Peripheral tissue oximetry: comparing three commercial near-infrared spectroscopy oximeters on the forearm

Norepinephrine versus phenylephrine on cerebral tissue oxygen saturation during prophylactic infusion to prevent spinal hypotension for Caesarean birth

BACKGROUND

Phenylephrine may cause a reduction in maternal cerebral tissue oxygen saturation (SctO2) during Caesarean birth to prevent spinal hypotension; however, the effect of norepinephrine has not been assessed. We hypothesized that norepinephrine was more effective than phenylephrine in maintaining SctO2 when preventing spinal hypotension during Caesarean birth.

METHODS

We conducted a randomized, double-blind, controlled study. Sixty patients were randomly assigned to prophylactic norepinephrine or phenylephrine to maintain blood pressure during spinal anesthesia for Caesarean birth. SctO2, systolic blood pressure, and heart rate were recorded. The primary outcome was the incidence of a 10% reduction of intraoperative SctO2 from baseline or more during Caesarean birth.

RESULTS

The norepinephrine group had a lower incidence of more than 10% reduction of intraoperative SctO2 from baseline than that of the phenylephrine group (13.3% vs 40.0%, P = .02). The change in SctO2 after 5 minutes of norepinephrine infusion was higher than that after phenylephrine infusion (-3.4 ± 4.7 vs -6.2 ± 5.6, P = .04). The change in SctO2 after 10 minutes of norepinephrine infusion was higher than that after phenylephrine infusion (-2.5 ± 4.4 vs -5.4 ± 4.6, P = .006). The norepinephrine group showed greater left- and right-SctO2 values than the phenylephrine group at 5 to 10 minutes. However, the change in systolic blood pressure was comparable between the 2 groups.

CONCLUSION

Norepinephrine was more effective than phenylephrine in maintaining SctO2 when preventing spinal hypotension during Caesarean birth. However, the changes in clinical outcomes caused by differences in SctO2 between the 2 medications warrant further studies.

Tissue Oximetry Changes during Postoperative Dangling in Lower Extremity Free Flap Reconstruction: A Pilot Study

Background: Lower extremity free flap dangling protocols are still widely practiced, despite a paucity of evidence for their use. This pilot study investigates the use of tissue oximetry to provide further insight into the physiological effect of postoperative dangling in lower limb free flap transfer. Methods: Ten patients undergoing lower extremity free flap reconstruction were included in this study. Free flap tissue oxygen saturation (StO₂) was continuously measured using non-invasive near-infrared spectroscopy. Measurements were performed on the free flap and contralateral limb during dangling from postoperative day (POD) 7 until 11, according to the local dangling protocol. Results: StO₂ values measured in the free flap diminished to 70 ± 13.7% during dangling. This minimum StO₂ was reached significantly later, and correspondingly the area under the curve (AUC) was significantly larger on POD 11 compared to the start of the dangling protocol on POD 7, reflecting an improving free flap microvascular reactivity. The dangling slope was equal between the free flap and contralateral leg. The reperfusion slope was significantly flatter on POD 7 compared to the other PODs (p < 0.001). Thereafter, no significant differences between PODs were observed. Patients with a history of smoking had significantly lower tissue oximetry values compared to non-smokers. Conclusions: The application of tissue oximetry during dangling provides further insight into the physiological effect (i.e., changes in microcirculatory function) of the free flap of the reconstructed lower extremity. This information could potentially be useful to either revise or disrupt the use of such dangling protocols.

Perioperative Hyperspectral Imaging to Assess Mastectomy Skin Flap and DIEP Flap Perfusion in Immediate Autologous Breast Reconstruction: A Pilot Study

Mastectomy skin flap necrosis (MSFN) and partial DIEP (deep inferior epigastric artery perforator) flap loss represent two frequently reported complications in immediate autologous breast reconstruction. These complications could be prevented when areas of insufficient tissue perfusion are detected intraoperatively. Hyperspectral imaging (HSI) is a relatively novel, non-invasive imaging technique, which could be used to objectively assess tissue perfusion through analysis of tissue oxygenation patterns (StO₂%), near-infrared (NIR%), tissue hemoglobin (THI%), and tissue water (TWI%) perfusion indices. This prospective clinical pilot study aimed to evaluate the efficacy of HSI for tissue perfusion assessment and to identify a cut-off value for flap necrosis. Ten patients with a mean age of 55.4 years underwent immediate unilateral autologous breast reconstruction. Prior, during and up to 72 h after surgery, a total of 19 hyperspectral images per patient were acquired. MSFN was observed in 3 out of 10 patients. No DIEP flap necrosis was observed. In all MSFN cases, an increased THI% and decreased StO₂%, NIR%, and TWI% were observed when compared to the vital group. StO₂% was found to be the most sensitive parameter to detect MSFN with a statistically significant lower mean StO₂% (51% in the vital group versus 32% in the necrosis group, p < 0.0001) and a cut-off value of 36.29% for flap necrosis. HSI has the potential to accurately assess mastectomy skin flap perfusion and discriminate between vital and necrotic skin flap during the early postoperative period prior to clinical observation. Although the results should be confirmed in future studies, including DIEP flap necrosis specifically, these findings suggest that HSI can aid clinicians in postoperative mastectomy skin flap and DIEP flap monitoring.

Near-Infrared Spectroscopy (NIRS) versus Hyperspectral Imaging (HSI) to Detect Flap Failure in Reconstructive Surgery: A Systematic Review

Rapid identification of possible vascular compromise in free flap reconstruction to minimize time to reoperation improves achieving free flap salvage. Subjective clinical assessment, often complemented with handheld Doppler, is the golden standard for flap monitoring; but this lacks consistency and may be variable. Non-invasive optical methods such as near-infrared spectroscopy (NIRS) and hyperspectral imaging (HSI) could facilitate objective flap monitoring. A systematic review was conducted to compare NIRS with HSI in detecting vascular compromise in reconstructive flap surgery as compared to standard monitoring. A literature search was performed using PubMed and Embase scientific database in August 2021. Studies were selected by two independent reviewers. Sixteen NIRS and five HSI studies were included. In total, 3662 flap procedures were carried out in 1970 patients using NIRS. Simultaneously; 90 flaps were performed in 90 patients using HSI. HSI and NIRS flap survival were 92.5% (95% CI: 83.3–96.8) and 99.2% (95% CI: 97.8–99.7). Statistically significant differences were observed in flap survival (p = 0.02); flaps returned to OR (p = 0.04); salvage rate (p < 0.01) and partial flap loss rate (p < 0.01). However, no statistically significant difference was observed concerning flaps with vascular crisis (p = 0.39). NIRS and HSI have proven to be reliable; accurate and user-friendly monitoring methods. However, based on the currently available literature, no firm conclusions can be drawn concerning non-invasive monitoring technique superiority

