Accuracy of a point-of-care blood gas analyzer in gastric tonometry measurements of intramucosal pH (pHi) and P_{CO 2} gap

Purpose

We assessed the accuracy of a point-of-care blood gas analyzer in providing data from saline samples obtained by gastrointestinal tonometry (Tonometrics Catheter; Tonometrics Division, Instrumentarium, Helsinki, Finland) for the calculation of intramucosal pH (pHi) and the P_{CO 2} gap (intramucosal P_{CO 2} − Pa_{CO 2}).

Methods

We compared the point-of-care analyzer (Opti; AVL Medical Instruments, Schaffhausen, Switzerland; “Opt”) with a conventional analyzer (Compact 2 AVL Medical Instruments, Schaffhausen; “Elect”) in a clinical study (Elect being taking as the standard). In an in vitro study, P_{CO 2} data of tonometer saline (Pr_{CO 2}) from Opt and Elect were compared with P_{CO 2} data from a continuous air tonometer (Tonocap Tonometrics Division, Instrumentarium) for a bottle containing a mixed P_{CO 2} gas. Data were evaluated by the Bland-Altman method.

Results

In the clinical study, the bias (B) and precision (P) were: B = 0.223 and P = 0.056 for pHi, B = −14.0 and P = 2.43 (mmHg) for Pr_{CO 2}, and B = −16.7 and P = 2.6 (mmHg) for the P_{CO 2} gap (n = 27). In the in vitro study, the bias between the two values (Pr_{CO 2} and bottle P_{CO 2}) was −1.98 mmHg and precision was 1.23 mmHg for Elect, but for Opt, these values were −22.09 mmHg and 3.15 mmHg, respectively (n = 18).

Conclusion

Opt is not suitable for measuring pHi and the P_{CO 2} gap because it does not provide an accurate P_{CO 2} for tonometry saline.