Tissue Oxygen Monitoring Research Articles

Intramuscular Microvascular Flow Sensing for Flap Monitoring in a Porcine Model of Arterial and Venous Occlusion.

Commercially available near infrared spectroscopy devices for continuous free flap tissue oxygenation (StO2) monitoring can only be used on flaps with a cutaneous component. Additionally, differences in skin quality and pigmentation may alter StO2 measurements. Here, we present a novel implantable heat convection probe that measures microvascular blood flow for peripheral monitoring of free flaps, and is not subject to the same issues that limit the clinical utility of near-infrared spectroscopy. The intratissue microvascular flow-sensing device includes a resistive heater, 4 thermistors, a small battery, and a Bluetooth chip, which allows connection to a smart device. Convection of applied heat is measured and mathematically transformed into a measurement of blood flow velocity. This was tested alongside Vioptix T.Ox in a porcine rectus abdominis myocutaneous flap model of arterial and venous occlusion. After flap elevation, the thermal device was deployed intramuscularly, and the cutaneous T.Ox device was applied. Acland clamps were alternately applied to the flap artery and veins to achieve 15 minutes periods of flap ischemia and congestion with a 15 minutes intervening recovery period. In total, five devices were tested in three flaps in three separate pigs over 16 vaso-occlusive events. Flow measurements were responsive to both ischemia and congestion, and returned to baseline during recovery periods. Flow measurements corresponded closely with measured StO2. Cross-correlation at zero lag showed agreement between these two sensing modalities. Two novel devices tested simultaneously on the same flap showed only minor variations in flow measurements. This novel probe is capable of detecting changes in tissue microcirculatory blood flow. This device performed well in a swine model of flap ischemia and congestion, and shows promise as a potentially useful clinical tool. Future studies will investigate performance in fasciocutaneous flaps and characterize longevity of the device over a period of several days.

Invasive brain tissue oxygen and intracranial pressure (ICP) monitoring versus ICP-only monitoring in pediatric severe traumatic brain injury.

Severe traumatic brain injury (TBI) is a leading cause of disability and death in the pediatric population. While intracranial pressure (ICP) monitoring is the gold standard in acute neurocritical care following pediatric severe TBI, brain tissue oxygen tension (PbtO2) monitoring may also help limit secondary brain injury and improve outcomes. The authors hypothesized that pediatric patients with severe TBI and ICP + PbtO2 monitoring and treatment would have better outcomes than those who underwent ICP-only monitoring and treatment. Patients ≤ 18 years of age with severe TBI who received ICP ± PbtO2 monitoring at a quaternary children's hospital between 1998 and 2021 were retrospectively reviewed. The relationships between conventional measurements of TBI were evaluated, i.e., ICP, cerebral perfusion pressure (CPP), and PbtO2. Differences were analyzed between patients with ICP + PbtO2 versus ICP-only monitoring on hospital and pediatric intensive care unit (PICU) length of stay (LOS), length of intubation, Pediatric Intensity Level of Therapy scale score, and functional outcome using the Glasgow Outcome Score-Extended (GOS-E) scale at 6 months postinjury. Forty-nine patients, including 19 with ICP + PbtO2 and 30 with ICP only, were analyzed. There was a weak negative association between ICP and PbtO2 (β = -0.04). Conversely, there was a strong positive correlation between CPP ≥ 40 mm Hg and PbtO2 ≥ 15 and ≥ 20 mm Hg (β = 0.30 and β = 0.29, p < 0.001, respectively). An increased number of events of cerebral PbtO2 < 15 mm Hg or < 20 mm Hg were associated with longer hospital (p = 0.01 and p = 0.022, respectively) and PICU (p = 0.015 and p = 0.007, respectively) LOS, increased duration of mechanical ventilation (p = 0.015 when PbtO2 < 15 mm Hg), and an unfavorable 6-month GOS-E score (p = 0.045 and p = 0.022, respectively). An increased number of intracranial hypertension episodes (ICP ≥ 20 mm Hg) were associated with longer hospital (p = 0.007) and PICU (p < 0.001) LOS and longer duration of mechanical ventilation (p < 0.001). Lower minimum hourly and average daily ICP values predicted favorable GOS-E scores (p < 0.001 for both). Patients with ICP + PbtO2 monitoring experienced longer PICU LOS (p = 0.018) compared to patients with ICP-only monitoring, with no significant GOS-E score difference between groups (p = 0.733). An increased number of cerebral hypoxic episodes and an increased number of intracranial hypertension episodes resulted in longer hospital LOS and longer duration of mechanical ventilator support. An increased number of cerebral hypoxic episodes also correlated with less favorable functional outcomes. In contrast, lower minimum hourly and average daily ICP values, but not the number of intracranial hypertension episodes, were associated with more favorable functional outcomes. There was a weak correlation between ICP and PbtO2, supporting the importance of multimodal invasive neuromonitoring in pediatric severe TBI.

