Predictive validity of a novel non-invasive estimation of effective shunt fraction in critically ill patients

Intensive Care Medicine Experimental

Gordon B. Drummond¹  Emma M. Chang¹  Andrew Bretherick²  J Kenneth Baillie³ 

[1] Anaesthesia, Critical Care and Pain Medicine, Royal Infirmary of Edinburgh, EH16 4SA, Edinburgh, UK;Anaesthesia, Critical Care and Pain Medicine, Royal Infirmary of Edinburgh, EH16 4SA, Edinburgh, UK;MRC Institute of Genetics and Molecular Medicine, The University of Edinburgh, EH4 2XU, Edinburgh, UK;Anaesthesia, Critical Care and Pain Medicine, Royal Infirmary of Edinburgh, EH16 4SA, Edinburgh, UK;The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, EH25 9RG, Edinburgh, UK;

关键词: Oxygen;    Shunt fraction;    Arterial blood gas;    Respiratory failure;   

DOI  :  10.1186/s40635-019-0262-1

来源: Springer

【 摘 要 】

BackgroundAccurate measurement of pulmonary oxygenation is important for classification of disease severity and quantification of outcomes in clinical studies. Currently, tension-based methods such as P/F ratio are in widespread use, but are known to be less accurate than content-based methods. However, content-based methods require invasive measurements or sophisticated equipment that are rarely used in clinical practice. We devised two new methods to infer shunt fraction from a single arterial blood gas sample: (1) a non-invasive effective shunt (ES) fraction calculated using a rearrangement of the indirect Fick equation, standard constants, and a procedural inversion of the relationship between content and tension and (2) inferred values from a database of outputs from an integrated mathematical model of gas exchange (DB). We compared the predictive validity—the accuracy of predictions of PaO2 following changes in FIO2—of each measure in a retrospective database of 78,159 arterial blood gas (ABG) results from critically ill patients.ResultsIn a formal test set comprising 9,635 pairs of ABGs, the median absolute error (MAE) values for the four measures were as follows: alveolar-arterial difference, 7.30 kPa; PaO2/FIO2 ratio, 2.41 kPa; DB, 2.13 kPa; and ES, 1.88 kPa. ES performed significantly better than other measures (p < 10-10 in all comparisons). Further exploration of the DB method demonstrated that obtaining two blood gas measurements at different FIO2 provides a more precise description of pulmonary oxygenation.ConclusionsEffective shunt can be calculated using a computationally efficient procedure using routinely collected arterial blood gas data and has better predictive validity than other analytic methods. For practical assessment of oxygenation in clinical research, ES should be used in preference to other indices. ES can be calculated at http://baillielab.net/es.

【 授权许可】

CC BY