Gas Measurements Research Articles

Validation of a sensor system for the measurement of breath ammonia using selected-ion flow-tube mass spectrometry

The measurement of trace breath gases is of growing interest for its potential to provide non-invasive physiological information in health and disease. While instrumental techniques such as selected-ion flow-tube mass spectrometry (SIFT-MS) can achieve this, these are less suitable for clinical application. Sensitive sensor-based systems for breath ammonia could be more widely deployed, but have proven challenging to develop. This work demonstrates the sequential analytical validation of an electrochemical impedance-based sensor system for the measurement of ammonia in breath using SIFT-MS. Qualitative and relative responses between the two methods were comparable, although there were consistent differences in absolute concentration. When tested in artificial breath ammonia, sensors had a relative impedance sensitivity of 3.43 × 10-5ppbv-1for each breath in the range of 249-1653 ppbv (r2= 0.87,p< 0.05). When correlated with SIFT-MS using human breath (n= 14), ammonia was detected in the range of 100-700 ppbv (r= 0.78,p< 0.001), demonstrating acceptable sensitivity, reproducibility and dynamic range for clinical application.

Correlation between EtCO2 and PCO2 in patients undergoing critical care transport

ABSTRACT OBJECTIVES End-tidal carbon dioxide (EtCO2) monitoring is widely used as a surrogate for the partial pressure of carbon dioxide (PCO2) in critically ill patients receiving manual or mechanical ventilation in prehospital, emergency, and critical care settings. Specific targets for ETCO2 are a key component of Emergency Medical Services (EMS) protocols, especially for specific patient groups such as those with traumatic brain injury. However, the correlation between EtCO2 and venous or arterial PCO2 is uncertain. We aimed to assess the correlation between EtCO2 and PCO2 in intubated patients undergoing critical care transport (CCT), and in specific subgroups of patients. METHODS We performed a retrospective review of patients undergoing emergency transport by a multi-state CCT agency. Patients were included if they had an advanced airway and both an EtCO2 and PCO2 reading within 5 minutes of each other. We obtained data on patient demographics, transport characteristics, medical categories, vital signs, lab values, and specific interventions. We performed univariable and multivariable binary logistic regression to assess the association between delta PCO2 and these characteristics. RESULTS We included 6,459 patients (mean age 58.4 years [SD 18.5], 57.1% male), of which a subset of 551 patients had multiple EtCO2-PCO2 measurements within 5 minutes. The median (IQR) initial delta PCO2 was 12.9 mmHg (7.1, 21.9). 3,967 (61.4%) patients had a delta PCO2 >10 mmHg and 1,843 (28.5%) had a delta PCO2 >20 mmHg. We identified an independent association between delta PCO2 >10 mmHg and age, male sex, interfacility transport, venous sampling site, respiratory rate, hypotension, hypoxia, and thoracostomy. In patients with multiple blood gas measurements, 76% had delta PCO2 >10 mmHg over the duration of the transport. CONCLUSIONS We identified substantial differences between EtCO2 and PCO2 across patients with medical and traumatic conditions undergoing critical care transport. The PCO2 assessment should be strongly considered as part of ventilatory management in patients encountered in emergency and critical care settings.

A Novel Calibration Scheme of Gas Sensor Array for a More Accurate Measurement Model of Mixed Gases.

Gas sensor arrays (GSAs) usually encounter challenges due to the cross-contamination of mixed gases, leading to reduced accuracy in measuring gas mixtures. However, with the advent of artificial intelligence, there is a promising avenue for addressing this issue effectively. In pursuit of more accurate mixed gas measurements, we proposed a measurement model leveraging neural networks. Our approach involved employing the encoder of an autoencoder network (AEN) to extract features from experimental data, while fully connected layers were utilized for predicting concentrations of mixed gases. To refine the neural network parameters, we employed a variational autoencoder to generate additional data resembling the distribution of experimental data. Subsequently, we designed a domain difference maximum entropy technique to identify optimal concentration points for the calibration data. These calibration points were instrumental in training the fully connected layers, enhancing the model's accuracy. During practical usage, with the AEN configuration fixed, the model can be fine-tuned by using a small subset of test points across large-scale GSA deployments. Simulation and practical measurement results demonstrated the efficacy of our proposed measurement model, boasting high accuracy, with confidence intervals for relative errors of the four gas measurements below 3% at the 95% confidence level. Besides, the calibration scheme reduced the number of test points compared with traditional methods, reducing the cost of labor and equipment.

