Various techniques have been employed for the early detection of perioperative cerebral ischaemia and hypoxia. Cerebral near-infrared spectroscopy (NIRS) is increasingly used in this clinical scenario to monitor brain oxygenation. However, it is unknown whether perioperative cerebral NIRS monitoring and the subsequent treatment strategies are of benefit to patients.
To assess the effects of perioperative cerebral NIRS monitoring and corresponding treatment strategies in adults and children, compared with blinded or no cerebral oxygenation monitoring, or cerebral oxygenation monitoring based on non-NIRS technologies, on the detection of cerebral oxygen desaturation events (CDEs), neurological outcomes, non-neurological outcomes and socioeconomic impact (including cost of hospitalization and length of hospital stay).
We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2016, Issue 12), Embase (1974 to 20 December 2016) and MEDLINE (PubMed) (1975 to 20 December 2016). We also searched the World Health Organization (WHO) International Clinical Trials Registry Platform for ongoing studies on 20 December 2016. We updated this search in November 2017, but these results have not yet been incorporated in the review. We imposed no language restriction.
We included all relevant randomized controlled trials (RCTs) dealing with the use of cerebral NIRS in the perioperative setting (during the operation and within 72 hours after the operation), including the operating room, the postanaesthesia care unit and the intensive care unit.
Data collection and analysis
Two authors independently selected studies, assessed risk of bias and extracted data. For binary outcomes, we calculated the risk ratio (RR) and its 95% confidence interval (CI). For continuous data, we estimated the mean difference (MD) between groups and its 95% CI. As we expected clinical and methodological heterogeneity between studies, we employed a random-effects model for analyses and we examined the data for heterogeneity (I2 statistic). We created a ‘Summary of findings’ table using GRADEpro.
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
Use of cerebral near-infrared spectroscopy (NIRS) for monitoring brain oxygenation during or after surgery in adults and children
The review question
We assessed the effects of monitoring the brain with cerebral near-infrared spectroscopy (NIRS), and treatments based on it, during and after surgery in adults and children. We aimed to determine whether NIRS detects reduced oxygen supply to the brain, which would allow the use of interventions to improve nervous system, mental process (cognition) and other outcomes that can have an impact on patients’ hospital length of stay and costs.
The human brain needs a lot of oxygen (has a high oxygen consumption) and is very sensitive to reduced oxygen supply. Successful treatment for low levels of oxygen in the brain during or after surgery relies on early diagnosis of a lack of oxygen. Cerebral NIRS is increasingly used for the early detection of lack of oxygen to the brain. It uses near-infrared light (700 to 1000 nanometres) to penetrate through the superficial layers of the head, including the scalp and the skull, to show the cerebral tissue.
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.
Quality of the evidence
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.