Tissue Oximeter Research Articles

Cerebral and Skeletal Muscle Tissue Oxygenation during Exercise in Children with Sickle Cell Anemia

Introduction: Sickle cell anemia (SCA) causes impaired tissue oxygenation. Children with SCA have lower peak fitness levels compared to controls. The contribution of alterations in skeletal muscle and cerebral tissue oxygenation to exercise limitation in SCA remains unclear. Near infrared spectroscopy (NIRS) is a validated, non-invasive method to measure tissue oxygen saturation. We hypothesize that compared to controls, children with SCA will exhibit greater reductions in regional tissue oxygen saturation (StO2) measured in the quadriceps (vastus lateralis) and pre frontal cortex (PFC) across all workloads during maximal cardiopulmonary exercise testing (CPET). Methods: We used the CASMED ELITE NIRS tissue oximeter to measure tissue oxygen saturation in the PFC and vastus lateralis (VL) muscle during all phases of maximal CPET, including warm up, active exercise and recovery, in 17 subjects with SCA (mean age 13.5 years) and 13 controls (mean age 15.2 years). Maximal CPET was conducted by cycle ergometry using a standard ramp protocol until volitional exhaustion was reached by all participants. Peak oxygen consumption (VO2) was measured from breath-by breath gas exchange data collected during CPET. Results: All subjects and controls completed maximal CPET without adverse events. Peak VO2 was not statistically different in subjects with SCA versus controls (25.3±4.7 vs 29.5±8.9 mL/kg/min, p=0.22). Compared to controls, subjects with SCA had significantly lower PFC StO2 at all time points during exercise, including warm up, 20%, 40%, 60%, 80% and 100% of peak work load (p<0.01) (Figure 1a). Subjects with SCA demonstrated a significant decrease in PFC StO2 from warm up to 80% peak work load (-3.0±2.9% , p=0.002) and from warm up to 100% peak work load (-5.4±3.4 %, p<0.001) (Figure 1b). In contrast, controls did not demonstrate significant decreases in PFC StO2 from warm up to any point during exercise testing. VL StO2 did not significantly differ between subjects and controls during exercise (p=0.149, Figure 1c). Subjects with SCA demonstrated a significant increase in VL StO2 from warm up to 0% (+3.2±2.8%, p<0.001) and 20% peak work load (+2.3±2.5%, p=0.002) and a significant decrease in StO2 from warm up to 60% (-4.8±4.6%, p<0.001), 80% (-8.6±5.9%, p<0.001) and 100% peak work load (-10.5±6.3%, p<0.001) (Figure 1d). Controls had significant increase in VL StO2 from warm up to 0% peak work load (+4.3±4.0%, p=0.02) and a significant decrease only at 80% (-6.5±6.3%, p=0.003). Differences in PFC and VL StO2 between subjects and controls were also examined at the highest VO2 achieved by all participants. At a VO2 of 17.6 mL/kg/min, PFC StO2 was significantly lower in subjects with SCA versus controls (69.2±6.6 vs 79.5±5.3%, p<0.001). There was a trend toward lower VL StO2 in subjects versus controls (67.7±9.0 vs 73.2±7.9%, p=0.09). Conclusion: Unlike VL tissue oxygenation, PFC tissue oxygenation is relatively well preserved in subjects with SCA and controls during maximal CPET. However, compared to controls, subjects with SCA have lower PFC tissue oxygenation at warm up and during exercise as well as demonstrate significantly greater decreases in PFC tissue oxygenation during later stages of exercise. In contrast, VL tissue oxygenation is similar at warm up and during exercise for subjects and controls. VL tissue oxygenation increases during initial stages of exercise in a similar fashion in subjects with SCA and controls but subsequent decreases from warm up are greater in subjects with SCA during later stages of exercise. Future studies may further elucidate how SCA contributes to these observed differences in regional tissue oxygenation during exercise and their potential impact on exercise safety and fitness in this population. Disclosures No relevant conflicts of interest to declare.

Transfusion in adults and children undergoing neurosurgery: the outcome evidence.