Abstract 4136700: Sodium-Potassium Pump: Newly O-GlcNAc Protein Offering Potential Benefits in Hemorrhagic Shock situation

Hemorrhagic shock(HS) results from significant blood loss, leading to insufficient oxygen delivery, which causes metabolic changes and multi-organ dysfunction.The HS-related acute kidney injury developed by the patient are mainly due to alteration in Na/K ATPase.In previous O-GlcNAcylomic studies, we identified the Na/K ATPase as potentially O-GlcNAcylated.O-GlcNAcylation, a post-translational modification, plays a role in various cellular processes, such as cell survival and stress response.O-GlcNAcylation may have beneficial effect in shock situations. The objective of this study is to ascertain whether Na/K ATPase is O-GlcNAcylated and to elucidate its potential role during HS. Hemorrhagic shock was induced by an exsanguination of rats.They were then randomly treated or not with an O-GlcNAcase inhibitor, the NButGT(10mg/kg), to increase O-GlcNAc level.Blood pressure and heart rate were monitored throughout the experiment.Blood samples were collected for complete blood analysis, including biochemistry and gas measurements. kidneys were immediately frozen for histological and biochemical studies.To study the O-GlcNAcylation of Na/K ATPase an immunoprecipitation and Wheat Germ Agglutinin(WGA) based lectin affinity gel electrophoresis were used. HEK cells were treated with or without NButGT(100µM,6 hours) and/or ouabain(Na/K ATPase inhibitor) and a colorimetric kit was assessed to study O-GlcNAcylation impact on Na/K ATPase activity. O-GlcNAc levels increased by 2 folds in heart and kidney due to the NButGT treatment(p&lt;0.05).Mean arterial pressure(MAP,p&lt;0.01) and bicarbonate(p&lt;0.01) are restored in treated group as kalemia(Sham:4.2 ± 0.1;HS:4.7±0.1;NButGT:4.3 ±0.1;mmol/L;p&lt;0.05) and natremia(Sham:141.5±0.4;HS:139.8±0.5;NButGT:141.9 ±0.4; mmol/L;p&lt;0.01).The study of the O-GlcNAcylation of the Na/K ATPase validated its O-GlcNAcylation.Histological analysis of the kidney showed that HS decreased Na/K ATPase expression, but treatment restored it(Sham:15.1±1.1;HS:10.3±0.6;NButGT:13.78±1.1;%area;p&lt;0.05). An acute increase in O-GlcNAc levels through NButGT enhances Na/K ATPase activity. Increased O-GlcNAcylation during hemorrhagic shock restored MAP and reduced indicators of metabolic acidosis.Treatment with NButGT restored natremia and kalemia.This effect is linked to an increase in the expression and activity of Na/K ATPase.Our study is the first to confirm that Na/K ATPase is regulated by O-GlcNAcylation, particularly in terms of its localization and stability.

Insights into Target Gas-Oxygen Interactions in Highly Sensitive Gas Sensors Using Data-Driven Methods.

