Hyperoxemia and hypoxemia impair cellular oxygenation: a study in healthy volunteers.

INTRODUCTION: Administration of oxygen therapy is common, yet there is a lack of knowledge on its ability to prevent cellular hypoxia as well as on its potential toxicity. Consequently, the optimal oxygenation targets in clinical practice remain unresolved. The novel PpIX technique measures the mitochondrial oxygen tension in the skin (mitoPO2) which allows for non-invasive investigation on the effect of hypoxemia and hyperoxemia on cellular oxygen availability. RESULTS: During hypoxemia, SpO2 was 80 (77-83)% and PaO2 45(38-50) mmHg for 15 min. MitoPO2 decreased from 42(35-51) at baseline to 6(4.3-9)mmHg (p < 0.001), despite 16(12-16)% increase in cardiac output which maintained global oxygen delivery (DO2). During hyperoxic breathing, an FiO2 of 40% decreased mitoPO2 to 20 (9-27) mmHg. Cardiac output was unaltered during hyperoxia, but perfused De Backer density was reduced by one-third (p < 0.01). A PaO2 < 100 mmHg and > 200 mmHg were both associated with a reduction in mitoPO2. CONCLUSIONS: Hypoxemia decreases mitoPO2 profoundly, despite complete compensation of global oxygen delivery. In addition, hyperoxemia also decreases mitoPO2, accompanied by a reduction in microcirculatory perfusion. These results suggest that mitoPO2 can be used to titrate oxygen support.

A simulation of skin mitochondrial Po2 in circulatory shock.

Circulatory shock is the inadequacy to supply mitochondria with enough oxygen to sustain aerobic energy metabolism. A novel noninvasive bedside measurement was recently introduced to monitor the mitochondrial oxygen tension in the skin (mitoPo2). As the most downstream marker of oxygen balance in the skin, mitoPo2 may provide additional information to improve shock management. However, a physiological basis for the interpretation of mitoPo2 values has not been established yet. In this paper, we developed a mathematical model of skin mitoPo2 using a network of parallel microvessels, based on Krogh's cylinder model. The model contains skin blood flow velocity, heterogeneity of blood flow, hematocrit, arteriolar oxygen saturation, and mitochondrial oxygen consumption as major variables. The major results of the model show that normal physiological mitoPo2 is in the range of 40-60 mmHg. The relationship of mitoPo2 with skin blood flow velocity follows a logarithmic growth curve, reaching a plateau at high skin blood flow velocity, suggesting that oxygen balance remains stable while peripheral perfusion declines. The model shows that a critical range exists where mitoPo2 rapidly deteriorates if skin perfusion further decreases. The model intuitively shows how tissue hypoxia could occur in the setting of septic shock, due to the profound impact of microcirculatory disturbance on mitoPo2, even at sustained cardiac output. MitoPo2 is the result of a complex interaction between all factors of oxygen delivery and microcirculation. This mathematical framework can be used to interpret mitoPo2 values in shock, with the potential to enhance personalized clinical trial design.NEW & NOTEWORTHY This is the first paper to simulate mitochondrial oxygen tension in skin in circulatory shock. The relationships of mitoPo2 with parameters of (microcirculatory) oxygen delivery aid in the understanding of noninvasive bedside measurement of mitoPo2 values and show that mitochondrial oxygen tension is two orders of magnitude higher than classically assumed. The model can be used to enhance clinical trial design investigating mitoPo2 as a resuscitation target in circulatory shock.

Novel CineECG enables anatomical 3D localization and classification of bundle branch blocks.

AIMS: Ventricular conduction disorders can induce arrhythmias and impair cardiac function. Bundle branch blocks (BBBs) are diagnosed by 12-lead electrocardiogram (ECG), but discrimination between BBBs and normal tracings can be challenging. CineECG computes the temporo-spatial trajectory of activation waveforms in a 3D heart model from 12-lead ECGs. Recently, in Brugada patients, CineECG has localized the terminal components of ventricular depolarization to right ventricle outflow tract (RVOT), coincident with arrhythmogenic substrate localization detected by epicardial electro-anatomical maps. This abnormality was not found in normal or right BBB (RBBB) patients. This study aimed at exploring whether CineECG can improve the discrimination between left BBB (LBBB)/RBBB, and incomplete RBBB (iRBBB). METHODS AND RESULTS: We utilized 500 12-lead ECGs from the online Physionet-XL-PTB-Diagnostic ECG Database with a certified ECG diagnosis. The mean temporo-spatial isochrone trajectory was calculated and projected into the anatomical 3D heart model. We established five CineECG classes: 'Normal', 'iRBBB', 'RBBB', 'LBBB', and 'Undetermined', to which each tracing was allocated. We determined the accuracy of CineECG classification with the gold standard diagnosis. A total of 391 ECGs were analysed (9 ECGs were excluded for noise) and 240/266 were correctly classified as 'normal', 14/17 as 'iRBBB', 55/55 as 'RBBB', 51/51 as 'LBBB', and 31 as 'undetermined'. The terminal mean temporal spatial isochrone contained most information about the BBB localization. CONCLUSION: CineECG provided the anatomical localization of different BBBs and accurately differentiated between normal, LBBB and RBBB, and iRBBB. CineECG may aid clinical diagnostic work-up, potentially contributing to the difficult discrimination between normal, iRBBB, and Brugada patients.

Biomarkers for the prediction of venous thromboembolism in critically ill COVID-19 patients.

BACKGROUND: Venous thromboembolism (VTE) is a frequent complication in critically ill patients with coronavirus disease 2019 (COVID-19) and is associated with mortality. Early diagnosis and treatment of VTE is warranted. OBJECTIVE: To develop a prediction model for VTE in critically ill COVID-19 patients. PATIENTS AND METHODS: In this retrospective cohort study, 127 adult patients with confirmed COVID-19 infection admitted to the intensive care unit of two teaching hospitals were included. VTE was diagnosed with either ultrasound or computed tomography scan. Univariate receiver operating characteristic (ROC) curves were constructed for Positive End Expiratory Pressure, PaO2/FiO2 ratio, platelet count, international normalized ratio, activated partial thromboplastin time as well as levels of fibrinogen, antithrombin, D-dimer and C-reactive protein (CRP). Multivariate analysis was done using binary linear regression. RESULTS: Variables associated with VTE in both univariate and multivariate analysis were D-dimer and CRP with an area under the curve (AUC) of 0.64, P = 0.023 and 0.75, P = 0.045, respectively. Variables indicating hypoxemia were not predictive. The ROC curve of D-dimer and CRP combined had an AUC of 0.83, P < 0.05. Categorized values of D-dimer and CRP were used to compute a mean absolute risk for the combination of these variables with a high positive predictive value. The predicted probability of VTE with a D-dimer > 15 in combination with a CRP > 280 was 98%. The negative predictive value of D-dimer was low. CONCLUSION: Elevated CRP and D-dimer have a high positive predictive value for VTE in critically ill COVID-19 patients. We developed a prediction table with these biomarkers that can aid clinicians in the timing of imaging in patients with suspected VTE.