Systematic review of near-infrared spectroscopy determined cerebral oxygenation during non-cardiac surgery

Utilization of NIRS Monitor to Compare the Regional Cerebral Oxygen Saturation Between Dexmedetomidine and Propofol Sedation in Mechanically Ventilated Critically ill Patients with Sepsis- A Prospective Randomized Control Trial

Aim & Background: Delirium frequently occurs in the acute phase of sepsis and is associated with increased ICU and hospital length of stay, duration of mechanical ventilation, and higher mortality rates. We utilized the Near-Infrared Spectroscopy monitor to measure and compare the regional cerebral oxygen saturation in mechanically ventilated patients of sepsis receiving either dexmedetomidine or propofol sedation and assessed the association between delirium and regional cerebral oxygen saturation. Methods: A single center prospective randomized control trial conducted over a period of two years, 54 patients were included, equally divided between propofol and dexmedetomidine groups. Patients received a blinded study drug, propofol (10 mg/mL) or dexmedetomidine (5 mcg/mL) via infusion pump according to randomization. Infusion rates were adjusted every 10 min based on weight-based titration tables, aiming for target sedation (RASS -2 to 0). Management components included pain monitoring using the CPOT score and delirium assessment using CAM-ICU score. Results: Dexmedetomidine group showed higher mean regional cerebral oxygen saturation as compared to propofol group (P = .036). No significant differences were found in mechanical ventilation or ICU stay durations, delirium-free days, or sedation cessation reasons. Delirium occurred in 36 patients, with lower mean regional cerebral oxygen saturation as compared to non-delirious patients. Conclusion: The dexmedetomidine group had higher regional cerebral oxygen saturation compared to the propofol group. Delirious patients showed lower cerebral oxygen saturation than non-delirious patients, suggesting a link between sedation type, cerebral oxygenation, and delirium. CTRI registration: REF/2021/11/048655 N.

Cerebral oximetry in high-risk surgical patients: where are we?

PURPOSE OF REVIEW

This review aims to summarize the latest evidence on the role of near-infrared spectroscopy (NIRS) in monitoring cerebral oxygenation in high-risk surgical patients, including both cardiac and noncardiac surgeries, and to present a new algorithm for its application.

RECENT FINDINGS

NIRS effectively measures brain oxygen saturation noninvasively, proving valuable in cardiac surgeries to reduce neurological complications, though its impact on nonneurological outcomes is less clear. In noncardiac surgeries, NIRS can help prevent complications like postoperative cognitive dysfunction, particularly in high-risk and major surgeries. Studies highlight the variability of cerebral oxygenation impacts based on surgical positions, with mixed results in positions like the beach chair and sitting positions. A structured algorithm for managing cerebral desaturation has been proposed to optimize outcomes by addressing multiple factors contributing to blood oxygen content and delivery.

SUMMARY

Despite its limitations, including spatial resolution and interindividual variability, NIRS is a useful tool for intraoperative cerebral monitoring. Further studies are needed to confirm its broader applicability in noncardiac surgeries, but current evidence supports its role in reducing postoperative complications especially in cardiac surgeries.

Prospective single-center study on the reliability of ipsilateral cerebral oximetry using near-infrared spectroscopy as a predictor for selective shunting during carotid endarterectomy

OBJECTIVE

Many techniques are available for the intraoperative assessment of brain perfusion during carotid endarterectomy, such as carotid stump pressure, near-infrared spectroscopy, somatosensory evoked potentials, transcranial Doppler, electroencephalography, and clinical assessment. The decision for selective carotid shunt insertion is dependent on clinical deterioration or the detection of cerebral hypoperfusion after cross-clamping of the internal carotid artery. Monitoring cerebral oximetry using near-infrared spectroscopy is a noninvasive technique for cerebral oxygen saturation measurement, reflecting changes in cerebral blood flow during carotid endarterectomy. The aim of this study was to evaluate the reliability of near-infrared spectroscopy as a predictor of selective shunting during carotid endarterectomy.

METHODS

In total, 47 conventional carotid endarterectomy surgeries were performed at our hospital between March 2016 and December 2021. All surgeries were performed under a regional cervical block supplemented with local infiltration anesthesia. All patients were monitored by cerebral oximetry using bilateral near-infrared spectroscopy probes and clinical assessment through communication with the patient (numerical, visual, and verbal) to indicate a selective shunt. Near-infrared spectroscopy values were recorded before and after internal carotid cross-clamping and after declamping. Any decrease in ipsilateral cerebral oximetry-near-infrared spectroscopy values equal to or more than 20% from the pre-clamping baseline reading associated with deterioration in neurological status (hemiparesis, aphasia, or deterioration in level of consciousness) after internal carotid artery cross-clamping was considered an indication for intraluminal carotid shunting.

RESULTS

After internal carotid artery cross-clamping, 5 of 47 patients (10.6%) developed a significant drop in cerebral oxygen saturation associated with obvious clinical assessment deterioration in verbal communication and weakness in contralateral arm power. A Pruitt-Inahara carotid shunt was subsequently inserted, and 42 patients remained stable throughout surgery. The average decline in ipsilateral near-infrared spectroscopy values was 23.8% in patients with clinical deterioration. The average decline was 8.6% in patients who remained stable.

CONCLUSIONS

Monitoring ipsilateral cerebral oximetry using near-infrared spectroscopy is an easy and reliable method for indicating selective shunting during carotid endarterectomy. A 20% decrease in ipsilateral brain tissue oximetry after internal carotid artery cross-clamping provides a reliable cut-off value for selective intraluminal carotid shunting during carotid endarterectomy.

Cerebrovascular dysregulation and postoperative cognitive alterations after carotid endarterectomy

There are controversial data about the effect of carotid endarterectomy regarding postoperative cognitive function. Our aim was to analyze the effect of cerebral tissue saturation monitored by near-infrared spectroscopy (NIRS) on cognitive function. Perioperative data of 103 asymptomatic patients undergoing elective carotid surgery under general anesthesia were analyzed. Preoperatively and 3 months after the operation, MMSE (Mini Mental State Examination) and MoCA (Montreal Cognitive Assessment) tests were conducted. For cerebral monitoring, NIRS was used, and the lowest rSO2 value and the degree of desaturation were calculated. Cognitive changes were defined as one standard deviation change from the preoperative test scores, defined as postoperative neurocognitive decline (PNCD) and cognitive improvement (POCI). PNCD was found in 37 patients (35.92%), and POCI was found in 18 patients (17.47%). Female gender, patients with diabetes, and the degree of desaturation were independently associated with PNCD. The degree of desaturation during the cross-clamp period negatively correlated with the change in the MoCA scores (R =  - 0.707, p = 0.001). The 15.5% desaturation ratio had 86.5% sensitivity and 78.8% specificity for discrimination. For POCI, a desaturation of less than 12.65% had 72.2% sensitivity and 67.1% specificity. POCI was associated with lower preoperative MOCA scores and a lower degree of desaturation. We found a significant relation between the change of postoperative cognitive function proven by the MoCA test and cerebral tissue saturation during the clamping period in patients undergoing carotid endarterectomy.

Intraoperative haemodynamic monitoring and management of adults having non-cardiac surgery: Guidelines of the German Society of Anaesthesiology and Intensive Care Medicine in collaboration with the German Association of the Scientific Medical Societies

Haemodynamic monitoring and management are cornerstones of perioperative care. The goal of haemodynamic management is to maintain organ function by ensuring adequate perfusion pressure, blood flow, and oxygen delivery. We here present guidelines on "Intraoperative haemodynamic monitoring and management of adults having non-cardiac surgery" that were prepared by 18 experts on behalf of the German Society of Anaesthesiology and Intensive Care Medicine (Deutsche Gesellschaft für Anästhesiologie und lntensivmedizin; DGAI).

Establishment and validation of a risk prediction model for delayed neurocognitive recovery associated with cerebral oxygen saturation monitoring

BACKGROUND

Delayed neurocognitive recovery (DNR) is a common complication in patients undergoing laparoscopic surgery, and there are currently no effective therapies. It is vital to provide a reliable basis for clinical prediction. This study tried to analyse the risk factors for DNR in patients undergoing laparoscopic colorectal surgery and to establish a risk prediction model.