Transfusion is a common practice during neurosurgery. However, there is no evidence-based consensus on transfusion practice in neurosurgery. This review summarizes the evidence pertinent to the commonly used transfusion triggers in neurosurgical patients. In the field of neurosurgery, there is only one randomized controlled trial, performed in patients with traumatic brain injury, to investigate the transfusion trigger of red blood cells. There is a lack-of-quality evidence pertinent to the transfusion triggers of other blood products. Most of the transfusion triggers used for neurosurgical patients are extrapolated from the evidence based on studies performed in nonneurosurgical patients. Clinical experience and expert opinions have played a major role in transfusion practice in neurosurgery. There is a scarcity of high-quality outcome-based evidence for transfusion practice in neurosurgery. In the absence of quality evidence, the transfusion practice in neurosurgical patients should be based on the understanding of the complex pathophysiology related to anemia and coagulopathy and the balance between the risks and benefits associated with blood product transfusion. The practice guided by tissue oximeter and viscoelastic tests appears promising, but needs to be validated by future studies.

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

ObjectiveMaintaining 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 designProspective, observational study. AnimalsA group of 30 healthy client-owned adult horses admitted to the equine hospital between July 2017 and July 2018. MethodsThe 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. ResultsThe 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 relevanceThe 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.

MP13: Association between the quantity of subcutaneous fat and the inter-device agreement of two tissue oximeters

Introduction: Near-infrared spectroscopy (NIRS) can be used to monitor the oxygen saturation of hemoglobin in any given superficial tissue. However, the measurements provided by different oximeters can vary a lot. Little is known about the specific patient characteristics that could affect the inter-device agreement of tissular oximeters. This study aimed to evaluate the association between the quantity of subcutaneous fat (assessed by skinfold thickness) and the inter-device agreement of two tissue oximeters, the INVOS 5100c and the Equanox 7600. Methods: In this prospective cohort study, tissue saturations and skinfold thickness were measured at four different sites on both sides of the body in healthy adult (≥18 years old) volunteers. The association between the quantity of subcutaneous fat (assessed by skinfold thickness) and the inter-device agreement (absolute difference between the oximetry values provided by the two oximeters) was first assessed with a Pearson's correlation and a scatter plot. Subsequently, a linear mixed model was used to evaluate the impact of the subcutaneous fat and other covariables (age, sex) on the inter-device agreement while adjusting for the repeated measurements across different sites for the same volunteers. Results: From January to March 2015, 53 healthy volunteers were included in this study with ages ranging between 20 and 81 years old, on which a total of 848 measures were taken. Higher skinfold measures were associated with an increase in the difference between measures provided by both oximeters (Slope = -0.59, Pearson correlation coefficient = -0.51, p < 0.001). This observed association persisted in a linear mixed model (-0.48 [95% confidence interval {CI}-0.61 to -0.36], p < 0.001). The sex of the volunteers also influenced the inter-oximeter agreement (Women:-5.77 [95%CI -8.43 to -3.11], p < 0.001), as well as the forearm sites (Left forearm: −7.16 [95%CI -9.85 to –4.47], p < 0.001; right forearm: −7.01 [95%CI -9.61 to −4.40], p < 0.001). Conclusion: The quantity of subcutaneous fat, as well as the sex of the volunteers and the measurement sites, impacted the inter-device agreement of two commonly used oximeters. Given these findings, monitoring using tissue oximetry should be interpreted with great care when there is a significant quantity of subcutaneous fat.

Handheld Tissue Oximetry for the Prehospital Detection of Shock and Need for Lifesaving Interventions: Technology in Search of an Indication?

