In order to avoid the discomfort of the catheter-based technique of esophageal pH measurement, a catheter-free, wireless pH system (Bravo, Medtronic, MN, USA) has been developed. In addition to improved patient comfort [25], the capsule-based pH system has the potential advantages of fixed placement of the pH electrode, minimizing the risk of slipping into the stomach, and of allowing for prolonged recordings. The longer duration of pH monitoring has been suggested to increase the sensitivity of reflux monitoring in identifying patients with gastroesophageal reflux [26]. Recognized contraindications for the use of the Bravo capsule are hemorrhagic diathesis, esophageal varices, severe esophagitis, patients with a cardiac pacemaker or defibrillator, and pregnancy.

The pH system consists of a capsule and a telemetry receiver. The capsule includes a pH electrode, an internal battery and a transmitter. The capsule simultaneously measures and transmits pH data using radiotelemetry to the portable receiver. The delivery system for the pH capsule is most commonly passed transorally after completion of an upper endoscopy and attached to the mucosa of the distal esophagus. The capsule is designed to detach in 3–7 days and then pass through the gastrointestinal tract. There are reports of the probe remaining attached for longer periods usually without consequence [26] but sometimes requiring endoscopic removal [26].

Wireless esophageal pH monitoring is associated with fewer adverse symptoms and less interference with normal daily activities and is preferred by patients [27], though there are still limitations associated with the wireless technique. The wireless pH capsule is associated with thoracic discomfort in 10–65% of the patients. The severity of chest symptoms ranges from a mild foreign-body sensation to severe chest pain, although the latter is uncommon. In rare cases, the pain is so severe that endoscopic removal of the capsule is necessary [28–30].

Possible problems with the capsule-based pH system include technical problems such as premature detachment of the capsule or interruption of the radiotelemetry signal. Detachment of the pH capsule is suggested by an abrupt pH drop as the sensor dislocates into the stomach with an increasing pH reaching above 7 as gastric motility propels the pH capsule into the duodenum. In a small proportion of patients with unsuccessful recordings, pH monitoring has to be repeated as a consequence of these technical problems [21].

The standard duration of recording for catheter-based esophageal pH testing is 24 hr. For the wireless pH system is 48 hr, though approximately 10% of wireless probes detach prior to the completion of this period [26, 31]. The extended recording capabilities of the wireless pH system as compared with the conventional catheter-based technique appear to increase the sensitivity of the test. Studies have demonstrated that by increasing the pH recording time from 24 to 48 h, the yield of the procedure increases in capturing more abnormal pH tests or symptom-associated reflux events [28].

The 48 hr data can be interpreted using an average of the 2 days, or alternatively using only the 24-hr period with the greatest acid exposure, termed “worst day analysis”. A significant increase in the sensitivity of the pH testing is seen, together with a small decrease in specificity, when using the worst day data as compared to either 24 hr data or averaged 48 hr data [21, 22].

Consistent positioning of the pH electrode is vital for obtaining reliable esophageal pH data and for comparison to normative population data values. Studies performed using catheters with multiple pH sensors for simultaneous pH recording at different levels in the esophagus have unsurprisingly shown greater acid exposure in the distal esophagus compared to more proximally [32, 33]. Consequently, esophageal acid detection will be significantly reduced when the distance from the lower esophageal sphincter (LES) to the recording level increases, and therefore accurate pH probe placement is essential for a reliable diagnosis of GERD. Typically, the pH electrode should be placed close enough to the stomach to sample the region most affected by gastroesophageal reflux without displacing into the stomach during the course of the study, noting that the gastroesophageal junction migrates approximately 2–4 cm during deglutition [34, 35]. By convention, the catheter-based pH electrode is placed 5 cm above the manometrically defined upper border of the LES [36]. Therefore, esophageal manometry must be performed prior to the pH study to ensure correct placement. Placement on the basis of the pH profile recorded on withdrawal of the electrode from the stomach has been found to be inferior to placement based on manometric LES localization [21, 37].

