Therefore, the vast majority of the variation in the difference in oxygen saturation comes from variations in venous oxygen saturation. Meanwhile, among hospitalized patients, the arterial oxygen saturation is maintained in a tight range (typically between 88-100%). The venous oxygen saturation varies quite a bit, between roughly 10%-95%.
The difference in oxygen saturation is the difference between the venous and arterial oxygen saturation (shown below). This can be done with the use of a third assumption. It would be nice to have a way to convert a VBG directly into an ABG, without having to know the arterial oxygen saturation. Unfortunately, most VBGs aren't obtained with a simultaneous pulse oximetry.
#META ORIGINAL REDACTED EMAIL PLUS#
This provides a way to estimate ABG values based on a combination of VBG values plus simultaneous pulse oximetry. This creates the saturation model, which may be summarized as follows (where k1 and k2 are empirically derived constants): Thus, the change in pH may be approximated as proportional to the change in carbon dioxide: However, the first-order approximation of any curve is a straight line. The relationship between pH and CO2 is complex, based partially on the Henderson-Hasselbach equation. The next question is what effect this change in the CO2 will have on the pH. If we assume that most patient's hands have a similar respiratory quotient, then the change in CO2 between arterial and venous gas should be proportional to the change in oxygen content (where k1 is an empirically derived constant): Tissues in the hand extract oxygen and generate carbon dioxide (in a ratio equal to the respiratory quotient). Imagine blood flowing from the radial artery to a vein in the hand. The initial concept is simple, albeit perhaps over-simplified.
No (including his or her identity) to avoid any potential ethical or personal conflict. Now that I am a blogger, I can present this research in my blog. It has weighed on me that I failed to publish these results, which I continue to believe are valid and potentially useful. No's data (he had painstakingly measured ABG and VBG values in a nearly simultaneous fashion, yielding surprisingly precise results). However, I couldn't find anything that matched Dr. I reached out to some additional investigators who had recently published data, and obtained one fresh dataset. No's data, the manuscript was not publishable. No) may have been concerned that the manuscript would compete with his own work. One of the reviewers selected by the journal was an investigator who had provided me with the highest quality data in the paper. The manuscript was revised a bit and submitted to a second journal.
However, whether this information is useful in clinical practice is debatable”)(1). No major flaws were found in the analysis, but it was deemed to be irrelevant (one reviewer wrote “This meta-analysis describes well a way to calculate ABG from VBG. This work was initially submitted to Critical Care Medicine, where it was rejected. Many generously shared their data with me.īased on this data, I developed formulae for conversion of VBG values into ABG values. To investigate further, I requested post-publication data from several researchers who had published studies comparing ABG vs. I had some ideas for converting VBG values into ABG values. To understand it, you need to know a bit of the story behind it. This post is about a research project I did as a pulmonary critical care fellow in 2011.
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