More homogeneous capillary flow and oxygenation in deeper cortical layers correlate with increased oxygen extraction

Our understanding of how capillary blood flow and oxygen distribute across cortical layers to meet the local metabolic demand is incomplete. We addressed this question by using two-photon imaging of resting-state microvascular oxygen partial pressure (PO₂) and flow in the whisker barrel cortex in awake mice. Our measurements in layers I-V show that the capillary red-blood-cell flux and oxygenation heterogeneity, and the intracapillary resistance to oxygen delivery, all decrease with depth, reaching a minimum around layer IV, while the depth-dependent oxygen extraction fraction is increased in layer IV, where oxygen demand is presumably the highest. Our findings suggest that more homogeneous distribution of the physiological observables relevant to oxygen transport to tissue is an important part of the microvascular network adaptation to local brain metabolism. These results will inform the biophysical models of layer-specific cerebral oxygen delivery and consumption and improve our understanding of the diseases that affect cerebral microcirculation.

A method for measuring brain partial pressure of oxygen in unanesthetized unrestrained subjects: the effect of acute and chronic hypoxia on brain tissue PO(2)

The level of tissue oxygenation provides information related to the balance between oxygen delivery, oxygen utilization, tissue reactivity and morphology during physiological conditions. Tissue partial pressure of oxygen (PtO(2)) is influenced by the use of anesthesia or restraint. These factors may impact the absolute level of PtO(2). In this study we present a novel fiber optic method to measure brain PtO(2). This method can be used in unanesthetized, unrestrained animals, provides absolute values for PO(2), has a stable calibration, does not consume oxygen and is MRI compatible. Brain PtO(2) was studied during acute hypoxia, as well as before and after 28 days of high altitude acclimatization. A sensor was chronically implanted in the frontal cortex of eight Wistar rats. It is comprised of a fiber optic probe with a tip containing material that fluoresces with an oxygen dependent lifetime. Brain PtO(2) declines by 80% and 76% pre- and post-acclimatization, respectively, when the fraction of inspired oxygen declines from 0.21 to 0.08. In addition, a linear relationship between brain PtO(2) and inspired O(2) levels was demonstrated r(2)=0.98 and r(2)=0.99 (pre- and post-acclimatization). Hypoxia acclimatization resulted in an increase in the overall brain PtO(2) by approximately 35%. This paper demonstrates the use of a novel chronically implanted fiber optic based sensor for measuring absolute PtO(2). It shows a very strong linear relationship in awake animals between inspired O(2) and tissue O(2), and shows that there is a proportional increase in PtO(2) over a range of inspired values after exposure to chronic hypoxia.

Tissue pO2 of orthotopic 9L and C6 gliomas and tumor-specific response to radiotherapy and hyperoxygenation

PURPOSE

Tumor hypoxia is a well-known therapeutic problem; however, a lack of methods for repeated measurements of glioma partial pressure of oxygen (pO(2)) limits the ability to optimize the therapeutic approaches. We report the effects of 9.3 Gy of radiation and carbogen inhalation on orthotopic 9L and C6 gliomas and on the contralateral brain pO(2) in rats using a new and potentially widely useful method, multisite in vivo electron paramagnetic resonance oximetry.

METHODS AND MATERIALS

Intracerebral 9L and C6 tumors were established in the left hemisphere of syngeneic rats, and electron paramagnetic resonance oximetry was successfully used for repeated tissue pO(2) measurements after 9.3 Gy of radiation and during carbogen breathing for 5 consecutive days.

RESULTS

Intracerebral 9L gliomas had a pO(2) of 30-32 mm Hg and C6 gliomas were relatively hypoxic, with a pO(2) of 12-14 mm Hg (p < 0.05). The tissue pO(2) of the contralateral brain was 40-45 mm Hg in rats with either 9L or C6 gliomas. Irradiation resulted in a significant increase in pO(2) of the 9L gliomas only. A significant increase in the pO(2) of the 9L and C6 gliomas was observed in rats breathing carbogen, but this effect decreased during 5 days of repeated experiments in the 9L gliomas.