In the gas-sensing mechanism of a metal-oxide-semiconductor (n-type) gas sensor, oxygen adsorption or desorption on the oxide surface leads to an increase or decrease in the resistance of the gas sensor system. Additionally, oxygen can be adsorbed again at the location where initially adsorbed oxygen reacted with the target gas. Thus, the adsorption-desorption equilibrium of the reducing gas on the oxide surface is a significant factor in determining the sensitivity and reaction rate. In particular, for ultralow-concentration gas measurements, the relative concentration of oxygen was very high. To design an ultrasensitive gas sensor, not only the reaction of the target gas but also the competing reaction between the target gas and oxygen must be considered. Although qualitative investigations of these complex relationships have been performed according to the gas concentration and flow rate, reliable quantitative results are limited. In this study, a quantitative approach was used to understand the correlation between oxygen and a target gas by applying data analysis methods. We investigated the behavior of oxygen and the target molecules depending on the gas concentration and flow rate using the parts per billion level of the acetone gas sensor. Initial response data according to various detection conditions were processed using principal component analysis and K-means clustering; as a result, four types of reaction behaviors were inferred for 15 types of reaction conditions. Furthermore, the response time, depending on the detection conditions, can be distinguished using the suggested categorization. Our investigation suggests a possibility beyond simple optimization through the data analysis of the gas-sensing results.

Age of air from in situ trace gas measurements: insights from a new technique

Abstract. The age of air is an important transport diagnostic that can be derived from trace gas measurements and compared to global chemistry climate model output. We describe a new technique to calculate the age of air, measuring transport times from the Earth's surface to any location in the atmosphere based on simultaneous in situ measurements of multiple key long-lived trace gases. The primary benefits of this new technique include (1) optimized ages of air consistent with simultaneously measured SF6 and CO2; (2) age of air from the upper troposphere through the stratosphere; (3) estimates of the second moment of age spectra that have not been well constrained from measurements; and (4) flexibility to be used with measurements across multiple instruments, platforms, and decades. We demonstrate the technique on aircraft and balloon measurements from the 1990s, the last period of extensive stratospheric in situ sampling, and several recent missions from the 2020s, and compare the results with previously published and modeled values.

Combing mobile electrical capacitance tomography with Fourier neural operator for 3D fluidized beds measurement

AbstractDespite the practical importance, 3D measurements of gas–solid distribution in fluidized beds calls for further breakthroughs. Here an approach combing a recently developed mobile electrical capacitance tomography (ECT) sensor with Fourier Neural Operator (FNO) is developed, in which the fluidized bed is divided into a series of cross‐sectional slices along axial direction. At any given instant, the gas–solid distribution in one slice is measured by mobile ECT and the others, meantime, are predicted by FNO pre‐trained using experimental data. We verified this approach via computational fluid dynamics (CFD) simulations and experimental measurement of static object (i.e., cone, cylinder, and sphere) in fluidized bed. Following we applied this approach to direct measure 3D gas–solid distribution in a bubbling fluidized bed, and found that satisfactory image correlation coefficients and solid concentration average absolute deviation could be obtained, which indicates the proposed approach is promising for 3D fluidized bed measurements.

Natural H2 Transfer in Soil: Insights from Soil Gas Measurements at Varying Depths

The exploration of natural H2 is beginning in several countries. One of the most widely used methods for detecting promising areas is to measure the H2 percentage of the air contained in soils. All data show temporal and spatial variabilities. The gradient versus depth is not usually measured since the standard procedure is to drill and quickly install a tube in the soil to pump out the air. Drill bits used do not exceed one meter in length. These limitations have been overcome thanks to the development of a new tool that enables percussion drilling and gas measurements to be carried out with the same tool until 21 feet deep. This article shows the results obtained with this method in the foreland of the Colombian Andes. The variation of the gradient as a function of depth provides a better understanding of H2 leakage in soils. Contrary to widespread belief, this gradient is also highly variable, and, therefore, often negative. The signal is compatible with random and discontinuous H2 bubbles rising, but not with a permanent diffusive flow. Near-surface bacterial consumption should result in a H2 increase with depth; it may be true for the first tens of centimeters, but it is not observed between 1 and 5 m. The results show that, at least in this basin, it is not necessary to measure the H2 content at depths greater than the conventional one-meter depth to obtain a higher signal. However, the distance between the measured H2 peaks versus depth may provide information about the H2 leakage characteristics and, therefore, help quantify the near-surface H2 flow.

