% and/or 70% of the baseline. In the adjusted analysis, acute aortic dissection could be found as an independent predictor of an adverse neurological outcome (5 permanent, all in acute dissections, and 9 temporary dysfunctions), while there was no association between the occurrence of adverse neurological outcome and the values of regional cerebral oxygen saturation during UCP.

NIRS seems to be a reliable instrument to recognize a relevant disruption of cerebral cross-perfusion during UCP. A drop of brain oxygen saturation to 40% and/or 70% of the baseline can be considered a threshold value for sufficient cerebral cross-perfusion, at least under the flow and temperature management presented.