GASTRIC ANALYSIS, GASTRIC ACID STIMULATION TEST, AND pH MONITORING
Analysis of the gastric juice yields information about the secretory activity of the gastric mucosa and the presence or degree of gastric retention in patients thought to have pyloric or duodenal obstruction. It is also useful for diagnosing diseases such as Zollinger-Ellison syndrome.
The patient is kept NPO for 8 to 12 hours before the proce-dure. Any medications that affect gastric secretions are withheld for 24 to 48 hours before the test. Smoking is not allowed on the morning before the test, because it increases gastric secretions. A small nasogastric tube with a catheter tip marked at various points is inserted through the nose. When the tube is at a point slightly less than 50 cm (21 inches) distant, it should be within the stom-ach, lying along the greater curvature. Once in place, the tube is secured to the patient’s cheek and the patient is placed in a semi-reclining position. The entire stomach contents are aspirated by gentle suction into a syringe, and gastric samples are collected every 15 minutes for the next hour.
The gastric acid stimulation test usually is performed in con-junction with gastric analysis. Histamine or pentagastrin is ad-ministered subcutaneously to stimulate gastric secretions. It is important to inform the patient that this injection may produce a flushed feeling. The nurse monitors blood pressure and pulse frequently to detect hypotension. Gastric specimens are collected after the injection every 15 minutes for 1 hour and are labeled to indicate the time of specimen collection after histamine injection. The volume and pH of the specimen are measured. In certain in-stances, cytologic study by the Papanicolaou technique may be used to determine the presence or absence of malignant cells. Enzyme analysis of the gastric juice may be indicated.
Important diagnostic information to be gained from gastric analysis includes the ability of the mucosa to secrete HCl. This ability is altered in various disease states, including
• Pernicious anemia—patients with this disease secrete no acid under basal conditions or after stimulation
• Severe chronic atrophic gastritis or gastric cancer—patients with these diseases secrete little or no acid
• Peptic ulcer—patients with peptic ulcers secrete some acid
• Duodenal ulcers—patients with duodenal ulcers usually secrete an excess amount of acid
Esophageal reflux of gastric acid may be diagnosed by ambu-latory pH monitoring. The patient is NPO for 6 hours before the test, and all medications affecting gastric secretions are withheld for 24 to 36 hours before the test. A probe that measures pH is placed through the nose and into position about 5 inches above the lower esophageal sphincter. It is connected to an external recording device and is worn for 24 hours while the patient con-tinues his or her normal daily activities. The end result is a com-puter analysis and graphic display of the results. This test allows for the direct correlation between chest pain and reflux episodes (Wolfe, 2000).
A Bernstein test may be performed to evaluate complaints of acid-related chest or epigastric pain. HCl is instilled through a small feeding tube positioned in the esophagus. This is done to try to elicit reported chest pain. Resultant signs and symptoms are compared with the usual symptoms the patient reports. How-ever, since the advent of ambulatory pH monitoring, this previ-ously popular evaluation tool is used infrequently (Wolfe, 2000).