CONCLUSION

These results highlight the tumor-specific effect of radiation (9.3.Gy) on tissue pO(2) and the different responses to carbogen inhalation. The ability of electron paramagnetic resonance oximetry to provide direct repeated measurements of tissue pO(2) could have a vital role in understanding the dynamics of hypoxia during therapy that could then be optimized by scheduling doses at times of improved tumor oxygenation.

Influence of partial pressure of oxygen in blood samples on measurement performance in glucose-oxidase-based systems for self-monitoring of blood glucose

BACKGROUND

Partial pressure of oxygen (pO2) in blood samples can affect blood glucose (BG) measurements, particularly in systems that employ the glucose oxidase (GOx) enzyme reaction on test strips. In this study, we assessed the impact of different pO2 values on the performance of five GOx systems and one glucose dehydrogenase (GDH) system. Two of the GOx systems are labeled by the manufacturers to be sensitive to increased blood oxygen content, while the other three GOx systems are not.

METHODS

Aliquots of 20 venous samples were adjusted to the following pO2 values: <45, ~70, and ≥150 mmHg. For each system, five consecutive measurements on each sample aliquot were performed using the same test strip lot. Relative differences between the mean BG results at pO2 ~70 mmHg, which is considered to be similar to pO2 in capillary blood samples, and the mean BG result at pO2 <45 and ≥150 mmHg were calculated.

RESULTS

For all tested GOx systems, mean relative differences in the BG measurement results were between 6.1% and 22.6% at pO2 <45 mmHg and between -7.9% and -14.9% at pO2 ≥150 mmHg. For both pO2 levels, relative differences of all tested GOx systems were significant (p < .0001). The GDH system showed mean relative differences of -1.0% and -0.4% at pO2 values <45 and ≥150 mmHg, respectively, which were not significant.

CONCLUSIONS

These data suggest that capillary blood pO2 variations lead to clinically relevant BG measurement deviations in GOx systems, even in GOx systems that are not labeled as being oxygen sensitive.

Simultaneous measurement of pulmonary partial pressure of oxygen and apparent diffusion coefficient by hyperpolarized 3He MRI

Hyperpolarized (3)He (HP (3)He) MRI shows promise to assess structural and functional pulmonary parameters in a sensitive, regional, and noninvasive way. Structural HP (3)He MRI has applied the apparent diffusion coefficient (ADC) for the detection of disease-induced lung microstructure changes at the alveolar level, and HP (3)He pulmonary partial pressure of oxygen (pO(2)) imaging measures the oxygen transfer efficiency between the lung and blood stream. Although both parameters are affected in chronic obstructive pulmonary disease (COPD), a quantitative assessment of the regional correlation of the two parameters has not been reported in the literature. In this work, a single acquisition technique for the simultaneous measurement of ADC and pO(2) is presented. This technique is based on the multiple regression method, in which a general linear estimator is used to retrieve the values of ADC and pO(2) from a series of measurements. The measurement uncertainties are also analytically derived and used to find an optimal measurement scheme. The technique was first tested on a phantom model, and then on an in vivo normal pig experiment. A case study was performed on a COPD patient, which showed that in a region of interest ADC was 29% higher while oxygen depletion rate was 61% lower than the corresponding global average values.

Burn trauma in skeletal muscle results in oxidative stress as assessed by in vivo electron paramagnetic resonance