Improved prehospital methods for assessing the need for lifesaving interventions (LSIs) are needed to gain critical lead time in the care of the injured. We hypothesized that threshold values using prehospital handheld tissue oximetry would detect occult shock and predict LSI requirements. This was a prospective observational study of adult trauma patients emergently transported by helicopter. Patients were monitored with a handheld tissue oximeter (InSpectra Spot Check; Hutchinson Technology Inc, Hutchinson, MN), continuous vital signs, and 21 laboratory measurements obtained both in the field with a portable analyzer and at the time of admission. Shock was defined as base excess ≥ 4 or lactate > 3 mmol/L. Eighty-eight patients were enrolled with a median Injury Severity Score of 16 (interquartile range, 5-29). The median hemoglobin saturation in the capillaries, venules, and arterioles (StO2) value for all patients was 82% (interquartile range, 76%-87%; range, 42%-98%). StO2 was abnormal (< 75%) in 18 patients (20%). Eight were hypotensive (9%) and had laboratory-confirmed evidence of occult shock. StO2 correlated poorly with shock threshold laboratory values (r = −0.17; 95% confidence interval, −0.33 to 1.0; P = .94). The area under the receiver operating curve was 0.51 (95% confidence interval, 0.39-0.63) for StO2 < 75% and laboratory-confirmed shock. StO2 was not associated with LSI need on admission when adjusted for multiple covariates, nor was it independently associated with death. Handheld tissue oximetry was not sensitive or specific for identifying patients with prehospital occult shock. These results do not support prehospital StO2 monitoring despite its inclusion in several published guidelines.

Validation of a Second-Generation Near-Infrared Spectroscopy Monitor in Children With Congenital Heart Disease.

Cerebral oximetry using near-infrared spectroscopy is a noninvasive optical technology to detect cerebral hypoxia-ischemia and develop interventions to prevent and ameliorate hypoxic brain injury. Cerebral oximeters are calibrated and validated by comparison of the near-infrared spectroscopy-measured cerebral O2 saturation (SctO2) to a "field" or reference O2 saturation (REF CX) calculated as a weighted average from arterial and jugular bulb oxygen saturations. In this study, we calibrated and validated the second-generation, 5 wavelength, FORE-SIGHT Elite with the medium sensor (source-detector separation 12 and 40 mm) for measurement of SctO2 in children with congenital heart disease. After institutional review board approval and written informed consent, 63 children older than 1 month and ≥2.5 kg scheduled for cardiac catheterization were enrolled. Self-adhesive FORE-SIGHT Elite medium sensors were placed on the right and left sides of the forehead. Blood samples for calculation of REF CX were drawn simultaneously from the aorta or femoral artery and the jugular bulb before (T1) and shortly after (T2) baseline hemodynamic measurements. FORE-SIGHT Elite SctO2 measurements were compared to the REF CX (REF CX = [0.3 SaO2] + [0.7 SjbO2]) using Deming regression, least squares linear regression, and Bland-Altman analysis. Sixty-one subjects (4.5 [standard deviation 4.4] years of age; 17 [standard deviation 13] kg, male 56%) completed the study protocol. Arterial oxygen saturation ranged from 64.7% to 99.1% (median 96.0%), jugular bulb venous oxygen saturation from 34.1% to 88.1% (median 68.2%), the REF CX from 43.8% to 91.4% (median 76.9%), and the SctO2 from 47.8% to 90.8% (median 76.3%). There was a high degree of correlation in SctO2 between the right and left sensors at a given time point (within subject between sensor correlation r = 0.91 and 95% confidence interval [CI], 0.85-0.94) or between T1 and T2 for the right and left sensors (replicates, within subject between time point correlation r = 0.95 and 95% CI, 0.92-0.96). By Deming regression, the estimated slope was 0.966 (95% CI, 0.786-1.147; P = .706 for testing against null hypothesis of slope = 1) with a y intercept of 2.776 (95% CI, -11.102 to 16.654; P = .689). The concordance correlation coefficient was 0.873 (95% CI, 0.798-0.922). Bland-Altman analysis for agreement between SctO2 and REF CX that accounted for repeated measures (both in times and sensors) found a bias of -0.30% (95% limits of agreement: -10.56% to 9.95%). This study calibrated and validated the FORE-SIGHT Elite tissue oximeter to accurately measure SctO2 in pediatric patients with the medium sensor.

Utility of a Finger-Mounted Tissue Oximeter with Near-Infrared Spectroscopy to Evaluate Limb Ischemia in Patients with Peripheral Arterial Disease.