Adjustable and Magnetic Resonance Imaging Conditional Implantation of a Licox Brain Tissue Oxygenation Probe in Neurosurgery: Technical Note

Continuous bedside brain tissue oxygen monitoring is an essential part of managing comatose patients with acute brain injury. Maintenance of adequate brain oxygenation has been established as an important goal in neurocritical care to prevent patients from secondary ischemia. As patients with subarachnoid hemorrhage and traumatic brain injury often require early magnetic resonance imaging, conventionally implanted metal bolts are disadvantageous due to massive artifacts. We hereby report a novel technique of magnetic resonance imaging conditional bedside implantation of a brain tissue oxygenation probe. We performed bedside implantation of a Licox brain tissue oxygenation probe with a peripheral venous cannula that is placed through a plastic bolt placed on a burr hole. Bedside implantation of a Licox brain tissue oxygenation probe was successfully performed in a novel fashion. This article describes the feasibility of a novel technique of bedside implantation of a Licox brain tissue oxygenation probe, resulting in a length-adjustable insertion and rigid fixation without metal artifacts in early magnetic resonance imaging.

P56: Morbidity and Mortality Associated with Intra-Aortic Counterpulsation Balloon Pump Use

Background: Postoperative acute limb ischemia (pALI) is a vascular emergency better prevented than treated. Knowledge of the predisposing factors is vital to prevention and early recognition. In this study, we examined the predictors and risk of 30-day postoperative mortality of pALI among patients who underwent open-heart surgery. Methods: We retrospectively analyzed data collected at a single university hospital as part of the Society of Thoracic Surgeons National Adult Cardiac Surgery database between January 2006 and January 2018. The primary outcome was pALI (coded in STS as CVaLbIsc) defined as any ischemic event of the arterial system of either upper or lower limbs. For this analysis transcatheter procedure and entries with the missing outcome variable were excluded. The final sample was divided into 2 groups based on the presence of pALI or not. Logistics regression model was used to assess for association between pALI and the preop variable. KM curves were plotted to compare survival probability between the 2 groups. Results: Among the 5231 records included in this analysis, there were 60 (1.15%) cases of pALI. Multivariate regression model adjusting for known risk factors of acute limb ischemia showed preop IABP use (OR 4.16(95%CI 2.22 - 7.80), p=<.0001); body surface area (OR 0.19 (95%CI 0.07 - 0.52), p= 0.001); emergent/urgent procedures (OR 2.57 (95%CI 1.32 - 4.98), p=0.005; history of PVD (OR 4.89 (95%CI 2.83 - 8.43), p=<.0001); preop IV steroid use (OR 3.07 (95%CI 1.32 - 7.16), p=0.009; history of infective endocarditis (OR 3.66 (95%CI 1.61 - 8.29), p=0.002; Cardiogenic shock (OR 2.86 (95%CI 1.41 - 5.78), p=0.003) are independent predictors of pALI. ROC curve AUC of final model= 0.83. Conclusion: A knowledge of the above risk factors may help identify at-risk individuals that may benefit from perioperative limb tissue oxygenation or perfusion monitoring thereby facilitating prompt diagnosis and intervention.

PHOTOACOUSTIC PHASE ANGLE FOR NONINVASIVE MONITORING OF MICROCIRCULATORY CHANGE IN HUMAN SKIN: A PRELIMINARY INVESTIGATION

Measurement using the currently available tissue oxygen monitoring systems, such as pulse oximeter, is unreliable in patients with compromised microcirculation. Others offer high diagnostic accuracy, but are complicated and expensive in their operation. This paper is motivated to study the use of photoacoustic (PA) phase change as a predictor of skin tissue oxygen levels. This work used EPOCH 650 ultrasonic flaw detector with a longitudinal transducer and a red laser light of wavelength 633 nm for measurement of PA signals. This pilot study was conducted on a group of four human subjects. The pressure waves were collected from their anterior left arm under three experimental conditions, namely at rest, venous and arterial blood flow occlusions, for extraction of hemoglobin absorption dependent phase information.