Using a mouse model, we tested the hypotheses that severe burn trauma causes metabolic disturbances in skeletal muscle, and that these can be measured and repeatedly followed by in vivo electron paramagnetic resonance (EPR). We used a 1.2-GHz (L-band) EPR spectrometer to measure partial pressure of oxygen (pO(2)) levels, redox status and oxidative stress following a non-lethal burn trauma model to the left hind limbs of mice. Results obtained in the burned mouse gastrocnemius muscle indicated a significant decrease in tissue pO(2) immediately (P=0.032) and at 6 h post burn (P=0.004), compared to the gastrocnemius of the unburned hind limb. The redox status of the skeletal muscle also peaked at 6 h post burn (P=0.027) in burned mice. In addition, there was an increase in the EPR signal of the nitroxide produced by oxidation of the hydroxylamine (CP-H) probe at 12 h post burn injury, indicating a burn-induced increase in mitochondrial reactive oxygen species (ROS). The nitroxide signal continued to increase between 12 and 24 h, suggesting a further increase in ROS generation post burn. These results confirm genomic results, which indicate a downregulation of antioxidant genes and therefore strongly suggest the dysfunction of the mitochondrial oxidative system. We believe that the direct measurement of tissue parameters such as pO(2), redox and ROS by EPR may be used to complement measurements by nuclear magnetic resonance (NMR) in order to assess tissue damage and the therapeutic effectiveness of antioxidant agents in severe burn trauma.

Findings and Prognostic Value of Lung Ultrasonography in Coronal Virus Disease 2019 (COVID-19) Pneumonia

PURPOSE

We used lung ultrasonography to identify features of COVID-19 pneumonia and to evaluate the prognostic value.

PATIENTS AND METHODS

We performed lung ultrasonography on 48 COVID-19 patients in an intensive care unit (ICU) (Wuhan, China) using a 12-zone method. The associations between lung ultrasonography score, PaO2/FiO2, APACHE II, SOFA, and PaCO2 with 28-day mortality were analyzed and the receiver operator characteristic curve was plotted.

RESULTS

25.9% areas in all scanning zones presented with B7 lines and 23.5% with B3 lines (B-pattern) on lung ultrasonography; 13% areas with confluent B lines (B-pattern), 24.9% in areas with consolidations, and 9.9% in areas with A lines. Pleural effusion was observed in 2.8% of areas. Lung ultrasonography score was negatively correlated with PaO2/FiO2 (n = 48, r = -0.498, P < 0.05) and positively correlated with APACHE II (n = 48, r = 0.435, P < 0.05). Lung ultrasonography score was independently associated with 28-day mortality. The areas under receiver operator characteristic curves of lung ultrasonography score were 0.735 (95% CI: 0.586-0.844). The sensitivity, specificity, and cutoff values were 0.833, 0.722, and 22.5, respectively.

CONCLUSIONS

Lung ultrasonography could be used to assess the severity of COVID-19 pneumonia, and it could also reveal the pathological signs of the disease. The lung ultrasonography score on ICU admission was independently related to the ICU 28-day mortality.

Proof of Concept Study to Assess the Influence of Oxygen Partial Pressure in Capillary Blood on SMBG Measurements

BACKGROUND

Measurement results provided by blood glucose monitoring systems (BGMS) can be affected by various influencing factors. For some BGMS using glucose oxidase (GOx)-based test strips, one of these factors is the oxygen partial pressure (pO₂) of the applied blood sample. Because assessing the potential influence of pO₂ when measuring capillary blood samples is not straight-forward, we performed a proof of concept study.

METHOD

Influence of pO₂ was investigated for two GOx-based BGMS (BGMS A and B). Measurement results of the GOx-based BGMS were compared with measurement results from a pO₂-independent BGMS (BGMS C). A total of 119 samples from 60 subjects were measured, twice with BGMS C, then 6 times each with BGMS A and BGMS B or vice versa, and again twice with BGMS C. Immediately afterward, pO₂ was determined. Linear regression analysis based on relative differences between results from BGMS A or BGMS B and results from BGMS C was performed to estimate the degree of pO₂ influence.

RESULTS

The relative bias between the lowest and highest pO₂ values differed by 14.3% for BGMS A, indicating a pO₂ influence that might be clinically relevant, and by 9.7% for BGMS B, indicating that pO₂ influence may be too small to be reliably detected because of the BGMS' imprecision.

CONCLUSIONS

This proof of concept study showed that with the procedures used, a potentially clinically relevant influence of pO₂ in capillary blood samples on GOx-based BGMS could be detected. Further larger-scale studies are needed to verify this influence.