Measurement of Tissue Oximetry in Standing Unsedated and Sedated Horses

Near infrared spectroscopy (NIRS) noninvasively measures peripheral tissue oxygen saturation (StO₂) and may be useful to detect early changes in StO₂ in anaesthetized and critically ill horses. This study aimed to identify the muscle belly that provided the highest percentage of successful StO₂ readings and the highest mean StO₂ value. Fifty adult horses were enrolled in a prospective controlled study. StO₂ was measured at six different muscles in each horse, for each intervention: hair overlying the muscle was clipped (post clipping: PC), clipped skin was cleaned with chlorhexidine (post-surgical prepping: PP) and medetomidine was administered intravenously (post medetomidine: PM). Mean StO₂ values were calculated for each muscle, and a linear effects model was used to assess the effect of muscle group and intervention on StO₂. The sartorius muscle gave the highest percentage of successful StO₂ values (p < 0.001) and the highest mean (90% CI) StO₂ values for the PC, PP and PM interventions. Surgical prepping of the skin increased the success for measurement of StO₂ values. For all muscles, administration of medetomidine was associated with lower StO₂ values (p < 0.001). In conclusion, of the muscles examined, the sartorius muscle may be the preferred muscle to measure StO₂ in horses, and clipping and cleaning of the probe placement site is recommended.

Exploring personalized postoperative non-invasive tissue oximetry in DIEP flap breast reconstruction

Abstract

Early detection of vascular compromise after autologous breast reconstruction is crucial to enable timely re-exploration for flap salvage. Several studies proposed non-invasive tissue oximetry for early identification of ischemia of deep inferior epigastric perforator (DIEP) flaps. The present study aimed to explore the utility of non-invasive tissue oximetry following DIEP flap surgery using a personalized oxygenation threshold.

Methods

Patients undergoing immediate/delayed DIEP flap surgery were included in this prospective observational study. DIEP flap tissue oxygenation (StO2) was monitored continuously using near-infrared spectroscopy. A baseline measurement was performed by positioning one sensor at the marked position of the major inferior epigastric perforator on the abdomen. A new sensor was positioned postoperatively on the transplanted tissue. In unilateral procedures, postoperative StO2 values of the native breast were also obtained. Measurements were continued for 24 h.

Results

Thirty patients (42 flaps) were included. Fourteen patients (46.7%) had an uncomplicated postoperative course. A minor complication was observed in thirteen patients; in five patients, at least one major complication occurred, requiring re-exploration. Median StO2 readings were significantly lower in patients with major complications compared to uncomplicated cases. In fourteen unilateral DIEP flap procedures, StO2 values of the native breast were similar to the preoperative baseline measurement (92%; p = 0.452).

Conclusions

Non-invasive tissue oximetry following DIEP flap surgery could aid in early detection of vascular compromise. StO2 values of the native breast and abdominal wall preoperatively can be used interchangeably and can serve as personalized reference value.

Level of evidence: Level IV, diagnostic / prognostic study.

Selective internal carotid artery cross-clamping increases the specificity of cerebral oximetry for indication of shunting during carotid endarterectomy

BACKGROUND

An indication for selective shunting during carotid endarterectomy (CEA) is based on monitoring during a procedure. Cerebral oximetry (CO) using near-infrared spectroscopy (NIRS) may be a simple technique, but its relevance during CEA, especially with respect to cutoff values indicating shunt implantation, still needs to be elucidated.

METHODS

One hundred twenty five patients underwent CEA under local anesthesia (LA) and were monitored clinically throughout the whole procedure. The patients were also monitored using bilateral NIRS probes during surgery. The NIRS values were recorded and evaluated before and after selective cross-clamping, firstly by the external carotid artery (ECA), followed by the internal carotid artery (ICA). The decrease in the ipsilateral CO values, with respect to the indication of shunting, was only analyzed after selective cross-clamping of the ICA. The decision to use an intraluminal shunt was solely based on the neurological status evaluation after ICA cross-clamping.

RESULTS

One hundred five patients (85%) were stable throughout the CEA, while 20 patients (15%) clinically deteriorated during surgery. The mean drop in the CO after selective ICA clamping in clinically stable patients was 6%, while in patients with clinical deterioration, the NIRS decreased by 14.5% (p < 0.05). When the cutoff value for selective shunting was set as a 10% decrease of the ipsilateral CO after selective ICA clamping, the sensitivity of the technique was 100% and the specificity 83.0%.

CONCLUSIONS

Our study showed that a 10% decrease in the ipsilateral brain tissue oximetry after selective cross-clamping the ICA provides a reliable cutoff value for selective shunting during CEA. Despite the availability of a variety of monitoring tools, the NIRS may be an easy, reliable option, especially in the scenario of acute CEA in general anesthesia.

Improved Exercise Tolerance, Oxygen Delivery, and Oxygen Utilization After Transcatheter Aortic Valve Implantation for Severe Aortic Stenosis

Background

Transcatheter aortic valve implantation (TAVI) represents an effective therapeutic procedure, particularly in patients with severe aortic stenosis. We hypothesized that the decreased afterload induced by TAVI would improve exercise capacity by enhancing oxygen uptake in working muscles.

Methods

A standardized exercise test was performed in patients with severe aortic stenosis the day before TAVI and within 5 days thereafter. The main study endpoint was the workload achieved during a 5-minute standardized exercise test. Using electrical cardiometry and near-infrared spectroscopy, we explored and compared the changes in cardiac index (CI), as well as muscular and cerebral tissue oximetry, during the 2 exercise tests.