Objective: To investigate whether a finger-mounted tissue oximeter is useful in evaluating limb blood flow in patients with peripheral arterial disease (PAD).Materials and Methods: Seventy-two patients with PAD were included, and the ankle-brachial index (ABI), transcutaneous oxygen pressure (TcPO2), and skin perfusion pressure (SPP) were measured. The regional tissue oxygenation saturation (rSO2) was measured using a finger-mounted tissue oximeter at the ankle, dorsal foot, and each dorsal and plantar toe. Correlations between rSO2 and ABI and between TcPO2 and SPP were analyzed. The patients were divided into three groups: Fontaine IIa (F-IIa), IIb (F-IIb), and III and IV (F-III/IV) groups. The difference in rSO2 between each group was analyzed.Results: Significant correlations were observed between rSO2 and TcPO2 and between rSO2 and SPP. TcPO2 and SPP in the F-III/IV group were significantly lower than those in the F-IIa group. rSO2 in the F-IIb and F-III/IV groups was significantly lower than that in the F-IIa group.Conclusion: The measurement of rSO2 using finger-mounted tissue oximetry is quick, simple, and painless. It can be used on any skin area and is useful to evaluate limb circulation in patients with PAD.

Association Between the Quantity of Subcutaneous Fat and the Inter-Device Agreement of 2 Tissue Oximeters

This study aimed to evaluate the association between the quantity of subcutaneous fat (assessed by skinfold thickness) and the inter-device agreement of 2 tissue oximeters. This is a prospective cohort study. This study was conducted in a tertiary care academic urban hospital. Healthy volunteers were recruited. All patients recruited had their tissue saturations and skinfold thickness measured at 4 different sites (shoulder, forearm, knee, and calf) on both sides of the body using 2 tissue oximeters, the INVOS 5100C and the EQUANOX 7600. Higher skinfold measures were associated with an increase in the difference between measures provided by both oximeters (slope = -0.59, Pearson correlation coefficient = -0.51, p < 0.001). This observed association persisted in a linear mixed model (-0.48 [95% confidence interval [CI] -0.61 to -0.36], p < 0.001). The sex of the volunteers also influenced the inter-oximeter agreement (women: -5.77 [95% CI -8.43 to -3.11], p < 0.001), as well as the forearm sites (left forearm: -7.16 [95% CI -9.85 to -4.47], p < 0.001; right forearm:-7.01 [95% CI -9.61 to -4.40], p < 0.001). The inter-device agreement of the 2 studied oximeters is correlated to the quantity of subcutaneous fat. Monitoring using tissue oximetry should be interpreted with great care when sensors are placed on sites with a significant quantity of subcutaneous fat. In addition to the monitoring of cerebral oximetry, following the variations of saturations at the same peripheral site seems to remain the most secure way to use that technology for the monitoring of critically ill patients.

In vivo precision assessment of a near-infrared spectroscopy-based tissue oximeter (OxyPrem v1.3) in neonates considering systemic hemodynamic fluctuations.

The aim was to determine the precision of a noninvasive near-infrared spectroscopy (NIRS)-based tissue oximeter (OxyPrem v1.3). Using a linear mixed-effects model, we quantified the variability for cerebral tissue oxygenation (StO2) measurements in 35 preterm neonates to be 2.64%, a value that meets the often-articulated clinicians' demand for a precise tissue oxygenation measurement. We showed that the variability of StO2 values measured was dominated by spontaneous systemic hemodynamic fluctuations during the measurement, meaning that precision of the instrument was actually even better. Based on simultaneous and continuous measurements of peripheral arterial oxygenation and cerebral StO2 with a second sensor, we were able to determine and quantify the physiological instability precisely. We presented different methods and analyses aiming at reducing this systematic physiological error of in vivo precision assessments. Using these methods, we estimated the precision of the OxyPrem tissue oximeter to be ≤ 1.85 % . With our study, we deliver relevant information to establish highly precise cerebral oxygenation measurements with NIRS-based oximetry, facilitating the further development toward a substantially improved diagnosis and treatment of patients with respect to brain oxygenation.

Approaches for calibration and validation of near-infrared optical methods for oxygenation monitoring.