Temporal variation in the response of tumors to hyperoxia with breathing carbogen and oxygen

The effect of hyperoxygenation with carbogen (95% O₂ + 5% CO₂) and 100% oxygen inhalation on partial pressure of oxygen (pO₂) of radiation-induced fibrosarcoma (RIF-1) tumor was investigated. RIF-1 tumors were innoculated in C3H mice, and aggregates of oximetry probe, lithium phthalocyanine (LiPc), was implanted in each tumor. A baseline tumor pO₂ was measured by electron paramagnetic resonance (EPR) oximetry for 20 minutes in anesthetized mice breathing 30% O₂ and then the gas was switched to carbogen or 100 % oxygen for 60 minutes. These experiments were repeated for 10 days. RIF-1 tumors were hypoxic with a baseline tissue pO₂ of 6.2–8.3 mmHg in mice breathing 30% O₂. Carbogen and 100% oxygen significantly increased tumor pO₂ on days 1 to 5, with a maximal increase at approximately 32–45 minutes on each day. However, the extent of increase in pO₂ from the baseline declined significantly on day 5 and day 10. The results provide quantitative information on the effect of hyperoxic gas inhalation on tumor pO₂ over the course of 10 days. EPR oximetry can be effectively used to repeatedly monitor tumor pO₂ and test hyperoxic methods for potential clinical applications.

A New Time-Window Prediction Model For Traumatic Hemorrhagic Shock Based on Interpretable Machine Learning

ABSTRACT

Early warning prediction of traumatic hemorrhagic shock (THS) can greatly reduce patient mortality and morbidity. We aimed to develop and validate models with different stepped feature sets to predict THS in advance. From the PLA General Hospital Emergency Rescue Database and Medical Information Mart for Intensive Care III, we identified 604 and 1,614 patients, respectively. Two popular machine learning algorithms (i.e., extreme gradient boosting [XGBoost] and logistic regression) were applied. The area under the receiver operating characteristic curve (AUROC) was used to evaluate the performance of the models. By analyzing the feature importance based on XGBoost, we found that features in vital signs (VS), routine blood (RB), and blood gas analysis (BG) were the most relevant to THS (0.292, 0.249, and 0.225, respectively). Thus, the stepped relationships existing in them were revealed. Furthermore, the three stepped feature sets (i.e., VS, VS + RB, and VS + RB + sBG) were passed to the two machine learning algorithms to predict THS in the subsequent T hours (where T = 3, 2, 1, or 0.5), respectively. Results showed that the XGBoost model performance was significantly better than the logistic regression. The model using vital signs alone achieved good performance at the half-hour time window (AUROC = 0.935), and the performance was increased when laboratory results were added, especially when the time window was 1 h (AUROC = 0.950 and 0.968, respectively). These good-performing interpretable models demonstrated acceptable generalization ability in external validation, which could flexibly and rollingly predict THS T hours (where T = 0.5, 1) prior to clinical recognition. A prospective study is necessary to determine the clinical utility of the proposed THS prediction models.

PO2-based biodosimetry evaluation using an EPR technique acts as a sensitive index for chemotherapy

The partial pressure of oxygen (PO₂) in the tumor microenvironment directly affects tumor sensitivity to chemotherapy. In the present study, a lithium phthalocyanine probe was implanted into MCF-7 human breast cancer cells, followed by transplant of the cells into nude mice. The present study used an electron paramagnetic resonance (EPR) oximetry measuring technique to dynamically monitor PO₂ in the tumor microenvironment prior to and following chemotherapy, and aimed to determine the precise time window in which the microenvironmental PO₂ peaked following chemotherapy. The results indicated that PO₂ was significantly higher in breast cancer compared with control (P<0.05). Following four cycles of chemotherapy, the activity of NADH dehydrogenase, succinate-cytochrome c reductase and cytochrome c oxidase in the mitochondria of cells was significantly reduced when compared with their activity prior to chemotherapy (P<0.05). Regional blood flow in tumor tissues undergoing chemotherapy was significantly lower than that prior to chemotherapy (P<0.05). The rate of cellular apoptosis in the PO₂ peak-based chemotherapy group was significantly greater than that in the conventional chemotherapy group after two and four cycles of chemotherapy (P<0.05). Tumor volume in the PO₂ peak-based chemotherapy group was significantly reduced compared with that in the 0.9% NaCl solution control and the conventional chemotherapy groups after four cycles of chemotherapy (P<0.05). The tumor inhibitory rate of the experimental group was significantly higher than that of the conventional chemotherapy group (P<0.01). In conclusion, the present study may provide guidance for the development of effective strategies depending on tumor-maximal response to chemotherapy in an oxygen-rich environment. Additionally, the present study aimed to establish a foundation for a clinical noninvasive assessment intended to guide treatment and formulate individual regimens, in order to improve cancer therapeutics, sensitivity monitoring and curative effect estimation.