Design of On‐Chip Multi‐Slot Chalcogenide Waveguide for Mid‐Infrared Methane Sensing

ABSTRACTA chalcogenide (ChG) multi‐slot waveguide gas sensor with ChG as the core layer and silicon dioxide (SiO2) as the under‐cladding layer is proposed. Multi‐slot waveguide can be used in the mid‐infrared gas measurement. The optimized power confinement factor (PCF) of the ChG multi‐slot waveguide can be up to 41.3%, which is ∼20% higher than that of the optimized single‐slot waveguide. At the absorption line located at 3.291 μm for methane (CH4) measurement, the limits of detection (LoD) of single‐slot, double‐slot, triple‐slot, quadruple‐slot waveguide sensors are determined to be 68.9, 57.4, 52, 48.6 parts per million (ppm), respectively. Compared with other waveguide sensors in the mid‐infrared, the PCF of the proposed multi‐slot ChG/SiO2 waveguide sensor is enhanced by five times, which has the potential for highly sensitive gas sensing.

Active near‐infrared laser heterodyne system based on supercontinuum laser source for gas measurement

AbstractThe performance of an active near‐infrared laser heterodyne system using a supercontinuum light source as the light signal for trace species detection is experimentally demonstrated. The characteristics of the supercontinuum light source and the data processing methods used in heterodyne detection are described. The measurement of methane (CH₄) and carbon dioxide (CO₂) absorption spectra was carried out in the laboratory to evaluate the active laser heterodyne system, and high‐resolution absorption spectra of CO₂ and CH₄ were recorded simultaneously. The stability of the active laser heterodyne system is analyzed using Allan variance analysis of long‐term observation data. The active near‐infrared laser heterodyne detection system demonstrated in this paper has great potential for the development of industrial parks' gas monitoring.

Accelerating T1 relaxation time measurements of noble gas using transverse low-frequency square-wave magnetic field modulation.

The longitudinal relaxation time (T1) of noble gas nuclear spins is a critical parameter for evaluating the performance of an atomic comagnetometer, significantly influencing the signal-to-noise ratio of the system. Traditional measurement techniques, such as the free induction decay method combined with the spin growth technique (FIDSG), are time-consuming for gases with extended T1 durations, such as 21Ne, and are prone to substantial environmental variability. Here, we propose the transverse low-frequency square-wave magnetic field modulation (LSMM) method for the rapid measurement of T1. The experiment indicates that the LSMM significantly condenses the measurement time to 19.2% of the original, thereby diminishing the robustness demands of the system. Although a minor discrepancy of up to 3 min (or 1.3%) exists between LSMM and FIDSG results, the LSMM method provides strong support for calibrating the performance of comagnetometer cells and conducting various nuclear spin polarization experiments, thereby improving efficiency and reducing energy loss.

Simultaneous Measurement of Gaseous HONO and NO2− in Solutions from Aqueous Nitrate Photolysis Mediated by Organics

Field studies suggest that NO3− photolysis may play a more significant role than previously thought. In this study, we concurrently measured HONO, NO2, and NO2− in situ to gain a deeper understanding of the photogenerated HONO transfer to air and to better constrain the rate constants of NO3− photolysis. The presence of fatty acids (e.g., nonanoic acid, NA), which are naturally present in the environment, significantly increases the production of photogenerated HONO and NO2. With an increase in oxygen percentage, the release rate of photoinduced HONO slowed, while the release rate of NO2 accelerated. The measured JNO3− value averaged 1.65 × 10−5 s−1, which is two orders of magnitude higher than values reported in similar systems. The HONO transfer rate from the solutions increased from 2.3 × 10−4 s−1 to 5.6 × 10−4 s−1 as the NA concentration increased from 0.1 to 20 mM. This can be attributed to the accumulation of NO2− induced by NA at the interface. Within this interfacial region, NO2− in the solutions becomes more prone to transfer into gaseous HONO, suggesting that photogenerated NO2− hosted in atmospheric droplets may serve as a temporary reservoir of atmospheric HONO without illumination, influencing the atmospheric oxidizing capacity in the region for hours. Therefore, simultaneous measurements of both gas and particle phase photoproducts are recommended to better constrain the rate constants of NO3− photolysis, thereby enhancing the accuracy of predicting the photochemical production of HONO in the atmosphere.

