| With the development of critical care medicine mechanical ventilation (MV) has been adopted more widely than ever before. MV not only saves patients' lives but also gives rise to some complications. Ventilator-associated pneumonia (VAP) is one of frequent and severe complications. Literatures have reported some mechanisms of VAP occurring, but have seldom touched gastropulmonary infection route of VAP. Very limited research only focused on a single point, thus the results were not believable. In this study, we investigated four steps of gastropulmonary infection route from different angles among the same mechanically ventilated patients. OBJECTIVES: To understand the role of gastropulmonary infection route in VAP and to provide scientific basis for prevention and treatment of VAP. METHODS: 1. A randomized, two-period crossover trial was employed to detect gastroesophageal regurgitation and pulmonary microaspiration of gastric contents by injecting 99Tc-DTPA into the patients' stomach to serve as determinant marker on the second day and fourth day after initiation of MV. After 99Tc-DTPA was injected into stomach, the patients were put in the required position. Then the oropharyngeal and bronchial secretion were suctioned and 2ml of blood was drawn at 1, 2, 3,4, and 5 hours. At last, all the samples were sent to nuclear medicine laboratory and measured level of radioactivity. 2. Within 24 hours of MV, gastric juice, oropharyngeal secretion and tracheal aspirate were collected for qualitative or quantitative culture at almost same time, then the cultures were repeated every other day until the end points extubation, suspected VAP, or death. Bronchoalveolar lavage was performed within 12 hours when a patient was suspected of VAP and bronchoalveolar lavage fluid (BALF) was collected for quantitative culture. All isolates were stored in refrigerator of 40C. If isolates from stomach in a same VAP patient were same species as that from respiratory tract according to methods routinely used and preceded that from oropharyx and respiratory tract, IRS-PCR was used to determine whether the isolates from stomach and respiratory tract were identical. 3. Within 24hrs after initiation of mechanical ventilation, gastric fluid was obtained and neutralized to pH 7 by 100mM Tris-HCl buffer. After centrifugation at 2000g for 10 min the supernatant was stored in aliquots at -700C for SIgAdetection. PH value of gastric fluid was tested daily until the end points extubation, suspected VAP, or death. 4. Within 24hrs after initiation of mechanical ventilation, 2 ml of blood was drawn for serum immunoglobulins (IgA, IgG and IgM) detection, BALF was collected, frozen, thawed, and centrifuged at 4000g for 10 min, then the supernatant was stored in aliquots at -700C for SIgA measure. RESULTS: 1. There was higher incidence of gastroesophageal regurgitation and relatively lower incidence of microaspiration in patients receiving MV. Moreover, the radioactivity recovered in deep tracheal aspirates and incidence of microaspiration were significantly higher when patients were in supine position than they were in semirecumbent position. In addition, the radioactivity of orapharyngeal secretion and deep tracheal aspirates obtained at the fifth hour was higher than that of samples at the first hour in both positions. However, the difference in the oraphanryngeal radioactivity count at the fifth hour and the first hour in supine position was not significantly bigger than that in semirecumbent position. The difference in the deep tracheal radioactivity count at the fifth hour and the first hour was significantly bigger in supine position than that in semirecumbent position. 2. IRS-PCR showed most of pathogens for VAP and bacteria that colonized in stomach were identical. 3. SIgA level of gastric fluid was significantly lower in patients with stomach colonization compared to patients without stomach colonization, whereas pH value of gastric fluid significantly higher. 4. SIgA level of BALF in patients with VAP was significantly lower tha...
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