Acid gastroesophageal reflux reports in infants: a comparison of esophageal pH monitoring and multichannel intraluminal impedance measurements

Standard protocol devised by the Japanese Pediatric Impedance Working Group for combined multichannel intraluminal impedance-pH measurements in children

Multichannel intraluminal impedance-pH measurements (MII-pH) are useful for evaluating acid and non-acid gastroesophageal reflux (GER). However, the use of MIH-pH is not yet established in Japan. The Japanese Pediatric Impedance Working Group (Japanese-PIG) convened to devise a standard protocol for MII-pH in Japanese children. The expert members of the Japanese-PIG collected data on pediatric MII-pH from the relevant literature in English, including the standard protocol of MII-pH presented by the European PIG, and the insights of international experts. The resultant consensus was included in the contents of the standard protocol of MII-pH. The standard protocol included standardization of the indication, methodology, and interpretation of MII-pH in Japanese children. The criteria for abnormal GER by MII-pH were defined using the Reflux Index and number of total reflux episodes independently in children aged < 1 year and those aged ≥ 1 year. Moreover, a significant relationship between GER and symptoms was identified using the symptom index and symptom association probability approach. We conclude that the current version of the protocol for MII-pH is tentative because it is not based on data from Japanese children. Further studies are needed to render this protocol clinically beneficial and expand its use in Japan.

On respiratory manifestations of gastroesophageal reflux disease

One of the manifestations of gastroesophageal reflux disease (GERD) is extraesophageal symptoms, in particular, from the upper and lower respiratory tract. Gastroesophageal reflux is capable of both causing respiratory symptoms independently and aggravating the course of already existing diseases of the respiratory system. The article presents available in the literature current information on the pathogenesis of GERD respiratory symptoms, their clinical course, considerations of diagnosis and treatment.

Detection of gastro-oesophageal reflux in the neonatal unit

AIM

To determine whether a pH probe or multichannel intraluminal impedance (MII) more frequently detected gastro-oesophageal reflux and test the hypothesis that acid reflux was associated with lower baseline impedance.

METHODS

A prospective study of infants in whom reflux was suspected and evaluated using combined pH and multichannel impedance. Studies were considered abnormal if the acid index was >10% or there were >79MII reflux events in 24 hours. The acid index was the percentage of total study time with a pH

RESULTS

Forty-two infants [median gestational age 31 (range 23-42) weeks] were assessed. Only nine infants (21%) had abnormal studies, seven detected by pH monitoring, one by MII monitoring and one by both techniques (p = 0.04). After correcting for gestational age and post-natal age, baseline impedance remained negatively correlated with the acid index (r = -0.34, p = 0.038) and the maximum ACT (r = -0.44, p = 0.006).

CONCLUSION

Clinical suspicion of reflux was frequently incorrect, and reflux was more frequently detected by a pH probe. The inverse relationship of acid reflux to baseline impedance suggests that mucosal disruption may result from acid reflux in this population.

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Key Words

• Baseline oesophageal impedance
• Multichannel intraluminal impedance
• pH study

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MESH Headings Collapse

Grants

• National Institute for Health Research (NIHR) Biomedical Research Centre at Guy's and St Thomas' NHS Foundation Trust and King's College London

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Affiliation(s)

Thomas Rossor MRC Centre in Allergic Mechanisms of Asthma, King's College London, London, UK Department of Women and Children's Health, School of Life Course Sciences, Faculty of Life Sciences and Medicine, King's College London, London, UK
Ingran Lingam Neonatal Intensive Care Centre, King's College Hospital NHS Foundation Trust, London, UK
Abdel Douiri Department of Primary Care and Public Health Sciences, King's College London, London, UK NIHR Biomedical Research Centre, Guy's and St Thomas' NHS Foundation Trust, King's College London, London, UK
Ravindra Bhat Neonatal Intensive Care Centre, King's College Hospital NHS Foundation Trust, London, UK
Anne Greenough MRC Centre in Allergic Mechanisms of Asthma, King's College London, London, UK Department of Women and Children's Health, School of Life Course Sciences, Faculty of Life Sciences and Medicine, King's College London, London, UK NIHR Biomedical Research Centre, Guy's and St Thomas' NHS Foundation Trust, King's College London, London, UK

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On respiratory manifestations of gastroesophageal reflux disease

One of the manifestations of gastroesophageal reflux disease (GERD) is extraesophageal symptoms, in particular, from the upper and lower respiratory tract. Gastroesophageal reflux is capable of both causing respiratory symptoms independently and aggravating the course of already existing diseases of the respiratory system. The article presents available in the literature current information on the pathogenesis of GERD respiratory symptoms, their clinical course, considerations of diagnosis and treatment.

On respiratory manifestations of gastroesophageal reflux disease

One of the manifestations of gastroesophageal reflux disease (GERD) is extraesophageal symptoms, in particular, from the upper and lower respiratory tract. Gastroesophageal reflux is capable of both causing respiratory symptoms independently and aggravating the course of already existing diseases of the respiratory system. The article presents available in the literature current information on the pathogenesis of GERD respiratory symptoms, their clinical course, considerations of diagnosis and treatment.

Gastro-Oesophageal Reflux and Apnoea: Is There a Temporal Relationship?

BACKGROUND

Gastro-oesophageal reflux (GOR) and apnoea are common in infants; whether there is a causal relationship is controversial.

OBJECTIVES

To determine whether there was a temporal relationship between GOR and apnoea, in particular, the frequency of obstructive apnoeas and if the frequency of GOR episodes correlated with apnoea frequency when maturity at testing was taken into account.

METHODS

Polysomnography and pH/multichannel intraluminal impedance (MII) studies were performed. Apnoeas were classified as central, obstructive, or mixed. MII events were classified as acidic (pH <4) or weakly acidic (4 < pH < 7). Apnoea frequency in the 5-min period after a reflux event was compared to that in the 5-min period preceding the event and that in a 5-min reflux-free period (control period).

RESULTS

Forty infants (median gestational age 29 [range 24-42] weeks) were assessed at a post-conceptional age of 37 (30-54) weeks. Obstructive (n = 580), central (n = 900), and mixed (n = 452) apnoeas were identified; 381 acid reflux events were detected by MII and 153 by the pH probe only. Apnoeas were not more frequent following GOR than during control periods. Both the frequency of apnoeas (p = 0.002) and GOR episodes (p = 0.01) were inversely related to post-conceptional age at testing, but were not significantly correlated with each other when controlled for post-conceptional age.