Partitioning of Neutral PFAS in Homes and Release to the Outdoor Environment: Results from the IPA Campaign.

The distribution and fate of per- and polyfluoroalkyl substances (PFAS) in homes are not well understood. To address this, we measured nine neutral PFAS in dust, airborne particles, dryer lint, and on heating and air conditioning (HAC) filters in 11 homes in North Carolina as part of the Indoor PFAS Assessment (IPA) Campaign and compared them with concurrently collected gas and cloth measurements. Fluorotelomer alcohols (FTOHs) contributed most (≥75%) to total (∑) measured neutral PFAS concentrations in dust, HAC filter, and dryer lint samples, with mean ∑(FTOH) concentrations of 207 ng/g, 549 ng/g, and 84 ng/g, respectively. In particles, perfluorooctane sulfonamidoethanols (FOSEs) dominated, with a mean ∑(FOSE) concentration of 0.28 ng/m3 or 75,467 ng/g. For FTOHs and FOSEs, resulting mean dust-air, HAC filter-air, dryer lint-air and particle-air partition coefficients in units of log(m3/μg) ranged (across species) from -5.1 to -3.6, -4.9 to -3.5, -5.4 to -4.1, and -3.2 to -0.78, respectively. We estimate that cloth, gas phase, and HAC filters are the largest reservoirs for FTOHs, while cloth, HAC filters, and dust are the largest reservoirs for FOSEs. Release rates of neutral PFAS from homes to the outdoor environment are reported.

Low oxygen saturation and discordant arterial blood gas measures have diagnosed a case of hemoglobinopathy

Pulse oximeter is a simple non-invasive equipment used to determine patient’s arterial blood oxygen saturation (SpO2). However, in some people, arterial blood gas measures (SaO2) are normal and low SpO2 values are related to hemoglobin variant rather than cardiac or pulmonary illnesses. Aim. We present a case of thalassemia that manifested with low SpO2 and discordant SaO2. Conclusion. When examining a patient with an unusually low SpO2, the differential diagnosis of a suspected hemoglobin variant should be investigated. Establishing an accurate diagnosis as soon as possible may help avoid unnecessary tests.

Evaluation of Current and Future Aviation Fuels at High-Pressure Rich-Quench-Lean-Type Combustor Conditions

Abstract Decarbonizing the aviation sector is one of the biggest challenges to minimize climate change effects associated with carbon dioxide emission. Sustainable aviation fuels will play a major role in this context especially for long-distance flights where hydrogen or all-electric propulsion systems do not present a feasible alternative. In addition, aromatic-free sustainable aviation fuels offer a promising solution to lower soot emissions of aeroengines. Jet A-1 as reference fuel, two blends, and two neat synthesized paraffinic kerosenes (SPKs) from hydroprocessed esters and fatty acids (HEFA) were tested to characterize the combustion behavior of drop-in/near drop-in fuels. Experiments in an optically accessible high-pressure rich-quench-lean (RQL)-type combustor at typical aeroengine conditions were performed using optical diagnostics, exhaust gas, and particle sampling measurements to delineate the fuel effects on spray, flame, and emission characteristics. Measurements were performed at pressures up to 10 bar, air preheating temperatures up to 773 K and primary zone equivalence ratios up to 1.66. Liquid fuel distribution and fuel placement were found to be sensitive to fuel properties. By contrast, no pronounced influence on flame position and shape were observed. As a consequence, NOx and CO emissions of the tested fuels differed only moderately. However, particulate matter measurements at the fuel richest operating condition showed a clear fuel ranking with the lowest particle emissions evident for the two neat HEFA-SPK samples. Moreover, the particle volume concentration at the fuel richest condition followed the expected trend with fuel H-content.