Optimal Partial Pressure of Oxygen Affects Outcomes in Patients With Severe Traumatic Brain Injury

Introduction Severe traumatic brain injury (TBI) is a leading cause of death and disability. Not all neuronal damage occurs at the time of primary injury, but rather TBI initiates a cascade of events that leads to secondary brain injury. Oxygenation is one crucial factor in maintaining brain tissue homeostasis post-injury. We performed a retrospective review of patients admitted to a single trauma center after TBI. Statistical analysis was performed to ascertain if the measured partial pressure of oxygen (PaO₂) affected overall outcome at the time of discharge from the hospital. Materials and Methods Statistical analysis was performed retrospectively on patients admitted with a Glasgow Coma Scale (GCS) < 8 and a diagnosis of TBI. GCS and Glasgow Outcome Scale (GOS) were calculated from physical examination findings at the time of hospital discharge or death. Patient data were separated into two groups: those with consistently higher average PaO₂ scores (≥ 150 mmHg; n = 7) and those with lower average PaO₂ scores (< 150 mmHg; n = 8). The minimum requirement to be categorized in the consistently higher group was to have an average hospital day 1 through 5 PaO₂ value of ≥ 150 mmHg. Results Patients with consistent hospital Day 1 through 5 PaO₂ scores of ≥ 150 mmHg had statistically significant higher GCS scores at the end of intensive care unit (ICU)-level care or hospital discharge (mean = 12, p = 0.01), compared to those in group 2 with lower PaO₂ levels (mean = 7.9). There was no statistically significant difference in GOS when comparing the two groups (p = 0.055); however, the data did show a trend toward significance. Discussion and Conclusion In our study we analyzed patients diagnosed with TBI and stratified them into groups based on PaO₂ ≥ or < 150 mmHg. We demonstrate overall outcome improvement based on GCS with a trend toward improved GOS. The GCS showed statistical significance in patients with PaO₂ consistently ≥ 150 mmHg versus those in group 2 over the first five days of hospitalization.

Mapping Alveolar Oxygen Partial Pressure in COPD Using Hyperpolarized Helium-3: The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study

Chronic obstructive pulmonary disease (COPD) and emphysema are characterized by functional and structural damage which increases the spaces for gaseous diffusion and impairs oxygen exchange. Here we explore the potential for hyperpolarized (HP) 3He MRI to characterize lung structure and function in a large-scale population-based study. Participants (n = 54) from the Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study, a nested case-control study of COPD among participants with 10+ packyears underwent HP 3He MRI measuring pAO2, apparent diffusion coefficient (ADC), and ventilation. HP MRI measures were compared to full-lung CT and pulmonary function testing. High ADC values (>0.4 cm2/s) correlated with emphysema and heterogeneity in pAO2 measurements. Strong correlations were found between the heterogeneity of global pAO2 as summarized by its standard deviation (SD) (p < 0.0002) and non-physiologic pAO2 values (p < 0.0001) with percent emphysema on CT. A regional study revealed a strong association between pAO2 SD and visual emphysema severity (p < 0.003) and an association with the paraseptal emphysema subtype (p < 0.04) after adjustment for demographics and smoking status. HP noble gas pAO2 heterogeneity and the fraction of non-physiological pAO2 results increase in mild to moderate COPD. Measurements of pAO2 are sensitive to regional emphysematous damage detected by CT and may be used to probe pulmonary emphysema subtypes. HP noble gas lung MRI provides non-invasive information about COPD severity and lung function without ionizing radiation.