Abstract 545: Incidence, Predictors And Risk Of 30-day Mortality Of Postoperative Acute Limb Ischemia Following Open-Heart Surgery

Introduction: Postoperative acute limb ischemia (pALI) is a vascular emergency better prevented than treated. Knowledge of the predisposing factors is vital to prevention and early recognition. In this study, we examined the incidence, predictors, and the risk of 30-day mortality of pALI among patients who underwent open-heart surgery. Methods: We retrospectively analyzed data collected at a single university hospital as part of the Society of Thoracic Surgeons National Adult Cardiac Surgery database between January 2006 and January 2018. The primary outcome was pALI (coded in STS as CVaLbIsc) defined as any ischemic event of the arterial system of either upper or lower limbs. For this analysis transcatheter procedure and entries with the missing outcome variable were excluded. The final sample was divided into 2 groups based on the presence of pALI or not. Logistics regression models were used to assess for association between pALI and the preop variables. KM curves were plotted to compare survival probability between the 2 groups. Results: Among the 5231 records included in this analysis, there were 60 (1.15%) cases of pALI. Multivariate regression model adjusting for known risk factors of acute limb ischemia showed body surface area (OR 0.19 (95%CI 0.07 - 0.52), p= 0.001); emergent/urgent procedures (OR 2.57 (95%CI 1.32 - 4.98), p=0.005; history of PVD (OR 4.89 (95%CI 2.83 - 8.43), p=&lt;.0001); preop IABP use (OR 4.16(95%CI 2.22 - 7.80), p=&lt;.0001); preop IV steroid use (OR 3.07 (95%CI 1.32 - 7.16), p=0.009; history of infective endocarditis (OR 3.66 (95%CI 1.61 - 8.29), p=0.002; Cardiogenic shock (OR 2.86 (95%CI 1.41 - 5.78), p=0.003) are independent predictors of pALI. ROC curve AUC of the final model= 0.83. Conclusion: A knowledge of the above risk factors may help identify at-risk individuals that may benefit from perioperative limb tissue oxygenation or perfusion monitoring thereby facilitating prompt diagnosis and intervention.

Assessment by Multi‐Distance Hyperspectral NIRS of Changes in the Oxidation State of Cytochrome C Oxidase (oxCCO) to Carotid Artery Compressions

IntroductionThe occlusion of the common carotid artery (CCA) during carotid endarterectomy (CEA) is associated with a risk of cerebral ischemia due to inadequate collateral blood flow1. By monitoring tissue oxygen saturation (StO2), near‐infrared spectroscopy (NIRS) is frequently employed during CEA2 to determine sufficient oxygen delivery. However, StO2 is only a proxy of oxygen metabolism and an unreliable marker of ischemic injury. In contrast, cytochrome c oxidase (oxCCO) is an enzyme in the mitochondrial electron transport chain and therefore a specific marker of aerobic metabolism3. Thus, the aim of this study was to assess the ability of a multi‐distance hyperspectral (hs) NIRS to monitor changes in StO2 and oxCCO during CCA compressions in healthy participants. We hypothesized that changes in oxCCO concentration would be greater in the brain (i.e., long source‐detector distance, SDD) than in the extracerebral tissue (i.e., short SDD), and this difference would be larger than that of StO2.MethodsWe modified an in‐house built hsNIRS4 to include a second channel for acquiring data at two SDD (1 and 3 cm) to detect potential changes in the extracerebral tissue. Data from 10 young, healthy participants was acquired continuously during one 30‐second unilateral digital CCA compression, performed ipsilateral to the location of the optic probes. In addition, cerebral blood flow index was determined using diffuse correlation spectroscopy and mean arterial blood pressure by finger photoplethysmography.ResultsDuring CCA compression, the change in oxCCO at 3 cm vs. 1 cm (0.4 ± 0.3 µM vs. 0.06 ± 0.1 µM, p = 0.027) was approximately 50% greater than the change in StO2 at 3 cm vs. 1cm (‐4.0 ± 2.2% vs. 1.2 ± 0.7% p = 0.007). The corresponding decrease in cerebral blood flow was 57 ± 14% (p &lt; 0.001 vs. baseline). Mean arterial blood pressure increased 4 ± 1 mmHg (p &lt; 0.001 vs. baseline).DiscussionA larger difference between the two distances was observed for oxCCO than StO2, likely due to the greater concentration of mitochondria in the brain compared to extracerebral tissues. Collecting multi‐distance hsNIRS demonstrated the enhanced sensitivity of oxCCO to the brain. Lastly, this study demonstrates the utility of momentary unilateral CCA compressions as a fast, easy, and strong perturbation for transiently altering cerebral inflow and metabolism.References(1) Aceto, Eur. J. Anestesiol.(2020); (2) Yu, Cochrane Database Syst. Rev.(2014); (3) Bale, J. Biomed. Opt. (2020); (4) Rajaram, Brain Sci (2020).