Precision and uncertainty in natural gas calorific value estimation: advanced combinatorial predictive models for complex pipeline systems

Abstract In recent years, natural gas pipelines have been characterized by multiple intake points, the mixing of different gas sources, and significant variations in gas quality. The existing volumetric measurement system is no longer suitable for the development and operation of natural gas pipelines in China. To ensure accurate and equitable implementation of natural gas measurement, there is a gradual shift towards energy measurement. However, due to numerous measurement interfaces, installing chromatographs at all measurement stations would lead to substantial investment costs. Therefore, predicting the calorific value of natural gas is a key technology for energy measurement. In view of the issues existing in the current methods of obtaining natural gas calorific value, different prediction models of natural gas calorific value are constructed. According to the influencing factors of natural gas calorific value, the uncertainty evaluation is carried out, and the accuracy of different calorific value prediction models is analyzed by case data. The maximum error of regression equation (RE), response surface analysis (RSA), BP neural network and genetic algorithm (GA) prediction model is 2.29%, 0.43%, 0.59% and 0.45% respectively. However, the combined calorific value (CCV)prediction model is 0.41%. The results indicate that the predicted value calculated by the CCV prediction model is closer to the actual value and has higher prediction performance, which provides a new method for the calorific value prediction and measurement management of natural gas.&amp;#xD;

Electromagnetic and Radon Earthquake Precursors

Earthquake forecasting is arguably one of the most challenging tasks in Earth sciences owing to the high complexity of the earthquake process. Over the past 40 years, there has been a plethora of work on finding credible, consistent and accurate earthquake precursors. This paper is a cumulative survey on earthquake precursor research, arranged into two broad categories: electromagnetic precursors and radon precursors. In the first category, methods related to measuring electromagnetic radiation in a wide frequency range, i.e., from a few Hz to several MHz, are presented. Precursors based on optical and radar imaging acquired by spaceborne sensors are also considered, in the broad sense, as electromagnetic. In the second category, concentration measurements of radon gas found in soil and air, or even in ground water after being dissolved, form the basis of radon activity precursors. Well-established mathematical techniques for analysing data derived from electromagnetic radiation and radon concentration measurements are also described with an emphasis on fractal methods. Finally, physical models of earthquake generation and propagation aiming at interpreting the foundation of the aforementioned seismic precursors, are investigated.

Shale gas leakage and fault activation: Insight from the 2021 Luxian MS 6.0 earthquake, China

In the region of large gas fields, extensive research has been conducted on earthquakes induced by industrial production in shale gas fields. However, limited attention has been given to the impact of post-earthquake events on shale gas reservoir leakage and fault activation. The Luxian MS 6.0 earthquake, which occurred on 16 September 2021 in the Luzhou shale gas field, has raised concerns about post-earthquake shale gas leakage. Post-earthquake measurements of soil gases (Rn, CO2, CH4, and H2) and isotopic analyses (δ13CCO2, δ13CCH4 and δDCH4) in the Luzhou shale gas field area reveal that the Huayingshan fault zone, a natural pathway for shale gas leakage, was not activated by the Luxian earthquake and did not exhibit any further shale gas leakage after the 2021 earthquake. Furthermore, the seismogenic fault, which was impacted by the earthquake, did not damage the shale gas reservoir, causing shale gas leakage. This study provides an important foundation for future research on shale gas extraction and seismic activity in the region.

