Abstract: We included 15 studies in the review, comprising a total of 1822 adult participants. There are 12 studies awaiting classification, and eight ongoing studies. None of the 15 included studies considered the paediatric population. Four studies were conducted in the abdominal and orthopaedic surgery setting (lumbar spine, or knee and hip replacement), one study in the carotid endarterectomy setting, and the remaining 10 studies in the aortic or cardiac surgery setting. The main sources of bias in the included studies related to potential conflict of interest from industry sponsorship, unclear blinding status or missing participant data. Two studies with 312 participants considered postoperative neurological injury, however no pooled effect estimate could be calculated due to discordant direction of effect between studies (low-quality evidence). One study (N = 126) in participants undergoing major abdominal surgery reported that 4/66 participants experienced neurological injury with blinded monitoring versus 0/56 in the active monitoring group. A second study (N = 195) in participants having coronary artery bypass surgery reported that 1/96 participants experienced neurological injury in the blinded monitoring group compared with 4/94 participants in the active monitoring group. We are uncertain whether active cerebral NIRS monitoring has an important effect on the risk of postoperative stroke because of the low number of events and wide confidence interval (RR 0.25, 95% CI 0.03 to 2.20; 2 studies, 240 participants; low-quality evidence). We are uncertain whether active cerebral NIRS monitoring has an important effect on postoperative delirium because of the wide confidence interval (RR 0.63, 95% CI 0.27 to 1.45; 1 study, 190 participants; low-quality evidence). Two studies with 126 participants showed that active cerebral NIRS monitoring may reduce the incidence of mild postoperative cognitive dysfunction (POCD) as defined by the original studies at one week after surgery (RR 0.53, 95% CI 0.30 to 0.95, I2 = 49%, low-quality evidence). Based on six studies with 962 participants, there was moderate-quality evidence that active cerebral oxygenation monitoring probably does not decrease the occurrence of POCD (decline in cognitive function) at one week after surgery (RR 0.62, 95% CI 0.37 to 1.04, I2 = 80%). The different type of monitoring equipment in one study could potentially be the cause of the heterogeneity. We are uncertain whether active cerebral NIRS monitoring has an important effect on intraoperative mortality or postoperative mortality because of the low number of events and wide confidence interval (RR 0.63, 95% CI 0.08 to 5.03, I2= 0%; 3 studies, 390 participants; low-quality evidence). There was no evidence to determine whether routine use of NIRS-based cerebral oxygenation monitoring causes adverse effects. The effects of perioperative active cerebral NIRS monitoring of brain oxygenation in adults for reducing the occurrence of short-term, mild POCD are uncertain due to the low quality of the evidence. There is uncertainty as to whether active cerebral NIRS monitoring has an important effect on postoperative stroke, delirium or death because of the low number of events and wide confidence intervals. The conclusions of this review may change when the eight ongoing studies are published and the 12 studies awaiting assessment are classified. More RCTs performed in the paediatric population and high-risk patients undergoing non-cardiac surgery (e.g. neurosurgery, carotid endarterectomy and other surgery) are needed.

Plain-language summary: The evidence is current to December 2016. We updated our search in November 2017, but these results have not yet been incorporated in the review. We included 15 completed randomized controlled trials involving 1822 participants. There are 8 ongoing studies and 12 waiting further assessment. None of the completed studies included infants or children. In four studies participants were undergoing abdominal or orthopaedic surgery, one study included participants undergoing a procedure to restore proper blood flow to the brain, and in the remaining 10 studies participants were undergoing large blood vessel or heart surgery with or without heart bypass. The studies all used cerebral NIRS in the operating room, with only two also using cerebral NIRS in the intensive care unit. The control groups were monitored using methods such as heart rate and mean arterial blood pressure, electroencephalogram, transcranial doppler, bispectral index, oxygen saturation in the jugular vein, evoked potentials or cerebral tissue oxygen partial pressure. Overall, the different studies varied in their approach to the review question. We did not pool (combine) the data for the outcome postoperative neurological injury because of variations between studies. One study with 126 participants having major abdominal surgery reported that 4/66 versus 0/56 participants experienced neurological injury with blinded and active monitoring, respectively. A second study with 195 participants undergoing coronary artery bypass surgery reported that 1/96 versus 4/94 participants suffered neurological injury in the blinded (masked) and active (with active treatments) monitoring groups, respectively. We are unsure whether active NIRS monitoring has an important effect on the risk of postoperative stroke and delirium because there was a low number of events and the result was not precise (2 studies, 240 participants; 1 study, 190 participants, respectively; low-quality evidence). Based on two studies with 126 participants, we found low-quality evidence that cerebral NIRS monitoring may reduce the number of participants with mild cognitive impairment at one week after surgery. Based on six studies with 962 participants, we found moderate-quality evidence that monitoring with cerebral NIRS probably leads to little or no decrease in the number of participants with a decline in cognitive function one week after surgery. We are uncertain whether active cerebral oxygenation monitoring has a crucial effect on intraoperative or postoperative deaths because there was a low number of events and the result was not precise (3 studies, 390 participants; low-quality evidence). We did not find any detrimental effects of the routine use of NIRS-based brain oxygenation monitoring. Overall, it is uncertain whether active NIRS monitoring has a crucial effect on postoperative stroke, delirium or death because of the imprecision of the results (low-quality evidence). Therefore, the effects of active cerebral NIRS monitoring on postoperative nervous system injury, delirium, decline in cognitive function and death are uncertain. For some outcomes, such as postoperative stroke or other neurological injury, the evidence was based on few studies with limited numbers of participants. Reporting of outcomes was often incomplete for all study participants, as was reporting of the study design, such as blinding. Some studies had potential conflicts of interest from industry sponsorship.