The Complex Relationship Between Cooling Parameters and Neuroprotection in a Model of Selective Hypothermia.

BackgroundHypothermia remains the best studied neuroprotectant. Despite extensive positive large and small animal data, side effects continue to limit human applications. Selective hypothermia is an efficient way of applying neuroprotection to the brain without the systemic complications of global hypothermia. However, optimal depth and duration of therapeutic hypothermia are still unknown. We analyzed a large animal cohort study of selective hypothermia for statistical relationships between depth or duration of hypothermia and the final stroke volume.MethodsA cohort of 30 swine stroke subjects provided the dataset for normothermic and selective hypothermic animals. Hypothermic parameters including duration, temperature nadir, and an Area Under the Curve measurement for 34 and 30°C were correlated with the final infarct volumes measured by MRI and histology.ResultsBetween group comparisons continue to demonstrate a reduction in infarct volume with selective hypothermia. Histologically-derived infarct volumes were 1.2 mm3 smaller in hypothermia-treated pigs (P = 0.04) and showed a similar, but non-significant reduction in MRI (P = 0.15). However, within the selective hypothermia group, more intense cooling, as measured through increased AUC 34 and decreased temperature nadir was associated with larger infarct proportions by MRI [Pearson's r = 0.48 (p = 0.05) and r = −0.59 (p = 0.01), respectively]. Reevaluation of the entire cohort with quadratic regression demonstrated a U-shaped pattern, wherein the average infarct proportion was minimized at 515 degree-minutes (AUC34) of cooling, and increased thereafter. In a single case of direct brain tissue oxygen monitoring during selective hypothermia, brain tissue oxygen strongly correlated with brain temperature reduction over the course of selective hypothermia to 23°C.ConclusionsIn a large animal model of selective hypothermia applied to focal ischemia, there is a non-monotone relationship between duration and depth of hypothermia and stroke volume reduction. This suggests a limit to depth or duration of selective hypothermia for optimal neuroprotection. Further research is required to delineate more precise depth and duration limits for selective hypothermia.

New aspects in neurointensive and emergency medicine: the most important studies in a review and overview

Die vorliegende Übersichtsarbeit fasst wichtige klinische Studien der neurologischen Notfall- und Intensivmedizin zwischen 2020 und 2021 zusammen zu den Themen: rekanalisierende Therapie beim ischämischen Schlaganfall, Anwendbarkeit und Auswirkung eines zerebralen Sauerstoffgewebemonitorings bei Subarachnoidalblutung, Wirksamkeit induzierter Hypothermie bei Patienten mit „cardiac arrest“ (CA), Wertigkeit früher kranialer Bildgebung nach CA, Relevanz eines schnellen Managements und medikamentöser Therapie beim Status epilepticus sowie Inzidenz von Critical-illness-Polyneuropathie-Myopathie bei intensivpflichtigen COVID-Patienten.

Smartphone-Based and Miniaturized Electrochemical Biosensing System for L-Lactate Detection

Real-time detection of L-lactate is crucial in monitoring tissue oxygenation and organ metabolism in surgery patients during the perioperative period. Traditional commercial L-lactate detection techniques using bulky and expensive instruments are time-consuming, hindering timely feedback in the operating room. Herein, utilizing the modified screen-printed carbon electrode, a portable and user-friendly smartphone-based electrochemical biosensing system, integrated with a miniaturized potentiostat via wireless transmission, was successfully constructed for bedside detection of L-lactate. It has a wide sensing range from 0.05–10 mM and a low limit of detection (9.1 μM). Bland–Altman analysis shows an acceptable agreement with the values of a mean difference (0.114 ± 0.3482) between results obtained with the commercial blood gas analysis instrument and the developed portable system. Accordingly, the developed portable system exhibits a great potential in point-of-care testing owing to its portability and rapid response in L-lactate detection during perioperative monitoring.