METHODS

A retrospective analysis of the clinical data and DNR status of patients undergoing laparoscopic colorectal surgery at Xiangya Hospital of Central South University from March 2018 to July 2020 was conducted. Logistic regression was performed to analyse the related risk factors for DNR post-operatively, and the predictive model of DNR post-operatively was constructed and validated internally. Patients who underwent laparoscopic colorectal surgery between January and July 2021 were also selected for external validation of the predictive model, to ultimately investigate the risk factors for DNR in patients undergoing laparoscopic colorectal surgery.

RESULTS

The incidence of DNR in patients undergoing laparoscopic colorectal surgery was 15.2% (31/204). The maximum variability of cerebral oxygen, age, education, and pre-existing diabetes was related to the incidence of DNR (p < 0.05). The risk prediction model of DNR after laparoscopic colorectal surgery was established. The internal and external validation showed that the discrimination was good (the AUCs were 0.751 and 0.694, respectively).

CONCLUSIONS

The risk prediction model of DNR related to cerebral oxygen saturation monitoring shows good predictive performance and clinical value, providing a basis for postoperative DNR prevention.

Lawrence K, Chui J, Diop M. Assessing changes in regional cerebral hemodynamics in adults with a high-density full-head coverage time-resolved near-infrared spectroscopy device

Significance

Cerebral oximeters have the potential to detect abnormal cerebral blood oxygenation to allow for early intervention. However, current commercial systems have two major limitations: (1) spatial coverage of only the frontal region, assuming that surgery-related hemodynamic effects are global and (2) susceptibility to extracerebral signal contamination inherent to continuous-wave near-infrared spectroscopy (NIRS).

Aim

This work aimed to assess the feasibility of a high-density, time-resolved (tr) NIRS device (Kernel Flow) to monitor regional oxygenation changes across the cerebral cortex during surgery.

Approach

The Flow system was assessed using two protocols. First, digital carotid compression was applied to healthy volunteers to cause a rapid oxygenation decrease across the ipsilateral hemisphere without affecting the contralateral side. Next, the system was used on patients undergoing shoulder surgery to provide continuous monitoring of cerebral oxygenation. In both protocols, the improved depth sensitivity of trNIRS was investigated by applying moment analysis. A dynamic wavelet filtering approach was also developed to remove observed temperature-induced signal drifts.

Results

In the first protocol (28 ± 5 years; five females, five males), hair significantly impacted regional sensitivity; however, the enhanced depth sensitivity of trNIRS was able to separate brain and scalp responses in the frontal region. Regional sensitivity was improved in the clinical study given the age-related reduction in hair density of the patients (65 ± 15 years; 14 females, 13 males). In five patients who received phenylephrine to treat hypotension, different scalp and brain oxygenation responses were apparent, although no regional differences were observed.

Conclusions

The Kernel Flow has promise as an intraoperative neuromonitoring device. Although regional sensitivity was affected by hair color and density, enhanced depth sensitivity of trNIRS was able to resolve differences in scalp and brain oxygenation responses in both protocols.

Post-Intensive Care Syndrome in Neurocritical Care Patients

Post-intensive care syndrome (PICS) refers to unintended consequences of critical care that manifest as new or worsening impairments in physical functioning, cognitive ability, or mental health. As intensive care unit (ICU) survival continues to improve, PICS is becoming increasingly recognized as a public health problem. Studies that focus on PICS have typically excluded patients with acute brain injuries and chronic neurodegenerative problems. However, patients who require neurocritical care undoubtedly suffer from impairments that overlap substantially with those encompassed by PICS. A major challenge is to distinguish between impairments related to brain injury and those that occur as a consequence of critical care. The general principles for the prevention and management of PICS and multidomain impairments in patients with moderate and severe neurological injuries are similar including the ICU liberation bundle, multidisciplinary team-based care throughout the continuum of care, and increasing awareness regarding the challenges of critical care survivorship among patients, families, and multidisciplinary team members. An extension of this concept, PICS-Family (PICS-F) refers to the mental health consequences of the intensive care experience for families and loved ones of ICU survivors. A dyadic approach to ICU survivorship with an emphasis on recognizing families and caregivers that may be at risk of developing PICS-F after neurocritical care illness can help improve outcomes for ICU survivors. In this review, we will summarize our current understanding of PICS and PICS-F, emerging literature on PICS in severe acute brain injury, strategies for preventing and treating PICS, and share our recommendations for future directions.

Non-Invasive Tools in Perioperative Stroke Risk Assessment for Asymptomatic Carotid Artery Stenosis with a Focus on the Circle of Willis

This review aims to explore advancements in perioperative ischemic stroke risk estimation for asymptomatic patients with significant carotid artery stenosis, focusing on Circle of Willis (CoW) morphology based on the CTA or MR diagnostic imaging in the current preoperative diagnostic algorithm. Functional transcranial Doppler (fTCD), near-infrared spectroscopy (NIRS), and optical coherence tomography angiography (OCTA) are discussed in the context of evaluating cerebrovascular reserve capacity and collateral vascular systems, particularly the CoW. These non-invasive diagnostic tools provide additional valuable insights into the cerebral perfusion status. They support biomedical modeling as the gold standard for the prediction of the potential impact of carotid artery stenosis on the hemodynamic changes of cerebral perfusion. Intraoperative risk assessment strategies, including selective shunting, are explored with a focus on CoW variations and their implications for perioperative ischemic stroke and cognitive function decline. By synthesizing these insights, this review underscores the potential of non-invasive diagnostic methods to support clinical decision making and improve asymptomatic patient outcomes by reducing the risk of perioperative ischemic neurological events and preventing further cognitive decline.

Machines, mathematics, and modules: the potential to provide real-time metrics for pain under anesthesia

The brain-based assessments under anesthesia have provided the ability to evaluate pain/nociception during surgery and the potential to prevent long-term evolution of chronic pain. Prior studies have shown that the functional near-infrared spectroscopy (fNIRS)-measured changes in cortical regions such as the primary somatosensory and the polar frontal cortices show consistent response to evoked and ongoing pain in awake, sedated, and anesthetized patients. We take this basic approach and integrate it into a potential framework that could provide real-time measures of pain/nociception during the peri-surgical period. This application could have significant implications for providing analgesia during surgery, a practice that currently lacks quantitative evidence to guide patient tailored pain management. Through a simple readout of "pain" or "no pain," the proposed system could diminish or eliminate levels of intraoperative, early post-operative, and potentially, the transition to chronic post-surgical pain. The system, when validated, could also be applied to measures of analgesic efficacy in the clinic.

Early Neurocognitive Function With Propofol or Desflurane Anesthesia After Laser Laryngeal Surgery With Low Inspired Oxygen

PURPOSE

The effects of general anesthetics on cognitive impairment are unclear and complicated. Laser laryngeal surgery (LLS) requires the administration of low levels of oxygen, which may increase the risk of desaturation and brain function impairment. This prospective randomized trial aimed to compare the effects of desflurane and propofol-based general anesthesia on the occurrence of early postoperative cognitive decline in elderly patients undergoing LLS.

METHODS

Seventy-three patients classified as American Society of Anesthesiologists grade I or II and at least 65 years of age were randomly allocated to receive either desflurane-based (Group D) or propofol-based (Group P) anesthesia during LLS. The standard anesthesia protocol was performed, with a bispectral index between 40 and 60 and a mean arterial pressure within 20% of baseline values. Intraoperative regional oxygen saturation values were recorded. Each patient was assessed using the mini-mental state examination (MMSE) test during the preoperative period (baseline), 30 min after extubation in the postanesthesia care unit, and 1, 3, and 24 h after surgery.

RESULTS

MMSE scores improved slightly in both groups compared to baseline during the early postoperative period, but these increases were not statistically significant. No significant differences were identified in MMSE scores between groups. Only three patients (9.6%) in group D and one patient (3.1%) in group P developed cognitive impairment (p = 0.583).

CONCLUSION

Low intraoperative inspired oxygen concentration during short-duration LLS did not reduce early postoperative cognitive function in elderly patients. Desflurane or propofol-based anesthesia had similar effects on early neurocognition after LLS.