A case of plateau heart disease misdiagnosed as chronic pulmonary heart disease

This paper reports a case of plateau heart disease in Qinghai-Tibetan plateau who had recurrent symptoms of chest tightness and shortness of breath for 6 years but was misdiagnosed as chronic pulmonary heart disease. Plateau heart disease was diagnosed by thoracic computed tomography, pulmonary arteriography, pulmonary function tests and examination of medical history. Through the detailed analysis and differential diagnosis of this case, the aim is to distinguish between high-altitude heart disease and high-altitude chronic pulmonary heart disease, with the hope of achieving new breakthroughs in the diagnosis and treatment of this condition in the future.

Conservative oxygen supplementation versus usual oxygen supplementation among septic medical intensive care units patients: A before-after investigation

Patients admitted in the intensive care unit (ICU) are always managed with excessive high fraction of inspired oxygen and have hyperoxia for a significant period of time, which has potential harms. The guidelines for the management of patients in ICUs do not provide the target values for partial pressure of oxygen or arterial oxyhemoglobin saturations. The study was a before-after investigation comparing two time periods in which different oxygenation strategies were applied. Data of oxygen control, outcome measures, and mortality of a total of 273 patients (>18 years) admitted at least for 2 days in ICUs and received treatment for the sepsis were retrospectively collected and analyzed. Patients were received usual oxygen supplementation (targeted partial pressure of oxygen: 150 mmHg; a high fraction of inspired oxygen: 0.4; UOS cohort; n = 142) or conservative oxygen supplementation (targeted partial pressure of oxygen: 70-100 mmHg; a high fraction of inspired oxygen as low as possible; COS cohort; n = 131). Mechanical ventilation-free hours were significantly higher for patients of COS cohort than those of UOS cohort (77.99 ± 21.26 h/patient vs 70.01 ± 23.57 h/patient, p = 0.016). ICUs length of stays of patients of COS cohort was fewer than those of UOS cohort (7.05 ± 2.13 days/patient vs 7.69 ± 2.43 days/patients, p = 0.016). The probability of survival of patients was higher among patients of COS cohort than those of UOS cohort (p = 0.049). A higher number of patients from UOS cohort needed vasopressors than those from COS cohort (55 vs 35, p = 0.039). Conservative oxygen supplementation to maintain partial pressure of oxygen was improved outcome measures and decreases mortality as compared to that of usual oxygen supplementation.Level of Evidence: III.Technical Efficacy Stage: 4.

Expression and Variations in EPAS1 Associated with Oxygen Metabolism in Sheep

Endothelial PAS domain protein 1 gene (EPAS1) is a member of the HIF gene family. This gene encodes a transcription factor subunit that is involved in the induction of oxygen-regulated genes. Several studies have demonstrated that a mutation in EPAS1 could affect oxygen sensing, polycythemia, and hemoglobin level. However, whether EPAS1 mutation affects sheep oxygen metabolism is still unknown. Therefore, we explored the relationship between the variation of EPAS1 and oxygen metabolism in sheep. In this study, variations in ovine EPAS1 exon 15 were investigated in 332 Tibetan sheep and 339 Hu sheep by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis. In addition, we studied the effect of these variations on blood gas in 176 Tibetan sheep and 231 Hu sheep. Finally, the mRNA expression of EPAS1 in six tissues of Hu sheep and Tibetan sheep living at different altitudes (2500 m, 3500 m, and 4500 m) was analyzed by real-time quantitative PCR (RT-qPCR). Four alleles (A, B, C, and D) were detected, and their distributions highly differed between Tibetan sheep and Hu sheep. In Tibetan sheep, B was the dominant allele, and C and D alleles were rare, whereas all four alleles were common in Hu sheep. Six single nucleotide polymorphisms (SNPs) were identified between the four alleles and one of them was non-synonymous (p.F606L). While studying the blood gas levels in Tibetan sheep and Hu sheep, one variant region was found to be associated with an elevated pO₂ and sO₂, which suggested that variations in EPAS1 are associated with oxygen metabolism in sheep. RT-qPCR results showed that EPAS1 was expressed in the six tissues of Hu sheep and Tibetan sheep at different altitudes. In addition, the expression of EPAS1 in four tissues (heart, liver, spleen, and longissimus dorsi muscle) of Hu sheep was lower than that in Tibetan sheep from three different altitudes, and the expression of EPAS1 was positively correlated with the altitude. These results indicate that the variations and expression of EPAS1 is closely related to oxygen metabolism.