Is Sphingosine-1-Phosphate a Regulator of Tumor Vascular Functionality?

Simple SummaryDespite substantial theoretical and experimental support for using vascular normalization as cancer therapy, effectively achieving this strategy in the clinic remains complex. In the present paper, we propose a novel potential approach for the induction of tumor vascular normalization, reduction of hypoxia, and improvement of conventional treatment in cancer patients. This approach consists of the pharmacological modulation of a patient’s plasma S1P levels which through a PDGF signaling can enhance tumor vasculature functionality and reduce hypoxia. This approach is proposed following a clinical observation in pancreatic adenocarcinoma patients and pre-clinical data in different in vivo tumor models, and is supported by a review of the literature describing the biological role of S1P in vascular functionality regulation.Increasing evidence indicates that tumor vasculature normalization could be an appropriate strategy to increase therapies’ efficacy in solid tumors by decreasing hypoxia and improving drug delivery. We searched for a novel approach that reduces hypoxia and enhances chemotherapy efficacy in pancreatic adenocarcinoma which is characterized by disrupted blood vasculature associated with poor patient survival. Clinical significance of plasma levels of the angiogenic lipid sphingosine-1-phosphate (S1P) was assessed at baseline in 175 patients. High plasma S1P concentration was found to be a favorable prognostic/predictive marker in advanced/metastatic pancreatic adenocarcinoma patients treated by gemcitabine alone but not in patients receiving a combination gemcitabine and PDGFR-inhibitor. In pancreatic adenocarcinoma PDX models, oral administration of an S1P lyase inhibitor (LX2931) significantly increased plasma S1P levels, decreased tumor expression of the hypoxia marker (CA IX), and enhanced chemotherapy efficacy when combined with gemcitabine treatment. The direct effect of S1P on tumor oxygenation was assessed by administration of S1P onto tumor-grafted CAM model and measuring intra-tumoral pO2 using a tissue oxygen monitor. S1P increased pO2 in a tumor-CAM model. Thus, increasing plasma S1P is a promising strategy to decrease tumor hypoxia and enhance therapy efficacy in solid tumors. S1P may act as a tumor vasculature normalizer.

Brain Oxygen Optimization in Severe Traumatic Brain Injury (BOOST-3): a multicentre, randomised, blinded-endpoint, comparative effectiveness study of brain tissue oxygen and intracranial pressure monitoring versus intracranial pressure alone

IntroductionManagement of traumatic brain injury (TBI) includes invasive monitoring to prevent secondary brain injuries. Intracranial pressure (ICP) monitor is the main measurement used to that intent but cerebral hypoxia can...

Prediction of return of spontaneous circulation during cardiopulmonary resuscitation by pulse-wave cerebral tissue oxygen saturation: a retrospective observational study

BackgroundIt is difficult to predict the return of spontaneous circulation (ROSC) during cardiopulmonary resuscitation (CPR). Cerebral tissue oxygen saturation during CPR, as measured by near-infrared spectroscopy (NIRS), is anticipated to predict ROSC. General markers of cerebral tissue oxygen saturation, such as the tissue oxygenation index (TOI), mainly reflect venous oxygenation, whereas pulse-wave cerebral tissue oxygen saturation (SnO2), which represents hemoglobin oxygenation in the pulse wave within the cerebral tissue, is an index of arterial and venous oxygenation. Thus, SnO2 may reflect arterial oxygenation to a greater degree than does TOI. Therefore, we conducted this study to verify our hypothesis that SnO2 measured during CPR can predict ROSC.MethodsCardiac arrest patients who presented at the Emergency Department of Yamagata University Hospital in Japan were included in this retrospective, observational study. SnO2 and TOI were simultaneously measured at the patient’s forehead using an NIRS tissue oxygenation monitor (NIRO 200-NX; Hamamatsu Photonics, Japan). We recorded the initial, mean, and maximum values during CPR. We plotted receiver operating characteristic curves and calculated the area under the curve (AUC) to predict ROSC.ResultsForty-two patients were included. SnO2 was significantly greater in the ROSC group than in the non-ROSC group in terms of the initial (37.5% vs 24.2%, p = 0.015), mean (44.6% vs 10.8%, p < 0.001), and maximum (79.7% vs 58.4%, p < 0.001) values. Although the initial TOI was not significantly different between the two groups, the mean (45.1% vs 36.8%, p = 0.018) and maximum (71.0% vs 46.3%, p = 0.001) TOIs were greater in the ROSC group than in the non-ROSC group. The AUC was 0.822 for the mean SnO2 (95% confidence interval [CI]: 0.672–0.973; cut-off: 41.8%), 0.821 for the maximum SnO2 (95% CI: 0.682–0.960; cut-off: 70.8%), and 0.809 for the maximum TOI (95% CI: 0.667–0.951; cut-off: 49.3%).ConclusionSnO2 values measured during CPR, including immediately after arrival at the emergency department, were higher in the ROSC group than in the non-ROSC group.

