Combined multichannel intraluminal impedance (MII) and pH monitoring in the evaluation of gastroesophageal reflux (GER) in symptomatic preterm newborn.

Aims. GER is common in preterm newborn, due to some promoting factors such the almost fixed lying position, the large fluid enteral intake, the frequent nurse handling and the use of permanent feeding tubes. Twentyfour- hour pH monitoring has traditionally represented the gold standard for GER detection: it recognizes GER episodes as a pH drop <4 and is able to indicate their duration and frequency. The instrument’s software can also calculate RipH (percentage of time during which pH is <4), which represents a good index of the exposure of oesophageal mucosa to gastric acidity. The major limit of pH monitoring is that it cannot identify non-acid GER episodes: this is relevant in the evaluation of GER in preterm newborn, because milk feeding buffers gastric pH for a long time after meal; moreover, pH monitoring does not give any information about physical composition of refluxate and is not able to describe bolus movement inside the oesophagus. MII is a new technique which is able to detect GER episodes as electrical impedance changes occurring inside oesophageal lumen. A GER episode can be recognized by MII only if it reaches at least two consecutive dipoles on the catheter (about 4–4.5 cm above LES) and for this reason it is unable to identify short segment non-acid episodes. It can also distinguish retrograde movement (GER) from antegrade movement (swallow) and identify the height reached by each GER episode above LES. Combined MII-pH monitoring allows the detection of both acid and non-acid GER episodes and for this reason it can be useful in preterm newborn whose gastric pH is often buffered by frequent milk meals. We aimed to describe GER features in preterm newborns with symptoms of GER, highlighting differences in GER detection between MII alone and combined MII-pH monitoring. Methods. Fifty-three preterm newborns (mean GE 29 weeks, range 24–33 weeks; mean BW 1274 g, range 500–2250 g) having GER symptoms (frequent regurgitations and/or post-prandial desaturations) underwent 24-h recording of simultaneous MII and pH monitoring. For each infant, we calculated the number and the duration of GER episodes detected by both pH monitoring and MII: MII-detected episodes were then divided into acid and non-acid according to pH value. Results. The mean number of pH-detected episodes was 54.68; a mean of 53.13 episodes was detected by MII (acid: 12.85; non acid: 41.83). Mean acid oesophageal exposure was 11.23% (0.45% detected by MII and 10.79% by pH monitoring), while mean non-acid oesophageal exposure was 1.99% (detected only by MII). Conclusions. Combined MII-pH monitoring seems to be the best choice to diagnose GER in preterm newborn, allowing the detection of a significantly higher number of GER episodes (mean 112.87) than MII alone. Combined MII-pH monitoring can detect all the acid episodes: long-segment acid GER are detected both by MII and pH monitoring, while short-segment acid GER are identified only by pH monitoring. MII monitoring can also recognize long-segment non-acid episodes, which are frequent in milk fed infants; the major limitation of this technique is that it is unable to detect short segment non-acid episodes. This limitation is particularly relevant in preterm newborn, whose oesophageal length is usually between 6 and 10 cm: for this reason, the incidence of non-acid episodes and the exposure of distal oesophageal mucosa to non-acid GER risk to be significantly under considered. For this reason, in preterm newborn we suggest the combined use of MII and pH monitoring, we also wish that MII software will be further improved to be able to detect also short segment non-acid episodes, whose correlation with acute events such as apnoeas and desaturations is still uncertain.