LEVEL OF EVIDENCE

2 Laryngoscope, 133:640-646, 2023.

Do Cerebral Cortex Perfusion, Oxygen Delivery, and Oxygen Saturation Responses Measured by Near-Infrared Spectroscopy Differ Between Patients Who Fail or Succeed in a Spontaneous Breathing Trial? A Prospective Observational Study

BACKGROUND

Alterations in perfusion to the brain during the transition from mechanical ventilation (MV) to a spontaneous breathing trial (SBT) remain poorly understood. The aim of the study was to determine whether changes in cerebral cortex perfusion, oxygen delivery (DO₂), and oxygen saturation (%StiO₂) during the transition from MV to an SBT differ between patients who succeed or fail an SBT.

METHODS

This was a single-center prospective observational study conducted in a 16-bed medical intensive care unit of the University Hospital Leuven, Belgium. Measurements were performed in 24 patients receiving MV immediately before and at the end of a 30-min SBT. Blood flow index (BFI), DO₂, and %StiO₂ in the prefrontal cortex, scalene, rectus abdominis, and thenar muscle were simultaneously assessed by near-infrared spectroscopy using the tracer indocyanine green dye. Cardiac output, arterial blood gases, and systemic oxygenation were also recorded.

RESULTS

During the SBT, prefrontal cortex BFI and DO₂ responses did not differ between SBT-failure and SBT-success groups (p > 0.05). However, prefrontal cortex %StiO₂ decreased in six of eight patients (75%) in the SBT-failure group (median [interquartile range 25-75%]: MV = 57.2% [49.1-61.7] vs. SBT = 51.0% [41.5-62.5]) compared to 3 of 16 patients (19%) in the SBT-success group (median [interquartile range 25-75%]: MV = 65.0% [58.6-68.5] vs. SBT = 65.1% [59.5-71.1]), resulting in a significant differential %StiO₂ response between groups (p = 0.031). Similarly, a significant differential response in thenar muscle %StiO₂ (p = 0.018) was observed between groups. A receiver operating characteristic analysis identified a decrease in prefrontal cortex %StiO₂ > 1.6% during the SBT as an optimal cutoff, with a sensitivity of 94% and a specificity of 75% to predict SBT failure and an area under the curve of 0.79 (95% CI: 0.55-1.00). Cardiac output, systemic oxygenation, scalene, and rectus abdominis BFI, DO₂, and %StiO₂ responses did not differ between groups (p > 0.05); however, during the SBT, a significant positive association in prefrontal cortex BFI and partial pressure of arterial carbon dioxide was observed only in the SBT-success group (SBT success: Spearman's ρ = 0.728, p = 0.002 vs. SBT failure: ρ = 0.048, p = 0.934).

CONCLUSIONS

This study demonstrated a reduced differential response in prefrontal cortex %StiO₂ in the SBT-failure group compared with the SBT-success group possibly due to the insufficient increase in prefrontal cortex perfusion in SBT-failure patients. A > 1.6% drop in prefrontal cortex %StiO₂ during SBT was sensitive in predicting SBT failure. Further research is needed to validate these findings in a larger population and to evaluate whether cerebral cortex %StiO₂ measurements by near-infrared spectroscopy can assist in the decision-making process on liberation from MV.

Effect of combined use of cerebral oximetry and electroencephalogram monitoring on the incidence of perioperative neurocognitive disorders in adult cardiac and non-cardiac surgery: A systematic review of randomized and non-randomized trials

Background: There is insufficient evidence to recommend using either intraoperative cerebral oximetry or (processed) electroencephalogram (EEG) alone for preventing perioperative neurocognitive disorders (PNDs). Objective: To evaluate the effectiveness of combined use of cerebral oximetry and electroencephalogram-guided anesthesia on the incidence of PNDs in adult patients undergoing cardiac and non-cardiac interventions. Methods: A PICOS - based systematic review of English articles using Pubmed and Embase (from inception to August 2022) was performed. There were no exclusion criteria regarding the type of the study. Abstract proceedings and new study protocols or ongoing studies were not included. Review articles were analyzed in search of eligible references. All possible terms that were illustrative of PNDs were used. Results: Among the 63 full manuscripts that were analyzed in detail, 15 met the inclusion criteria. We found 2 retrospective, 8 prospective observational and 5 randomized controlled trials of which 1 did not evaluate the use of neuromonitoring in the randomization process. The definition and the methods used to diagnose PNDs were very heterogeneous. Only 8 studies used an algorithm to avoid/treat cerebral oxygen desaturation and/or to treat EEG abnormalities. Overall, there was a tendency towards less PNDs in studies where such an algorithm was used. Conclusions: Our results suggest that integrating information obtained from cerebral oximetry and an EEG monitor may reduce the incidence of PNDs whenever an adapted algorithm is used to improve brain function.

Distribution of ventilation and oxygenation in surgical obese patients ventilated with high versus low positive end-expiratory pressure: A substudy of a randomised controlled trial

BACKGROUND

Intra-operative ventilation using low/physiological tidal volume and positive end-expiratory pressure (PEEP) with periodic alveolar recruitment manoeuvres (ARMs) is recommended in obese surgery patients.

OBJECTIVES

To investigate the effects of PEEP levels and ARMs on ventilation distribution, oxygenation, haemodynamic parameters and cerebral oximetry.

DESIGN

A substudy of a randomised controlled trial.

SETTING

Tertiary medical centre in Geneva, Switzerland, between 2015 and 2018.

PATIENTS

One hundred and sixty-two patients with a BMI at least 35 kg per square metre undergoing elective open or laparoscopic surgery lasting at least 120 min.

INTERVENTION

Patients were randomised to PEEP of 4 cmH 2 O ( n  = 79) or PEEP of 12 cmH 2 O with hourly ARMs ( n  = 83).

MAIN OUTCOME MEASURES

The primary endpoint was the fraction of ventilation in the dependent lung as measured by electrical impedance tomography. Secondary endpoints were the oxygen saturation index (SaO 2 /FIO 2 ratio), respiratory and haemodynamic parameters, and cerebral tissue oximetry.

RESULTS

Compared with low PEEP, high PEEP was associated with smaller intra-operative decreases in dependent lung ventilation [-11.2%; 95% confidence interval (CI) -8.7 to -13.7 vs. -13.9%; 95% CI -11.7 to -16.5; P  = 0.029], oxygen saturation index (-49.6%; 95% CI -48.0 to -51.3 vs. -51.3%; 95% CI -49.6 to -53.1; P  < 0.001) and a lower driving pressure (-6.3 cmH 2 O; 95% CI -5.7 to -7.0). Haemodynamic parameters did not differ between the groups, except at the end of ARMs when arterial pressure and cardiac index decreased on average by -13.7 mmHg (95% CI -12.5 to -14.9) and by -0.54 l min -1  m -2 (95% CI -0.49 to -0.59) along with increased cerebral tissue oximetry (3.0 and 3.2% on left and right front brain, respectively).

CONCLUSION

In obese patients undergoing abdominal surgery, intra-operative PEEP of 12 cmH 2 O with periodic ARMs, compared with intra-operative PEEP of 4 cmH 2 O without ARMs, slightly redistributed ventilation to dependent lung zones with minor improvements in peripheral and cerebral oxygenation.

TRIAL REGISTRATION

NCT02148692, https://clinicaltrials.gov/ct2.

Effects of different levels of controlled hypotension on regional cerebral oxygen saturation and postoperative cognitive function in patients undergoing total knee arthroplasty

Background

Controlled hypotension technique was usually used to reduce intraoperative bleeding, and it could improve visualization of the surgical field during total knee arthroplasty (TKA). However, inappropriate controlled hypotension, through reducing cerebral blood flow or cerebral perfusion pressure, may cause postoperative cognitive dysfunction (POCD), so it is important to identify the appropriate level of controlled hypotension. Objective: To investigate the effects of different levels of controlled hypotension on regional cerebral oxygen saturation and postoperative cognitive function in patients undergoing TKA.

Methods

Patients meeting inclusion criteria were enrolled through preoperative visits and basic information was obtained. The patients were randomly divided into three groups: Group A, MAP was maintained at 90–100% of the baseline; Group B, MAP was maintained at 80–90% of the baseline; Group C, MAP was maintained at 70–80% of the baseline. The MAP, HR, and rSO₂ were observed and recorded during the operation. The C-reactive protein (CRP), hemoglobin (Hb) and MMSE score at 1, 3, and 7 days after operation were recorded. SPSS25.0 was used for data analysis.