CONCLUSIONS

These results suggest that GOR does not cause apnoea.

How to Care for Patients with EA-TEF: The Known and the Unknown

PURPOSE OF REVIEW

Guidelines were recently published highlighting why esophageal atresia (EA) patients are prone to complication risks, and the need for long-term follow-up. In this review, we will focus on how to investigate and treat potential complications, as well as the pros and cons of different investigative and treatment modalities, and what areas continue to need further research.

RECENT FINDINGS

EA patients are at high risk for gastroesophageal reflux and esophageal strictures, and the sequela that result. Extraintestinal manifestations of gastroesophageal reflux disease (GERD) can appear similar to other pathologic diagnoses commonly found in EA patients, such as congenital stricture, eosinophilic esophagitis, esophageal dysmotility, tracheomalacia, recurrent fistula, aspiration, etc. Therefore, it is important to have a standardized way to monitor for these issues. pH impedance allows for detection of nonacid reflux and the height of reflux, which are important in correlating symptoms with reflux episodes. A multidisciplinary approach is beneficial in evaluating and monitoring EA patients in the long term.

The overlap of gastroesophageal reflux disease and functional constipation in children: the efficacy of constipation treatment

OBJECTIVES

This study was designed to investigate the frequency of gastroesophageal reflux disease (GERD) in children with functional constipation (FC). It was structured to assess the improvement level in reflux symptoms by measuring the acid reflux in these patients after they had received FC treatment.

METHODS

Ninety-four children who suffered from constipation were evaluated prospectively. Data forms were completed to assess the GERD symptoms in all the cases. Twenty-four-hour pH meter monitoring was performed in 55 of the patients with GERD symptoms. The cases with abnormal acid reflux were treated by conventional therapy for FC. These cases were re-evaluated for GERD symptoms and weekly defecation frequency, and 24-h pH meter monitoring was performed at the end of a 3-month period.

RESULTS

An abnormal level of acid reflux was determined in 23 of the 55 cases. After the constipation treatment, a significant improvement was achieved in the acid reflux index and GERD symptoms, whereas the weekly defecation frequency increased.

CONCLUSION

GERD is a frequent problem in children with FC. Treatment of the constipation can improve the reflux symptoms and abnormal acid reflux in these cases. Physicians should bear in mind the co-occurrence of these two prevalent problems for better disease management.

Gastroesophageal Reflux Disease

Gastroesophageal reflux (GER) is a normal physiologic process. It is important to distinguish GER from GER disease (GERD) since GER does not require treatment. Although a diagnosis of GERD can largely be based on history and physical alone, endoscopy and pH impedance studies can help make the diagnosis when there in atypical presentation. In children and adolescents, lifestyle changes and acid suppression are first-line treatments for GERD. In infants, acid suppression is not effective, but a trial of hydrolyzed formula can be considered, as milk protein sensitivity can be difficult to differentiate from GER symptoms.

Impedance Testing in Esophageal Atresia Patients

Esophageal atresia patients are predisposed to gastroesophageal reflux as a result of the altered esophageal anatomy and motility. These patients experience significant morbidity from gastroesophageal reflux. As a result, an effective way to diagnose and monitor for reflux is crucial. pH-metry is able to quantify acid burden, ensure that acid suppression is adequate during long-term follow-up, and correlate acid reflux to symptoms. pH with impedance is additionally able to detect non-acid reflux as well as volume clearance, both of which also correlate with patient symptoms. It is also able to correlate extra-gastrointestinal symptoms to reflux, which may help guide treatment. If complications associated with uncontrolled reflux are identified, aggressive reflux management is necessary, oftentimes requiring surgical intervention.

Comparison of multichannel intraluminal impedance-pH monitoring and reflux scintigraphy in pediatric patients with suspected gastroesophageal reflux

AIM

To evaluate the agreement of multichannel intraluminal impedance-pH monitoring (MII-pHM) and gastroesophageal reflux scintigraphy (GES) for the diagnosis of gastroesophageal reflux disease.

METHODS

Seventy-five consecutive patients with suspected gastroesophageal reflux disease (GERD) underwent 24-h combined MII-pHM recording and one hour radionuclide scintigraphy during the course of the MII-pHM study. Catheters with 6 impedance channels and 1 pH sensor were placed transnasally. Impedance and pH data analysis were performed automatically and manually. For impedance monitoring, reflux was defined as a retrograde 50% drop in impedance, starting distally and propagating retrogradely to at least the next two more proximal measuring channels. Reflux index (RI, percentage of the entire record that esophageal pH is < 4.0) greater than 4.2% for pHM and number of refluxes more than 50 for 24 h for MII were accepted as positive test results. At scintigraphy, 240 frames of 15 seconds duration were acquired in the supine position. Gastroesophageal reflux was defined as at least one reflux episode in the esophagus. After scintigraphic evaluation, impedance-pH recordings and scintigraphic images were evaluated together and agreement between tests were evaluated with Cohen's kappa.

RESULTS

Sufficient data was obtained from 60 (80%) patients (34 male, 56.7%) with a mean age of 8.7 ± 3.7 years (range: 2.5-17.3 years; median: 8.5 years). Chronic cough, nausea, regurgitation and vomiting were the most frequent symptoms. The mean time for recording of MII-pHM was 22.8 ± 2.4 h (range: 16-30 h; median: 22.7 h). At least one test was positive in 57 (95%) patients. According to diagnostic criteria, GERD was diagnosed in 34 (57.7%), 44 (73.3%), 47 (78.3%) and 51 (85%) patients by means of pHM, MII, GES and MII-pHM, respectively. The observed percentage agreements/κ values for GES and pHM, GES and MII, GES and MII-pHM, and MII and pHM are 48.3%/-0.118; 61.7%/-0.042; 73.3%/0.116 and 60%/0.147, respectively. There was no or slight agreement between GES and pHM alone, MII alone or MII-pHM. pH monitoring alone missed 17 patients compared to combined MII-pHM. The addition of MII to pH monitoring increased the diagnosis rate by 50%.

CONCLUSION

No or slight agreement was found among pH monitoring, MII monitoring, MII-pH monitoring and GES for the diagnosis of gastroesophageal reflux disease.