Results

Thirty patients completed the study protocol. Compared with the pre-TAVI period, patients achieved a higher median workload after TAVI (316 Joules [interquartile range {IQR}: 169–494] vs 190 Joules [IQR: 131–301], P = 0.002). Baseline CI increased from 2.5 l/min per m² (IQR: 2.1–2.9) to 2.9 l/min per m² (IQR: 2.5–3.2; P = 0.009), whereas CI at the end of the exercise test increased from 4.5 l/min per m² (IQR: 3.4–5.3) to 4.7 l/min per m² (3.4–6.4; P = 0.019). At the end of the exercise test, cerebral tissue oximetry increased from 70% (IQR: 65–72) to 74% (IQR: 66–78), and muscle tissue oximetry increased from 62% (IQR: 58–65) to 71% (65–74; P = 0.046 and P < 0.001, respectively).

Conclusions

Early improvement of exercise capacity after TAVI is associated with increased CI and better oxygen utilization in the brain and skeletal muscles.

Mitochondrial oxygen monitoring with COMET: verification of calibration in man and comparison with vascular occlusion tests in healthy volunteers

Mitochondria are the primary consumers of oxygen and therefore an important location for oxygen availability and consumption measurement. A technique has been developed for mitochondrial oxygen tension (mitoPO₂) measurement, incorporated in the COMET. In contrast to most textbooks, relatively high average mitoPO₂ values have been reported. The first aim of this study was to verify the validity of the COMET calibration for mitoPO₂ measurements in human skin. The second aim was to compare the dynamics of mitoPO₂ to several other techniques assessing tissue oxygenation. Firstly, we performed a two-point calibration. Mitochondrial oxygen depletion was achieved with vascular occlusion. A high mitoPO₂ was reached by local application of cyanide. MitoPO₂ was compared to the arterial oxygen partial pressure (PaO₂). Secondly, for deoxygenation kinetics we compared COMET variables with the LEA O2C, SenTec OxiVenT™ and Medtronic INVOS™ parameters during a vascular occlusion test. 20 healthy volunteers were recruited and resulted in 18 datasets (2 times 9 subjects). The lowest measured mitoPO₂ value per subject had a median [IQR] of 3.0 [1.0–4.0] mmHg, n = 9. After cyanide application the mitoPO₂ was 94.1 mmHg [87.2–110.9] and did not differ significantly (n = 9, p = 0.5) from the PaO₂ of 101.0 [98.0–106.0] mmHg. In contrast to O2C, OxiVenT™ and INVOS parameters, mitoPO₂ declined within seconds with pressure on the probe. The kinetics from this decline are used to mitochondrial oxygen consumption (mitoVO₂). This study validates the calibration of the COMET device in humans. For mitoVO₂ measurements not only blood flow cessation but application of local pressure is of great importance to clear the measurement site of oxygen-carrying erythrocytes.

Comparison of INVOS 5100C and Nonin SenSmart X-100 oximeter performance in preterm infants with spontaneous apnea

BACKGROUND

Tissue oximeters are not interchangeable. Two instruments with sensors dedicated to preterm infants-INVOS 5100C and Nonin SenSmart X-100-have not yet been compared.

METHODS

By measuring cerebral oxygenation in ten preterm infants with spontaneous apneic episodes defined by pulse oximeter readings (SpO₂) below 80%, as well as tissue oxygenation during vascular occlusion on the forearm of ten adults, simultaneously we compared performance in the hypoxic range.

RESULTS

We found the mean conversion equations to be StO_{2,SenSmart X-100} = 0.34 × StO_{2,INVOS 5100C} + 44.8% during apnea in infants and StO_{2,SenSmart X-100} = 0.59 × StO_{2,INVOS 5100C} + 34.4% during vascular occlusion. The individual regressions displayed large and statistically significant variations in both infants and adults. In three infants the INVOS sensor showed very little reaction to decreases in SpO₂.

CONCLUSIONS

These findings confirm that different NIRS devices give very different estimates when the oxygenation is low. The large variation when compared to SpO₂ suggest that the sensor placement is very important in preterm infants.

The vascular occlusion test using multispectral imaging: a validation study : The VASOIMAGE study

Multispectral imaging (MSI) is a new, non-invasive method to continuously measure oxygenation and microcirculatory perfusion, but has limitedly been validated in healthy volunteers. The present study aimed to validate the potential of multispectral imaging in the detection of microcirculatory perfusion disturbances during a vascular occlusion test (VOT). Two consecutive VOT's were performed on healthy volunteers and tissue oxygenation was measured with MSI and near-infrared spectroscopy (NIRS). Correlations between the rate of desaturation, recovery and the hyperemic area under the curve (AUC) measured by MSI and NIRS were calculated. Fifty-eight volunteers were included. The MSI oxygenation curves showed identifiable components of the VOT, including a desaturation and recovery slope and hyperemic area under the curve, similar to those measured with NIRS. The correlation between the rate of desaturation measured by MSI and NIRS was moderate: r = 0.42 (p = 0.001) for the first and r = 0.41 (p = 0.002) for the second test. Our results suggest that non-contact multispectral imaging is able to measure changes in regional oxygenation and deoxygenation during a vascular occlusion test in healthy volunteers. When compared to measurements with NIRS, correlation of results was moderate to weak, most likely reflecting differences in physiology of the regions of interest and measurement technique.

Near-Infrared Spectroscopy in Extremely Preterm Infants

With advances in neonatal care, survival of premature infants at the limits of viability has improved significantly. Despite these improvement in mortality, infants born at 22-24 weeks gestation are at a very high risk for short- and long-term morbidities associated with prematurity. Many of these diseases have been attributed to abnormalities of tissue oxygenation and perfusion. Near-infrared spectroscopy utilizes the unique absorption properties of oxyhemoglobin and deoxyhemoglobin to provide an assessment of regional tissue oxygen saturation, which can be used to calculate the fractional tissue oxygen extraction. This allows for a non-invasive way to monitor tissue oxygen consumption and enables targeted hemodynamic management. This mini-review provides a brief and complete overview of the background and physiology of near-infrared spectroscopy, practical use in extremely preterm infants, and potential applications in the neonatal intensive care unit. In this mini-review, we aim to summarize the three primary application sites for near-infrared spectroscopy, disease-specific indications, and available literature regarding use in extremely preterm infants.

