Gastroenterology training and education

Discuss the indications for 24 hr pH study?

• Patients with symptoms clinically suggestive of GORD, who fail to respond during a high dose therapeutic trial of a PPI
• Patients with symptoms clinically suggestive of GORD without oesophagitis or with an unsatisfactory response to a high dose PPI in whom anti-reflux surgery is contemplated
• Patients with persistent GORD symptoms despite anti-reflux surgery

Discuss whether PPI treatment needs to be stopped prior to pH study?

This depends on the purpose of pH study. So PPI should be continued if the pH study is being done to analyse correlation between symptoms and acid exposure. However, if the purpose is to exclude excess acid exposure, PPI should be stopped.
Mostly pH studies are done without stopping PPI.

Discuss the technical details of the test?

• The basic equipment requirements for ambulatory oesophageal pH studies are a portable data logger for data storage, a pH electrode and software (with computer) for analysis of pH data.
• The pH electrode is passed through a nostril and positioned 5 cm above the superior margin of the lower oesophageal sphincter (LOS). The LOS is identified by manometry. Alternative methods of pH electrode placement like pH step-up, fluoroscopy, endoscopic measurements and body height formulas are inferior to manometry.
• The rationale behind the 5 cm spacing is to avoid possible electrode displacement into the stomach, especially during swallow-induced oesophageal shortening.
• Once the pH electrode is placed and connected to the data logger, the patient carries on his usual day to day activity. He returns the data logger the next day.
• Data loggers sample intra oesophageal pH eight times every minute.  It also has an event marker that can be activated by the patient during the study to indicate the timing of symptoms.
• Thus, the raw data obtained from an ambulatory pH study are the number of reflux events, the oesophageal acid exposure time associated with each event, and the timing and nature of symptoms.

What are the pitfalls of pH study?

• pH recordings in asymptomatic subjects reveal that acid reflux is a normal, physiological occurrence.
• Up to a quarter of patients with oesophagitis had a normal pH study, emphasising that oesophageal pH monitoring is associated with a significant false negative rate.
• Thus, pH monitoring has clear limitations in defining pathological acid reflux. However, it is the only investigation that can provide information on whether patients’ symptoms are related to episodes of acid reflux (symptom index)
• In the absence of oesophagitis, there is no gold standard for the definition of GERD, making it impossible to establish the accuracy of any diagnostic test.

Discuss the analysis of pH study?

• A fall below pH 4 in oesophageal pH has been conventionally taken to indicate acid reflux.
• 24 hours pH study generates 14,400 data points besides event marker data.
  A number of variables have been described that have value in discriminating patients with acid reflux symptoms from asymptomatic controls: percentage total time oesophageal pH<4; percentage time upright oesophageal pH<4, percentage time supine oesophageal pH<4; number of episodes oesophageal pH<4; number of episodes oesophageal pH<4 for more than 5 minutes; and the longest single episode oesophageal pH<4.  A composite score like Demeester score was developed to express them. However, the composite score has no advantage over the simpler percentage total time oesophageal pH<4 in discriminating patients with GORD from asymptomatic controls.
• Physiological acid reflux is defined as (from the largest published series): percentage total time oesophageal pH<4 <5%; percentage upright time oesophageal pH<4 <8%; percentage supine time oesophageal pH<4 <3%; number of episodes pH<4 for >5 minutes <3.
• The symptom index is the number of symptom episodes associated with acid reflux as a percentage of the total number of symptom episodes. However, few symptoms and frequent acid reflux episodes may lead to a positive symptom index due to a chance association.
• The symptom sensitivity index was developed in an attempt to account for the limitations of the symptom index. It is defined as the number of acid reflux episodes associated with symptoms as a percentage of the total number of acid reflux episodes.  A positive symptom sensitivity index was arbitrarily defined as at least 10%.

Discuss wireless pH study?

• A catheterless pH monitoring system comprises a plastic capsule that houses a pH sensor and a transmitter. The capsule is fixed on the oesophageal wall at endoscopy. The capsule continuously monitors oesophageal pH and transmits the data every few seconds to a small receiver worn by the patient. After a few days, the capsule detaches from the oesophageal wall and passes through the digestive tract.
• Catheterless oesophageal pH monitoring is suitable for patients who do not tolerate nasal intubation.
• The wireless system has the potential advantage of extended recording up to 48 hours but is also considerably more expensive than catheter-based monitoring.
• Catherless pH system is NICE approved in UK (http://www.nice.org.uk/nicemedia/pdf/IPG%20187%20A4v2.pdf)

Discuss impedance monitoring?

This is a new technique designed to detect intraluminal bolus movement. When combined with pH it allows for detection of gastroesophageal reflux independent of pH (i.e., both acid and non-acid reflux).  Clinical value of it is uncertain.

Oesophageal manometry

Discuss the indications for oesophageal manometry?

• To diagnose suspected primary oesophageal motility disorders (e.g. achalasia and diffuse oesophageal spasm)
• To diagnose suspected secondary oesophageal motility disorders occurring in association with systemic diseases (e.g. systemic sclerosis)
• To guide the accurate placement of pH electrodes for ambulatory pH monitoring studies
• As part of the pre-operative assessment of some patients undergoing anti-reflux procedures (patients with atypical symptoms)
• To reassess oesophageal function in patients who have been treated for a primary oesophageal disorder (eg. sub-optimal clinical response to pneumatic balloon dilatation) or undergone anti-reflux surgery (e.g. dysphagia following fundoplication)

Discuss the technical details of manometry?

• The basic hardware required for manometry comprises a pressure sensing apparatus that detects changes in luminal pressure and converts this to an electrical signal, and a recording device that amplifies and stores this information for subsequent analysis.
• The position of the catheter is verified by asking the patient to take a deep breath. Intra-abdominal pressure readings go up with inspiration and down on expiration. Conversely, pressure readings taken within the thoracic cavity go down on inspiration and up on expiration.
• The station pull-through technique allows identification of the location and length of the sphincter high pressure zone (HPZ). The lower oesophageal sphincter (LOS) resting pressure (pressure of HPZ minus intra-gastric pressure) is then estimated.
• A series of wet swallows (5mL of water) are used to examine LOS relaxation.
• Oesophageal body motility is subsequently assessed using a further series of wet swallows

Discuss the contraindications to oesophageal manometry and pH monitoring?

• Suspected or confirmed pharyngeal or upper oesophageal obstruction
• severe coagulopathy (but not anticoagulation within the therapeutic range)
• Bullous disorders of the oesophageal mucosa
• Cardiac conditions in which vagal stimulation is poorly tolerated.

Patients with peptic strictures, oesophageal ulcers, oesophageal or junctional tumours, varices or large diverticulae are at increased risk of complications from blind oesophageal intubation and such conditions are a relative contra-indication to performing manometry and pH monitoring. In such cases, endoscopic or radiologic guidance may be considered.

Ref

1. British Society of Gastroenterology: Guidelines for oesophageal manometry and pH monitoring.