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Catheter-Based pH Testing
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13
FerminFontan, OscarTalledo,
andPeterNau
Introduction
Catheter-based pH testing dates to 1969 when Spencer J. published in the British Journal of Surgery the rst report on prolonged intraesophageal pH monitoring in patients with
gastroesophageal reux [1]. He documented up to 18h of esophageal pH monitoring in the inpatient setting and showed that prolonged monitoring was feasible and well tolerated by patients.
Later in the 1970s, Johnson and DeMeester reported full 24-h pH
testing. It was during this initial work that they developed their
composite scoring system that would later evolve into a validated
scoring system for the identication of pathologic gastroesophageal reux [2, 3].
With the advent of proton pump inhibitors (PPI) in 1989, the
management of acid-related pathologies such as peptic ulcer disease and gastroesophageal reux disease (GERD) underwent a
dramatic change. At present, antisecretory therapy has become
the mainstay in the treatment of GERD [4]. Low-risk patients pre-
F. Fontan · O. Talledo · P. Nau (*)
University of Iowa Carver College of Medicine, Iowa City, IA, USA
e-mail: oscar-talledozevallos@uiowa.edu; peter-nau@iowa.edu
© Society of American Gastrointestinal and Endoscopic Surgeons
(SAGES) 2023
A. D. Patel et al. (eds.), The SAGES Manual of Physiologic
Evaluation of Foregut Diseases,
https://doi.org/10.1007/978-3-031-39199-6_13
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senting with uncomplicated GERD symptoms are offered
4–8weeks of empiric PPI treatment as the initial approach. The
preponderance of trials assessing for resolution of esophagitis 4
and 8 weeks after medical management showed a higher
proportion of patients with all grades healed at week 8 compared
with week 4 [5, 6].
Response to medical therapy can have a high sensitivity in the
diagnosis of GERD but a low and variable specicity [7]. In up to
40% of these subjects, there is no response to therapy. Following
conrmation of compliance of the dosing and appropriate timing,
most providers will switch to a second-generation PPI or increase
the dose to twice daily [8]. In cases where symptoms persist
despite optimal medical therapy and lifestyle modications, a
diagnostic workup including pH testing becomes fundamental
[9]. A special subset of patients including those with underlying
risk factors (Caucasians, male, 50years of age or older, obese,
smokers, heavy alcohol user), and/or alarms symptoms, should be
offered endoscopy early on in their workup in order to exclude
esophageal metaplasia and potential esophageal malignancies
[10].
F. Fontan et al.
Dening GERD
Another critical evolution that has paralleled the advent of PPIs
has been the signicant improvement in the general understanding of the full spectrum of GERD. This disease is dened by the
presence of gastric acid reux into the esophagus which is associated with mild or moderate/severe symptoms occurring two or
more times per week and at least once per week, respectively.
Heartburn, regurgitation, and dysphagia are classically known as
typical symptoms, whereas belching, nausea, wheezing, globus
sensation, chest pain, hoarseness, and cough are considered atypical symptoms [11].
Classic GERD is characterized by reux symptoms in association with various degrees of esophageal erosive ndings. The
Los Angeles (LA) classication system for esophagitis grading
was published in 1999 and is currently implemented as a stan-
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Table 13.1 Los Angeles classication
Grade A At least one mucosal break no longer than 5mm that does not
extend between the tops of two mucosal folds
Grade B At least one mucosal break more than 5mm long that does not
extend between the tops of two mucosal folds
Grade C At least one mucosal break that is continuous between the tops
of two or more mucosal folds but which involve less than 75%
of the circumference
Grade D At least one mucosal break which involves at least 75% of the
esophageal circumference
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dardized tool to categorize the degree of erosive esophagitis
(Table13.1) [12].
Interestingly, up to 70% of patients with classic GERD symptoms have no evidence of erosive changes on endoscopy. Of this
group, 50% have abnormal pH test results and thus belong to the
non-erosive reux disease (NERD) category [13, 14]. The remain-
ing 50% belong to a subset of patients with esophageal hypersensitivity and functional heartburn. These patients have chronic
typical heartburn symptoms attributed to the esophagus without
evidencing any other underlying etiology. Together, these presentations account for 90% of the heartburn patients who fail optimal
antisecretory therapy.
The importance in distinguishing this subset of patients with
physiologic acid levels in the setting of subjective reux disease is
the disparate responses to available therapeutic modalities. Not
every patient will require conventional antireux medication, and
not every patient would benet from surgery.
Catheter-Based pH Testing Device
The general components of catheter-based pH monitoring systems are a exible catheter with pH sensors and a data logger
(Fig.13.1).