Detecting and sourcing GHGs and atmospheric trace gases in a municipal waste treatment plant using coupled chemistry and isotope compositions

Landfill operations and waste processing facilities are important and highly heterogeneous sources of both greenhouse gases (GHGs) and non-GHG air pollutants in the atmosphere. This arises the need for detailed apportionment of waste sources in order to locate and subsequently reduce emissions from landfills. Here, a time series of in situ measurements of atmospheric trace gases and spatial allocation of specific emission source types under different processing phases and environmental conditions were conducted in and in the surroundings of a Municipal Solid Waste Treatment Plant (MSWTP) in south-western Poland. Results revealed that several individual GHG sources dominated across the waste processing facility and that GHGs concentrations displayed spatial seasonality. An increase in the ground-level CH4 concentrations, from ∼ 30.3 to 56.3 ppmv, was observed close (∼5 – 10 m) to the major emission sources within the MSWTP. While hotspot areas generally yielded elevated CH4 concentrations near the soil surface, these were relatively low (2.4 to 8.9 ppmv) along the facility’s fence line. The study of the corresponding δ13C delineated the extent of dispersion plumes downwind emission hotspots, characterized by a 13C depletion (around 4.0 ‰) in the atmospheric CH4 and CO2. For CH4, emissions were isotopically discriminated between the extraction wells at active quarters/cells (δ13C = –58.3 ± 1.1 ‰) and biogas produced in the biological waste treatment installation (δ13C = –62.7 ± 0.7 ‰). Most of the trace compounds (non-methane hydrocarbons, halocarbons, oxygen-bearing organic gases, ketones, nitrogenous and sulphurous gases, and other admixture compounds) detected at the ground surface were linked to the CH4- and CO2-rich spots. Despite the relatively high variability in the concentrations of organic and inorganic compounds observed at the MSWTP active zones, our results suggest that they do not have a meaningful impact on the surrounding air quality.

Associations of arterial oxygen partial pressure with all‑cause mortality in critically ill ischemic stroke patients: a retrospective cohort study from MIMIC IV 2.2

BackgroundAs a supportive treatment, the effectiveness of oxygen therapy in ischemic stroke (IS) patients remains unclear. This study aimed to evaluate the relationships between arterial partial pressure of oxygen (PaO2) and both consciousness at discharge and all-cause mortality risk in ICU IS patients.MethodsBlood gas measurements for all patients diagnosed with IS were extracted from the MIMIC-IV database. Patients were classified into four groups based on their average PaO2 during the first ICU day: hypoxemia (PaO2 < 80 mmHg), normoxemia (PaO2 80–120 mmHg), mild hyperoxemia (PaO2 121–199 mmHg), and moderate/severe hyperoxemia (PaO2 ≥ 200 mmHg). The primary endpoint was 90-day all-cause mortality. Secondary outcomes included the level of consciousness at discharge, assessed by the Glasgow Coma Scale (GCS), and 30-day all-cause mortality. Multivariate Cox regression and Restricted cubic spline (RCS) analysis were used to investigate the relationship between mean PaO2 and mortality, and to assess the nonlinear association between exposure and outcomes.ResultsThis study included a total of 946 IS patients. The cumulative incidence of 30-day and 90-day all-cause mortality increased with decreasing PaO2 levels. RCS analysis revealed a nonlinear relationship between PaO2 and the risk of 30-day all-cause mortality (nonlinear P < 0.0001, overall P < 0.0001), as well as a nonlinear association between PaO2 and 90-day all-cause mortality (nonlinear P < 0.0001, overall P < 0.0001). The results remained consistent after excluding the small subset of patients who received reperfusion therapy. Sensitivity analysis indicated that the favorable impact on survival tends to increase with the extended duration of elevated PaO2.ConclusionsFor IS patients who do not receive reperfusion therapy or whose recanalization status is unknown, a lower PaO2 early during ICU admission is considered an independent risk factor for short-term and recent mortality. Adjusting respiratory parameters to maintain supraphysiological levels of PaO2 appears to be beneficial for survival, although this finding requires further validation through additional studies.Trial registrationNot applicable.