Result

When the MAP had a decrease among the three groups, rSO₂ did not decrease significantly, and none of the patients experienced POCD which was measured by MMSE. And there was no correlation between the decline in rSO₂ and that in MAP.

Conclusion

No POCD was experienced in the three groups, and we recommend that the controlled hypotensive target indicated by MAP was maintained at 70–80% of the baseline which not only decreases intraoperative bleeding and improve the quality of the surgical field, but also is still within safe levels.

Comparing near-infrared spectroscopy-measured cerebral oxygen saturation and corresponding venous oxygen saturations in children with congenital heart disease: a systematic review and meta-analysis

BACKGROUND

Near-infrared spectroscopy (NIRS) is a non-invasive approach that measures cerebral regional oxygen saturation (rScO₂). In this study, we evaluated the evidence on the validity of NIRS and the interchangeability between NIRS and common invasive approaches by exploring the correlation and consistency and comparing the mean and standard deviation between the NIRS rScO₂ and jugular bulb venous oxygen saturation (SjvO₂) as well as central venous oxygen saturation (ScvO₂) in the perioperative period of children with congenital heart disease (CHD).

METHODS

We searched electronic bibliographic databases (PubMed, The Cochrane Library and Embase) and screened the studies that met the inclusion criteria. We included cross-sectional studies of CHD pediatric patients in the perioperative period receiving both tests for NIRS rScO₂ and SjvO₂ or NIRS rScO₂ and ScvO₂. Methodological quality assessment and heterogeneity analyses were performed. We qualitatively summarized the results of Bland-Altman's analysis. Meta-regression, subgroup analyses, and sensitivity analyses were carried out to explore the causes of heterogeneity.

RESULTS

There was no significant difference in Cohen's d between rScO₂ and ScvO₂ or between rScO₂ and SjvO₂ (Cohen's d =0.06, 95% CI: -0.16 to 0.28; Cohen's d =0.03, 95% CI: -0.25 to 0.31, respectively) and notable heterogeneity existed (I²=76.0%, P<0.001; I²=73.6%, P<0.001, respectively). A positive linear correlation was present between rScO₂ and ScvO₂ or between rScO₂ and SjvO₂ (r=0.58, 95% CI: 0.54 to 0.63; r=0.60, 95% CI: 0.54 to 0.66, respectively) and the heterogeneity was not significant (I²=36.7%, P=0.065; I²=12.7%, P=0.328, respectively). In most studies, the 95% limits of agreements of Bland-Altman's analysis were large. No evidence of publication bias was observed.

CONCLUSIONS

The rScO₂ measured by NIRS reflected the SjvO₂ and ScvO₂ monitored by invasive measurements in the perioperative period of children with CHD to some extent. However, wide limits of agreements between rScO₂ and SjvO₂ as well as ScvO₂ indicated that NIRS and SjvO₂ as well as ScvO₂ are not interchangeable. Whether NIRS plays a prominent role in monitoring cerebral oxygen saturation in children with CHD needs further research.

Perspectives: Regional brain oxygen saturation: beyond the brain there is also life

Abstract:

Some procedures, such as cardiovascular surgery, may compromise brain perfusion and require careful management to preserve the integrity of the central nervous system. In this setting, regional cerebral oxygen saturation [rSO2] emerges as an alternative, minimally invasive, monitoring system. The mechanism by which regional oxygen is measured is based on the refraction and absorption of a signal with a specific wavelength. Diagnostic and therapeutic algorithms for these settings. This would allow for a more rational use of goal-directed therapies that reduce morbidity and mortality in these patients.

The Predictive Power of Near-Infrared Spectroscopy in Improving Cognitive Problems in Patients Undergoing Brain Surgeries: A Systematic Review

One of the main objectives in neurosurgical procedures is the prevention of cerebral ischemia and hypoxia leading to secondary brain injury. Different methods for early detection of intraoperative cerebral ischemia and hypoxia have been used. Near-infrared spectroscopy (NIRS) is a simple, non-invasive method for monitoring cerebral oxygenation increasingly used today. The aim of this study was to systematically review the brain monitoring with NIRS in neurosurgery. The search process resulted in the detection of 324 articles using valid keywords on the electronic databases, including Embase, PubMed, Scopus, Web of Science, and Cochrane Library. Subsequently, the full texts of 34 studies were reviewed, and finally 11 articles (seven prospective studies, three retrospective studies, and one randomized controlled trial) published from 2005 to 2020 were identified as eligible for systematic review. Meta-analysis was not possible due to high heterogeneity in neurological and neurosurgical conditions of patients, expression of different clinical outcomes, and different standard reference tests in the studies reviewed. The results showed that NIRS is a non-invasive cerebral oximetry that provides continuous and measurable cerebral oxygenation information and can be used in a variety of clinical settings.

Restricted, optimized or liberal fluid strategy in thoracic surgery: A narrative review

Perioperative fluid balance has a major impact on clinical and functional outcome, regardless of the type of interventions. In thoracic surgery, patients are more vulnerable to intravenous fluid overload and to develop acute respiratory distress syndrome and other complications. New insight has been gained on the mechanisms causing pulmonary complications and the role of the endothelial glycocalix layer to control fluid transfer from the intravascular to the interstitial spaces and to promote tissue blood flow. With the implementation of standardized processes of care, the preoperative fasting period has become shorter, surgical approaches are less invasive and patients are allowed to resume oral intake shortly after surgery. Intraoperatively, body fluid homeostasis and adequate tissue oxygen delivery can be achieved using a normovolemic therapy targeting a “near-zero fluid balance” or a goal-directed hemodynamic therapy to maximize stroke volume and oxygen delivery according to the Franck–Starling relationship. In both fluid strategies, the use of cardiovascular drugs is advocated to counteract the anesthetic-induced vasorelaxation and maintain arterial pressure whereas fluid intake is limited to avoid cumulative fluid balance exceeding 1 liter and body weight gain (~1-1.5 kg). Modern hemodynamic monitors provide valuable physiological parameters to assess patient volume responsiveness and circulatory flow while guiding fluid administration and cardiovascular drug therapy. Given the lack of randomized clinical trials, controversial debate still surrounds the issues of the optimal fluid strategy and the type of fluids (crystalloids versus colloids). To avoid the risk of lung hydrostatic or inflammatory edema and to enhance the postoperative recovery process, fluid administration should be prescribed as any drug, adapted to the patient's requirement and the context of thoracic intervention.

The Use of Cerebral Oximetry in Surgery: A Systematic Review and Meta-analysis of Randomized Controlled Trials

OBJECTIVE

The evidence on the use of cerebral oximetry during surgery to minimize postoperative neurologic complications remains uncertain in the literature. The present authors aimed to assess the value of cerebral oximetry in the prevention of postoperative cognitive dysfunction, postoperative delirium, and postoperative stroke in adults undergoing surgery.

DESIGN

A systematic review and meta-analysis.

SETTING

The surgery room.

PARTICIPANTS

Adult patients (ages ≥18 years) undergoing surgery.

INTERVENTIONS

Cerebral oximetry monitoring.

MEASUREMENTS AND MAIN RESULTS

Databases of Ovid MEDLINE, Ovid EMBASE, and CENTRAL were systematically searched from their inception until December 2020 for randomized controlled trials comparing cerebral oximetry monitoring with either blinded or no cerebral oximetry monitoring in adults undergoing surgery. Observational studies, case reports, and case series were excluded. Seventeen studies (n = 2,120 patients) were included for quantitative meta-analysis. Patients who were randomized to cerebral oximetry monitoring had a lower incidence of postoperative cognitive dysfunction (studies = seven, n = 969, odds ratio [OR] 0.23, 95% confidence interval [CI] 0.11-0.48, p = 0.0001; evidence = very low). However, no significant differences were observed in the incidence of postoperative delirium (studies = five, n = 716, OR 0.81, 95% CI 0.53-1.25, p = 0.35; evidence = high), and postoperative stroke (studies = seven, n = 1,087, OR 0.72, 95% CI 0.30-1.69, p = 0.45; evidence = moderate).