The reference electrodes can be placed either outside the
esophagus or internally, built into the catheter. The probes measure approximately 2mm in diameter which facilitates transnasal
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Fig. 13.1 Catheter-based pH testing system. (Courtesy of Diversatek Healthcare Milwaukee, WI)
F. Fontan et al.
placement. Most commercially available devices sample data
every 4–10s, and pH testing is usually carried out for approximately 24 h or more, depending on patient tolerance. The data
logger varies across the different brands, but in general it is
available to be worn on a shoulder strap or a waist belt. Patients
are instructed to select the “ingestion” setting at the beginning of
their meals and to leave this option selected for the duration of the
meal. If ingestion is not occurring, the default “no ingestion” setting is selected. There are other buttons to indicate presence of
symptoms and to indicate when the patient is laying supine or
sleeping.
If patients are inaccurate, study results may be reported as
falsely positive or negative. In addition to the artifacts generated
by meal periods, isolated pH drops can be seen and are referred to
as “pseudo-reux” and originating from the monitoring circuit
itself [15]. On the other hand, gradual acidication can be seen in
patients who have esophageal retention, due to inefcient emptying such as in achalasia.
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Different studies have demonstrated that the sensitivity of
catheter-based pH monitoring is not as high as previously thought.
The percentage of false-negative results in patients with typical
symptoms has been shown to be greater than 20%, and in the case
of atypical symptomatology, outcomes have shown to be even less
accurate. This is in part due to proximal probes, which sensitivity
has been reported to be as low as 50% [16, 17]. Hence, patient
compliance to test instructions and detail to their recordings are a
critical component for test accuracy.
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Technique
Esophageal pH testing is considered a safe procedure usually performed in the ambulatory setting. For safety reasons, patients are
typically requested to fast for 6h, depending on the institutional
protocol. After calibration of the sensors, patient education, and
consent, local aerosol/topical anesthetics is applied to the nasopharynx to decrease patient discomfort and to facilitate transnasal
catheter introduction. The placement of the probe takes approximately 10min. The sensors are typically positioned 5cm above
the upper level of the lower esophageal sphincter (LES) as determined by esophageal manometry. Depending on the manufacturer, there may be additional sensors that can be placed 10cm
below the stomach or 15cm proximal to the LES. These extra
sensors can better dene the proximal extent of reux in the setting of atypical manifestations of GERD [18]. After conrming an
adequate location, and securely taping the catheter in place,
patients are instructed to resume daily activities and attempt to
reproduce normal scenarios that would usually precipitate their
symptoms [19]. No clear guidelines on dietary restrictions exist,
and recommendations vary across different providers and specialties. Patients are discharged home and provided with diaries for
them to document time of symptom occurrence, time of their
meals and content, time of upright and recumbent positions, and
time of administration of any acid-suppressing medication if
taken during the study.
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F. Fontan et al.
Indications
When considering the utility of objective pH analysis, the ultimate trajectory of the patient’s care must be considered. For those
patients who do not desire or would not be candidates for operative intervention, the value of pH testing differs from an individual being considered for a surgery. Indications for testing in those
who are on a medical management pathway are those with classic
GERD symptoms who fail 4 weeks of PPI therapy or have an
incomplete response. This is also the management algorithm for
those with atypical symptoms of GERD who do not see symptom
resolution after a trial of PPIs. In contrast, patients with complications of reux such as erosive esophagitis (LA grade C or D
esophagitis), peptic stricture, or Barrett’s esophagus, pH testing to
conrm the diagnosis is of low utility [20].
The preponderance of patients being evaluated for an endoscopic or surgical antireux procedure should be tested prior to
proceeding with any interventions. This is secondary to the fact
that up to 25% of patients with LA grade B esophagitis will have
normal acid exposure on objective testing [21]. It is critical to
identify those individuals with esophageal hypersensitivity and
functional heartburn as they will not improve with an antireux
procedure. In the case of patients who have undergone previous
endoscopic or surgical antireux therapy and who continue to
have GERD symptoms, pH testing is also recommended [22].
Another common indication for testing is obese patients with subjective GERD symptoms that are being evaluated for bariatric surgery. In a recent study, preoperative GERD evaluation including
intraesophageal pH testing detected pathology which altered procedure selection from sleeve gastrectomy to Roux-en-Y gastric
bypass in 24.8% [23].
