Ambulatory 24-hour double-probe pH monitoring: The importance of manometry

Objective: Historically, manometry has been used for sphincter localization before ambulatory 24-hour double-probe pH monitoring to ensure accurate placement of the probes. Recently, direct-vision placement (DVP), using transnasal fiberoptic laryngoscopy (TFL), has been offered as an alternative technique. Presumably, DVP might be used to precisely place the proximal (pharyngeal) pH probe; however, using DVP, there appears to be no way to accurately position the distal (esophageal) probe. The purpose of this study was to evaluate the accuracy of DVP for pH probe placement using manometric measurement as the gold standard. Methods: Thirty patients undergoing pH monitoring participated in this prospective study. Each subject underwent manometric examination of the esophagus to determine the precise location of the upper and lower esophageal sphincters (LES and LES). In addition, external anatomic landmarks were used to estimate interprobe distances. A physician blinded to the manometry results then placed a pH catheter using DVP so that the proximal probe was located just above the UES. The results were recorded and compared with those obtained by manometry. Results: Accurate DVP of the proximal pH probe was achieved in 70% (23 of 30) of the subjects. The use of external anatomic landmarks to estimate interprobe distance resulted in accurate positioning of the distal probe in only 40% (12 of 30) of the subjects. Using fixed interprobe distances of 15 cm and 20 cm, distal probe position accuracy was 3% (I of 30) and 40% (12 of 30), respectively. Therefore, using DV-P, the distal esophageal probe was in an incorrect position in 60% to 97% of subjects. Conclusion: For double-probe pH monitoring, the proximal probe can be accurately positioned by DVP; however, there is no precise way to determine the interprobe distance required to correctly position the distal pH probe. Failure to accurately position the distal probe results in grossly inaccurate esophageal acid-exposure times. Thus, manometry is needed to ensure valid double-probe pH monitoring data.