Pulse oximetry for arterial oxygenation monitoring and tissue oximetry for monitoring of cerebral oxygenation or muscle oxygenation are based on quantitative in vivo diffuse optical spectroscopy. However, in both cases the information on absolute or relative concentration of human tissue constituents and especially on hemoglobin oxygenation can often not be retrieved by model-based analysis. An in vivo calibration against an accepted reference measurement can be a practical alternative. Pulse oximeters and most of commercial cerebral tissue oximeters rely on empirical calibration based on invasive controlled human desaturation studies. As invasive in vivo tests on healthy subjects are ethically disputable and should be limited to exceptional cases this calibration practice is unsatisfactory. We present the current status and problems of calibration and validation in pulse oximetry and cerebral tissue oximetry including the pros and cons of in vivo as well as in vitro methods. We emphasize various digital and physical phantom approaches and discuss the prospects of their application and possible further developments.

P022 Severe disease activity in UC is associated with mucosal hypoxia measured endoscopically

Tissue hypoxia has been shown to be a key microenvironmental regulator of mucosal barrier function and inflammation in pre-clinical models of colitis. However, the role of mucosal hypoxia in the pathogenesis of UC has yet to be extensively studied in IBD patients. Visible light spectroscopy can be utilised to measure the haemoglobin (Hb) oxygen saturations (%) colonic mucosa during endoscopy. Carbonic anhydrase 9 (CA-9) is a hypoxia-inducible protein and endogenous marker of hypoxia. The aim of this study was to compare mucosal oxygen saturations in normal and inflamed colonic mucosa in UC patients and assess relationship with disease activity. Patients undergoing colonoscopy were prospectively recruited in a single academic centre, with >3800 IBD patients. Endoscopies were performed using CO2 insufflation. Measurements of colonic mucosal Hb saturations were performed segmentally and from zones of transition from inflamed to normal mucosa, using an endoscopic probe (applied to intact mucosa) and tissue oximeter (T-Stat System, Spectros).Endoscopic severity was graded using the endoscopic Mayo score. Mucosal biopsies were obtained to grade histologic activity and for protein analysis. 38 patients were included in this study; n = 7 controls, n = 31 UC; male=25 (65.7%). The median age of UC patients was 39 years (IQR 34.6- 55.9). n = 5 had Mayo 0, n = 9 Mayo 1, n = 11 Mayo 2 and n = 6 Mayo 3 activity. At the time of the procedure, five patients were on biologic therapy, five immunomodulators and six on steroids. The median rectal saturation in the control group was 76.2% (IQR 73–80),compared with 77% (IQR 73.8–80.6) in the UC cohort (Mayo 0–3 inclusive) (p = 1.00). There was no significant difference across any colonic segment between these two cohorts. The median rectal mucosal O2 saturation in Mayo 0 was 77.6% (77.4–81.2),Mayo 1: 80.6% (77–83.8), Mayo 2: 75.4% (73.5–79.2) and Mayo 3:73.3% (68.7–74.8) (p = 0.02). Mucosal Hb Saturations (%) by disease severity. CA9 protein expression was significantly higher in biopsies with Mayo 2–3 activity compared with Mayo 0-1 disease. CA-9 protein expression in rectal biopsies. Mucosal O2 saturation is significantly decreased in severely active UC and oxygen signalling pathways are activated suggesting that mucosal hypoxia is an important determinant of disease severity in UC. These observations suggest the potential for oxygen signalling pathways as novel therapeutic targets.

Progress of monitoring methods and preventions of disorder of blood supplying of expanded flaps

To summarize the monitoring methods and preventions of the disorder of blood supplying of expanded flaps, so as to provide some references for improving the survival of expanded flaps. The domestic and abroad related literature about the disorder of blood supplying of expanded flaps was reviewed and analyzed. Handheld Doppler, digital subtraction angiography, computer tomographic angiography, magnetic resonance angiography, and fluorescein angiography can be used as reliable preoperative imaging methods in designing expanded flaps with rich blood supply. Several techniques can be used for monitoring the blood supply of expanded flaps during the early postoperative period including traditional monitoring via physical examination, monitoring via dynamic infrared thermography, near-infrared spectroscopy tissue oximeter, external and implantable Doppler, and more recently developed diffuse correlation spectroscopy. Surgical delay, bloodletting, leech therapy, hyperbaric oxygen, and so on can decrease the risk of necrosis in expanded flaps. The survival of expanded flap is influenced by many factors. Preoperative design by using handheld Doppler and new imaging technology and postoperative early detection of blood supply can provide references of timely intervention, so that ischemic necrosis of the flaps can be reduced, and the success rate of surgery can be improved.