Use of Near-infrared Spectroscopy and Implantable Doppler for Postoperative Monitoring of Free Tissue Transfer for Breast Reconstruction: A Systematic Review and Meta-analysis

BACKGROUND

Failure to accurately assess the perfusion of free tissue transfer (FTT) in the early postoperative period may contribute to failure, which is a source of major patient morbidity and healthcare costs. This systematic review and meta-analysis aim to evaluate and appraise current evidence for the use of near-infrared spectroscopy (NIRS) and/or implantable Doppler (ID) devices compared with conventional clinical assessment (CCA) for postoperative monitoring of FTT in reconstructive breast surgery.

METHODS

A systematic literature search was performed in accordance with the preferred reporting items for systematic reviews guidelines. Studies in human subjects published within the last decade relevant to the review question were identified. Meta-analysis using random-effects models of FTT failure rate and STARD scoring was then performed on the retrieved publications.

RESULTS

Nineteen studies met the inclusions criteria. For NIRS and ID, the mean sensitivity for the detection of FTT failure is 99.36% and 100% respectively, with average specificity of 99.36% and 97.63%, respectively. From studies with sufficient reported data, meta-analysis results demonstrated that both NIRS [OR = 0.09 (0.02-0.36); P < 0.001] and ID [OR = 0.39 (0.27-0.95); P = 0.04] were associated with significant reduction of FTT failure rates compared with CCA.

CONCLUSIONS

The use of ID and NIRS provided equivalent outcomes in detecting FTT failure and were superior to CCA. The ability to acquire continuous objective physiological data regarding tissue perfusion is a perceived advantage of these techniques. Reduced clinical staff workload and minimized hospital costs are also perceived as positive consequences of their use.

Measurement of peripheral muscle oxygen saturation in conscious healthy horses using a near-infrared spectroscopy device

OBJECTIVE

Maintaining adequate muscle tissue oxygenation is of paramount importance during equine general anesthesia. The objectives of this study were to assess the feasibility, reliability and repeatability of near-infrared spectroscopy (NIRS) muscle oximetry using the Inspectra m650 in conscious healthy adult horses.

STUDY DESIGN

Prospective, observational study.

ANIMALS

A group of 30 healthy client-owned adult horses admitted to the equine hospital between July 2017 and July 2018.

METHODS

The probe of an Inspectra m650 NIRS tissue oximeter was placed on the hairless surface of five muscle sites (omotransversarius, triceps long head, extensor carpi ulnaris, vastus lateralis and lateral digital extensor) on the left side of the body of each standing, unsedated horse. Each site had muscle oxygenation (StO₂) recordings measured in triplicate and statistical modeling used to assess the reading reliability and repeatability within and between muscle sites.

RESULTS

The readings acquired at the vastus lateralis and extensor carpi ulnaris muscle sites had highly repeatable values [mean (90% confidence interval): StO₂, 95% (93.8%, 96.5%) and 93% (91.6%, 93.9%), respectively; intraclass correlation coefficients, 0.92 and 0.80, respectively]. These two sites also had high reliability (represented by the percentage of successful readings; 70% and 86%, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

The use of NIRS muscle oxygenation technology is a clinically feasible means to assess tissue oxygenation in horses. The vastus lateralis and extensor carpi ulnaris muscle sites provided the most reliable and repeatable readings when using the Inspectra m650 machine in horses.

Cerebral oximetry performance testing with a 3D-printed vascular array phantom

Cerebral oximetry based on near-infrared spectroscopy represents a unique noninvasive tool for real-time surgical monitoring, yet studies have shown a significant discrepancy in accuracy among commercial systems. Towards the establishment of a standardized method for performance testing, we have studied a solid phantom approach - based on a 3D-printed cerebrovascular module (CVM) incorporating an array of 148 cylindrical channels - that has several advantages over liquid phantoms. Development and characterization of a CVM prototype are described, including high-resolution imaging and spectrophotometry measurements. The CVM was filled with whole bovine blood tuned over an oxygen saturation range of 30-90% and molded-silicone layers simulating extracerebral tissues were used to evaluate penetration depth. Saturation measurement accuracy was assessed in two commercially-available clinical cerebral oximeters. For one oximeter, both neonatal and pediatric sensors showed a high degree of precision, whereas accuracy was strongly dependent on saturation level and extracerebral geometry. The second oximeter showed worse precision, yet greater robustness to variations in extracerebral layers. These results indicate that 3D-printed channel array phantoms represent a promising new approach for standardized testing of clinical oximeters.

Algorithms for mapping kidney tissue oxygenation during normothermic machine perfusion using hyperspectral imaging

The lack of donor grafts is a severe problem in transplantation medicine. Hence, the improved preservation of existing and the usage of organs that were deemed untransplantable is as urgent as ever. The development of novel preservation techniques has come into focus. A promising alternative to traditional cold storage is normothermic machine perfusion (NMP), which provides the benefit of improving the organs' viability and of assessing the organs' status under physiological conditions. For this purpose, methods for evaluating organ parameters have yet to be developed. In a previous study, we determined the tissue oxygen saturation (StO2) of kidneys during NMP with hyperspectral imaging (HSI) based on a discrete wavelength (DW) algorithm. The aim of the current study was to identify a more accurate algorithm for StO2 calculation. A literature search revealed three candidates to test: a DW algorithm and two full spectral algorithms - area under a curve and partial least square regression (PLSR). After obtaining suitable calibration data to train each algorithm, they were evaluated during NMP. The wavelength range from 590 to 800 nm was found to be appropriate for analyzing StO2 of kidneys during NMP. The PLSR method shows good results in analyzing the tissues' oxygen status in perfusion experiments.

Wireless, battery-free optoelectronic systems as subdermal implants for local tissue oximetry

Monitoring regional tissue oxygenation in animal models and potentially in human subjects can yield insights into the underlying mechanisms of local O2-mediated physiological processes and provide diagnostic and therapeutic guidance for relevant disease states. Existing technologies for tissue oxygenation assessments involve some combination of disadvantages in requirements for physical tethers, anesthetics, and special apparatus, often with confounding effects on the natural behaviors of test subjects. This work introduces an entirely wireless and fully implantable platform incorporating (i) microscale optoelectronics for continuous sensing of local hemoglobin dynamics and (ii) advanced designs in continuous, wireless power delivery and data output for tether-free operation. These features support in vivo, highly localized tissue oximetry at sites of interest, including deep brain regions of mice, on untethered, awake animal models. The results create many opportunities for studying various O2-mediated processes in naturally behaving subjects, with implications in biomedical research and clinical practice.

