Continuous bedside monitoring of brain tissue oxygen levels is a crucial component in the management of comatose patients suffering from acute brain injury on neurointensive care units. Ensuring ...sufficient brain oxygenation is recognized as an essential objective within neurocritical care, aimed at safeguarding patients from secondary ischemia. Hypoperfusion in occipital and the posterior watershed regions often remains undetected, as the placement of probes in these areas is challenging. A major concern is that patients would have to lie on the traditionally used implanted bolts due to the occipital entry point of the probes. Therefore, we present a novel technique compatible with magnetic resonance imaging that enables bedside placement of brain tissue oxygen probes without the use of a bolt in these areas.
We conducted bedside implantations of Licox brain tissue oxygenation probes through Frazier's point utilizing peripheral venous cannulas on burr holes eliminating the need for bolts.
A novel approach was successfully established for the bedside implantation of a Licox brain tissue oxygenation probe for occipital regions.
This technical note describes the feasibility of a novel, simple, and straightforward bedside technique for boltless implantation of Licox brain tissue oxygen probes leading to rigid fixation and compatibility with magnetic resonance imaging.
The Tibetans' better aerobic exercise capacity at altitude remains ill-understood. We tested the hypothesis that Tibetans display better muscle and brain tissue oxygenation during exercise in ...hypoxia. Using near-infrared spectrometry (NIRS) to provide indices of tissue oxygenation, we measured oxy- and deoxy-hemoglobin (O
Hb and HHb, respectively) responses of the vastus lateralis muscle and the right prefrontal cortex in ten Han Chinese and ten Tibetans during incremental cycling to exhaustion in a pressure-regulated chamber at simulated sea-level (air at 1 atm: normobaric normoxia) and 5,000 m (air at 0.5 atm: hypobaric hypoxia). Hypoxia reduced aerobic capacity by ∼22% in both groups (
= 0.8,
< 0.001 vs. normoxia), while Tibetans consistently outperformed their Han Chinese counterpart by ∼32% in normoxia and hypoxia (
= 1.0,
= 0.008). We found cerebral O
Hb was higher in Tibetans at normoxic maximal effort compared Han (
= 0.001), while muscle O
Hb was not different (
= 0.240). Hypoxic exercise lowered muscle O
Hb in Tibetans by a greater extent than in Han (interaction effect:
< 0.001 vs. normoxic exercise). Muscle O
Hb was lower in Tibetans when compared to Han during hypoxic exercise (
= 0.9,
= 0.003), but not during normoxic exercise (
= 0.4,
= 0.240). Muscle HHb was not different between the two groups during normoxic and hypoxic exercise (
= 0.778). Compared to Han, our findings revealed a higher brain tissue oxygenation in Tibetans during maximal exercise in normoxia, but lower muscle tissue oxygenation during exercise in hypoxia. This would suggest that the Tibetans privileged oxygenation of the brain at the expense of that of the muscle.
Background The primary aim was to explore the association of global cerebral physiological variables including intracranial pressure (ICP), cerebrovascular reactivity (PRx), cerebral perfusion ...pressure (CPP), and deviation from the PRx-based optimal CPP value ( increment CPPopt; actual CPP-CPPopt) in relation to brain tissue oxygenation (pbtO2) in traumatic brain injury (TBI).
Methods A total of 425 TBI patients with ICP- and pbtO2 monitoring for at least 12 h, who had been treated at the neurocritical care unit, Addenbrooke's Hospital, Cambridge, UK, between 2002 and 2022 were included. Generalized additive models (GAMs) and linear mixed effect models were used to explore the association of ICP, PRx, CPP, and CPPopt in relation to pbtO(2.) PbtO(2) < 20 mmHg, ICP > 20 mmHg, PRx > 0.30, CPP < 60 mmHg, and increment CPPopt < - 5 mmHg were considered as cerebral insults.
Results PbtO(2) < 20 mmHg occurred in median during 17% of the monitoring time and in less than 5% in combination with ICP > 20 mmHg, PRx > 0.30, CPP < 60 mmHg, or increment CPPopt < - 5 mmHg. In GAM analyses, pbtO(2 )remained around 25 mmHg over a large range of ICP (0;50 mmHg) and PRx - 1;1, but deteriorated below 20 mmHg for extremely low CPP below 30 mmHg and increment CPPopt below - 30 mmHg. In linear mixed effect models, ICP, CPP, PRx, and increment CPPopt were significantly associated with pbtO(2), but the fixed effects could only explain a very small extent of the pbtO(2) variation.
