Ambulatory 24-Hour Double-Probe pH Monitoring: The Importance of Manometry

The authors’ technique of ambulatory 24-hour double-probe (simultaneous esophageal and pharyngeal) pH monitoring was first reported in 1986, and has been well described since. A manometer is inserted through the nasal cavity and advanced through the esophagus into the stomach. It is then slowly withdrawn and the locations of the lower and upper esophageal sphincters (LES and UES) are recorded. Esophageal motility is also assessed by having the patient perform wet and dry swallows with the manometer in the esophageal body. A catheter with pH probes located on its surface is then placed so that the distal probe is located 5 cm above the LES. The distal probe location above the LES has been standardized, because otherwise esophageal acid exposure data would be unreliable and inconsistent.

Location of the proximal probe has until recently been more controversial. Some gastroenterologists have recommended pH catheters with fixed interprobe distances (commonly 15 cm or 20 cm) that result in the proximal probe being located below the UES in the proximal esophagus.10 Most otolaryngologists place the proximal probe above the UES by using catheters with variable interprobe distances. The correct interprobe distance is determined by manometry and allows the esophageal probe to be 5 cm above the LES and the pharyngeal probe to be placed behind the laryngeal inlet just proximal to the UES. It has recently been reported that proximal probes located below the UES will result in a significant number of falsenegative pH studies for laryngopharyngeal reflux (LPR). Thus, an accurately placed pharyngeal probe is essential to evaluate patients for the presence or absence of LPR.

Recently, as an alternative to manometric pH probe placement, direct-vision placement (DVP) using transnasal fiberoptic laryngoscopy (TFL) was reported.  This technique involves inserting the pH catheter under direct vision so that the proximal pH probe is encompassed by the mucosa of the UES. The distance between the proximal and distal pH probe is fixed at 15 cm. Using this methodology, the location of the distal pH probe in relationship to the LES is unknown, and thus valid interpretation of the esophageal pH data is impossible.

The present study was performed to verify the accuracy of the DVP technique for pharyngeal pH probe placement. Furthermore, we evaluated the accuracy of using fixed interprobe distances to place the distal esophageal probe 5 cm above the LES. Finally, a method using external measurements of the neck and thorax to calculate the correct interprobe distance was evaluated.

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Paul E. Johnson, MD; Jamie A. Koufman, MD; Lisa J. Nowak, LPN; Peter C. Belafsky, MD, PhD; Gregory N. Postma, MD

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