In vivo validation of cerebral near-infrared spectroscopy: a review

We summarize the available in vivo validation of cerebral near-infrared spectroscopy (NIRS) oximetry to inform future in vivo validation strategies. In particular, to establish a way forward in the assessment of NIRS instrumentation for future randomized trials, a systematic literature search is performed. The records are screened and abstracts are assessed to select studies fulfilling our inclusion criteria. Twenty-two pediatric and 28 adult studies are analyzed after exclusion of three articles in each group. All studies compare regional cerebral tissue oxygenation measured by cerebral NIRS to invasive measurement of central or jugular venous oxygen saturation. In studies without Bland-Altman plots, we extracted data from scatter plots enabling estimation of mean difference (MD), standard deviation (SD), and limits of agreement (LOA). To assess the agreement between rStO 2 (regional cerebral tissue oxygenation) estimated by NIRS and by blood samples, weighted averages of the MDs and SDs from each study are calculated. We found a fair agreement between the overall mean of cerebral tissue oxygenation and the mean of a reference value measured by co-oximetry whatever NIRS instrument or site of blood sampling used. Cerebral oxygenation overestimates the reference at low values, some instruments apparently more than others. Thus, a high degree of scatter and a lack of a good reference method complicate in vivo validation of NIRS. It is difficult to draw any firm conclusions despite the large number of studies, and the result of this review leaves us questioning if more of such validation studies of cerebral NIRS oximetry are really needed. Furthermore, the combination of lack of validation and poor repeatability is an important issue when designing a randomized clinical trial of implementing cerebral NIRS oximetry into clinical care.

Cross-section and feasibility study on the non-invasive evaluation of muscle hemodynamic responses in Duchenne muscular dystrophy by using a near-infrared diffuse optical technique

Duchenne muscular dystrophy (DMD) is an X-linked debilitating muscular disease that may decrease nitric oxide (NO) production and lead to functional muscular ischemia. Currently, the 6-minute walk test (6-MWT) and the North Star Ambulatory Assessment (NSAA) are the primary outcome measures in clinical trials, but they are severely limited by the subjective consciousness and mood of patients, and can only be used in older and ambulatory boys. This study proposed using functional near-infrared spectroscopy (fNIRS) to evaluate the dynamic changes in muscle hemodynamic responses (gastrocnemius and forearm muscle) during a 6-MWT and a venous occlusion test (VOT), respectively. Muscle oxygenation of the forearm was evaluated non-invasively before, during and after VOT in all participants (included 30 DMD patients and 30 age-matched healthy controls), while dynamic muscle oxygenation of gastrocnemius muscle during 6-MWT was determined in ambulatory participants (n = 18) and healthy controls (n = 30). The results reveal that impaired muscle oxygenation was observed during 6-MWT in DMD patients that may explain why the DMD patients walked shorter distances than healthy controls. Moreover, the results of VOT implied that worsening muscle function was associated with a lower supply of muscle oxygenation and may provide useful information on the relationship between muscular oxygen consumption and supply for the clinical diagnosis of DMD. Therefore, the method of fNIRS with VOT possesses great potential in future evaluations of DMD patients that implies a good feasibility for clinical application such as for monitoring disease severity of DMD.

Muscular tissue oxygen saturation during robotic hysterectomy and postoperative nausea and vomiting: exploring the potential therapeutic thresholds

The relationship between muscular tissue oxygen saturation (SmtO₂) during surgery and postoperative nausea and vomiting (PONV) remains to be determined. Patients undergoing robotic hysterectomy participated in this prospective cohort study. SmtO₂ of the brachioradialis muscle in the forearm was continuously monitored during surgery. Thresholds based on relative changes or absolute values were systematically assigned. The relationship between thresholds and PONV was investigated based on threshold analysis (i.e., exceeding or not exceeding a threshold), area under the curve analysis (i.e., the size of the area enclosed by the SmtO₂ trace and threshold), and multivariable analysis by accounting for recognized PONV risk factors. PONV occurred in 35 of 106 patients (33%). Based on the multivariable analysis, the SmtO₂ threshold of 20% above baseline correlated with less PONV (OR 0.39; 95% CI 0.16-0.93; p = 0.034), and the following values correlated with more PONV: 5% below baseline (OR 2.37; 95% CI 1.26-4.45; p = 0.007), 20% below baseline (OR 16.08; 95% CI 3.05-84.73; p = 0.001), < 70% (OR 2.86; 95% CI 1.17-6.99; p = 0.021) and < 60% (OR 6.55; 95% CI 1.11-38.53; p = 0.038). Our study suggests that a potential therapeutic goal for PONV prophylaxis may be to maintain SmtO₂ at > 70% and above baseline.

Prospective observational study on assessing the hemodynamic relevance of patent ductus arteriosus with frequency domain near-infrared spectroscopy

BACKGROUND

What constitutes a hemodynamically relevant patent ductus arteriosus (hrPDA) in preterm infants is unclear. Different clinical and echocardiographic parameters are used, but a gold standard definition is lacking. Our objective was to evaluate associations between regional cerebral tissue oxygen saturation (rcStO₂), fraction of tissue oxygen extraction (rcFtO₂E) measured by frequency domain near-infrared spectroscopy (fd-NIRS) and their correlation to echocardiographic, Doppler-ultrasound, and clinical parameters in preterm infants with and without a hrPDA.

METHODS

In this prospective observational study, 22 infants < 1500 g (mean [± SD]: gestational age 28.6 [±1.8] weeks, birth weight 1076 [±284] g, median (interquartile range) postnatal age at measurement 7.6 (4.6-12.9) d) with a clinical suspicion of hrPDA were analysed. Twelve infants had left-to-right shunt through PDA, and in 6 of these the PDA was classified as hrPDA based on pre-defined clinical and echocardiographic criteria. fd-NIRS, echocardiographic and Doppler-ultrasound examinations were performed. After identification of blood hemoglobin (Hb) as confounding factor, rcStO₂ and rcFtO₂E were corrected for this effect.