COMBINED 24-HOURS ESOPHAGEAL PH MONITORING AND MULTICHANNEL INTRALUMINAL IMPEDANCE FOR COMPARISON OF GASTROESOPHAGEAL REFLUX IN CHILDREN WITH TYPICAL VERSUS ATYPICAL SYMPTOMS OF GASTROESOPHAGEAL REFLUX DISEASE

BACKGROUND

- Gastroesophageal reflux disease is the most common esophageal disorder in pediatrics.

OBJECTIVE

- The aim of this study was to compare reflux parameters of typical and atypical symptoms of gastroesophageal reflux disease using 24-hour esophageal pH monitoring and multichannel intraluminal impedance in pediatric population.

METHODS

- In this prospective study, 43 patients aged less than 18 year with suspected gastroesophageal reflux disease were enrolled. The patients were divided into two groups based on the main presenting symptoms (typical versus atypical). Twenty four-hour pH monitoring and multichannel intraluminal impedance were performed in all the patients for comparing these two group regarding association of symptoms and reflux. Number of refluxes, pH related reflux, total reflux time, reflux more than 5 minutes, longest time of the reflux, lowest pH at reflux, reflux index were recorded and compared. Data comparison was done using SPSS.

RESULTS

- The mean age of the patients was 5.7±3.4 years and 65.1% were male. Out of 43 patients 24 cases had typical symptoms and 19 had atypical symptoms. The mean reflux events detected by multichannel intraluminal impedance was more than mean reflux events detected by pH monitoring (308.4±115.8 vs 69.7±66.6) with P value of 0.037, which is statistically significant. The mean symptom index and symptom association probability were 35.01% ± 20.78% and 86.42% ± 25.79%, respectively in multichannel intraluminal impedance versus 12.73% ± 12.48% and 45.16% ± 42.29% in pH monitoring (P value <0.001). Number of acid reflux was 46.26±47.16 and 30.9±22.09 for atypical and typical symptoms respectively. The mean symptom index was 18.12% ± 13.101% and 8.30% ± 10.301% in atypical and typical symptoms respectively (P=0.034). Bolus clearance was longer in atypical symptoms compared typical symptoms(P<0.05).

CONCLUSION

- Symptom index was significantly higher in atypical symptoms compared to typical symptoms. Higher number of acid reflux was found in children with atypical symptoms of reflux. Longer duration of bolus clearance was found in group with atypical symptoms of reflux.

Acid Rather Than Nonacid Reflux Burden Is a Predictor of Tooth Erosion

OBJECTIVES

The relation between tooth erosion (TE) and gastroesophageal reflux in children has not been clearly established, and there are no studies to determine the relation with refluxate height, nonacid reflux, and erosions. The aim of this study was to determine the relation between TE and acid and nonacid gastroesophageal refluxes measured using combined pH and multichannel intraluminal impedance (pH-MII).

METHODS

We conducted a prospective cohort study of children presenting for pH-MII testing. Once informed consent was obtained, patients completed questionnaires about their reflux symptoms and diet, and then underwent pH-MII catheter placement and a dental examination. The Keels-Coffield erosion index was used to score the extent and severity of TE. Reflux parameters of patients with and without TE were compared using Student t test and correlations were performed using Spearman correlations.

RESULTS

A total of 27 patients participated in the study, all of whom were on acid suppression at the time of pH-MII testing. Of the 27 patients, 10 (37%) had TE. There were significant positive correlations between acid reflux episodes (r = 0.44, P = 0.02), the percentage of time that acid reflux was present in the distal esophagus (r = 0.44, P = 0.02), and reflux index (r = 0.54, P = 0.004) with the number of TE in a given patient. The percentage of time that acid reflux was present in the proximal esophagus was positively correlated with the number of teeth erosions per patient with borderline significance (r = 0.38, P = 0.05).

CONCLUSIONS

There was a positive correlation between acid reflux parameters and TE. Acid, rather than nonacid reflux, seems to have a significant role in the pathogenesis of TE.

Combined multichannel intraluminal impedance-pH (MII-pH): multicenter report of normal values from 117 children

Although combined multichannel intraluminal impedance/esophageal pH monitoring (MII-pH) has replaced prolonged pH monitoring alone for assessing gastroesophageal reflux (GER) in the pediatric population, it does so in the absence of reference values for non-acid GER (NAGER). The purpose of this study was to identify a normal range of NAGER impedance values for infants and children. We evaluated EPM/MII tracings for patients referred for GER assessment to Nationwide Children's Hospital (Columbus, OH), Inova Children's Hospital, and Hospital Italiano (Buenos Aires, Argentina). We excluded tracings from patients who had AGER indices greater than 50 % of the upper end of normal (i.e., >3 % for children >12 months and >6 % for infants ≤ 12 months), had a positive temporal association of GER with symptoms, were on anti-reflux medications at the time of the study, and/or had a fundoplication prior to the study. We also excluded studies with durations shorter than 20 h. Values for NAGER percent time, NAGER episode frequency, frequency of proximal NAGER, and mean NAGER duration were calculated for upright position, recumbent, and total. Study population consisted of 46 infants (20 female [F]/26 male [M], median age 4.8 months [range 3 weeks-11.9 months]) with a median AGER index of 2.2 % (range 0.0-5.9 %) and 71 children (22 F/49 M, median age 7.2 years [range 1.3-17 years]) with a median AGER index of 1.1 % (range 0-3.0 %). Data are presented in tables in the text. The results of this study provide a range of values characteristic of infants and children with normal AGER indices and no positive temporal associations of GER with symptoms. These values may be used as references for comparison to identify infants and/or children who may be at risk of developing serious clinical manifestations due to abnormal patterns of GER.

Management of gastroesophageal reflux disease in pediatric patients: a literature review

Gastroesophageal reflux (GER), defined as the passage of gastric contents into the esophagus, is a physiologic process that occurs throughout the day in healthy infants and children. Gastroesophageal reflux disease (GERD) occurs when gastric contents flow back into the esophagus and produce symptoms. The most common esophageal symptoms are vomiting and regurgitation. Lifestyle changes are the first-line therapy in both GER and GERD; medications are explicitly indicated only for patients with GERD. Surgical therapies are reserved for children with intractable symptoms or who are at risk for life-threatening complications of GERD. The laparoscopic Nissen antireflux procedure is the gold standard for the treatment of this pathology. A literature search on PubMed and Cochrane Database was conducted with regard to the management of GERD in children to provide a view of state-of-the-art treatment of GERD in pediatrics.

