VALIDATION AND MODIFICATION OF THE pH METRY-ANALYSIS PROTOCOL WITH THE pH INDEPENDENT IMPEDANCE TECHNIQUE

Abstract

131 pH monitoring is considered the goldstandard in diagnosing gastroesophageal reflux (GER). However, it does not in fact measure reflux, but only pH values. Thus the parameters to define GER pH-wise were derived empirically. These parameters were evaluated for their validity of reflux recognition and modified using the intraesophageal impedance technique (IMP), a pH-independent method for the registration of bolus movement. Methods: Simultaneous pH-IMP-measurements were performed in 50 infants. Using the standardized ESPGAN protocol for the analysis of pH metry data, the parameters sampling rate (SR), cutoff value (CV: GER registration, if pH < CV), minimal GER duration (MD) and latency time (LT, i.e. time after end of GER, wherein pH-drops < CV are considered the same episode) were varied. A new parameter, pre-latency time (preLT, i.e. time before beginning of GER, wherein pH-drops < CV are neglected), was introduced. By software aided analysis the optimal set of parameters regarding sensitivity and positive prediction was determined. Results: During a total measuring time of 310 hours 1856 reflux episodes were identified by IMP and considered the reference data. 306 GER with pH < 4 should have been identified by pH metry. With the standard parameters (SR 15/min, CV pH 4, MD 15s, LT 30s) 307 GER were detected by pH metry: 145 true GER (sensitivity 47.4%) and 162 falsely identified episodes(positive prediction 47.2%). Using the best parameter set (SR 60/min, CV pH 4, MD 5s, LT 30s, preLT 3s) 150 true (sensitivity 49.0%) and 154 false (positive prediction 49.3%) GER were detected. Conclusions: The diagnostic potential of pH metry, its sensitivity and positive prediction in identifying acid reflux was validated with IMP as the reference. The empirically derived parameters for the analysis of pH metry data proved to be valuable using standard hard- and software. By increasing sampling rate, decreasing minimal GER duration and with the introduction of a new parameter, the pre-latency time, sensitivity and positive prediction could be slightly increased. However, due to its nonacidity, the major amount of GER is concealed to pH metry and only detected by the impedance technique.