Gastric Analysis Health Article

Definition

Gastric analysis consists of a series of tests used to analyze the contents of the stomach. The complete series involves:

• collecting residual gastric fluid from a fasting patient
• collecting basal secretions every 15 minutes for four hours
• intramuscular administration of a drug that stimulates gastric acid output
• collecting stomach secretions every 15 minutes for 90 minutes

The appearance, blood, bile, pH, volume, millimoles of H+ per liter, millimoles of H+ per volume, and millimoles of H+ per hour of each specimen is then evaluated.

Purpose

A gastric analysis is performed to evaluate gastric function by measuring the contents of a fasting patient's stomach the for acidity, appearance, and volume. The basal gastric secretion test is indicated for patients with obscure gastric pain, loss of appetite, and weight loss. It is also utilized for suspected peptic ulcer, severe gastritis, and Zollinger-Ellison (Z-E) syndrome.

The gastric acid stimulation test is indicated when abnormalities are found during the basal secretion test. These abnormalities can be caused by a number of disorders, including duodenal ulcer, pernicious anemia, and gastric cancer. While this test will detect abnormalities, x rays and other studies are necessary to obtain a definitive diagnosis.

Precautions

Because both the basal acid output test and the gastric acid stimulation test require gastric intubation through the mouth or nasal passage, neither test is recommended for patients with esophageal problems, aortic aneurysm, severe gastric hemorrhage, or congestive heart failure. The gastric acid output test is also not recommended in patients who are sensitive to pentagastrin (the drug used to stimulate gastric acid output).

Description

This test, whether performed for basal gastric acid secretion, gastric acid stimulation, or both, requires gastric intubation by mouth or through the nasal passage.

Basal gastric acid secretion

The patient should be fasting overnight (12 hours) prior to intubation. After allowing approximately 10 to 15 minutes for the patient to adjust to the presence of the tube, and with the patient in a sitting position, specimens are obtained every 15 minutes for a period of 90 minutes. The first two specimens are examined visibly for blood and volume but are discarded to eliminate gastric contents that might be affected by the stress of the intubation process. The patient is allowed no liquids during the test, and saliva must be ejected to avoid diluting the stomach contents.

The final four specimens collected during the test constitute the basal acid output. Each sample is titrated to pH 3.5 using 0.1 N sodium hydroxide. The millimoles of hydrogen ion in each sample are calculated from the

KEY TERMS

Achlorhydria—An abnormal condition in which hydrochloric acid is absent from the secretions of the gastric glands in the stomach.

Intubation—Insertion of a tube into a body canal or hollow organ, as into the stomach.

Pernicious anemia—One of the main types of anemia, caused by inadequate absorption of vitamin B₁₂ Symptoms include tingling in the hands, legs, and feet, spastic movements, weight loss, confusion, depression, and decreased intellectual function.

Subcutaneously—Under the skin.

Zollinger-Ellison syndrome—A rare condition characterized by severe and recurrent peptic ulcers in the stomach, duodenum, and upper small intestine, caused by a tumor or tumors, usually found in the pancreas. The tumor secretes the hormone gastrin, which stimulates the stomach and duodenum to produce large quantities of acid, leading to ulceration. Most often cancerous, the tumor must be removed surgically; otherwise total surgical removal of the stomach is necessary.

amount of base used to neutralize the stomach acid of each. The results of the closest three samples are averaged and multipled by four to give the millimoles of free hydrogen ions per hour. If analysis suggests abnormally low gastric secretion, the maximum acid output test is performed immediately afterward.

Gastric acid stimulation test

After the basal samples have been collected, the tube remains in place for the gastric acid stimulation test. Pentagastrin, or a similar drug that stimulates gastric acid output, is injected subcutaneously. After 15 minutes, a specimen is collected every 15 minutes for one hour. These specimens are called the post-stimulation specimens. As is the case with the basal gastric secretion test, the patient can have no liquids during this test, and their saliva must be ejected to avoid diluting the stomach contents. The maximal acid output (MAO) is determined by titrating each of the four specimens and averaging the results. The average is used to determine the millimoles of hydrogen ion produced per hour. Alternatively, the peak acid output (PAO) is determined by titrating each specimen and using the average hydrogen ion concentration of the highest two to calculate the acid produced in millimoles per hour.