sodium-pertechnetate-tc-99m and Pneumonia--Aspiration

The scintigraphic detection of small nocturnal aspirations of radio-labelled gastric contents is difficult in the presence of high remaining activity in the abdomen, causing a non-uniform background activity. This problem was examined in phantom experiments and a technique for interpolative background correction was further developed. The accuracy of this technique was found to be influenced by the distance between the lung and the abdominal source of activity, and the minimum detectable 'aspirated' activity was determined as 0.1 MBq at a distance of 15 cm and 1 MBq at 5 cm. The interpolative technique for background correction was evaluated on healthy volunteers and laryngectomized patients, examined 10 h after intragastric instillation of 200 MBq of 99Tcm-pertechnetate. After background subtraction, their calculated pulmonary mean net count value was comparable to that registered before the radioactive tracer was administered. No localized accumulation of activity was found in any of these controls. The technique was then applied clinically to 55 patients with chronic respiratory disorders and symptoms of gastroesophageal reflux. Aspiration was detected in 11 patients (20%). Five aspirators had asthma, two a chronic cough of unknown origin, two recurrent pulmonary infections, and one chronic bronchitis and chronic laryngitis respectively. Aspiration was detected among patients with and without demonstrated pathological gastroesophageal reflux.

Topics: Adult; Aged; Asthma; Chronic Disease; Female; Gastroesophageal Reflux; Humans; Hydrogen-Ion Concentration; Intubation, Gastrointestinal; Laryngectomy; Lung; Male; Middle Aged; Pneumonia, Aspiration; Radionuclide Imaging; Respiratory Tract Diseases; Sodium Pertechnetate Tc 99m

At present, there is no sensitive and specific test to confirm the clinical impression that a respiratory disorder is due to aspiration of gastric contents. Since intravenous technetium pertechnetate (99mTcO4-) has been shown to be safe, actively concentrated in the gastrointestinal tract, and secreted into gastric juice, we sought to determine whether 99mTcO4-, when given intravenously, is suitable to detect pulmonary aspiration of small amounts of gastric contents in rabbits. Biodistribution studies over 24 h revealed that 99mTcO4- persistently appeared in the stomach, thyroid, and salivary glands and did not appear in the lungs. Pharmacokinetic studies showed that 99mTcO4- was rapidly picked up by the stomach wall and secreted promptly into the stomach lumen and that the stomach wall persistently secreted 99mTcO4- into stomach contents for 24 h. By injecting 99mTcO4- through an intratracheal catheter in order to simulate aspiration, the radioactive threshold for imaging intrapulmonary 99mTcO4- was determined to range between less than 0.5 microCi and 2 microCi, depending on the amount of background activity in the blood pool. By measuring the radioactivity in stomach contents (microCi/g), over 24 h after intravenous injection of 2 mCi of 99mTcO4-, we were able to calculate the amount of aspirated stomach contents that our technique should reveal at various time points. We concluded from this preliminary feasibility study that 99mTcO4-, when given intravenously, is suitable to detect pulmonary aspiration of small amounts (less than or equal to 4 ml for 8 h after an intravenous dose of 2 mCi) of gastric contents in human patients. Since our biodistribution studies show that saliva as well as stomach contents are potential sources for any aspirated 99mTcO4-, how to distinguish aspiration of oropharyngeal from stomach contents remains to be determined. It also remains to be determined how long 99mTcO4- remains in the lungs after it has been instilled; clearance that is too rapid significantly decreases the ability of this agent to reveal aspiration.

Topics: Animals; Gastric Mucosa; Gastrointestinal Contents; Injections, Intravenous; Pneumonia, Aspiration; Rabbits; Radionuclide Imaging; Sodium Pertechnetate Tc 99m; Tissue Distribution