In wireless esophageal pH monitoring the pH sensor is most commonly placed according to endoscopic landmarks. By convention, the electrode is placed 6 cm above the squamocolumnar junction (SCJ), a position that has been derived from the findings of concurrent manometry and videofluoroscopy studies suggesting that the upper border of the LES high-pressure zone typically extends 1–1.5 cm above the SCJ [38]. Positioning the pH electrode 6 cm above the SCJ therefore approximates the standard 5 cm above the upper border of the manometrically defined LES electrode position of the catheter-based technique. Transnasal placement of the pH capsule normally requires prior manometry, as the electrode is positioned 5 cm above the upper border of the LES [39].

With esophageal bicarbonate secretion and swallowed saliva, esophageal pH is normally maintained between pH 5 and pH 7. Gastric acid secretion generates a highly acidic environment within the stomach, with a pH of 1–2, and rarely more than 3. During esophageal pH monitoring , gastroesophageal reflux events are detected as abrupt declines in intra-esophageal pH. Generally, episodes where pH falls below 4 are taken as evidence of reflux events. The arbitrary choice of the cut-off of pH 4 is supported by the observation that patients with symptomatic reflux usually report heartburn at an intraesophageal pH below this threshold [40]. Physiologic acid reflux seen in healthy subjects is characterized by reflux episodes that occur in the upright position most commonly after a meal and are rapidly cleared. Physiologic acid reflux rarely occurs while supine. In patients with mild reflux disease more reflux episodes occur, especially in the upright, postprandial period. With increasing severity of GERD, acid reflux increases first in the upright position, and thereafter typically becomes bipositional with acid reflux in both the upright and supine postures [41–43]. Both the duration and number of acid reflux episodes increase, resulting in prolonged esophageal acid exposure times.

The total percentage of time the pH is <4 is the most useful single discriminator between physiologic and pathologic reflux [36]. An abnormal pH test is defined by a value greater than the 95th percentile of normal controls, though this can vary depending on the age and gender distribution of the selected control population.

Another method of presenting esophageal acid exposure data is calculation of a composite score, comprised of six measured parameters, including (1) total percent time pH < 4; (2) percent time pH < 4 whilst upright; (3) percent time pH < 4 whilst recumbent; (4) the total number of reflux episodes; (5) the total number of reflux episodes longer than 5 min; (6) the duration of the longest reflux episode. This so-called DeMeester Composite Score , named for one of its original proponents [44], is automatically calculated and reported by most commercially available pH software. The most referenced value for an abnormal DeMeester composite score is a value larger than 14.7 [44]. Regardless of whether the composite score or individual acid exposure time is used, a detailed evaluation of the pH tracing is of fundamental importance to recognize and exclude artefacts and to assess symptom association [21].

Reflux symptoms such as heartburn and regurgitation are very common but as these symptoms are not specific for GERD, it is important to be able to determine if there is a temporal relationship between symptoms and reflux events. Such a relationship between symptoms and reflux episodes can be expressed numerically using symptom association analysis [45]. The most frequently used indices are the Symptom Index (SI) and the Symptom Association Probability (SAP) [46].

The Symptom Index is the percentage of symptoms preceded by a drop in esophageal pH below 4 within a time window, usually selected to be 5 min, divided by the total number of symptoms. The Symptom Index can be calculated for each symptom attributable to reflux, including heartburn, regurgitation, or atypical symptoms, such as chest pain or respiratory symptoms. A positive symptom association is declared if the symptom index is ≥50% (i.e., at least half of the reported symptoms are preceded within a 5-min time window by an intraesophageal pH below 4) [47]. The Symptom Index does not consider the total number of reflux episodes and does not include the total number of symptom events. When few symptoms are reported during the study period, the Symptoms Index is less relevant.

