© Springer International Publishing AG 2018Eytan Bardan and Reza Shaker (eds.)Gastrointestinal Motility Disorders https://doi.org/10.1007/978-3-319-59352-4_28
28. Gastric Emptying Studies
Gastroenterology Section, Temple University School of Medicine, 3401 North Broad Street, Philadelphia, PA 19140, USA
Henry P. Parkman
KeywordsGastric emptying scintigraphyWireless motility capsuleGastric emptyinbreath testGastroparesisDumping syndrome
Gastric emptying testing is useful in the evaluation of patients with dyspeptic symptoms in whom an upper endoscopy does not reveal a cause . Gastric emptying studies are important to help diagnose patients with gastroparesis as well as detecting rapid gastric emptying which might suggest dumping syndrome. There are three types of gastric emptying studies approved for clinical use: gastric emptying scintigraphy, breath testing using stable C-13 isotopes, and wireless motility capsule. Physicians and health care providers ordering these tests and managing patients who have had these tests for their evaluation need to know some aspects on how to perform the tests, how to interpret the tests, and how to use a gastric emptying test in patient management.
Gastric Emptying Testing
There are several clinical reasons for obtaining a gastric emptying study . The most common reason is the evaluation of a patient with dyspeptic symptoms such as nausea, vomiting, abdominal pain, early satiety, and postprandial fullness. A gastric emptying test is obtained after excluding ulcer, obstruction with an upper endoscopy. Another reason is the evaluation of patients with severe reflux symptoms not responding to proton pump inhibitors (PPIs) . These patients might have delayed gastric emptying partly responsible for their lack of improvement. Gastric emptying test may be performed in patients with constipation to help identify a pan-GI motility disorder. Patients with delayed gastric emptying and colonic inertia respond less favorable to total colectomy. At our center, we often obtain a whole gut transit scintigraphy study that assesses gastric emptying, small bowel transit, and colonic transit. Other centers use the wireless motility capsule which provides similar information. Diabetic patients with poor glycemic control may have delayed or erratic gastric emptying. Clinically, when a diabetic patient starts having hard to control glucoses, one should suspect that they now have gastroparesis. Occasionally, a gastric emptying test is obtained to evaluate a patient’s response to a prokinetic agent.
Results of a gastric emptying test can be normal, delayed, or rapid. Delayed gastric emptying often suggests gastroparesis . Some patient with functional dyspepsia may have delayed gastric emptying. Delayed gastric emptying was detected in 33.5% of 343 patients with functional dyspepsia seen in referral center . Independent factors predicting delayed gastric emptying include female gender, postprandial fullness (moderate to severe), and vomiting (severe). In addition, delayed gastric emptying can be seen in patients with anorexia, often with severe weight loss. Rapid gastric emptying suggests the dumping syndrome. Although this is more commonly seen after gastric surgery, it can also be seen in patients with functional dyspepsia . Rapid gastric emptying can also be seen in patients with cyclic vomiting syndrome during the asymptomatic phase . Rapid gastric emptying can also be seen postfundoplication—the wrap prevents fundic accommodation and leads to rapid movement of the ingested meal from the proximal stomach to the distal stomach.
There are several areas to appreciate with gastric emptying testing. First, gastric emptying rates measured by gastric motor testing generally correlate poorly with symptoms of gastroparesis. Patients can have severe nausea and vomiting with normal gastric emptying . These patients also represent a significant medical problem and are, for the most part, indistinguishable from those with gastroparesis. At our institution, 1499 patients underwent gastric emptying scintigraphy from September 2007 to January 2010 . GES was performed with ingestion of a liquid egg white meal with imaging at 0, 0.5, 1, 2, 3, and 4 h. Patients completed the Patient Assessment of Gastrointestinal Symptoms (PAGI-SYM). 629 of 1499 patients (42%) had increased retention at 4 h (>10%) consistent with gastroparesis. The symptoms correlating with gastric retention at 4 h included early satiety (r = 0.170; p < 0.01), vomiting (r = 0.143; p < 0.01), postprandial fullness (r = 0.123; p < 0.01), and loss of appetite (r = 0.122; p < 0.01). The r correlation coefficients are low suggesting poor correlation. Thus other factors in addition to gastric emptying appear to impact on patient’s symptoms. Second, there are relatively high interindividual and intraindividual variability in gastric emptying rates measured with gastric motor testing, which constitutes another limitation of gastric motor testing . The relative contributions to these variabilities of gastric motor testing methodology and biologic inconsistency in gastric emptying are not currently known. Finally, and importantly, the usefulness of emptying tests in directing therapy and predicting response is debated [9, 10]. Some other causes of nausea/vomiting can be associated with delayed GE. These include functional dyspepsia, GERD, cyclic vomiting syndrome, rumination syndrome, eating disorders (bulimia, anorexia nervosa), and superior mesenteric artery (SMA) syndrome.