CONCLUSION

Adult patients with cerebral oximetry monitoring were associated with a significant reduction of postoperative cognitive dysfunction. However, given the low certainty of evidence and substantial heterogeneity, more randomized controlled trials using standardized assessment tools for postoperative cognitive dysfunction and interventions of correcting cerebral desaturation are warranted to improve the certainty of evidence and homogeneity.

Effect of Deliberate Hypotension on Regional Cerebral Oxygen Saturation During Functional Endoscopic Sinus Surgery: A Randomized Controlled Trial

Background: Deliberate hypotension can reduce bleeding and improve visualization of the surgical field during functional endoscopic sinus surgery (FESS). However, hypotension may cause brain hypoperfusion and subsequent ischemic injuries, such as delayed awakening, stroke, postoperative delirium, and postoperative cognitive dysfunction. Near-infrared spectroscopy (NIRS) can be used to monitor real-time regional cerebral oxygen saturation (rSO₂) levels to estimate brain perfusion. The present study aimed to evaluate the change in rSO₂ induced by deliberate hypotension during FESS, and assess the impact of deliberate hypotension on the surgical process.

Material and Methods: A randomized controlled trial was registered with the Chinese clinical trial registry (ChiCTR2000039846). A total of 40 patients were enrolled and randomly divided into the control and intervention groups, and finally, 39 patients were analyzed. Deliberate hypotension was induced in the intervention group using nicardipine and esmolol, whereas the control group received general anesthesia without deliberate hypotension. We recorded mean arterial pressure (MAP), saturation of pulse oximetry (SpO₂), rSO₂, and heart rate (HR) before induction of anesthesia (T0), immediately after induction of anesthesia (T1), at the beginning of the operation (corresponding with the establishment of deliberate hypotension) (T2), 10 min (T3) and 20 min (T4) after the operation began, at the end of the operation (corresponding with the end of deliberate hypotension) (T5), and 5 min (T6) and 15 min (T7) after the operation. The partial pressure of end-tidal carbon dioxide (PetCO₂) was recorded at T1, T2, T3, T4, T5, and T6. The duration of surgery, intraoperative blood loss, tracheal extubation time, and the number of patients that experienced cerebral desaturation events (CDEs) were recorded. The surgical field was estimated postoperation based on the Fromme score.

Results: A 30% decrease from the baseline MAP resulted in a decrease of intraoperative bleeding, improvement in the quality of the surgical field, and the shortening of the duration of surgery during FESS in the intervention group compared with the control group. In addition, rSO₂ was reduced and no CDEs were experienced in the intervention group. Linear regression analysis demonstrated a correlation between the decline in rSO₂ and that in MAP.

Conclusions: A decrease in MAP to a certain level will cause a decrease of rSO₂ in patients undergoing FESS under general anesthesia. Based on our findings, we recommend that the deliberate hypotensive target indicated by MAP be reduced by 30%, while PetCO₂ is maintained at 35–40 mmHg and HR is maintained at about 60 beats per minute during FESS.

A Review of Monitoring Methods for Cerebral Blood Oxygen Saturation

In recent years, cerebral blood oxygen saturation has become a key indicator during the perioperative period. Cerebral blood oxygen saturation monitoring is conducive to the early diagnosis and treatment of cerebral ischemia and hypoxia. The present study discusses the three most extensively used clinical methods for cerebral blood oxygen saturation monitoring from different aspects: working principles, relevant parameters, current situations of research, commonly used equipment, and relative advantages of different methods. Furthermore, through comprehensive comparisons of the methods, we find that near-infrared spectroscopy (NIRS) technology has significant potentials and broad applications prospects in terms of cerebral oxygen saturation monitoring. Despite the current NIRS technology, the only bedside non-invasive cerebral oxygen saturation monitoring technology, still has many defects, it is more in line with the future development trend in the field of medical and health, and will become the main method gradually.

The role of non-invasive brain oximetry in adult critically ill patients without primary brain injury

A primary objective in intensive care and perioperative settings is to promote an adequate supply and delivery of oxygen to tissues and organs, particularly to the brain. Cerebral near infrared spectroscopy (NIRS) is a non-invasive, continuous monitoring technique, that can be used to assess cerebral oxygenation. Using NIRS to monitor cerebral oximetry is not new, and has been in widespread use in neonates and cardiac surgery for decades. In addition, it has become common to see NIRS being used in adult and pediatric cardiac surgery, acute neurological diseases, neurosurgical procedures, vascular surgery, severe trauma and other acute medical diseases. Furthermore, recent evidence suggests a role for NIRS in the perioperative settings; detecting and preventing episodes of cerebral desaturation aiming to reduce the development of post-operative delirium. NIRS is not without its limitations; these include the risk of extra-cranial contamination, spatial limitations and skin blood flow/volume changes, as well being a measure of localized blood oxygenation underneath the sensor. However, NIRS is a non-invasive technique and can, therefore, be used in those patients without indications or justification for invasive brain monitoring; non-neurosurgical procedures such as liver transplantation, major orthopedic surgery and critically illness where the brain is at risk. The aim of this manuscript was to discuss the physical principles of NIRS and to report the current evidence regarding its use in critically ill patients without primary non-anoxic brain injury.

Near-Infrared Spectroscopy in Neurocritical Care: A Review of Recent Updates

Neurocritical diseases and conditions are common causes of long-term disability and mortality. Early recognition and management of neurocritically ill patients is a significant challenge for neurosurgeons, neurologists, and neurointensivists. Although cerebral angiography, magnetic resonance imaging, computed tomography, and radionuclide imaging are useful in neuromonitoring and neuroimaging, they have several important limitations: they are not readily available, cannot be used for a continuous assessment of cerebral function, and frequently require patient transport to the radiological department. Near-infrared spectroscopy (NIRS) is an inexpensive, portable, noninvasive method that does not require advanced expertise and can be used at the bedside for critically ill patients without moving them to the radiology department. NIRS can detect and monitor multiple critical parameters, including cerebral oximetry, intracranial pressure, temperature, and cerebral blood flow. NIRS can be valuable for a wide variety of neurocritical diseases and conditions, such as ischemic and hemorrhagic strokes, severe traumatic brain injury, brain tumors, and perioperative neurosurgery. Although NIRS has been studied extensively in multiple neurocritical conditions, more evidence on its application is needed.

Advances in translational imaging of the microcirculation

The past few decades have seen an explosion in the development and use of methods for imaging the human microcirculation during health and disease. The confluence of innovative imaging technologies, affordable computing power, and economies of scale have ushered in a new era of "translational" imaging that permit us to peer into blood vessels of various organs in the human body. These imaging techniques include near-infrared spectroscopy (NIRS), positron emission tomography (PET), and magnetic resonance imaging (MRI) that are sensitive to microvascular-derived signals, as well as computed tomography (CT), optical imaging, and ultrasound (US) imaging that are capable of directly acquiring images at, or close to microvascular spatial resolution. Collectively, these imaging modalities enable us to characterize the morphological and functional changes in a tissue's microcirculation that are known to accompany the initiation and progression of numerous pathologies. Although there have been significant advances for imaging the microcirculation in preclinical models, this review focuses on developments in the assessment of the microcirculation in patients with optical imaging, NIRS, PET, US, MRI, and CT, to name a few. The goal of this review is to serve as a springboard for exploring the burgeoning role of translational imaging technologies for interrogating the structural and functional status of the microcirculation in humans, and highlight the breadth of current clinical applications. Making the human microcirculation "visible" in vivo to clinicians and researchers alike will facilitate bench-to-bedside discoveries and enhance the diagnosis and management of disease.