Monitoring Spinal Cord Tissue Oxygen in Patients With Acute, Severe Traumatic Spinal Cord Injuries.

To determine the feasibility of monitoring tissue oxygen tension from the injury site (pscto2) in patients with acute, severe traumatic spinal cord injuries. We inserted at the injury site a pressure probe, a microdialysis catheter, and an oxygen electrode to monitor for up to a week intraspinal pressure (ISP), spinal cord perfusion pressure (SCPP), tissue glucose, lactate/pyruvate ratio (LPR), and pscto2. We analyzed 2,213 hours of such data. Follow-up was 6-28 months postinjury. Single-center neurosurgical and neurocritical care units. Twenty-six patients with traumatic spinal cord injuries, American spinal injury association Impairment Scale A-C. Probes were inserted within 72 hours of injury. Insertion of subarachnoid oxygen electrode (Licox; Integra LifeSciences, Sophia-Antipolis, France), pressure probe, and microdialysis catheter. pscto2 was significantly influenced by ISP (pscto2 26.7 ± 0.3 mm Hg at ISP > 10 mmHg vs pscto2 22.7 ± 0.8 mm Hg at ISP ≤ 10 mm Hg), SCPP (pscto2 26.8 ± 0.3 mm Hg at SCPP < 90 mm Hg vs pscto2 32.1 ± 0.7 mm Hg at SCPP ≥ 90 mm Hg), tissue glucose (pscto2 26.8 ± 0.4 mm Hg at glucose < 6 mM vs 32.9 ± 0.5 mm Hg at glucose ≥ 6 mM), tissue LPR (pscto2 25.3 ± 0.4 mm Hg at LPR > 30 vs pscto2 31.3 ± 0.3 mm Hg at LPR ≤ 30), and fever (pscto2 28.8 ± 0.5 mm Hg at cord temperature 37-38°C vs pscto2 28.7 ± 0.8 mm Hg at cord temperature ≥ 39°C). Tissue hypoxia also occurred independent of these factors. Increasing the Fio2 by 0.48 increases pscto2 by 71.8% above baseline within 8.4 minutes. In patients with motor-incomplete injuries, fluctuations in pscto2 correlated with fluctuations in limb motor score. The injured cord spent 11% (39%) hours at pscto2 less than 5 mm Hg (< 20 mm Hg) in patients with motor-complete outcomes, compared with 1% (30%) hours at pscto2 less than 5 mm Hg (< 20 mm Hg) in patients with motor-incomplete outcomes. Complications were cerebrospinal fluid leak (5/26) and wound infection (1/26). This study lays the foundation for measuring and altering spinal cord oxygen at the injury site. Future studies are required to investigate whether this is an effective new therapy.

Numerical Optimisation of a NIRS Device for Monitoring Tissue Oxygen Saturation.