Cystic fibrosis: a surgical matter?

BACKGROUND

Gastroesophageal reflux disease (GERD) is very common in patients with chronic lung diseases. We evaluated the incidence of GERD in young patients with cystic fibrosis (CF) and defined the characteristics of gastroesophageal reflux episodes analyzed by pH-multichannel intraluminal impedance (pH-MII) and esophagogastric scintigraphy.

PATIENTS AND METHODS

Since 2010, 31 patients with CF underwent pH-MII. Scintigraphy and upper endoscopy were performed in positive GERD patients. Forced expiratory volume in 1 second (FEV1%) predicted was detected.

RESULTS

pH-MII was positive in 17/31 (54.8%) patients (mean age: 12.4 years; range: 4-17 years). pH monitoring detected an average of 64.6 acid reflux events 4.4 episodes >5 minutes in duration. The DeMeester score was 38.5. Impedance identified a mean number of reflux episodes of 66 (65.2% acid; 32% weakly acidic; 2.8% nonacidic), 28% of which reached the proximal esophagus. Esophageal transit and gastric emptying were delayed in 6/13 (46.1%) and in 5/15 (33.3%) cases, respectively. No differences were found in lung function between positive and negative GERD patients (P=0.88).

CONCLUSIONS

Pediatric patients with CF have a high incidence of GERD with acidic events. These patients should be investigated with pH-MII and scintigraphy in order to make an early diagnosis and determine the most appropriate follow-up.

Esophageal pH and Combined Impedance-pH Monitoring in Children

Esophageal pH monitoring is considered the gold standard for the diagnosis of gastroesophageal reflux disease because of the normal ranges across the pediatric age range. However, this method can only detect acid reflux. Multichannel intraluminal impedance-pH (MII-pH) monitoring has recently been used for the detection of bolus reflux in infants and children. This method allows for the detection of liquid, gas or mixed reflux in addition to acid, weakly acidic or weakly alkaline reflux. MII-pH monitoring can record the direction of flow and the height of reflux, which are useful parameters to identify an association between symptoms and reflux. However, the technique is limited by its high cost and the lack of normative data of MII-pH in the pediatric population. Despite certain limitations, MII-pH monitoring will become more common and gradually replace pH monitoring in the future, because pH monitoring is part of MII-pH.

Gastroesophageal reflux in patients treated for congenital diaphragmatic hernia: short- and long-term evaluation with multichannel intraluminal impedance

PURPOSE

The incidence of GER, related symptoms and complications in patients treated for congenital diaphragmatic hernia (CDH) are poorly defined. The aim was to evaluate incidence and development of GER in children treated for CDH in a short- and long-term follow-up period, identifying potential risk factors of morbidity.

METHODS

Thirty-six patients were evaluated with pH-MII at a median age of 6 months (T1) and re-evaluated with pH-MII and endoscopy at a median age of 5 years (T2).

RESULTS

The incidence of reflux was 83 % in T1 and 61 % in T2; the incidence of symptoms was 62 % in T1 and 38 % in T2. In both groups the reflux was mainly non-acidic. Patch, intrathoracic stomach and esophageal dysmotility were risk factors for GER.

CONCLUSIONS

The incidence of GER and symptoms decrease over the time but it was higher than in the literature, probably because it is mainly non-acidic and evaluable only with MII. The esophageal dysmotility was found to be the main risk factor. An high incidence of reflux and esophagitis was found also in asymptomatic patients, and so a close follow-up is recommended in all patients even if it is asymptomatic.

Gastroesophageal reflux in critically ill children: a review

Gastroesophageal reflux (GER) is very common in children due to immaturity of the antireflux barrier. In critically ill patients there is also a high incidence due to a partial or complete loss of pressure of the lower esophageal sphincter though other factors, such as the use of nasogastric tubes, treatment with adrenergic agonists, bronchodilators, or opiates and mechanical ventilation, can further increase the risk of GER. Vomiting and regurgitation are the most common manifestations in infants and are considered pathological when they have repercussions on the nutritional status. In critically ill children, damage to the esophageal mucosa predisposes to digestive tract hemorrhage and nosocomial pneumonia secondary to repeated microaspiration. GER is mainly alkaline in children, as is also the case in critically ill pediatric patients. pH-metry combined with multichannel intraluminal impedance is therefore the technique of choice for diagnosis. The proton pump inhibitors are the drugs of choice for the treatment of GER because they have a greater effect, longer duration of action, and a good safety profile.

Impedance-pH monitoring and conventional pH monitoring are complementary methods to detect association between gastroesophageal reflux and apnea-related symptoms in preterm infants and neonates

OBJECTIVE

To investigate the usefulness of Multichannel intraluminal impedance-pH (MII-pH) monitoring as compared with conventional pH monitoring for detecting Gastroesophageal reflux (GER) episodes and apnea-related symptom association in preterm infants and neonates.

METHODS

Twenty-three infants (16 preterm and 7 term infants) in hospital, who underwent 24-h MII-pH monitoring, were studied retrospectively. GER indices and apnea-related symptom association were measured by both MII-pH and conventional pH based analysis.

RESULTS

Of the total 998 GER episodes assessed by MII-pH monitoring, 407 (40.8%) were acidic and 590 (59.1%) were weakly acidic. A total of 1689 GER episodes were detected by conventional pH based analysis and 270 (16%) were related to retrograde bolus movement. A total of 313 apnea-related symptoms were reported. Five patients had a positive symptom association: 3 by MII-pH, 1 by both MII-pH and conventional pH, 1 only by conventional pH.

CONCLUSIONS

Addition of MII-pH monitoring to conventional pH monitoring improves the diagnostic yield of symptom association analysis in preterm infants and neonates with apnea-related symptoms. Conventional pH monitoring is still important in the era of impedance measurement.

Evaluation of esophageal motility and reflux in children treated for congenital diaphragmatic hernia with the use of combined multichannel intraluminal impedance and pH monitoring

BACKGROUND

Gastroesophageal reflux (GER) is frequently observed in children treated for congenital diaphragmatic hernia (CDH) at birth, as well as esophageal dysmotility, that has been hypothesized to be caused by innervatory anomalies. The aim of this study is to evaluate GER and dysmotility in young patients with CDH using pH-multichannel intraluminal impedance.