RESULTS

Overall mean ± standard deviation (normalised to a median Hb of 13.8 mg/dl) was 57 ±5% for rcStO₂ and 0.39 ±0.05 for rcFtO₂E. Comparing no-hrPDA with hrPDA infants, there were no significant differences in mean rcStO₂ (58 ±5% vs. 54 ±5%; p = .102), but in mean rcFtO₂E (0.38 ±0.05 vs. 0.43 ±0.05; p = .038). Echocardiographic parameter and Doppler indices did not correlate with cerebral oxygenation.

CONCLUSION

Oxygen transport capacity of the blood may confound NIRS data interpretation. Cerebral oxygenation determined by fd-NIRS provided additional information for PDA treatment decisions not offered by routine investigations. Whether indicating PDA therapy based on echocardiography complemented by data on cerebral oxygenation results in better outcomes should be investigated in future studies.

Comparison of tissue oximeters on a liquid phantom with adjustable optical properties: an extension

Cerebral near-infrared spectroscopy (NIRS) oximetry may help clinicians to improve patient treatment. However, the application of NIRS oximeters is increasingly causing confusion to the users due to the inconsistency of tissue oxygen haemoglobin saturation (StO2) readings provided by different oximeters. To establish a comparability of oximeters, in our study we performed simultaneous measurements on the liquid phantom mimicking properties of neonatal heads and compared the tested device to a reference NIRS oximeter (OxiplexTS). We evaluated the NIRS oximeters FORE-SIGHT, NIRO and SenSmart, and reproduced previous results with the INVOS and OxyPrem v1.3 oximeters. In general, linear relationships of the StO2 values with respect to the reference were obtained. Device specific hypoxic and hyperoxic thresholds (as used in the SafeBoosC study, www.safeboosc.eu) and a table allowing for conversion of StO2 values are provided.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

Investigating the Usability and Acute Effects of a Bedside Video Console to Prefrontal Cortical Activity Alterations: A Preclinical Study in Healthy Elderly

Elderly people at risk of developing cognitive decline; e.g., following surgery, may benefit from structured, challenging, and repetitive cognitive video training. This study assessed usability and acute effects of a newly developed bedside console (COPHYCON). Fifteen healthy elderly individuals performed a one-time 80-min intervention, including cognitive video games aimed at improving awareness and selective attention. Perceived usefulness and perceived ease of use (Technology Acceptance Model) were assessed together with measures of the achieved game level, reaction times, (in-) correct responses during ALERT and SELECT game play. Further, prefrontal cortical involvement of the regional cerebral hemoglobin saturation (rS02%) assessed with functional near infrared spectroscopy (fNIRS) (n = 5) and EEG power (n = 10) was analyzed. All participants completed the study without any adverse events. Perceived usefulness and perceived ease of use (TAM scores range 1-7) of the system varied between 3.9 and 6.3. The game levels reached for awareness varied between 9 and 11 (initial score 8-10), for reaction speed between 439 and 469 ms, and for correct responses between 74.1 and 78.8%. The highest level for the selective attention games was 2 (initial score 1), where reaction speed varied between 439 and 469 ms, correct responses between 96.2 and 98.5%, respectively. The decrease of rS02% in the right prefrontal cortex during gameplay was significantly (p < 0.001) lower, compared to the left prefrontal cortex. Four participants yielded significant lower rS02% measures after exergaming with the ALERT games (p < 0.000), but not with the SELECT games. EEG recordings of theta power significantly decreased in the averaged ~0.25-0.75 time interval for the left prefrontal cortex sensor across the cognitive game levels between the ALERT 1 and SELECT 1, as well as between SELECT 1 and 2 games. Participants rated the usability of the COPHYCON training positively. Further results indicate that video gaming may be an effective measure to affect prefrontal cortical functioning in elderly. The results warrant a clinical explorative study investigating the feasibility of the COPHYCON in a clinical setting.

Quantifying cerebral hypoxia by near-infrared spectroscopy tissue oximetry: the role of arterial-to-venous blood volume ratio

Tissue oxygenation estimated by near-infrared spectroscopy (NIRS) is a volume-weighted mean of the arterial and venous hemoglobin oxygenation. In vivo validation assumes a fixed arterial-to-venous volume-ratio (AV-ratio). Regulatory cerebro-vascular mechanisms may change the AV-ratio. We used hypotension to investigate the influence of blood volume distribution on cerebral NIRS in a newborn piglet model. Hypotension was induced gradually by inflating a balloon-catheter in the inferior vena cava and the regional tissue oxygenation from NIRS ( rStO 2 , NIRS ) was then compared to a reference ( rStO 2 , COX ) calculated from superior sagittal sinus and aortic blood sample co-oximetry with a fixed AV-ratio. Apparent changes in the AV-ratio and cerebral blood volume (CBV) were also calculated. The mean arterial blood pressure (MABP) range was 14 to 82 mmHg. PaCO 2 and SaO 2 were stable during measurements. rStO 2 , NIRS mirrored only 25% (95% Cl: 21% to 28%, p < 0.001 ) of changes in rStO 2 , COX . Calculated AV-ratio increased with decreasing MABP (slope: ? 0.007 · mmHg ? 1

Detection of critical cerebral desaturation thresholds by three regional oximeters during hypoxia: a pilot study in healthy volunteers

Background

Regional oximetry is increasingly used to monitor post-extraction oxygen status of the brain during surgical procedures where hemodynamic fluctuations are expected. Particularly in cardiac surgery, clinicians employ an interventional algorithm to restore baseline regional oxygen saturation (rSO₂) when a patient reaches a critical desaturation threshold. Evidence suggests that monitoring cardiac surgery patients and intervening to maintain rSO₂ can improve postoperative outcomes; however, evidence generated with one manufacturer’s device may not be applicable to others. We hypothesized that regional oximeters from different manufacturers respond uniquely to changes in oxygen saturation in healthy volunteers.

Methods

Three devices were tested: INVOS™ 5100C (Medtronic), EQUANOX™ 7600 (Nonin), and FORE-SIGHT™ (CASMED) monitors. We divided ten healthy subjects into two cohorts wearing a single sensor each from INVOS and EQUANOX (n = 6), or INVOS and FORE-SIGHT (n = 4). We induced and reversed hypoxia by adjusting the fraction of inspired oxygen. We calculated the magnitude of absolute rSO₂ change and rate of rSO₂ change during desaturation and resaturation, and determined if and when each device reached a critical interventional rSO₂ threshold during hypoxia.