The Symptom Association Probability is a statistical method to determine the relationship between symptoms and reflux episodes. The SAP is calculated by dividing the entire study’s pH data into consecutive 2-min segments. For each of these segments, it is determined whether reflux occurred in the segment, allowing for calculation of the total number of 2-min segments with and without reflux. Subsequently, it is determined whether or not a reflux episode occurred in the 2-min period before each symptom. A 2 × 2 contingency table is constructed in which the number of 2-min segments with and without symptoms, and with and without reflux events, are tabulated. Using the Fisher exact test, a p value is calculated and the SAP index is calculated as (1 − p) × 100% [48]. The cut-off value for a positive test is often defined as SAP ≥95%. However, even a statistically significant relationship between reflux events and symptoms does not necessarily imply causality [21]. The yield of the SI and SAP is greater when performed off- rather than on-acid suppressant therapy [22].

An important decision has to be made by the treating physician as to whether to perform pH testing on or off acid-suppressant medications. Esophageal pH testing without medication is more accurate, and a negative result (i.e., normal distal esophageal pH with negative symptom association) is very helpful in suggesting that the symptoms are not caused by acid reflux. Testing off-therapy is therefore often recommended for patients in whom there is a low index of clinical suspicion for GERD in order to “rule out” reflux as a cause of the symptoms [22]. Off-therapy pH testing may demonstrate abnormal reflux but this does not indicate causality between the reflux and the patient’s symptoms.

A positive pH test while off acid suppressant therapy does not necessarily explain why the patient is still having symptoms while taking PPIs. On-therapy testing is more commonly used to evaluate patients with refractory reflux symptoms despite medical therapy [22]. An abnormal esophageal pH test (i.e., increased amount of distal esophageal acid exposure with therapy and a positive symptom association for acid reflux) performed during therapy is helpful because it suggests that the acid suppression may be insufficient. In these situations, the use of dual pH electrodes to monitor both distal esophageal and gastric pH are sometimes recommended, especially for patients unresponsive to antireflux therapy [22]. Although intragastric pH measurement can help determine the efficacy of acid suppressive medications or suggest poor patient compliance, its clinical relevance is unclear because there is a paucity of data showing a correlation between intragastric pH and gastroesophageal reflux [49, 50]. A negative esophageal pH test while receiving therapy cannot exclude nonacid reflux being associated with the residual symptoms [21]. Combining intraluminal impedance and pH testing is postulated to be able to address this issue, but high quality data are lacking.

Ambulatory esophageal pH monitoring is not without its limitations. The sensitivity and specificity of catheter-based pH monitoring have traditionally been reported to be in the range of 87–96% and 97–100%, respectively [51, 52]. Importantly, these reports are based on studies consisting of patients with complicated reflux disease, manifested by severe esophagitis and manometrically defective lower esophageal sphincters. As there is a relationship between the severity of the disease and the discriminatory power of the test [53], the published data on sensitivity and specificity reflect the severity of reflux disease in the populations tested and may not necessarily apply to the ordinary patient with symptoms suggestive of reflux disease [46]. In more recent studies of patients with typical reflux symptoms and esophagitis, a sensitivity of 76–78% and a specificity of 93–95% were reported for the capsule-based technique of esophageal pH monitoring [26, 53]. The apparently lower discriminatory power of the capsule-based technique probably only reflects differences in the selection of the patient populations [21].

Patients most likely to benefit from an objective documentation of abnormal acid reflux are those without endoscopic evidence of GERD, who constitute up to two-thirds of all patients with typical reflux symptoms [54]. In these patients, catheter-based testing has a lower sensitivity of <71% [22] and capsule-based pH monitoring has a specificity of 93–95% and sensitivity as low as 36–42% [26, 53].