METHODS

Thirty children (17 boys and 13 girls) who underwent repair for CDH between 2002 and 2007 with a median age of 5.2 years (range, 3-10 years) were included in the study. All patients were operated on with a subcostal laparotomy incision and had a left-sided diaphragmatic defect. The defect repair required an artificial patch (Goretex, Gore Medical, Flagstaff, AZ) in 8 patients (27%) because of its size. We described impedance reflux parameters and some specific motility parameters studied on 10 standardized swallows.

RESULTS

The incidence of GER was 86%. Reflux was mainly nonacidic, postprandial, and short-term and reached only the distal esophagus. Esophageal dysmotility was observed only in the distal esophagus.

CONCLUSIONS

With the use of pH-multichannel intraluminal impedance, both GER and esophageal motility in patients with congenital malformations can be analyzed. In patients with CDH, impaired motility seems to involve only the distal esophagus. In this group, the specific pattern of reflux is probably caused by the involvement of gastroesophageal junction, without significant intrinsic innervation abnormalities as observed in patients with esophageal atresia.

Gastroesophageal reflux in young children treated for esophageal atresia: evaluation with pH-multichannel intraluminal impedance

OBJECTIVES

Gastroesophageal reflux (GER) and dismotility occur frequently after repair of esophageal atresia (EA). GER-associated complications can manifest either early or later; then precocious diagnosis and treatment are essential. The aim of the study was to evaluate characteristics of GER and esophageal clearance in children treated for EA with distal tracheoesophageal fistula, using pH-multichannel intraluminal impedance (pH-MII).

PATIENTS AND METHODS

Twenty-two children (ages 3-40 months) treated for EA at birth, and 20 normal children of similar age with suspected GER disease were included in the study. Impedance parameters were analyzed according to age and symptoms.

RESULTS

Reflux events were mainly nonacidic. About bolus exposure index, mean acid clearing time (MACT), and mean bolus clearing time (MBCT), a significant difference was found between 2 groups: the median MACT and MBCT were longer, with values of 281 and 39 seconds, respectively, in the EA group and 110 and 15 seconds in the control group (P < 0.0005).

CONCLUSIONS

Our data show that in young patients the majority of refluxes are not acid. This implies that the incidence of GER may be underestimated if pH-metry is used. The pH-MII is an ideal test in children because it studies both GER with its characteristics and motility pattern. The quality of reflux does not seem to influence the onset of symptoms that are related to an impaired esophageal clearance. Hence, this technique could be useful to study patients treated for EA, avoiding the onset of complications.

Temporal association of polysomnographic cardiorespiratory events with GER detected by MII-pH probe in the premature infant at term

OBJECTIVES

The aim of the study was to examine temporal association (TA) between polysomnographic cardiorespiratory (CR) events and gastroesophageal reflux (GER) in premature infants with persistent CR events at >39 weeks postmenstrual age and determine whether the use of multichannel intraluminal impedance (MII)-pH probe improves sensitivity of the TA compared with pH probe alone.

PATIENTS AND METHODS

Seven infants born between 24 and 29 weeks' gestational age with persistent CR events at 39 to 48 weeks' postmenstrual age underwent a polysomnography with MII-pH probe. Symptom index (SI) and symptom-associated probability were calculated for diverse types of reflux and CR events. SI and a Fisher exact test with variable association windows were calculated for obstructive apnea (OA). Odds ratios for an OA given a reflux event and for a reflux event given an OA were determined.

RESULTS

With a Fisher exact test, a subject-specific association between MII events and OA was found in the 3 patients who required a fundoplication or had the worse clinical GER. Some level of TA was found with SI and symptom-associated probability in 6 of 7 infants. Association was found for pH > 4 and pH ≤ 4 reflux events. pH-only events with no change of MII had only a limited role in generating CR events.

CONCLUSIONS

TA between CR events and GER was found in a single-subject-level analysis in some infants with persistent CR events at term. This TA suggests a causal relation between CR and reflux events that was further strengthened by the clinical outcomes of each infant.

Does reflux monitoring with multichannel intraluminal impedance change clinical decision making?

OBJECTIVES

Multichannel intraluminal impedance with pH (pH-MII) has become the criterion standard test for the evaluation of gastroesophageal reflux disease, but it is not clear whether the results of this test change clinical decision making. The goal of the present study was to determine the differences in clinical decision making by attending physicians based on the pH probe results versus MII results.

METHODS

We conducted a prospective study in which physicians were initially given pH probe results and asked how they would change the patient's clinical management based on these results. Physicians were then given the MII results and asked how their management would change. Physicians then were asked whether they believed MII affected their clinical decision making overall.

RESULTS

pH probe results changed clinical management 40% of the time and MII results changed clinical management an additional 22% of the time. Clinical decision making was not influenced by the performance of pH-MII on or off acid suppression. The escalation of acid suppression therapy was the main management change that occurred based on the pH-MII results.

CONCLUSIONS

The addition of MII to the standard pH probe resulted in a change in management in approximately 25% of the patients, suggesting that there may be a role for pH-MII in clinical practice.

Evaluation of esophageal motility and reflux in children treated for esophageal atresia with the use of combined multichannel intraluminal impedance and pH monitoring

BACKGROUND

Gastroesophageal reflux (GER) and dysmotility are frequent in patients treated for esophageal atresia (EA). This aim of this study is to evaluate GER and dysmotility in young EA patients using pH-multichannel intraluminal impedance (pH-MII).

METHODS

Fifteen patients with a mean age of 7.5 years (group 1) have been studied and compared with 15 children without congenital malformation, submitted to pH-MII for suspected GER (group 2). These latter patients serve as a control group of healthy subjects. The following impedance reflux and motility parameters have been studied on 10 standardized swallows: number of reflux episodes, mean acid clearing time, median bolus clearing time, bolus presence time, total bolus transit time, segmental transit time, and total propagation velocity.

RESULTS

In the group of EA patients, mean acid clearing time and median bolus clearing time were pathological. In the control group, all reflux parameters were normal. Patients with EA had significantly longer median bolus presence time at each measuring site, median total bolus transit time, and median segmental transit time and slower total propagation velocity (P < .001).

CONCLUSIONS

pH-multichannel intraluminal impedance evaluates both GER and motility patterns. Our report studies impedance parameters of esophageal motility in healthy children and in EA patients using only pH-MII.