Results

All devices responded to changes in oxygen directionally as expected. The median absolute rSO₂ change and the rate of rSO₂ change was significantly greater during desaturation and resaturation for INVOS compared with EQUANOX (P = 0.04). A similar but nonsignificant trend was observed for INVOS compared with FORE-SIGHT; our study was underpowered to definitively conclude there was no difference. A 10% relative decrease in rSO₂ during desaturation was detected by all three devices across the ten subjects. INVOS met a 20% relative decrease threshold in all subjects of both cohorts, compared to 1 with EQUANOX and 2 with FORE-SIGHT. Neither EQUANOX nor FORE-SIGHT reached a 50% absolute rSO₂ threshold compared with 4 and 3 subjects in each cohort with INVOS, respectively.

Conclusions

Significant differences exist between the devices in how they respond to changes in oxygen saturation in healthy volunteers. We suggest caution when applying evidence generated with one manufacturer’s device to all devices.

Electronic supplementary material

The online version of this article (doi:10.1186/s12871-016-0298-7) contains supplementary material, which is available to authorized users.

Reproducibility, interchangeability of measures, time to measure stabilization, and reference values of two tissue oximeters in healthy volunteers

This study aimed to compare two tissue oximeters, the INVOS 5100c and the Equanox 7600, in terms of their reproducibility and the interchangeability of their measures. In a randomized order, three measurements were taken at six different sites on both sides of the body in 53 healthy volunteers. Intraclass correlation coefficients (ICC) and within-subject standard deviation (Sw) were calculated for each device. The ICCs were compared using Fisher r-to-z transformation and the Sw were compared using paired-sample t-tests. We found no difference between the reproducibility of the INVOS {ICC=0.92 [95% confidence interval (CI) 0.90 to 0.93]} and Equanox [ICC=0.90 (95% CI 0.88 to 0.93)] in terms of ICCs (p=0.06). However, the Equanox [Sw=1.96 (95% CI 1.91 to 2.02)] showed a better Sw than the INVOS [Sw=2.11 (95% CI 2.05 to 2.17)] (p=0.019). Also, when compared directly to stable condition, the readings produced by the two oximeters varied considerably [ICC 0.43 (95% CI 0.36 to 0.49)]. When taken individually, both tissue oximeters displayed good reproducibility, the Equanox being slightly better than the INVOS in terms of absolute reproducibility. However, when compared, the oximeters showed poor interdevices agreement. Reference values were also described.

The SafeBoosC phase II clinical trial: an analysis of the interventions related with the oximeter readings

BACKGROUND

The SafeBoosC phase II randomised clinical trial recently demonstrated the benefits of a combination of cerebral regional tissue oxygen saturation (rStO2) by near-infrared spectroscopy (NIRS) and a treatment guideline to reduce the oxygen imbalance in extremely preterm infants.

AIMS

To analyse rStO2-alarm-related clinical decisions and their heterogeneity in the NIRS experimental group (NIRS monitoring visible) and their impact on rStO2 and SpO2.

METHODS

Continuous data from NIRS devices and the alarms (area under the curve of the rStO2 out of range had accumulated 0.2%h during 10 min), clinical data at discrete time points and interventions prompted by the alarms were recorded.

RESULTS

Sixty-seven infants had data that fulfilled the requirements for this analysis. 1107 alarm episodes were analysed. The alarm triggered a treatment guideline intervention in 25% of the cases; the type of intervention chosen varied among clinical sites. More than 55% of alarms were not followed by an intervention ('No action'); additionally, in 5% of alarms the rStO2 value apparently was considered non-reliable and the sensor was repositioned. The percentage of unresolved alarms at 30 min after 'No action' almost doubled the treatment guideline intervention (p<0.001). Changes in peripheral oxygen saturation (SpO2), were observed only after treatment guideline interventions.

CONCLUSIONS

This study shows that 25% of rStO2 alarms were followed by a clinical intervention determined by the treatment guideline. However, the rStO2 and SpO2 returned to normal ranges after the intervention, supporting the notion that decisions taken by the clinicians were appropriate.

TRIAL REGISTRATION NUMBER

ClinicalTrial.gov NCT01590316.

Comparison of Near-Infrared Oximeters in a Liquid Optical Phantom with Varying Intralipid and Blood Content

The interpretation of cerebral tissue oxygen saturation values (StO2) in clinical settings is currently complicated by the use of different near-infrared spectrophotometry (NIRS) devices producing different StO2 values for the same oxygenation due to differences in the algorithms and technical aspects. The aim was to investigate the effect of changes in scattering and absorption on the StO2 of different NIRS devices in a liquid optical phantom. We compared three continuous-wave (CW) with a frequency domain (FD) NIRS device. Responsiveness to oxygenation changes was only slightly altered by different intralipid (IL) concentrations. However, alterations in haematocrit (htc) showed a strong effect: increased htc led to a 20-35% increased response of all CW devices compared to the FD device, probably due to differences in algorithms regarding the water concentration.

Near-infrared spectroscopy: applications in neonates

Near-infrared spectroscopy (NIRS) offers non-invasive, in-vivo, real-time monitoring of tissue oxygenation. Changes in regional tissue oxygenation as detected by NIRS may reflect the delicate balance between oxygen delivery and consumption. Originally used predominantly to assess cerebral oxygenation and perfusion perioperatively during cardiac and neurosurgery, and following head trauma, NIRS has gained widespread popularity in many clinical settings in all age groups including neonates. However, more studies are required to establish the ability of NIRS monitoring to improve patient outcomes, especially in neonates. This review provides a comprehensive description of the use of NIRS in neonates.

Cerebral near infrared spectroscopy oximetry in extremely preterm infants: phase II randomised clinical trial

OBJECTIVE

To determine if it is possible to stabilise the cerebral oxygenation of extremely preterm infants monitored by cerebral near infrared spectroscopy (NIRS) oximetry.

DESIGN

Phase II randomised, single blinded, parallel clinical trial.

SETTING

Eight tertiary neonatal intensive care units in eight European countries.

PARTICIPANTS

166 extremely preterm infants born before 28 weeks of gestation: 86 were randomised to cerebral NIRS monitoring and 80 to blinded NIRS monitoring. The only exclusion criterion was a decision not to provide life support.

