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Slimline™ vs Glass

Are Antimony Catheters Reliable for Measuring Esophageal Acid Exposure?

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Pandolfino, John E., M.D.; Boniquit, Christopher, B.A.; Zhang, Qing, M.D.; Ghosh, Sudip, Ph.D.; Kahrilas, Peter J., M.D.

American Journal of Gastroenterology: September 2005 - Volume 100 - Issue - p S50
Supplement Abstracts Submitted for the 70th Annual Scientific Meeting of the American College of Gastroenterology: ESOPHAGUS
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Medicine/Division of Gastroenterology, Northwestern University, Chicago, IL.

Purpose: This study compared the pH recording accuracy of the Slimline™ antimony pH monitoring system and a conventional glass electrode catheter pH monitoring system during ambulatory conditions.

Methods: 18 asymptomatic subjects (13 males, 23–45 y/o) underwent simultaneous pH monitoring using the Slimline™ antimony pH electrode and MIC M3 glass pH electrode pH monitoring systems for 12 hours. The catheters were attached with tape and placed 5 cm above the LES. The subjects consumed 100 cc of orange juice and 100 cc of cranberry juice at 37°C to synchronize the data and measure pH electrode accuracy. After 11 hours the subjects returned to the lab and the catheter was advanced 10cm into the stomach for1 hour. Differences in% time the pH < 4 and number of reflux events were analyzed and compared by manual extraction of the data onto an excel spreadsheet. Agreement between the two systems in recording reflux events was analyzed by observing the point-by point discrepancy of + 0.5 pH units and also by performing a Kappa analysis for pH above and below 4.

Results: The correlation between Slimline™ and the Glass MIC M3 catheter was excellent for the total% time pH < 4 (r = 0.84) and there was no statistical difference in the median value measured by the two systems (Slimline™, 2.5%, Glass 1.9%, P = 0.77). The difference in recorded reflux events was also not significantly different between the two systems, with the absolute difference being 23 events (SD, 26.0). Although the point-by-point discrepancy was 28.2% (SD, 17.5%) when using a 0.5pH unit threshold, the agreement in terms of pH events above and below 4 was excellent (Kappa value, 0.89, SD, 0.09). In addition, the in-vivo pH measurement identified two Slimline™ catheters and one glass catheter that were malfunctioning.

Conclusions: The antimony Slimline™ pH catheter compares favorably to the Glass MIC M3 pH catheter in terms of measuring standard pH parameters. Although there is substantial point-by-point disagreement, it is typically less than 0.5 pH units and does not substantially alter diagnosis based on a threshold pH value of 4.

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