Esophageal impedance monitoring for gastroesophageal reflux

Dual pH-multichannel intraluminal impedance (pH-MII) is a sensitive tool for evaluating overall gastroesophageal reflux disease, and particularly for permitting detection of nonacid reflux events. pH-MII technology is especially useful in the postprandial period or at other times when gastric contents are nonacidic.pH-MII was recently recognized by the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition and the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition as being superior to pH monitoring alone for evaluation of the temporal relation between symptoms and gastroesophageal reflux. In children, pH-MII is useful to correlate symptoms with reflux (particularly nonacid reflux), to quantify reflux during tube feedings and the postprandial period, and to assess efficacy of antireflux therapy. This clinical review is simply an evidence-based overview addressing the indications, limitations, and recommended protocol for the clinical use of pH-MII in children.

Evaluation of esophageal motility using multichannel intraluminal impedance in healthy children and children with gastroesophageal reflux

OBJECTIVE

Multichannel intraluminal impedance (MII) directly evaluates esophageal bolus transport. There is a good correlation between MII and manometry in healthy adults, but there are no reports concerning children.The aim of the present study was to determine normal values of esophageal motility using only impedance measurements in healthy children and in a pediatric population with gastroesophageal reflux (GER).

PATIENTS AND METHODS

We described in the present study 60 children submitted to pH-MII for 24 hours for suspected GER. Patients were divided into 2 different groups on the basis of their pH-MII report. Group 1 patients showed acid GER, whereas group 2 patients had negative pH-MII analysis for GER despite symptoms. We described impedance reflux and motility parameters on 10 standardized swallows: number of reflux, mean acid clearing time, median bolus clearing time, bolus presence time, total bolus transit time, segmental transit time, and total propagation velocity.

RESULTS

In group 1, the median mean acid clearing time was 151 seconds, whereas the median mean bolus clearing time was 25 seconds. In group 2 patients, all of the reflux parameters were normal. In group 1 the median bolus presence time at each measuring site, the median total bolus transit time, and the median segmental transit time were significantly greater and total propagation velocity lower than values reported in group 2 (P < 0.001), if compared with those described for adult patients.

CONCLUSIONS

The pH-MII is an ideal test in children because it studies GER with its characteristics and motility pattern. Our report summarizes for the first time impedance motility parameters in healthy children.

Can acid (pH) refluxes predict multichannel intraluminal impedance refluxes? A correlation study

BACKGROUND AND AIM

The present study aims to explore if and when acid (pH) refluxes can predict refluxes detected by multichannel intraluminal impedance (MII) studies. This correlation may indicate whether pH probe-only and MII-pH studies are interchangeable.

METHODS

Prospective observational cross sectional study of symptomatic children (below 18 years) who had MII-pH studies done for gastroesophageal reflux. Clinical data were extracted from patient records. Non-parametric tests, Pearson's rho and receiver operating characteristic (ROC) curves were used for data analysis.

RESULTS

A total of 153 children were included in the study and 62% were on acid suppression. Indices for acid and MII refluxes correlated with each other only in those without acid suppression. This correlation was lost in children on acid suppression. There was no statistically significant difference in acid or MII reflux indices in children with or without acid suppression. Like acid reflux, indices for MII refluxes had good correlation with each other irrespective of acid suppression. Liquid and mixed MII refluxes showed excellent correlation with respective types of proximally migrating refluxes. The values for MII reflux indices derived from our patient population were in broad agreement with available pediatric and adult data.

CONCLUSIONS

A pH probe-only study in patients without acid suppression may reflect both acid and volume (MII) reflux activities adequately and can substitute for MII-pH study. The observed excellent correlation between acid and MII refluxes with proximal migration may justify using pH probe-only studies for extra esophageal symptoms in patients without acid suppression.

Comparison of esophageal pH and multichannel intraluminal impedance testing in pediatric patients with suspected gastroesophageal reflux

BACKGROUND

Multichannel intraluminal impedance (MII) is a pH-independent method of assessing gastroesophageal reflux.

AIM

To evaluate the diagnostic accuracy of MII-pH as compared with conventional pH monitoring in detecting reflux events (REs) and symptom association in different age groups.

METHODS

: A prospective direct comparison of 2 diagnostic techniques on 291 consecutive patients referred for suspected gastroesophageal reflux disease. Sensitivity and diagnostic accuracy of MII-pH versus pH monitoring and symptom association were measured.

RESULTS

MII-pH detected 13631 REs, 6260 (46%) of which were nonacid. The prevalence of weakly acid refluxes in the 24 hours and postprandial period as well as the proximal extension of refluxate were significantly greater in infants as compared with children (P < 0.001, P < 0.001, and P < 0.01, respectively). The diagnostic accuracy of combined MII-pH in revealing all RE and acid RE were significantly higher in infants as compared with children (92% vs 82%, P < 0.01 and 83% vs 76%, P < 0.04, respectively). The addition of MII to conventional pH monitoring significantly increases the diagnostic yield of symptom association analysis in revealing an association between atypical symptoms and refluxes irrespective of age, whereas in studying typical symptoms it was true only for infants.

CONCLUSIONS

Addition of MII to conventional pH monitoring significantly increases the diagnostic yield in detecting REs, prevalently in infants, and in revealing an association between refluxes and symptoms, prevalently respiratory ones and in infants group.

Pediatric gastroesophageal reflux clinical practice guidelines: joint recommendations of the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN) and the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN)

OBJECTIVE

To develop a North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN) and European Society for Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) international consensus on the diagnosis and management of gastroesophageal reflux and gastroesophageal reflux disease in the pediatric population.

METHODS

An international panel of 9 pediatric gastroenterologists and 2 epidemiologists were selected by both societies, which developed these guidelines based on the Delphi principle. Statements were based on systematic literature searches using the best-available evidence from PubMed, Cumulative Index to Nursing and Allied Health Literature, and bibliographies. The committee convened in face-to-face meetings 3 times. Consensus was achieved for all recommendations through nominal group technique, a structured, quantitative method. Articles were evaluated using the Oxford Centre for Evidence-based Medicine Levels of Evidence. Using the Oxford Grades of Recommendation, the quality of evidence of each of the recommendations made by the committee was determined and is summarized in appendices.

RESULTS

More than 600 articles were reviewed for this work. The document provides evidence-based guidelines for the diagnosis and management of gastroesophageal reflux and gastroesophageal reflux disease in the pediatric population.