An association between reflux of acidic gastric contents into the larynx and laryngeal symptoms has been proposed [55]. There are multiple alternative potential causes for these respiratory and laryngeal symptoms, and establishing reflux as the cause based on symptoms alone is unreliable [56, 57]. Measurement of distal esophageal acid exposure by catheter-based or wireless pH monitoring would be expected to be less than useful in assessment of the proximal esophagus. Indeed when distal esophageal acid exposure is used as an indication for antireflux surgery to address extraesophageal manifestations of reflux such as laryngeal symptoms, outcomes are usually suboptimal, particularly in patients who have already not successfully responded to antisecretory medical therapy [58, 59].

Attempts have been made to improve operative outcomes for such atypical symptoms of reflux by preoperative assessment of proximal esophageal acidification. Normative value for upper esophageal acid exposure have been defined [57]. The total time of pH < 4 in the proximal esophagus in normal subjects is similar to that measured in the distal esophagus. However, the number of reflux episodes is significantly higher when measured in the proximal esophagus. The widespread clinical utility of such systems remains unclear [60, 61].

Multichannel intraluminal impedance (MII) is a relatively new technique for evaluating esophageal bolus transit during swallowing and for monitoring gastroesophageal reflux independent of its pH.

The presence and movement of an intraesophageal bolus is detected by MII based on measuring differences in electrical conductivity within the esophagus (Fig. 4.2) [62]. Liquid boluses are better conductors than the empty oesophagus, leading to a rapid decline in intraluminal impedance when the bolus enters the impedance measuring segment [62]. Impedance returns to baseline once the bolus has exited the segment. Multiple impedance measuring segments mounted on the same catheter allow determination of the direction of bolus movement based on the timing of changes in impedance at individual levels. Proximal to distal (antegrade) progression of impedance changes is indicative of swallowing, whereas a distal to proximal (retrograde) progression indicates reflux episodes [63].

Multiple impedance-measuring segments can be added to a regular pH probe, and when combined as such MII-pH can evaluate the presence of refluxate independent of its pH and at the same time can differentiate between acid and nonacid reflux [21].

Impedance assessment is best added to pH measurements to give a more thorough evaluation of the function of the antireflux barrier [64].

Normal values for acid and nonacid reflux in healthy volunteers from multiple centers not receiving acid-suppressive therapy [65] have been published, as have various population-specific norms [66–68]. A hypothesis that proximal extension of the refluxate to the level of the larynx may be the cause of respiratory and laryngeal symptoms of reflux [7] is supported by MII findings [69].

MII-pH is a useful tool in expanding the group of patients expected to have a successful outcome after antireflux surgery. Prior to the introduction of MII, some patient with non-acidic reflux might have been denied surgery when in fact their symptoms might be improved by an antireflux procedure. It is now appreciated that there exists a subset of refluxers with normal pH studies but abnormal MII tests that will have good short-term outcomes after fundoplication [70].

MII-pH is now being increasingly employed in the assessment of patients with atypical symptoms of GERD [71–73]. However, the utility of this approach in patients being considered for antireflux surgery remain uncertain, with little evidence demonstrating a prognostic effect on post-surgical outcomes. There remains a paucity of studies comparing outcomes of extraesophageal symptoms of reflux disease after antireflux surgery based solely on ambulatory pH assessment as compared to studies including MII assessment. Reports are also emerging of poor correlation between pH studies and MII studies [74], where instead close correlation is expected if these studies are to be viewed as both sensitive and additive in the diagnosis of GERD.

After confirmation of GERD, but before undertaking antireflux surgery, regular preoperative tests are recommended to assess general fitness for surgery, including basic biochemical analysis, electrocardiography on some patients and other tests determined as necessary after appropriate history and examination of the patient.

While antireflux surgery is a reasonable, safe and cost-effective option for all patients with symptomatic reflux of stomach contents into the esophagus [75], the symptoms for which patient with reflux present for medical care are not always due to GERD. For example, a symptomatic pharyngeal pouch may concomitantly be present in a patient with elevated distal esophageal acid exposure. Clearly therapy directed towards the lower esophageal sphincter mechanism will not solve all problems of concern to the patient. For this reason, many surgeons will request a contrast esophagram to evaluate the entire esophagus prior to considering antireflux surgery.