Radionuclide Gastric Emptying Scintigraphy
For evaluating gastric emptying, the standard test is gastric emptying scintigraphy, which uses a radiolabeled isotope bound to solid food to image gastric emptying of a solid meal . Gastric emptying scintigraphy remains the best current test for measuring gastric emptying because it is sensitive, quantitative, and physiological. It is used to confirm the presence of gastric stasis after excluding structural or mucosal disorders.
There is variable methodology used at different centers. Most centers use a 99mTc sulfur colloid-labeled egg sandwich as a test meal . A consensus statement from the American Neurogastroenterology and Motility Society and the Society of Nuclear Medicine recommends a standardized method for measuring gastric emptying by scintigraphy . A low-fat egg white meal (Eggbeaters egg whites (ConAgra Foods, Inc.; Downers, IL) with imaging at 0, 1, 2, 4 h after meal ingestion, as described by a published multicenter protocol , provides standardized information about normal, delayed, and rapid gastric emptying and is currently the best way to conduct a scintigraphic gastric emptying test. Adoption of this standardized protocol will help resolve the lack of uniformity of testing, add reliability and credibility to the results, and improve the clinical utility of the gastric emptying test . This test meal has a low fat content and theoretically might produce different results than conventional meals.
The radiolabel needs to be cooked into the egg white so that the radioisotope binds to the solid phase, thus preventing elution of the radiotracer into the liquid phase with an erroneous measurement of the faster liquid phase of gastric emptying .
Imaging is performed in the anterior and posterior projections at least at four time points (0, 1, 2, and 4 h) [11, 12]. The 1 h image is used to help detect rapid gastric emptying. Our center also obtains a 30 min image to assess for rapid gastric emptying. The 2 and 4 h images are used to evaluate for delayed gastric emptying. Imaging for gastric emptying up to 4 h increases the detection of delayed gastric emptying and is now recommended as the standard in all tests to obtain reliable results for the detection of gastroparesis [13, 14]. When gastric scintigraphy is performed for shorter durations, the test is less reliable because of large variations in normal gastric emptying.
Patients should discontinue medications that may affect gastric emptying for an adequate period before this test based on drug half-life. Generally, this is for 3 days prior to the test. The drugs to be primarily concerned about include narcotic opioid analgesics and anticholingergic agents that can delay gastric emptying and prokinetic agents that can accelerate gastric emptying. Other agents may also impact on gastric emptying including those used to treat diabetes, including pramlintide (an amylin-like compound), and exenatide (a GPL1 receptor agonist). Serotonin receptor antagonists such as ondansetron, which have little effect on gastric emptying, may be given for severe symptoms before performance of gastric scintigraphy.
Diabetic patients should try to be in relatively good control for this test. Hyperglycemia (glucose level > 270 mg/dL) delays gastric emptying in diabetic patients. It is not unreasonable to defer gastric emptying testing until relative euglycemia is achieved to obtain a reliable determination of emptying parameters in the absence of acute metabolic derangement.
Premenopausal women have slower gastric emptying than men, so some advocate using separate reference values for premenopausal women .
Emptying of solids typically exhibits a lag phase followed by a prolonged linear emptying phase. The lag phase for solids represents the time required for trituration of solid food into 1- to 2-mm particles that can then empty through the pylorus . A variety of parameters can be calculated from the emptying profile of a radiolabeled meal. The simplest approach for interpreting a gastric emptying study is to report the percent retention at defined times after meal ingestion (usually 2 and 4 h). Curve-fitting techniques can calculate the half-emptying time, the time for half of the stomach contents to have emptied from the stomach. Extrapolation of the emptying curve to predict the half-emptying time may be unreliable if the emptying has not reached 50% during the actual imaging .
Measurement of gastric emptying of solids is more sensitive than measurement of gastric emptying of liquids for detection of symptomatic gastroparesis because emptying of liquids is often preserved until the disorder is advanced. Determination of emptying rates of liquid meals is less sensitive  and generally reserved for the evaluation of dumping syndrome and postgastric surgical disorders. In patients who have undergone gastric surgery, a dual solid and liquid emptying test may be indicated because symptoms may result from slow solid emptying or rapid liquid emptying.
Advances in scintigraphy may provide information on fundic and antral abnormalities. Regional gastric emptying can assess intragastric meal distribution and transit from the proximal to distal portions of the stomach and may provide greater information regarding fundal and antral function. Visual inspection of fundal and antral gastric emptying and quantification of regional emptying with fundic and antral regions of interest can be helpful for defining abnormal physiology and explaining dyspeptic symptoms, especially when global gastric emptying values are normal . Studies have shown an association between symptoms of nausea, early satiety, abdominal distention, and acid reflux with proximal gastric retention, whereas vomiting is associated more with delayed distal GE . Dynamic antral scintigraphy with frequent 1-s imaging can evaluate antral wall contractility and has been used in clinical research studies .