Tissue oximetry during cardiac surgery and in the cardiac intensive care unit: A prospective observational trial.

Background:Cerebral oximetry using near-infrared spectroscopy (NIRS) has well-documented benefits during cardiac surgery. The authors tested the hypothesis that NIRS technology can be used at other sites as a tissue oximeter during cardiac surgery and in the Intensive Care Unit (ICU).Aims:To establish feasibility of monitoring tissue oximetry during and after cardiac surgery, to examine the correlations between tissue oximetry values and cerebral oximetry values, and to examine correlations between oximetry values and mean arterial pressure (MAP) in order to test whether cerebral oximetry can be used as an index organ.Settings and Designs:A large, single-center tertiary care university hospital prospective observational trial of 31 patients undergoing cardiac surgery with cardiopulmonary bypass was conducted.Materials and Methods:Oximetry stickers were applied to both sides of the forehead, the nonarterial line forearm, and the skin above one paraspinal muscle. Data were collected from before anesthesia induction until extubation or for at least 24 h in patients who remained intubated.Statistical Analysis:Categorical variables were evaluated with Chi-square or Fisher's exact tests, while Wilcoxon rank-sum tests or student's t-tests were used for continuous variables.Results:The correlation between cerebral oximetry values and back oximetry values ranged from r = 0.37 to 0.40. The correlation between cerebral oximetry values and forearm oximetry values ranged from r = 0.11 to 0.13. None of the sites correlated with MAP.Conclusions:Tissue oximetry at the paraspinal muscle correlates with cerebral oximetry values while at the arm does not. Further research is needed to evaluate the role of tissue oximetry on outcomes such as acute renal failure, prolonged need for mechanical ventilation, stroke, vascular ischemic complications, prolonged ICU and hospital length of stay, and mortality in cardiac surgery.

Developing a compact multiple laser diode combiner with a single fiber stub output for handheld IoT devices

Many biomedical applications require an efficient combination and localization of multiple discrete light sources (e.g., fluorescence and absorbance imaging). We present a compact 6 channel combiner that couples the output of independent solid-state light sources into a single 400-μm-diameter fiber stub for handheld Internet of Things (IoT) devices. We demonstrate average coupling efficiencies > 80% for each of the 6 laser diodes installed into the prototype. The design supports the use of continuous wave and intensity-modulated laser diodes. This fiber-stub-type beam combiner could be used to construct custom multi-wavelength sources for tissue oximeters, microscopes and molecular imaging technologies. In order to validate its suitability, we applied the developed fiber-stub-type beam combiner to a multi-wavelength light source for a handheld IoT device and demonstrated its feasibility for smart healthcare through a tumor-mimicking silicon phantom.

Detecting Microsurgical Complications with ViOptix Tissue Oximetry in a Pediatric Myocutaneous Free Flap: Case Presentation and Literature Review

Background Microvascular compromise from arterial or venous occlusion is a common cause of free flap failure. The salvage rate following a microvascular compromise is dependent on detecting the problem early and intervening quickly. Methods The ViOptix tissue oximeter measures tissue oxygen saturation using the near-infrared spectroscopy technology. The ViOptix device has an alarm capability to warn of potential compromise to tissue perfusion. The tissue oximetry readings are visible on the bedside monitor and are relayed to a webpage link, which is accessible on a personal computer or mobile device, allowing real-time monitoring. This article presents a case where real-time monitoring allowed almost immediate detection of inadvertent pedicle compromise allowing flap salvage by repositioning without surgical intervention. Results In the case presented, the patient's nurse inadvertently positioned a pillow under the location of the vascular pedicle likely causing microvascular compression. The ViOptix reading dropped and for this reason the nurse contacted the Plastic Surgery team. The drop was confirmed remotely and the flap was urgently evaluated in person. Once the pillow was removed, the ViOptix readings normalized and Doppler signals strengthened in the flap. Discussion While tissue oximetry monitoring does not by itself ensure flap survival, it provides critical information than conventional flap monitoring would allow giving the microsurgeon the opportunity to make a quicker decision. ViOptix tissue oximeters are able to detect vascular compromise even before conventional clinical symptoms are present. Alas in several cases by the time clinical symptoms develop the flap may be beyond salvage.