Conclusions PbtO(2 )below 20 mmHg was relatively frequent and often occurred in the absence of disturbances in ICP, PRx, CPP, and increment CPPopt. There were significant, but weak associations between the global cerebral physiological variables and pbtO(2), suggesting that hypoxic pbtO2 is often a complex and independent pathophysiological event. Thus, other variables may be more crucial to explain pbtO(2) and, likewise, pbtO2 may not be a suitable outcome measure to determine whether global cerebral blood flow optimization such as CPPopt therapy is successful.
Genetic induction of hypoxia signaling by deletion of the von Hippel-Lindau (Vhl) protein in mesenchymal PDGFR-β+ cells leads to abundant HIF-2 dependent erythropoietin (EPO) expression in the cortex ...and outer medulla of the kidney. This rather unique feature of kidney PDGFR-β+ cells promote questions about their special characteristics and general functional response to hypoxia. To address these issues, we characterized kidney PDGFR-β+ EPO expressing cells based on additional cell markers and their gene expression profile in response to hypoxia signaling induced by targeted deletion of Vhl or exposure to low oxygen and carbon monoxide respectively, and after unilateral ureteral obstruction. CD73+, Gli1+, tenascin C+ and interstitial SMMHC+ cells were identified as zonally distributed subpopulations of PDGFR-β+ cells. EPO expression could be induced by Vhl deletion in all PDGFR-β+ subpopulations. Under hypoxemic conditions, recruited EPO+ cells were mostly part of the CD73+ subpopulation. Besides EPO production, expression of adrenomedullin and regulator of G-protein signaling 4 was upregulated in PDGFR-β+ subpopulations in response to the different hypoxic stimuli. Thus, different kidney interstitial PDGFR-β+ subpopulations exist, capable of producing EPO in response to different stimuli. Activation of hypoxia signaling in these cells also induces factors likely contributing to improved kidney interstitial tissue oxygenation.
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Intelligent systems in interventional healthcare depend on the reliable perception of the environment. In this context, photoacoustic tomography (PAT) has emerged as a non-invasive, functional ...imaging modality with great clinical potential. Current research focuses on converting the high-dimensional, not human-interpretable spectral data into the underlying functional information, specifically the blood oxygenation. One of the largely unexplored issues stalling clinical advances is the fact that the quantification problem is ambiguous, i.e. that radically different tissue parameter configurations could lead to almost identical photoacoustic spectra. In the present work, we tackle this problem with conditional Invertible Neural Networks (cINNs). Going beyond traditional point estimates, our network is used to compute an approximation of the conditional posterior density of tissue parameters given the measurement. To this end, an automatic mode detection algorithm extracts the plausible solution from the sample-based posterior. According to a comprehensive validation study based on both synthetic and real images, our approach is well-suited for exploring ambiguity in quantitative PAT.
Versatile silk protein-based material formats were studied to demonstrate bioresorbable, implantable optical oxygen sensors that can integrate with the surrounding tissues. The ability to ...continuously monitor tissue oxygenation in vivo is desired for a range of medical applications. Silk was chosen as the matrix material due to its excellent biocompatibility, its unique chemistry that facilitates interactions with chromophores, and the potential to tune degradation time without altering chemical composition. A phosphorescent Pd (II) benzoporphyrin chromophore was incorporated to impart oxygen sensitivity. Organic solvent-based processing methods using 1,1,1,3,3,3-hexafluoro-2-propanol were used to fabricate: 1) silk-chromophore films with varied thickness and 2) silk-chromophore sponges with interconnected porosity. All compositions were biocompatible and exhibited photophysical properties with oxygen sensitivities (i.e., Stern-Volmer quenching rate constants of 2.7–3.2 × 104 M−1) useful for monitoring physiological tissue oxygen levels and for detecting deviations from normal behavior (e.g., hyperoxia). The potential to tune degradation time without significantly impacting photophysical properties was successfully demonstrated. Furthermore, the ability to consistently monitor tissue oxygenation in vivo was established via a multi-week rodent study. Histological assessments indicated successful tissue integration for the sponges, and this material format responded more quickly to various oxygen challenges than the film samples.
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•Bioresorbable, tissue oxygen sensors made of silk and Pd (II) benzoporphyrin•Non-porous films and sponges fabricated using organic solvent processing methods•Photophysical properties offer good interpretability and dynamic range•Sponges exhibit interconnected porosity and excellent tissue integration•Sponges offered consistent performance to external stimuli during in vivo rat study
In patients at risk of hypoxic ischemic brain injury following cardiac arrest, we sought to: 1) characterize brain oxygenation and determine the prevalence of brain hypoxia, 2) characterize ...autoregulation using the pressure reactivity index and identify the optimal mean arterial pressure, and 3) assess the relationship between optimal mean arterial pressure and brain tissue oxygenation.