CONCLUSIONS

This document is intended to be used in daily practice for the development of future clinical practice guidelines and as a basis for clinical trials.

Acid gastroesophageal reflux in symptomatic infants is primarily a function of classic 2-phase and pH-only acid reflux event types

BACKGROUND

Combined esophageal pH monitoring (EPM) and multichannel intraluminal impedance (MII) reveal 4 unique acid gastroesophageal reflux (AGER) types in infants: classic 2-phase, single-phase, pH-only events (POEs), and re-reflux episodes. The extent to which different AGER event types contribute to AGER frequency, acid reflux exposure time (ARET), and the number of episodes lasting 5 minutes or longer, has never been reported. In this study, EPM/MII was used to assess AGER in symptomatic infants on the basis of these 4 AGER types.

MATERIALS AND METHODS

EPM/MII tracings from 12 symptomatic infants (<12 months old) were examined. Mean frequencies and durations of each AGER type, percentages of total ARET due to each AGER type, and percentages of different AGER types lasting 5 minutes or longer, were measured.

RESULTS

Of 926 total AGER events, 23.1%, 6.3%, 69.2%, and 1.5% were classic 2-phase, single-phase, POEs, and re-reflux episodes, respectively. In 20.2 hours of combined ARET, 52.3%, 2.3%, 42.4%, and 3.0% occurred during classic 2-phase, single-phase, POEs, and re-reflux episodes, respectively. Classic 2-phase and POE events were both more frequent than single-phase (P = 0.002 and P < 0.0001) and re-reflux (P = 0.002 and P < 0.0001) episodes, respectively. Increasing numbers of AGER episodes were strongly correlated with POEs (P = 0.0001). Of the 35 total AGER episodes that lasted 5 minutes or longer, 94% were classic 2-phase episodes or POEs (57% and 37%, respectively).

CONCLUSIONS

In symptomatic infants, total AGER episodes, total ARET, and AGER episodes lasting 5 minutes or longer are largely a function of classic 2-phase and pH-only AGER types.

Reliability of oesophageal pH recording for the detection of gastro-oesophageal reflux

OBJECTIVE

Despite the new gold standard oesophageal impedance monitoring, pH monitoring is still used frequently for detection of gastro-oesophageal reflux (GOR). Besides drops in pH from above to below pH4, drops of > or =1 unit are also used as a marker for GOR. In this study the objective was to investigate the accuracy of drops in pH for detection of GOR, using impedance monitoring as the gold standard.

MATERIAL AND METHODS

Nineteen GORD patients (9 M, 55+/-11 years) underwent combined 24-h pH-impedance recording off acid-suppressive therapy. All drops in pH > or =0.5 pH units, with a duration > or =4 s, reaching the nadir pH within 5 s after onset were included. Reflux events detected with impedance monitoring were taken as the reference.

RESULTS

In total, 2221 drops in pH were found; 47% were acid (nadir pH <4), 47% weakly acidic (nadir pH between pH7 and 4) and 5% were superimposed (pH drop starting below pH4). The sensitivities of acid, weakly acidic and superimposed pH drops > or =1 were 91%, 28%, 24%, respectively, and the percentages of false-positive reflux episodes were 20, 56 and 54, respectively. Acid reflux with a cut-off > or =0.5 and < or =3.3 had a moderate-to-good sensitivity (94-70%) and low false-positive percentages (23-13%). In contrast, weakly acidic and superimposed reflux showed greater false-positive than true-positive percentages for all cut-off values.

CONCLUSIONS

Compared to impedance monitoring, detection of reflux with pH monitoring is clearly inferior. When drops in pH > or =1 are used irrespective of nadir pH as an indicator of reflux episodes, the number of reflux episodes is overestimated. Decreases from above to below 4 with cut-offs between > or =0.5 and < or =3.3 are the most indicative of true reflux episodes.

Addition of pH-impedance monitoring to standard pH monitoring increases the yield of symptom association analysis in infants and children with gastroesophageal reflux

OBJECTIVE

To assess the additional yield of combined multichannel intraluminal pH-impedance (pH-MII) monitoring compared with standard pH monitoring on gastroesophageal reflux (GER) symptom associations in infants and children.

STUDY DESIGN

In 80 patients, 24-hour ambulatory pH-MII monitoring was performed. Tracings were analyzed with established pH-MII criteria. Symptoms of regurgitation and belching were excluded from analysis, because these were considered to be a direct consequence of GER. Standard GER-symptom correlation indices were calculated with: 1) standard pH monitoring; 2) MII detection of liquid and mixed bolus GER; 3) MII detection of all bolus GER (liquid, mixed, and gas); 4) pH-MII detection of all GER, including pH-only GER.

RESULTS

Fifty patients (21 children) were included. MII detection of all bolus GER yielded a significantly greater number of patients who were symptom-positive, 36 (72%) compared with 25 (50%) with standard pH-monitoring (P = .04). A positive symptom association was observed in 8 of 10 (80%) patients with pathological esophageal acid exposure and 28 of 40 (70%) patients with negative pH-findings.

CONCLUSIONS

A high proportion of patients with normal esophageal acid exposure had a positive symptom association on pH-MII monitoring. Including all MII-detected bolus GER and excluding pH-only GER for analysis optimizes the yield of GER-symptom associations in infants and children.

"pH-Only" acid reflux events in infants during later phases of the feeding cycle are less acidic and cleared more efficiently than classic 2-phase acid reflux events

BACKGROUND

Gastroesophageal acid exposure in infants is a function of 4 acid gastroesophageal reflux (AGER) types: classic 2-phase, single-phase, and pH-only events (POEs), as well as rereflux episodes. In symptomatic infants, classic 2-phase events and POEs make up the majority of total AGER events and AGER events lasting 5 minutes or longer, and are responsible for the majority of total gastroesophageal acid exposure. Also, in symptomatic infants, chemical clearance efficiency of classic 2-phase events has been shown to be influenced by feeding. Pathogenicity of AGER involves variables that include frequency, duration, and pH of AGER events. The purpose of this investigation was to compare classic 2-phase episodes and POEs on the basis of these variables during discrete periods related to feeding.

PATIENTS AND METHODS

Impedance/pH tracings from 12 symptomatic infants (median age 20 weeks) were examined. Mean frequencies, durations, and nadir pH values were calculated during feeding, the first hour postprandial (1stPP), the second hour postprandial (2ndPP), and fasting.