An important aspect when considering pH monitoring is the
decision to test the patient while on PPI therapy or to request full
cessation of antireux medications. A retrospective study including 250 patients tested while on PPI showed normal pH monitoring data, demonstrating that the clinical yield for pH testing while
on PPI therapy could be low [24]. The Lyon Consensus proposes
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that testing should always be performed off therapy to demonstrate baseline acid exposure time (AET) in “unproven GERD,”
meaning no (or low-grade) esophagitis at endoscopy, and no prior
positive pH testing. In contrast, the Lyon Consensus proposes that
patients with “proven GERD” be evaluated on double-dose PPI
therapy to establish correlation between refractory symptoms and
reux episodes and/or to exclude inadequate acid suppression or
poor compliance as the mechanism of persisting symptoms. This
assessment requires pH-impedance (vs. pH) monitoring since
most reux episodes on PPI therapy are weakly acidic (pH4–7)
[25]. It is also reasonable to consider pH monitoring on PPIs in a
revisional setting where there are only minor anatomic issues and
the underlying goal may be to defer a reoperation. When electing
to test off medication, the classic recommendation is to discontinue PPI medications at least 7days before the study. Other antiacids are typically discontinued 2 days prior to the study, and
these include Zantac (ranitidine), Tagamet (cimetidine), Axid
(nizatidine), Pepcid (famotidine).
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Interpretations
The key interrogans that should be answered by pH testing are as
follows: Is the distal esophageal acid exposure in excess of that
noted in normal individuals? And are the symptoms reported by
the subject, during pH monitoring, associated or not with reux?
Software packages generally provide a standard readout of pH
levels, which is later analyzed by providers for a more accurate
result (Fig.13.2). Time is displayed along the x-axis, and the pH
levels ranging from 0 to 8 are represented along the y-axis. The
data recorded by the catheter sensor in conjunction with patient
documentation allow providers to obtain the symptom index for
reux (SI), symptom association probability (SAP), and the
DeMeester score. The SAP determines the statistical validity of
symptom-reux association, while the SI provides data on the
strength of the association [26, 27]. The DeMeester score is a
composite calculation of severity characteristics of reux. It contemplates six different parameters [2, 28].
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Fig. 13.2 Screenshot of reux analysis software Digitrapper by Medtronic
(Covidien LP, a Medtronic company)
DeMeester score
Total number of reux episodes
Total time esophageal pH<4
Upright time esophageal pH<4
Supine time esophageal pH<4
Number of reux episodes lasting >5min
Longest reux episode
F. Fontan et al.
Among the pH monitoring metrics, AET (esophageal pH<4)
is the most reproducible, is reliably extracted from automated
analysis, and is predictive of response from medical and surgical
reux therapy. Acid exposure time<4% is considered denitively
normal (physiological) and >6%, considered denitively abnormal [2, 28]. The physiologic signicance of a pH<4 lies in the
fact that mucosal damage and symptoms occur when the esophageal lining is exposed to pH levels lower than 4 [20]. By analyzing
these parameters, providers can have a better understanding of the
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191
patient’s reux pattern, time of the day, esophageal clearance, and
triggers. DeMeester score serves as an objective tool that, in conjunction with endoscopic evaluation and clinical assessment,
allows for a more accurate diagnosis.
Conclusion
Catheter-based pH testing is, although less sensitive than other
available testing options, still a cost-effective and safe technology,
readily available in the armamentarium to diagnose GERD in
symptomatic patients.
References
1. Spencer J. Prolonged pH recording in the study of gastroesophageal
reux. Br J Surg. 1969;56:912–4.
2. Johnson LF, DeMeester TR.Twenty-four-hour pH monitoring of the distal esophagus. A quantitative measure of gastroesophageal reux. Am J
Gastroenterol. 1974;62:325–32.
3. Johnson LF, DeMeester TR.Development of the 24-hour intraesophageal
pH monitoring composite scoring system. J Clin Gastroenterol.
1986;8:52–8.
4. Vakil N, van Zanten SV, Kahrilas P, etal. The Montreal denition and
classication of gastroesophageal reux disease: a global evidence-based
consensus. Am J Gastroenterol. 2006;101:1900–20.
5. Castell DO, Kahrilas PJ, Richter JE, etal. Esomeprazole (40 mg) compared with lansoprazole (30 mg) in the treatment of erosive esophagitis.
Am J Gastroenterol. 2002;97:575–83.
6. Richter JE, Kahrilas PJ, Sontog SJ, et al. Comparing lansoprazole and
omeprazole in onset of heartburn relief: results of a randomized, controlled trial in erosive esophagitis patients. Am J Gastroenterol.
2001;96:3089–98.
7. Numans ME, etal. Short-term treatment with proton-pump inhibitors as
a test for gastroesophageal reux disease: a meta-analysis of diagnostic
test characteristics. Ann Intern Med. 2004;140:518–27.
8. Inadomi JM, McIntyre L, Bernard L, etal. Step-down from multiple- to
single-dose proton pump inhibitors (PPIs): a prospective study of patients
with heartburn or acid regurgitation completely relieved with PPIs. Am J
Gastroenterol. 2003;98:1940–4.
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