Clinical Accuracy of a Glucose Oxidase-Based Blood Glucose Test-Strip Across Extremes of Oxygen Partial Pressure

BACKGROUND

Glucose oxidase (GOx)-based blood glucose monitors (BGMs) are influenced by the partial pressure of oxygen (Po2) within the applied sample. Limited in-clinic data exists regarding the quantitative effect of Po2 in unmanipulated capillary fingertip blood samples across physiologically representative glucose and Po2 ranges.

METHOD

Clinical accuracy data were collected as part of a BGM manufacturer's ongoing post-market surveillance program for a commercially available GOx-based BGM test-strip. The data set comprised 29 901 paired BGM-comparator readings and corresponding Po2 values from 5 428 blood samples from a panel of 975 subjects.

RESULTS

A linear regression-calculated bias range of 5.22% (+0.72% [low Po2: 45 mm Hg] to -4.5% [high Po2: 105 mm Hg]); biases calculated as absolute at <100 mg/dL glucose was found. Below the nominal Po2 of 75 mm Hg, a linear regression bias of +3.14% was calculated at low Po2, while negligible impact on bias (regression slope: +0.002%) was observed at higher than nominal levels (>75 mm Hg). When evaluating BGM performance under corner conditions of low (<70 mg/dL) and high (>180 mg/dL) glucose, combined with low and high Po2, linear regression biases ranged from +1.52% to -5.32% within this small group of subjects and with no readings recorded at <70 mg/dL glucose at low and high Po2.

CONCLUSIONS

Data from this large-scale clinical study, performed on unmanipulated fingertip capillary bloods from a diverse diabetes population, indicate Po2 sensitivity of the BGM to be markedly lower than published studies, which are mainly laboratory-based, requiring artificial manipulation of oxygen levels in aliquots of venous blood.

Intraoperative partial pressure of oxygen measurement to predict flap survival

Introduction:

Flap monitoring using partial pressure of oxygen (pO₂) is a proven modality. Instruments needed are expensive and are not readily available to a clinician. Here, pO₂ of flap has been determined using readily available and cheap methods, and a cut-off value is calculated which helps in predicting flap outcome.

Methods and Results:

Total 235 points on 84 skin flaps were studied. Capillary blood was collected from flap and fingertip using 1-ml syringes after at least 30 min of flap inset, and pO₂ analysed using blood gas analyser. Fall/change of pO₂ (difference of mean of pO₂ [diff-pO₂]) was also calculated by subtracting the flap pO₂ from the finger pO₂. Flap was monitored clinically in post-operative period and divided into two groups depending on its survival with Group 1 – dead points and Group 2 – alive points. pO₂ and diff-pO₂ amongst both the groups were compared and found to be statistically different (P = 0.0001). Cut-off value calculated for pO₂ was found to be <86.3 mmHg with a sensitivity of 100% and specificity of 89.05%. The difference of >68.503 mmHg of flap pO₂ compared from finger pO₂ was calculated as a cut-off with sensitivity of 94.12 and specificity of 79.60%.

Conclusions:

Flap areas having intra-operative pO₂ value <86.3 mmHG have higher chances (60.71%) of getting necrosis later. Similarly, if diff-pO₂ compared to fingertip is >68.5 mmHg, chances of those points getting necrosed in post-operative period are high.