RESULTS

Compared with classic 2-phase events, POEs were cleared significantly more efficiently during 1stPP (3-fold, P = 0.02), 2ndPP (3-fold, P = 0.0001), and fasting (4.5-fold, P < 0.0001), and were less acidic during 2ndPP (1.9 +/- 0.15 vs 2.6 +/- 0.07, P = 0.0005) and fasting (1.5 +/- 0.12 vs 2.9 +/- 0.07, P < 0.0001). Whereas clearance of classic 2-phase events became increasingly less efficient, clearance of POEs did not fluctuate significantly during the course of the feeding cycle.

CONCLUSIONS

The lower acidity and more rapid clearance during 2ndPP and fasting suggest that POEs are likely to have a different clinical impact (compared with classic 2-phase AGER events) during later phases of the feeding cycle.

Role of the multichannel intraluminal impedance technique in infants and children

Recently, multichannel intraluminal impedance (MII) was added to the repertoire of tests available to study esophageal (patho)physiology in children. MII has since been used in 2 major areas. First, it has been used as a diagnostic test for gastroesophageal reflux disease (GERD). The main advantage over traditional pH monitoring is its ability to detect both acid and nonacid gastroesophageal reflux (GER) and to discern between liquid and gas GER.Although feasible with multiple pH sensors, the MII technique routinely detects the proximal extent of a GER episode. When a pH sensor is added to the MII-catheter, important information about the acidity of a GER event can be gathered.The second area in which the role of MII has been investigated is that of esophageal function testing. Manometry classically reveals information about esophageal pressure patterns and sphincter function, but does not inform us about bolus flow. MII not only detects the presence of esophageal flow but also adds information on the direction of flow, duration of bolus presence, completeness of bolus clearance, and composition of a bolus.The combination of MII with manometry enables determination of the relationship between esophageal pressures and flow and, therefore, enhances evaluation of esophageal function in terms of assessment of mechanisms of esophageal volume clearance. In addition, this technique will improve our understanding of (patho)physiological mechanisms in pediatric GERD and other esophageal motility disorders.

Ambulatory monitoring of GERD: current technology

Various techniques have been devised to diagnose, characterize, and classify gastroesophageal reflux (GER). Stationary techniques, such as fluoroscopy and scintigraphy, provide interesting anatomic and functional information related to GER but are not sensitive enough and are usually performed in nonphysiologic conditions. Ambulatory techniques for GER monitoring have been developed and used since 1974. The current available techniques include catheter and wireless pH-metry, Bilitec, and impedance-pH monitoring. Prolonged wireless pH monitoring can be useful to evaluate patients off and on proton pump inhibitor (PPI) treatment. Impedance-pH monitoring is being used increasingly in patients who have persistent symptoms on PPI therapy because it can establish an association between symptoms and weakly acidic or nonacid reflux. Bilitec is performed in patients suspected to have increased duodenogastroesophageal reflux (DGER). This article discusses the technical details, clinical indications, and applications of these diagnostic techniques.

High-resolution manometry and impedance-pH/manometry: valuable tools in clinical and investigational esophagology

Both high-resolution manometry (HRM) and impedance-pH/manometry monitoring have established themselves as research tools and both are now emerging in the clinical arena. Solid-state HRM capable of simultaneously monitoring the entire pressure profile from the pharynx to the stomach along with pressure topography plotting represents an evolution in esophageal manometry. Two strengths of HRM with pressure topography plots compared with conventional manometric recordings are (1) accurately delineating and tracking the movement of functionally defined contractile elements of the esophagus and its sphincters, and (2) easily distinguishing between luminal pressurization attributable to spastic contractions and that resultant from a trapped bolus in a dysfunctional esophagus. Making these distinctions objectifies the identification of achalasia, distal esophageal spasm, functional obstruction, and subtypes thereof. Ambulatory intraluminal impedance pH monitoring has opened our eyes to the trafficking of much more than acid reflux through the esophageal lumen. It is clear that acid reflux as identified by a conventional pH electrode represents only a subset of reflux events with many more reflux episodes being composed of less acidic and gaseous mixtures. This has prompted many investigations into the genesis of refractory reflux symptoms. However, with both technologies, the challenge has been to make sense of the vastly expanded datasets. At the very least, HRM is a major technological tweak on conventional manometry, and impedance pH monitoring yields information above and beyond that gained from conventional pH monitoring studies. Ultimately, however, both technologies will be strengthened as outcome studies evaluating their utilization become available.

Diurnal variation in the chemical clearance of acid gastroesophageal reflux in infants

BACKGROUND & AIMS

Clearance of acid gastroesophageal reflux is biphasic. During volume clearance, refluxed material is cleared from the esophagus by peristalsis, and during chemical clearance, acidified esophageal mucosa is neutralized by saliva and possibly secretions from the esophageal lumen. In this study, we examined the effects of feeding on the durations of volume clearance and chemical clearance.

METHODS

Combined pH/multichannel intraluminal impedance tracings from 12 symptomatic infants (median age, 20 weeks) were analyzed. Acid gastroesophageal reflux episodes having both volume clearance and chemical clearance components were grouped into 1 of 4 feeding cycle phases (feeding, first hour postprandial, second hour postprandial, and fasting).

RESULTS

Mean duration of volume clearance and chemical clearance was 7.0 +/- 2.3 and 36.3 +/- 8.5 minutes (P = .001), respectively, per patient and 24.7 +/- 2.7 and 127.5 +/- 10.7 seconds (P < .0001), respectively, per episode. Whereas volume clearance did not change throughout the feeding cycle, chemical clearance was significantly prolonged during fasting (132.2 +/- 18.4 seconds) compared with feeding (13.5 +/- 4.1 seconds, P = .0046) and 1st postprandial (64.0 +/- 19.4 seconds, P = .0333). Statistical analysis failed to demonstrate a significant relationship between nadir pH and chemical clearance (P = .3104) or between chemical clearance and the interaction between nadir pH and feeding cycle.

CONCLUSIONS

Chemical clearance is significantly prolonged during fasting in infants. Falling pH alone cannot explain declining chemical clearance efficiency during later postprandial periods. We speculate that inefficient chemical clearance during fasting is likely due to reduced efficiency of acid clearance mechanisms that could include salivation, swallowing, peristalsis, and/or intraluminal secretion.