INTERVENTIONS

Monitoring of cerebral oxygenation using NIRS in combination with a dedicated treatment guideline during the first 72 hours of life (experimental) compared with blinded NIRS oxygenation monitoring with standard care (control).

MAIN OUTCOME MEASURES

The primary outcome measure was the time spent outside the target range of 55-85% for cerebral oxygenation multiplied by the mean absolute deviation, expressed in %hours (burden of hypoxia and hyperoxia). One hour with an oxygenation of 50% gives 5%hours of hypoxia. Secondary outcomes were all cause mortality at term equivalent age and a brain injury score assessed by cerebral ultrasonography.

RANDOMISATION

Allocation sequence 1:1 with block sizes 4 and 6 in random order concealed for the investigators. The allocation was stratified for gestational age (<26 weeks or ≥ 26 weeks).

BLINDING

Cerebral oxygenation measurements were blinded in the control group. All outcome assessors were blinded to group allocation.

RESULTS

The 86 infants randomised to the NIRS group had a median burden of hypoxia and hyperoxia of 36.1%hours (interquartile range 9.2-79.5%hours) compared with 81.3 (38.5-181.3) %hours in the control group, a reduction of 58% (95% confidence interval 35% to 73%, P<0.001). In the experimental group the median burden of hypoxia was 16.6 (interquartile range 5.4-68.1) %hours, compared with 53.6 (17.4-171.3) %hours in the control group (P=0.0012). The median burden of hyperoxia was similar between the groups: 1.2 (interquartile range 0.3-9.6) %hours in the experimental group compared with 1.1 (0.1-23.4) %hours in the control group (P=0.98). We found no statistically significant differences between the two groups at term corrected age. No severe adverse reactions were associated with the device.

CONCLUSIONS

Cerebral oxygenation was stabilised in extremely preterm infants using a dedicated treatment guideline in combination with cerebral NIRS monitoring.Trial registration ClinicalTrial.gov NCT01590316.

A comparison between two NIRS oximeters (INVOS, OxyPrem) using measurement on the arm of adults and head of infants after caesarean section

Previously the NIRS oximeter OxyPrem was calibrated by comparison to the INVOS in a blood-lipid phantom. The aim of the present study was to test this calibration clinically. During vasculur occlusions in 10 adults and after birth in 25 term infants the relationship was OxyPrem = 1.24 x INVOS - 23.6% and OxyPrem = 1.15 x INVOS - 16.2% on the adult arm and infant head, respectively. The precsion during steady state was 4.0% (CI 3.4% to 4.6%) and 3.4% (CI 2.9% to 3.9%) on the arm, and 6.7% (CI 5.9% to 7.6%) and 4.7% (CI 3.5% to 5.9%) on the infant head for OxyPrem and INVOS, respectively. We conclude that the calibration on the blood-lipid phantom was unsuccessful in achieving agreement in clinical measurements.

Cerebral oxygenation after birth - a comparison of INVOS(®) and FORE-SIGHT™ near-infrared spectroscopy oximeters

Aim

To compare absolute values of regional cerebral tissue oxygenation (cStO₂) during haemodynamic transition after birth and repeatability during steady state for two commercial near‐infrared spectroscopy (NIRS) devices.

Methods

In a prospective observational study, the INVOS 5100C and FORE‐SIGHT were compared on 12 term newborns delivered by elective caesarean section. During the 10 min following umbilical cord clamping, cStO₂ was measured simultaneously with the neonatal sensors from each device. Repeated measurements were taken the following day.

Results

Three and 8 min after clamping, the mean cStO₂ value increased from 53.4% (CI 36.8–69.9%) to 86.0% (CI 80.2–91.7%) for INVOS and from 61.6% (CI 55.4–67.8%) to 82.2% (CI 77.7–86.7%) for FORE‐SIGHT. The Bland–Altman plot revealed decreasing difference (INVOS minus FORE‐SIGHT) (D) in absolute values (A) with increasing cStO2 (D = 0.5A – 38.19 p = <0.001). The mean steady‐state value on day two was 78.4% (CI 74.6–82.2%) and 86.2% (CI 85.0–87.4%) for INVOS and FORE‐SIGHT, respectively. The within‐subject standard deviation during steady‐state repeated measurements was 4.8% ± 0.86 for INVOS and 2.8% ± 0.5 for FORE‐SIGHT.

Conclusion

The INVOS and FORE‐SIGHT cStO₂ estimates showed oxygenation‐level‐dependent difference during birth transition. The better repeatability of FORE‐SIGHT could be due to the lower response to change in saturation.

Direct comparison between cerebral oximetry by INVOS(TM) and EQUANOX(TM) during cardiac surgery: a pilot study

INTRODUCTION

Several near-infrared spectroscopy oximeters are commercially available for clinical use, with lack of standardization among them. Accordingly, cerebral oxygen saturation thresholds for hypoxia/ischemia identified in studies conducted with INVOS(TM) models do not necessarily apply to other devices. In this study, the measurements made with both INVOS(TM) and EQUANOX(TM) oximeters on the forehead of 10 patients during conventional cardiac surgery are directly compared, in order to evaluate the interchangeability of these two devices in clinical practice.

METHODS

Cerebral oxygen saturation measurements were collected from both INVOS(TM) 5100C and EQUANOX(TM) 7600 before anesthetic induction (baseline), two minutes after tracheal intubation, at cardiopulmonary bypass onset/offset, at aortic cross-clamping/unclamping, at the end of surgery and whenever at least one of the two devices measured a reduction in cerebral oxygen saturation equal to or greater than 20% of the baseline value. Bland-Altman analysis was used to compare the bias and limits of agreement between the two devices.

RESULTS

A total of 140 paired measurements were recorded. The mean bias between INVOS(TM) and EQUANOX(TM) was -5.1%, and limits of agreement were ±16.37%. Considering the values as percent of baseline, the mean bias was -1.43% and limits of agreement were ±16.47. A proportional bias was observed for both absolute values and changes from baseline.

CONCLUSIONS

INVOS(TM) and EQUANOX(TM) do not seem to be interchangeable in measuring both absolute values and dynamic changes of cerebral oxygen saturation during cardiac surgery. Large investigations, with appropriate design, are needed in order to identify any device-specific threshold.