Intraoperative Monitoring of Cerebral NIRS Oximetry Leads to Better Postoperative Cognitive Performance: a Pilot Study

Objectives: The aim of this study is the assessment of the regional cerebral oximetry - NIRS (near infrared spectroscopy) as an intraoperative monitoring system to protect the patient against the incidents of brain desaturations. We hypothesize that patients monitored with NIRS present a smaller range of postoperative cognitive dysfunctions (POCD) in comparison with those without NIRS monitoring during lumbar spine surgery in a prone position.

Settings: This study was performed at the Clinical Department of Neurosurgery and Oncology of the Central Nervous System, Medical University of Lodz, Poland.

Participants: The study completed 43 adult patients qualified for the surgical treatment of lumbar spondylosis. Before the procedures they were randomized into two subgroups: one monitored intraoperatively by means of NIRS cerebral oximetry (INVOS 5100), which numbered 13 patients – 30.2% (13 NIRS devices were made available to the authors) and the other without NIRS intraoperative monitoring, totaling 30 people – 69.8%. The patients who presented a history of psychiatric, neurological and cardiovascular disorders which impair cognitive processes were disqualified from the study.

Primary And Secondary Outcome Measures: A comprehensive battery of neuropsychological tests was preoperatively performed on all patients. The subjects were then divided into two groups: with and without NIRS monitoring. Both groups were statistically homogeneous. Computerized anesthesia records were used to obtain intraoperative data: mean arterial pressure, heart rate, pulsoximetry and cerebral regional oxygenation. The depth of anesthesia monitor was not used. Besides, all the patients passed the same battery of neurocognitive tests 7 days and 1 month postoperatively. The Mann-Whitney test was performed to compare POCD and therefore assess the usefulness of NIRS as a monitoring mechanism during anesthesia in the prone position.

Results: There was a significant (p < 0.05) difference in the presence of cognitive deficiencies between the subgroup monitored with NIRS and the subgroup without NIRS. It included: Digit Span Test overall score and forward repetition score 7 days after operation, N- back Test results after 30 days in version 0 "back" - time, N-back Test version 1 "back" results in the number of correct answers and the number of errors.

Conclusions: NIRS cerebral oximetry may be useful in reducing postoperative cognitive complications in patients operated on in the prone positioning.

Trial Registration: RNN/556/08/KB – approval of the ethics committee at Medical University of Lodz, Poland.