Influence of Anemia on Postoperative Cognitive Function in Patients Undergo Hysteromyoma Surgery

Cognitive dysfunction is a common disease in aging population. This study aims to compare the influence of different degrees of anemia on the cognitive function of patients undergo hysteromyoma surgery. Sixty-one patients aged 18-60 years who underwent uterine fibroid surgery in the Second Affiliated Hospital of Shantou University Medical College from March 2019 to December 2020 were selected for this study. Patients were divided into three groups: group normal (Group N, patients have no anemia), group of mild anemia (Group Mi, patients have mild anemia) and group of moderate anemia (Group Mo, patients had moderate anemia). Combined spinal and epidural anesthesia were administered. Cognitive function tests were performed 1 day before the surgery and repeated at the 5th and 30th days after surgery. Peripheral venous blood samples from patients were collected before the surgery, right after surgery and at the 24th and 72nd hours after surgery. The contents of S-100β, IL-6, TNF-α and IL-1β in serum samples were determined by ELISA. It was found that there were no significant differences in general characteristics of patients among Group N, Group Mi and Group Mo (p > 0.05). Nine patients developed postoperative cognitive dysfunction after surgery, and the incidence was 14.75% (9/61). The incidence of postoperative cognitive dysfunction (POCD) was 40% in Group Mo, which was higher than that in Group N and Group Mi. The difference was statistically significant (p < 0.05). Inflammatory factors in patients with POCD were higher in post-surgery than before-surgery (p < 0.05), while there was no statistical significance in the difference of inflammatory factors of patients without POCD before and after surgery (p > 0.05). Taken together, this study suggested that moderate anemia could be a risk factor of POCD in patients undergoing hysteromyoma surgeries. This study will help surgeons developing measures for preventing the occurrence of POCD.

Hemodynamic Management of Acute Spinal Cord Injury: A Literature Review

The goal of acute spinal cord injury (SCI) management is to reduce secondary injuries and improve neurological recovery after its occurrence. This review aimed to explore the literature regarding hemodynamic management to reduce ischemic secondary injury and improve neurologic outcome following acute SCI. The PubMed database was searched for studies investigating blood flow, mean arterial pressure (MAP), and spinal cord perfusion pressure after SCI. The 2013 guidelines of the American Association of Neurological Surgeons/Congress of Neurological Surgeons recommended maintaining MAP at 85-90 mmHg for 7 days after SCI to potentially improve outcome. However, this recommendation was based on weak evidence for neurologic benefit. The maintenance of MAP will typically require vasopressors, which may have their own set of complications. More recently, studies have suggested the potential importance of considering spinal cord perfusion pressure in addition to the MAP. Further research on the hemodynamic management of acute SCI is required to determine how to optimize neurologic recovery. Evidence-based guidelines for hemodynamic management should acknowledge the gaps in knowledge and the limitations of the current literature.

Effects of milrinone on cerebral perfusion and postoperative cognitive function in spine surgery: Secondary analysis of a CONSORT-compliant randomized controlled trial

OBJECTIVE

To compare the effects of milrinone, sodium nitroprusside (SNP), and nitroglycerin (NTG) on induced hypotension, cerebral perfusion, and postoperative cognitive function in elderly patients undergoing spine surgery.

METHODS

Sixty patients >60 years scheduled for lumbar fusion surgery were assigned to receive milrinone (group M), SNP (group S), or NTG (group N). The administration of the study drug was initiated immediately after perivertebral muscle retraction and was stopped after completion of interbody fusion. Target blood pressure was a decrease of 30% in systolic blood pressure from baseline or mean blood pressure of 60 to 65 mm Hg. The regional cerebral venous oxygen saturation (rSVO2), as a measure of cerebral perfusion, and the change in perioperative Mini-Mental State Examination (MMSE) score, as a measure of postoperative cognitive function, were assessed.

RESULTS

During the administration of the study drug, the overall and lowest intraoperative rSVO2 values were significantly higher (P = .01 and P = .01, respectively), and the duration of rSVO2 <60% was shorter in group M than in the other groups (P = .03). In group M, intraoperative rSVO2 was not different from the basal value, whereas in groups S and N, rSVO2 was significantly lower than the basal value during the administration of the study drug, but then returned to the basal value after terminating the study drug. Basal MMSE scores were comparable among the 3 groups. The MMSE score on postoperative day 5 was higher in group M than the other groups.

CONCLUSIONS

Milrinone used to induce hypotension resulted in better intraoperative cerebral perfusion and postoperative cognitive function compared to SNP and nitroglycerin.

Neuromonitoring during general anesthesia in non-neurologic surgery

Cerebral complications are common in perioperative settings even in non-neurosurgical procedures. These include postoperative cognitive dysfunction or delirium as well as cerebrovascular accidents. During surgery, it is essential to ensure an adequate degree of sedation and analgesia, and at the same time, to provide hemodynamic and respiratory stability in order to minimize neurological complications. In this context, the role of neuromonitoring in the operating room is gaining interest, even in the non-neurolosurgical population. The use of multimodal neuromonitoring can potentially reduce the occurrence of adverse effects during and after surgery, and optimize the administration of anesthetic drugs. In addition to the traditional focus on monitoring hemodynamic and respiratory systems during general anesthesia, the ability to constantly monitor the activity and maintenance of brain homeostasis, creating evidence-based protocols, should also become part of the standard of care: in this challenge, neuromonitoring comes to our aid. In this review, we aim to describe the role of the main types of noninvasive neuromonitoring such as those based on electroencephalography (EEG) waves (EEG, Entropy module, Bispectral Index, Narcotrend Monitor), near-infrared spectroscopy (NIRS) based on noninvasive measurement of cerebral regional oxygenation, and Transcranial Doppler used in the perioperative settings in non-neurosurgical intervention. We also describe the advantages, disadvantage, and limitation of each monitoring technique.

The Association of Cerebral Desaturation During One-Lung Ventilation and Postoperative Recovery: A Prospective Observational Cohort Study

OBJECTIVES

This study was designed to investigate whether cerebral oxygen desaturations during thoracic surgery are predictive of patients' quality of recovery. As a secondary aim, the authors investigated the relationship among cerebral desaturations and postoperative delirium and hospital length of stay.

DESIGN

This study was a prospective observational cohort study.

SETTING

A single tertiary-care medical center from September 2012 through March 2014.

PATIENTS

Adult patients scheduled for elective pulmonary surgery requiring one-lung ventilation.

INTERVENTIONS

All patients were monitored with the ForeSight cerebral oximeter.

MEASUREMENTS AND MAIN RESULTS

The primary assessment tool was the Postoperative Quality of Recovery Scale. Delirium was assessed using the Confusion Assessment Method. Of the 117 patients analyzed in the study, 60 of the patients desaturated below a cerebral oximetry level of 65% for a minimum of 3 minutes (51.3%). Patients who desaturated were significantly less likely to have cognitive recovery in the immediate postoperative period (p = 0.012), which did not persist in the postoperative period beyond day 0. Patients who desaturated also were more likely to have delirium (p = 0.048, odds ratio 2.81 [95% CI 1.01-7.79]) and longer length of stay (relative duration 1.35, 95% CI 1.05-1.73; p = 0.020).

CONCLUSIONS

Intraoperative cerebral oxygen desaturations, frequent during one-lung ventilation, are associated significantly with worse early cognitive recovery, high risk of postoperative delirium, and prolonged length of stay. Large interventional studies on cerebral oximetry in the thoracic operating room are warranted.

Frequency-Domain Techniques for Cerebral and Functional Near-Infrared Spectroscopy

This article reviews the basic principles of frequency-domain near-infrared spectroscopy (FD-NIRS), which relies on intensity-modulated light sources and phase-sensitive optical detection, and its non-invasive applications to the brain. The simpler instrumentation and more straightforward data analysis of continuous-wave NIRS (CW-NIRS) accounts for the fact that almost all the current commercial instruments for cerebral NIRS have embraced the CW technique. However, FD-NIRS provides data with richer information content, which complements or exceeds the capabilities of CW-NIRS. One example is the ability of FD-NIRS to measure the absolute optical properties (absorption and reduced scattering coefficients) of tissue, and thus the absolute concentrations of oxyhemoglobin and deoxyhemoglobin in brain tissue. This article reviews the measured values of such optical properties and hemoglobin concentrations reported in the literature for animal models and for the human brain in newborns, infants, children, and adults. We also review the application of FD-NIRS to functional brain studies that focused on slower hemodynamic responses to brain activity (time scale of seconds) and faster optical signals that have been linked to neuronal activation (time scale of 100 ms). Another example of the power of FD-NIRS data is related to the different regions of sensitivity featured by intensity and phase data. We report recent developments that take advantage of this feature to maximize the sensitivity of non-invasive optical signals to brain tissue relative to more superficial extracerebral tissue (scalp, skull, etc.). We contend that this latter capability is a highly appealing quality of FD-NIRS, which complements absolute optical measurements and may result in significant advances in the field of non-invasive optical sensing of the brain.

