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Abstract: SA-OR46

Arterial pCO2 and Arterial pH from Venous Blood Gas Concurrent Measurements from 7470 Samples: An Easy Conversion of Venous to Arterial Blood by Formula

Session Information

Category: Fluid, Electrolytes, and Acid-Base Disorders

  • 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical

Authors

  • Araujo, Gabriela P., Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Rehman, Mohammed Z., Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Rueda Mantilla, Carlos A., Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Rosa, Robert M., Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Batlle, Daniel, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
Background

Venous blood gas sampling to estimate blood pH and pCO2 has become standard medical practice with limited scientific data to avoid the cumbersome performance of arterial sampling. Efforts to estimate arterial pCO2 from venous blood and, in particular, blood pH from venous pH suffer from the limitation of observations made in relatively small databases (at the most hundreds of patients) and it is not always clear that the measurements were done simultaneously. We reasoned that existing estimations of arterial pH and pCO2 from venous blood could be improved using contemporary data extracted from a large database available from the electronic medical record.

Methods

We used de-identified data on venous and arterial blood gas measurements from Northwestern Medicine over 7 years (2016-2023). We extracted data from de-identified subjects with a total of 7470 samples where it was verified that the sampling for venous and arterial blood gas performed at the same time and by the same blood gas laboratory. The data was provided by an independent observer and verified that the times of sampling coincided with each other.

Results

From the 7470 samples, the relationship between arterial and venous pCO2 was strong (r= 0.845) and as expected, the venous pCO2 was higher than arterial pCO2 (see dotted line vs. line of identity in red, Fig. left panel). The correlation between the venous pH and arterial pH in the same 7470 samples was also very strong (r = 0.9) and as anticipated the venous pH was lower than the corresponding arterial pH and therefore most of the pH points are below the line of identity (Fig. right panel).

Conclusion

The correlations between venous and arterial pH and pCO2 in a database unique because of the large sample size and concurrent measurements in venous and arterial blood show that estimations of each one of the two acid-base parameters can be reasonably made with formulas derived from the correlations here reported that will be incorporated in an App that should be available at the time of the ASN 2023 meeting.

Funding

  • Private Foundation Support