Prospective interventional study.
Quaternary ICU.
Adult patients with return of spontaneous circulation greater than 10 minutes and a postresuscitation Glasgow Coma Scale score under 9 within 72 hours of cardiac arrest.
All patients underwent multimodal neuromonitoring which included: 1) brain tissue oxygenation, 2) intracranial pressure, 3) jugular venous continuous oximetry, 4) regional saturation of oxygen using near-infrared spectroscopy, and 5) pressure reactivity index-based determination of optimal mean arterial pressure, lower and upper limit of autoregulation. We additionally collected mean arterial pressure, end-tidal CO2, and temperature. All data were captured at 300 Hz using ICM+ (Cambridge Enterprise, Cambridge, United Kingdom) brain monitoring software.
Ten patients (7 males) were included with a median age 47 (range 20-71) and return to spontaneous circulation 22 minutes (12-36 min). The median duration of monitoring was 47 hours (15-88 hr), and median duration from cardiac arrest to inclusion was 15 hours (6-44 hr). The mean brain tissue oxygenation was 23 mm Hg (SD 8 mm Hg), and the mean percentage of time with a brain tissue oxygenation below 20 mm Hg was 38% (6-100%). The mean pressure reactivity index was 0.23 (0.27), and the percentage of time with a pressure reactivity index greater than 0.3 was 50% (12-91%). The mean optimal mean arterial pressure, lower and upper of autoregulation were 89 mm Hg (11), 82 mm Hg (8), and 96 mm Hg (9), respectively. There was marked between-patient variability in the relationship between mean arterial pressure and indices of brain oxygenation. As the patients' actual mean arterial pressure approached optimal mean arterial pressure, brain tissue oxygenation increased (p < 0.001). This positive relationship did not persist when the actual mean arterial pressure was above optimal mean arterial pressure.
Episodes of brain hypoxia in hypoxic ischemic brain injury are frequent, and perfusion within proximity of optimal mean arterial pressure is associated with increased brain tissue oxygenation. Pressure reactivity index can yield optimal mean arterial pressure, lower and upper limit of autoregulation in patients following cardiac arrest.
Background
Splanchnic‐cerebral oxygenation ratio (SCOR), the ratio of splanchnic tissue oxygen (StO2s) to simultaneously measured cerebral tissue oxygen (StO2c), has been described as a surrogate to ...detect impaired splanchnic oxygenation associated with hypoperfusion status such as necrotizing enterocolitis. This concept is based on the presumption that any change in SCOR indicates a corresponding change in splanchnic tissue oxygenation as the numerator, whereas cerebral tissue oxygenation as the denominator remains stable. However, it is questionable to utilise this concept to detect splanchnic oxygenation changes in the context of packed red blood cell transfusion (PRBCT).
Aim
The current study examines the contribution of both cerebral and splanchnic oxygenation components to PRBCT‐associated SCOR changes in preterm infants.
Design
Prospective cohort study.
Setting
Neonatal intensive care.
Patients
Hemodynamically stable infants: Gestation <32 weeks; birth weight <1500 g; postmenstrual age <37 weeks: tolerating ≥120 ml/kg/day feed volume.
Interventions
PRBCT at 15 ml/kg, over 4 h.
Main Outcome Measures
Transfusion‐associated changes were determined by performing mixed models for repeated measures analysis between the 4‐h mean pre‐transfusion values (SCOR 0, StO2s 0, and StO2c 0) and the post‐transfusion hourly mean values for the next 28 h (SCOR 1–28, StO2s 1–28, and StO2c 1–28). Dunnett's method was used to adjust for the multiplicity of the p value.
Results
Of 30 enrolled infants 14 46.7% male; median IQR birth weight, 923 655–1064 g; gestation, 26.4 25.5–28.1 weeks; enrolment weight, 1549 1113–1882 g; and postmenstrual age, 33.6 32.4–35.0 weeks, one infant was excluded because of corrupted NIRS data. With the commencement of PRBCT, SCOR demonstrated a downward trend throughout the study period. This drift was associated with an increasing StO2c trend, while StO2s remained unchanged throughout the study period.
Conclusions and Relevance
PRBCT‐associated SCOR decrease suggests improvement in cerebral oxygenation rather than worsening splanchnic oxygenation. Our study underlines that it is necessary to determine individual components of SCOR, namely cerebral and splanchnic StO2 to understand SCOR changes in the context of PRBCT.
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