The response of a standardized fluid challenge during cardiac surgery on cerebral oxygen saturation measured with near-infrared spectroscopy

Near infrared spectroscopy (NIRS) has been used to evaluate regional cerebral tissue oxygen saturation (ScO₂) during the last decades. Perioperative management algorithms advocate to maintain ScO₂, by maintaining or increasing cardiac output (CO), e.g. with fluid infusion. We hypothesized that ScO₂ would increase in responders to a standardized fluid challenge (FC) and that the relative changes in CO and ScO₂ would correlate. This study is a retrospective substudy of the FLuid Responsiveness Prediction Using Extra Systoles (FLEX) trial. In the FLEX trial, patients were administered two standardized FCs (5 mL/kg ideal body weight each) during cardiac surgery. NIRS monitoring was used during the intraoperative period and CO was monitored continuously. Patients were considered responders if stroke volume increased more than 10% following FC. Datasets from 29 non-responders and 27 responders to FC were available for analysis. Relative changes of ScO₂ did not change significantly in non-responders (mean difference - 0.3% ± 2.3%, p = 0.534) or in fluid responders (mean difference 1.6% ± 4.6%, p = 0.088). Relative changes in CO and ScO₂ correlated significantly, p = 0.027. Increasing CO by fluid did not change cerebral oxygenation. Despite this, relative changes in CO correlated to relative changes in ScO₂. However, the clinical impact of the present observations is unclear, and the results must be interpreted with caution.Trial registration:http://ClinicalTrial.gov identifier for main study (FLuid Responsiveness Prediction Using Extra Systoles-FLEX): NCT03002129.

Assessment of the brain ischemia during orthostatic stress and lower body negative pressure in air force pilots by near-infrared spectroscopy

A methodology for the assessment of the cerebral hemodynamic reaction to normotensive hypovolemia, reduction in cerebral perfusion and orthostatic stress leading to ischemic hypoxia and reduced muscular tension is presented. Most frequently, the pilots of highly maneuverable aircraft are exposed to these phenomena. Studies were carried out using the system consisting of a chamber that generates low pressure around the lower part of the body - LBNP (lower body negative pressure) placed on the tilt table. An in-house developed 6-channel NIRS system operating at 735 and 850 nm was used in order to assess the oxygenation of the cerebral cortex, based on measurements of diffusely reflected light in reflectance geometry. The measurements were carried out on a group of 12 active pilots and cadets of the Polish Air Force Academy and 12 healthy volunteers. The dynamics of changes in cerebral oxygenation was evaluated as a response to LBNP stimuli with a simultaneous rapid change of the tilt table angle. Parameters based on calculated changes of total hemoglobin concentration were proposed allowing to evaluate differences in reactions observed in control subjects and pilots/cadets. The results of orthogonal partial least squares-discriminant analysis based on these parameters show that the subjects can be classified into their groups with 100% accuracy.

Dual-slope method for enhanced depth sensitivity in diffuse optical spectroscopy

Using diffusion theory, we show that a dual-slope method is more effective than single-slope methods or single-distance methods at enhancing sensitivity to deeper tissue. The dual-slope method requires a minimum of two sources and two detectors arranged in specially configured arrays. In particular, we present diffusion theory results for a symmetrical linear array of two sources (separated by 55 mm) that sandwich two detectors (separated by 15 mm), for which dual slopes achieve maximal sensitivity at a depth of about 5 mm for direct current (DC) intensity (as measured in continuous-wave spectroscopy) and 11 mm for phase (as measured in frequency-domain spectroscopy) under typical values of the tissue optical properties (absorption coefficient: ∼0.01mm^-1, reduced scattering coefficient: ∼1mm^-1). This result is a major advance over single-distance or single-slope data, which feature maximal sensitivity to shallow tissue (<2mm for the intensity, <5mm for the phase).

Multi-distance frequency-domain optical measurements of coherent cerebral hemodynamics

We report non-invasive, bilateral optical measurements on the forehead of five healthy human subjects, of 0.1 Hz oscillatory hemodynamics elicited either by cyclic inflation of pneumatic thigh cuffs, or by paced breathing. Optical intensity and the phase of photon-density waves were collected with frequency-domain near-infrared spectroscopy at seven source-detector distances (11-40 mm). Coherent hemodynamic oscillations are represented by phasors of oxyhemoglobin (O) and deoxyhemoglobin (D) concentrations, and by the vector D/O that represents the amplitude ratio and phase difference of D and O. We found that, on average, the amplitude ratio (|D/O|) and the phase difference (∠(D/O)) obtained with single-distance intensity at 11-40 mm increase from 0.1 and -330°, to 0.2 and -200°, respectively. Single-distance phase and the intensity slope featured a weaker dependence on source-detector separation, and yielded |D/O| and ∠(D/O) values of about 0.5 and -200°, respectively, at distances greater than 20 mm. The key findings are: (1) single-distance phase and intensity slope are sensitive to deeper tissue compared to single-distance intensity; (2) deeper tissue hemodynamic oscillations, which more closely represent the brain, feature D and O phasors that are consistent with a greater relative flow-to-volume contributions in brain tissue compared to extracerebral, superficial tissue.

Low vs high hemoglobin trigger for transfusion in vascular surgery: a randomized clinical feasibility trial

Current guidelines advocate to limit red blood cell (RBC) transfusion during surgery, but the feasibility and safety of such a strategy remain unclear, as the majority of evidence is based on postoperatively stable patients. We assessed the effects of a protocol aiming to restrict RBC transfusion throughout hospitalization for vascular surgery. Fifty-eight patients scheduled for lower limb bypass or open abdominal aortic aneurysm repair were randomly assigned, on hemoglobin drop below 9.7 g/dL, to either a low-trigger (hemoglobin &lt; 8.0 g/dL) or a high-trigger (hemoglobin &lt; 9.7 g/dL) group for RBC transfusion. Near-infrared spectroscopy assessed intraoperative oxygen desaturation in brain and muscle. Explorative outcomes included nationwide registry data on death and major vascular complications. The primary outcome, mean hemoglobin within 15 days of surgery, was significantly lower in the low-trigger group, at 9.46 vs 10.33 g/dL in the high-trigger group (mean difference, −0.87 g/dL; P = .022), as were units of RBCs transfused (median [interquartile range (IQR)], 1 [0-2] vs 3 [2-6]; P = .0015). Although the duration and magnitude of cerebral oxygen desaturation increased in the low-trigger group (median [IQR], 421 [42-888] vs 127 [11-331] minutes × %; P = .0036), muscle oxygenation was unaffected. The low-trigger group associated to a higher rate of death or major vascular complications (19/29 vs 8/29; hazard ratio, 3.20; P = .006) and fewer days alive outside the hospital within 90 days (median [IQR], 76 [67-82] vs 82 [76-84] days; P = .049). In conclusion, a perioperative protocol restricting RBC transfusion successfully separated hemoglobin levels and RBC units transfused. Exploratory outcomes suggested potential harm with the low-trigger group and warrant further trials before such a strategy is universally adopted. This trial was registered at www.clinicaltrials.gov as #NCT02465125.

Endovascular aortic repair reduces gluteal oxygenation

Background

Provoked gluteal claudication is a known risk after endovascular aortic repair (EVAR). Lowered gluteal muscle oxygenation (S_gmO₂) may be demonstrated by near-infrared spectroscopy (NIRS).

Purpose

To evaluate NIRS-determined S_gmO₂ in EVAR patients.

Material and Methods

NIRS-determined S_gmO₂ was used in an observational study design (n = 17). From the ambulatory setting, seven EVAR patients were included with reported gluteal claudication from medical records. In 10 patients scheduled for EVAR, S_gmO₂ was measured before and after the procedure. NIRS sensors were applied bilaterally on the gluteal region. Treadmill walking (12% incline, 2.4 km/h) was introduced to stress gluteal muscles.

Results

A reduced S_gmO₂ with regional side difference (P < 0.05) was noted in all 10 patients following EVAR and four reported gluteal claudication. In patients with gluteal claudication (n = 7), treadmill decreased S_gmO₂. The time to recover the S_gmO₂ was prolonged for tissue exposed to occluded hypogastric artery (median = 512 s, range = 73–1207 s vs. median = 137, range = 0–643 s; P = 0.046).