The present work aims to develop a wearable, textile-integrated NIRS-based tissue oxygen saturation (StO2) monitor for alerting mobility-restricted individuals - such as paraplegics - of critical tissue oxygen de-saturation in the regions such as the sacrum and the ischial tuberosity; these regions are proven to be extremely susceptible to the development of pressure injuries (PI).Using a combination of numerical methods including finite element analysis, image reconstruction, stochastic gradient descent with momentum (SGDm) and genetic algorithms, a methodology was developed to define the optimal combination of wavelengths and source-detector geometry needed for measuring the StO2 in tissue up to depths of 3 cm. The sensor design was optimised to account for physiologically relevant adipose tissue thicknesses (ATT) between 1 mm and 5 mm. The approach assumes only a priori knowledge of the optical properties of each of the three tissue layers used in the model (skin, fat, muscle) based on the absorption and scattering coefficients of four chromophores (O2Hb, HHb, H2O and lipid).The results show that the selected wavelengths as well as the source-detector geometries and number of sources and detectors depend on ATT and the degree and volume of the hypoxic regions. As a result of a genetic algorithm used to combine the various optimised designs into a single sensor layout, a group of four wavelengths was chosen, coinciding with the four chromophores and agreeing very well with literature. The optimised number of source points and detector points and their geometry resulted in good reconstruction of the StO2 across a wide range of layer geometries.

Monitoring Tissue Oxygen Dynamics with a Novel Implantable Hydrogel Sensor in Patients with Peripheral Arterial Disease

Monitoring Tissue Oxygen Dynamics with a Novel Implantable Hydrogel Sensor in Patients with Peripheral Arterial Disease

Hyperspectral imaging for perioperative monitoring of microcirculatory tissue oxygenation and tissue water content in pancreatic surgery \u2014 an observational clinical pilot study

BackgroundHyperspectral imaging (HSI) could provide extended haemodynamic monitoring of perioperative tissue oxygenation and tissue water content to visualize effects of haemodynamic therapy and surgical trauma. The objective of this study was to assess the capacity of HSI to monitor skin microcirculation and possible relations to perioperative organ dysfunction in patients undergoing pancreatic surgery.MethodsThe hyperspectral imaging TIVITA® Tissue System was used to evaluate superficial tissue oxygenation (StO2), deeper layer tissue oxygenation (near-infrared perfusion index (NPI)), haemoglobin distribution (tissue haemoglobin index (THI)) and tissue water content (tissue water index (TWI)) in 25 patients undergoing pancreatic surgery. HSI parameters were measured before induction of anaesthesia (t1), after induction of anaesthesia (t2), postoperatively before anaesthesia emergence (t3), 6 h after emergence of anaesthesia (t4) and three times daily (08:00, 14:00, 20:00 ± 1 h) at the palm and the fingertips until the second postoperative day (t5–t10). Primary outcome was the correlation of HSI with perioperative organ dysfunction assessed with the perioperative change of SOFA score.ResultsTwo hundred and fifty HSI measurements were performed in 25 patients. Anaesthetic induction led to a significant increase of tissue oxygenation parameters StO2 and NPI (t1–t2). StO2 and NPI decreased significantly from t2 until the end of surgery (t3). THI of the palm showed a strong correlation with haemoglobin levels preoperatively (t2:r = 0.83, p < 0.001) and 6 h postoperatively (t4: r = 0.71, p = 0.001) but not before anaesthesia emergence (t3: r = 0.35, p = 0.10). TWI of the palm and the fingertip rose significantly between pre- and postoperative measurements (t2–t3). Higher blood loss, syndecan level and duration of surgery were associated with a higher increase of TWI. The perioperative change of HSI parameters (∆t1–t3) did not correlate with the perioperative change of the SOFA score.ConclusionThis is the first study using HSI skin measurements to visualize tissue oxygenation and tissue water content in patients undergoing pancreatic surgery. HSI was able to measure short-term changes of tissue oxygenation during anaesthetic induction and pre- to postoperatively. TWI indicated a perioperative increase of tissue water content. Perioperative use of HSI could be a useful extension of haemodynamic monitoring to assess the microcirculatory response during haemodynamic therapy and major surgery.Trial registrationGerman Clinical Trial Register, DRKS00017313 on 5 June 2019

Application of the Kohonen neural network for monitoring tissue oxygen supply under hypoxic conditions

The article presents the results of application of the Kohonen artificial neural network (KANN) in assessing the oxygen status of human tissues, as well as for studying the adaptive-compensatory response of the body to functional load. In the experiment, the registered digital oxygen images of the tissue of 31 subjects were distributed into three classes using the KANN. Each group is characterised by different resistance of the organism to hypoxia. The research results have shown the effectiveness of using an artificial neural network structure and the possibility of its implementation for recognition of the functional state of a person under conditions of metabolic hypoxia; it seems relevant and has theoretical and practical significance in the framework of ecological physiology.

Utilization of Brain Tissue Oxygenation Monitoring and Association with Mortality Following Severe Traumatic Brain Injury.