Fundoplication is the most commonly performed antireflux procedure. The role of preoperative manometric evaluation of the esophagus prior to fundoplication is debated. Amongst the possible side-effects of fundoplication are included dysphagia and gas bloat syndrome, occurring in approximately 5–8% [76–79] and up to 40% [80] respectively of post fundoplication patients. It has been postulated that preoperative manometric investigation of the esophagus will predict postoperative side effects, particularly postoperative dysphagia. It has also been thought that the “tailoring” of the extent of the fundoplication, whether 90°, 360° or an intermediate extent, would achieve superior postoperative quality-of-life and patient satisfaction. A systematic review provides evidence that this is not the case, and an operation tailored to the manometric measurements of esophageal motility is unwarranted [8]. Nonetheless, many centers do perform preoperative manometry. This is often justified as pre-emptive management of possible postoperative problems. For the postoperative patients who presents with dysphagia (again, averaging 5–8% of all postoperative patients, but much higher in the immediate postoperative period), knowledge of esophageal motility may help guide management. Moreover, certain motility disorders can mimic GERD by demonstrating the same symptomatology. For example, achalasia cardia can present with substernal burning, regurgitation and elevated distal esophageal acid exposure, but in this case the etiology is not due to incompetency of the antireflux mechanism. Antireflux surgery in such patients would result in a very poor outcome, and hence preoperative manometry will be helpful in such patients. Other preoperative tests have been examined, such as nuclear medicine gastric emptying studies [81], but there are no data to support a correlation between their results and postoperative outcomes. Gastric emptying studies may be important however in patients who require reoperation, as it may provide indirect evidence for vagal nerve injury during the original surgery [8].

The antireflux mechanism of the lower esophagus is dependent upon multiple variables; the tone of the distal esophageal musculature (lower esophageal sphincter), the actions of the diaphragmatic crura, the intra-abdominal esophageal length and the orientation of the angle of His all affect competency of the antireflux mechanism. With proximal migration of the stomach or gastroesophageal junction through the diaphragmatic hiatus, this mechanism is disrupted. Therefore, there is a close association between gastroesophageal reflux disease and hiatal hernias.

Indications for treatment of hiatal hernia include symptoms of GERD, symptoms related to gastric obstruction due to the hernia, complications due to the hernia and a desire to prevent future complications.

Hiatal hernias have been divided into various subtypes. Type I hernias , also known as sliding hiatal hernias, have the gastroesophageal junction above the diaphragm with the remainder of the stomach located remaining in the usual subdiaphragmatic position. The major clinical significance of a Type I hernia is its association with reflux disease [82]. In patients with proven gastroesophageal reflux disease, with or without a sliding hiatal hernia, antireflux surgery is an option for the management of their condition [83, 84]. The indication for repair of a sliding (Type I) hiatal hernia is gastroesophageal reflux disease. The hernia is not the indication for the procedure. Occasionally, such hernias are thought to produce symptoms of dysphagia or rarely cause gastric ulceration. While these may occur, they are rare and repair of a Type I hernia is nearly always unnecessary in the absence of gastroesophageal reflux disease. Therefore, preoperative diagnostic workup for Type I hiatal hernia is directed toward confirming GERD.

Where more than just the gastroesophageal junction lies above the diaphragm but the actual fundus or body of the stomach (and often other organs too) then this is often termed a paraesophageal hernia. Such hernia are frequently divided into subtypes dependent on the extent of herniation of abdominal contents, but the treatment is more dependent on the area of the diaphragmatic defect and the orientation of the hernia contents rather on the specific subtype. Larger defects with more herniation of contents, particularly with a degree of volvulus are more likely to be symptomatic and have a greater indication for repair [85, 86].