Conclusions

EVAR affects gluteal muscle oxygenation. NIRS could be used to assess whether gluteal claudication is related to lowered S_gmO₂.

Optical Assessment of Spinal Cord Tissue Oxygenation Using a Miniaturized Near Infrared Spectroscopy Sensor

Despite advances in the treatment of acute spinal cord injury (SCI), measures to mitigate permanent neurological deficits in affected patients are limited. Immediate post-trauma hemodynamic management of patients, to maintain blood supply and improve oxygenation to the injured spinal cord, is currently one aspect of critical care which clinicians can utilize to improve neurological outcomes. However, without a way to monitor the response of spinal cord hemodynamics and oxygenation in real time, optimizing hemodynamic management is challenging and limited in scope. This study aims to investigate the feasibility and validity of using a miniaturized multi-wavelength near-infrared spectroscopy (NIRS) sensor for direct transdural monitoring of spinal cord oxygenation in an animal model of acute SCI. Nine Yorkshire pigs underwent a weight-drop T10 contusion-compression injury and received episodes of ventilatory hypoxia and alterations in mean arterial pressure (MAP). Spinal cord hemodynamics and oxygenation were monitored throughout by a non-invasive transdural NIRS sensor, as well as an invasive intraparenchymal sensor as a comparison. NIRS parameters of tissue oxygenation were highly correlated with intraparenchymal measures of tissue oxygenation. In particular, during periods of hypoxia and MAP alterations, changes of NIRS-derived spinal cord oxygenated hemoglobin and tissue oxygenation percentage corresponded well with the changes in spinal cord oxygen partial pressures measured by the intraparenchymal sensor. Our data confirm that during hypoxic episodes and as changes occur in the MAP, non-invasive NIRS can detect and measure real-time changes in spinal cord oxygenation with a high degree of sensitivity and specificity.

Monitoring spinal cord hemodynamics and tissue oxygenation: a review of the literature with special focus on the near-infrared spectroscopy technique

STUDY DESIGN

Review.

OBJECTIVES

Clinical studies have shown that the hemodynamic management of patients following acute spinal cord injury (SCI) is an important aspect of their treatment for maintaining spinal cord (SC) perfusion and minimizing ischemic secondary injury to the SC. While this highlights the importance of ensuring adequate perfusion and oxygenation to the injured cord, a method for the real-time monitoring of these hemodynamic measures within the SC is lacking. The purpose of this review is to discuss current and potential methods for SC hemodynamic monitoring with special focus on applications using near-infrared spectroscopy (NIRS).

METHODS

A literature search using the PubMed database. All peer-reviewed articles on NIRS monitoring of SC published from inception to May 2019 were reviewed.

RESULTS

Among 125 papers related to SC hemodynamics monitoring, 26 focused on direct/indirect NIRS monitoring of the SC.

DISCUSSION

Current options for continuous, non-invasive, and real-time monitoring of SC hemodynamics are challenging and limited in scope. As a relatively new technique, NIRS has been successfully used for monitoring human cerebral hemodynamics, and has shown promising results in intraoperative assessment of SC hemodynamics in both human and animal models. Although utilizing NIRS to monitor the SC has been validated, applying NIRS clinically following SCI requires further development and investigation.

CONCLUSIONS

NIRS is a promising non-invasive technique with the potential to provide real-time monitoring of relevant parameters in the SC. Currently, in its first developmental stages, further clinical and experimental studies are mandatory to ensure the validity and safety of NIRS techniques.

Clinical Brain Monitoring with Time Domain NIRS: A Review and Future Perspectives

Near-infrared spectroscopy (NIRS) is an optical technique that can measure brain tissue oxygenation and haemodynamics in real-time and at the patient bedside allowing medical doctors to access important physiological information. However, despite this, the use of NIRS in a clinical environment is hindered due to limitations, such as poor reproducibility, lack of depth sensitivity and poor brain-specificity. Time domain NIRS (or TD-NIRS) can resolve these issues and offer detailed information of the optical properties of the tissue, allowing better physiological information to be retrieved. This is achieved at the cost of increased instrument complexity, operation complexity and price. In this review, we focus on brain monitoring clinical applications of TD-NIRS. A total of 52 publications were identified, spanning the fields of neonatal imaging, stroke assessment, traumatic brain injury (TBI) assessment, brain death assessment, psychiatry, peroperative care, neuronal disorders assessment and communication with patient with locked-in syndrome. In all the publications, the advantages of the TD-NIRS measurement to (1) extract absolute values of haemoglobin concentration and tissue oxygen saturation, (2) assess the reduced scattering coefficient, and (3) separate between extra-cerebral and cerebral tissues, are highlighted; and emphasize the utility of TD-NIRS in a clinical context. In the last sections of this review, we explore the recent developments of TD-NIRS, in terms of instrumentation and methodologies that might impact and broaden its use in the hospital.

The Efficacy of Near-Infrared Spectroscopy Monitoring in Carotid Endarterectomy: A Prospective, Single-Center, Observational Study

There has been no gold standard for intraoperative monitoring in carotid endarterectomy (CEA) till now. The purpose of the current study was to investigate the value of near-infrared spectroscopy (NIRS) monitoring in CEA and explore the thresholds for intraoperative cerebral hypoperfusion. Eighty-four consecutive patients who underwent CEA surgery in Xuan Wu Hospital of Capital Medical University from August 2015 to June 2016 were enrolled in this study. All patients were intraoperatively monitored by transcranial Doppler ultrasonography (TCD) and NIRS. Regional oxygen saturation (rSO2) monitored by NIRS and blood flow velocity of the middle cerebral artery (V-MCA) monitored by TCD were continuously recorded. Correlation analysis was conducted for NIRS and TCD monitoring values. Intraoperative shunting was performed in five patients according to the TCD monitoring results and surgeon preference. During clamping of the carotid artery, the Pearson correlation index between rSO2 and V-MCA was 0.581 (P<0.001). A cut-off of 12.3% decrease of rSO2 was identified as the optimal threshold for intraoperative hypoperfusion indicated by TCD monitoring, when the sensitivity and specificity were 74.6% and 91.7%, respectively, with a 0.609 Kappa value. Physical examination immediately after operation showed no ischemic injury occurred, and no death and stroke occurred during the postoperative hospitalization. Our study demonstrated that NIRS could serve as a favorable monitoring tool during CEA. A 12.3% decrease of rSO2 could be adopted as a reliable threshold for intraoperative cerebral hypoperfusion.

Relationship Between Near-Infrared Spectroscopy-Derived Cerebral Oxygenation and Delirium in Critically Ill Patients: A Systematic Review

BACKGROUND

A common neurological complication of critical illness is delirium, defined as an acute change in level of consciousness, with impaired attention and disorganized thinking. Patients with delirium have increased risk of long-term cognitive dysfunction and mortality. The cause is unknown, which limits our ability to design therapeutic interventions. In patients undergoing surgery, low regional cerebral oxygenation (rSO2), as measured by near-infrared spectroscopy (NIRS), is associated with postoperative neurological dysfunction (eg delirium and long-term cognitive impairment). However, the relationship between NIRS-derived rSO2 and neurological outcomes in critically ill patients is unclear. The objective of this study was to assess the utilization of NIRS-derived rSO2 in critically ill patients outside the operating theater. We aimed to examine the relationship between rSO2 and neurological outcomes as well as to report rSO2 values in this population.

METHODS

The following databases were searched from inception to August 14, 2017: Ovid MedLine, Embase, Cochrane Library, and Web of Science.

RESULTS

Of 1410 articles identified by the search strategy, 8 were ultimately selected for final review. Most (7 of 8) were published since 2014. These studies included a total of 213 patients primarily with shock or respiratory failure. A variety of devices were used to measure rSO2, including INVOS and FORESIGHT. The duration of recording varied from 5 minutes to 72 hours. Four of the 8 studies reported on neurological outcomes. In all 4 studies, rSO2 was lower in critically ill patients who were delirious compared to controls, but this was only statistically significant in 2 of the studies. The heterogeneity in devices and duration of recording precluded meta-analysis.

CONCLUSIONS

There is limited literature describing rSO2 in critically ill patients outside the operating room. Although there may be a slight signal of an association between low rSO2 and delirium, more study is needed to explore this relationship.