A validation method for near-infrared spectroscopy based tissue oximeters for cerebral and somatic tissue oxygen saturation measurements

We describe the validation methodology for the NIRS based FORE-SIGHT ELITE® (CAS Medical Systems, Inc., Branford, CT, USA) tissue oximeter for cerebral and somatic tissue oxygen saturation (StO2) measurements for adult subjects submitted to the United States Food and Drug Administration (FDA) to obtain clearance for clinical use. This validation methodology evolved from a history of NIRS validations in the literature and FDA recommended use of Deming regression and bootstrapping statistical validation methods. For cerebral validation, forehead cerebral StO2 measurements were compared to a weighted 70:30 reference (REF CXB) of co-oximeter internal jugular venous and arterial blood saturation of healthy adult subjects during a controlled hypoxia sequence, with a sensor placed on the forehead. For somatic validation, somatic StO2 measurements were compared to a weighted 70:30 reference (REF CXS) of co-oximetry central venous and arterial saturation values following a similar protocol, with sensors place on the flank, quadriceps muscle, and calf muscle. With informed consent, 25 subjects successfully completed the cerebral validation study. The bias and precision (1 SD) of cerebral StO2 compared to REF CXB was −0.14 ± 3.07%. With informed consent, 24 subjects successfully completed the somatic validation study. The bias and precision of somatic StO2 compared to REF CXS was 0.04 ± 4.22% from the average of flank, quadriceps, and calf StO2 measurements to best represent the global whole body REF CXS. The NIRS validation methods presented potentially provide a reliable means to test NIRS monitors and qualify them for clinical use.

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.

MP009: Reliability and interchangeability of measures of two tissue oximeters in healthy volunteers

Introduction: Near-infrared spectroscopy (NIRS) is a non-invasive, continuous and painless method of monitoring oxygen saturation of hemoglobin in any given superficial tissue. Given that hemodynamic instability can affect the oxygen saturation, NIRS could prove to be an interesting tool in quantifying tissue oxygenation, consequently guiding clinical management. The aim of this study was to compare the reliability of two commonly used tissue oximeters, the INVOS 5100c from Covidien and the Equanox 7600 from Nonin. We postulated the Equanox (a more recent tissue oximeter) would have a better reliability than the INVOS. As a secondary outcome, we evaluated whether the measures given by the two oximeters were comparable. Methods: The study population was composed of healthy adult volunteers. Three measurements were taken at six different sites on both sides of the body in a randomized order. Two different sensors were used for each measure. From these measures, two intra-class correlations (ICC) - one inter-sensor and the other intra-sensor - were calculated for each device and compared using the Fisher’s r-to-z transformation method. An additional inter-device ICC was also calculated. We considered ICCs over 0.75 as an indicator of good reliability, while ICCs under 0.40 were considered to represent poor reliability. The sample size was calculated based on the calculation of a unidirectional confidence interval for a parametric ICC. Expecting a 0.75 ICC value, we concluded that 53 participants needed to be recruited in order to attain 80% power and a range of 0.1 towards the low values. Results: Fifty-three healthy volunteers (27 men and 26 women) with a mean age of 31 years (standard deviation 10) were recruited. We found no differences between the repeatability of the INVOS and the Equanox for both inter and intra-sensor reliability (ICC=0.94 (95% confidence interval (CI) 0.86-0.97) versus ICC=0.92 (95%CI 0.86-0.95), p=0.42 and ICC=0.94 (95%CI 0.89-0.96) versus ICC=0.96 (95%CI 0.93-0.98), p=0.21, respectively). However, when compared directly, we found that the readings produced by the two oximeters varied considerably (ICC 0.18 (95%CI -0.10 to 0.43). Conclusion: When taken individually, both tissue oximeters displayed good inter and intra-sensor reliability. However, they oximeters displayed poor inter-devices agreement, their readings varying considerably amongst each other.