The aim of this study was to describe the utilization patterns of brain tissue oxygen (PbtO2) monitoring following severe traumatic brain injury (TBI) and determine associations with mortality, health care use, and pulmonary toxicity. We conducted a retrospective cohort study of patients from United States trauma centers participating in the American College of Surgeons National Trauma Databank between 2008 and 2016. We examined patients with severe TBI (defined by admission Glasgow Coma Scale score≤8) over the age of 18years who survived more than 24h from admission and required intracranial pressure (ICP) monitoring. The primary exposure was PbtO2 monitor placement. The primary outcome was hospital mortality, defined as death during the hospitalization or discharge to hospice. Secondary outcomes were examined to determine the association of PbtO2 monitoring with health care use and pulmonary toxicity and included the following: (1) intensive care unit length of stay, (2) hospital length of stay, and (3) development of acute respiratory distress syndrome (ARDS). Regression analysis was used to assess differences in outcomes between patients exposed to PbtO2 monitor placement and those without exposure by using propensity weighting to address selection bias due to the nonrandom allocation of treatment groups and patient dropout. A total of 35,501 patients underwent placement of an ICP monitor. There were 1,346 (3.8%) patients who also underwent PbtO2 monitor placement, with significant variation regarding calendar year and hospital. Patients who underwent placement of a PbtO2 monitor had a crude in-hospital mortality of 31.1%, compared with 33.5% in patients who only underwent placement of an ICP monitor (adjusted risk ratio 0.84, 95% confidence interval 0.76-0.93). The development of the ARDS was comparable between patients who underwent placement of a PbtO2 monitor and patients who only underwent placement of an ICP monitor (9.2% vs. 9.8%, adjusted risk ratio 0.89, 95% confidence interval 0.73-1.09). PbtO2 monitor utilization varied widely throughout the study period by calendar year and hospital. PbtO2 monitoring in addition to ICP monitoring, compared with ICP monitoring alone, was associated with a decreased in-hospital mortality, a longer length of stay, and a similar risk of ARDS. These findings provide further guidance for clinicians caring for patients with severe TBI while awaiting completion of further randomized controlled trials.

The effect of selective cerebral perfusion on cerebral versus somatic tissue oxygenation during aortic coarctation repair in neonates and infants

BackgroundSuboptimal tissue perfusion and oxygenation may be the root cause of certain perioperative complications in neonates and infants having complicated aortic coarctation repair. Practical, effective, and real-time monitoring of organ perfusion and/or tissue oxygenation may provide early warning of end-organ mal-perfusion.Methods Neonates/infants who were scheduled for aortic coarctation repair with cardiopulmonary bypass (CPB) and selective cerebral perfusion (SCP) from January 2015 to February 2017 in Children’s Hospital of Nanjing Medical University participated in this prospective observational study. Cerebral and somatic tissue oxygen saturation (SctO2 and SstO2) were monitored on the forehead and at the thoracolumbar paraspinal region, respectively. SctO2 and SstO2 were recorded at different time points (baseline, skin incision, CPB start, SCP start, SCP end, aortic opening, CPB end, and surgery end). SctO2 and SstO2 were correlated with mean arterial pressure (MAP) and partial pressure of arterial blood carbon dioxide (PaCO2).ResultsData of 21 patients were analyzed (age=75±67 days, body weight=4.4±1.0 kg). SstO2 was significantly lower than SctO2 before aortic opening and significantly higher than SctO2 after aortic opening. SstO2 correlated with leg MAP when the measurements during SCP were (r=0.67, p<0.0001) and were not included (r=0.46, p<0.0001); in contrast, SctO2 correlated with arm MAP only when the measurements during SCP were excluded (r=0.14, p=0.08 vs. r=0.66, p<0.0001). SCP also confounded SctO2/SstO2’s correlation with PaCO2; when the measurements during SCP were excluded, SctO2 positively correlated with PaCO2 (r=0.65, p<0.0001), while SstO2 negatively correlated with PaCO2 (r=-0.53, p<0.0001).Conclusions SctO2 and SstO2 have distinct patterns of changes before and after aortic opening during neonate/infant aortic coarctation repair. SctO2/SstO2’s correlations with MAP and PaCO2 are confounded by SCP. The outcome impact of combined SctO2/SstO2 monitoring remains to be studied.