Event-related changes of the prefrontal cortex oxygen delivery and metabolism during driving measured by hyperspectral fNIRS.

Recent technological advancements in optical spectroscopy allow for the construction of hyperspectral (broadband) portable tissue oximeters. In a series of our recent papers we have shown that hyperspectral NIRS (hNIRS) has similar or better capabilities in the absolute tissue oximetry as frequency-domain NIRS, and that hNIRS is also very efficient in measuring temporal changes in tissue hemoglobin concentration and oxygenation. In this paper, we extend the application of hNIRS to the measurement of event-related hemodynamic and metabolic functional cerebral responses during simulated driving. In order to check if hNIRS can detect event-related changes in the brain, we measured the concentration changes of oxygenated (HbO2) and deoxygenated (HHb) hemoglobin and of the oxidized state of cytochrome c oxidase, on the right and left prefrontal cortices (PFC) simultaneously during simulated driving on sixteen healthy right-handed participants (aged between 22-32). We used our in-house hNIRS system based on a portable spectrometer with cooled CCD detector and a driving simulator with a fully functional steering wheel and foot pedals. Each participant performed different driving tasks and participants were distracted during some driving conditions by asking general knowledge true/false questions. Our findings suggest that more complex driving tasks (non-distracted) deactivate PFC while distractions during driving significantly activate PFC, which is in agreement with previous fMRI results. Also, we found the changes in the redox state of the cytochrome C oxidase to be very consistent with those in the concentrations of HbO2 and HHb. Overall our findings suggest that in addition to the suitability of absolute tissue oximetry, hyperspectral NIRS may also offer advantages in functional brain imaging. In particular, it can be used to measure the metabolic functional brain activity during actual driving.

Muscle Oxygen Saturation Improves Diagnostic Association Between Initial Vital Signs and Major Hemorrhage: A Prospective Observational Study.

ObjectivesDuring initial assessment of trauma patients, vital signs do not identify all patients with life‐threatening hemorrhage. We hypothesized that a novel vital sign, muscle oxygen saturation (SmO2), could provide independent diagnostic information beyond routine vital signs for identification of hemorrhaging patients who require packed red blood cell (RBC) transfusion.MethodsThis was an observational study of adult trauma patients treated at a Level I trauma center. Study staff placed the CareGuide 1100 tissue oximeter (Reflectance Medical Inc., Westborough, MA), and we analyzed average values of SmO2, systolic blood pressure (sBP), pulse pressure (PP), and heart rate (HR) during 10 minutes of early emergency department evaluation. We excluded subjects without a full set of vital signs during the observation interval. The study outcome was hemorrhagic injury and RBC transfusion ≥ 3 units in 24 hours (24‐hr RBC ≥ 3). To test the hypothesis that SmO2 added independent information beyond routine vital signs, we developed one logistic regression model with HR, sBP, and PP and one with SmO2 in addition to HR, sBP, and PP and compared their areas under receiver operating characteristic curves (ROC AUCs) using DeLong's test.ResultsWe enrolled 487 subjects; 23 received 24‐hr RBC ≥ 3. Compared to the model without SmO2, the regression model with SmO2 had a significantly increased ROC AUC for the prediction of ≥ 3 units of 24‐hr RBC volume, 0.85 (95% confidence interval [CI], 0.75–0.91) versus 0.77 (95% CI, 0.66–0.86; p < 0.05 per DeLong's test). Results were similar for ROC AUCs predicting patients (n = 11) receiving 24‐hr RBC ≥ 9.ConclusionsSmO2 significantly improved the diagnostic association between initial vital signs and hemorrhagic injury with blood transfusion. This parameter may enhance the early identification of patients who require blood products for life‐threatening hemorrhage.