The swallowing mechanism prevents aspiration of gastric contents almost completely in normal subjects, and the cough reflex usually clears the airway before injury is produced when aspiration does occur. However, the aspiration of foreign material into the lung carries a substantial morbidity and mortality. It is the leading mechanism in the pathogenesis of nosocomial pneumonia, and is a very common event in the ICU (Table...?). The average hospital stay is increased by 21 days in surgical patients who aspirate, and the mortality of aspiration exceeds 50 per cent in almost all reported series.
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Aspiration of gastric contents produces a severe chemical pneumonitis, although the injury is attenuated if the pH of the aspirate is 2.4 or greater. Secondary bacterial infection does not invariably occur following aspiration. All forms of aspiration may eventually result in pneumonia, although community-acquired aspiration pneumonias are usually anaerobic whereas nosocomial events are mixed infections. The most common anaerobic organisms recovered following aspiration are Bacteroides, Fusobacterium, and Peptostreptococcus. Aerobic and facultative organisms are most commonly Staph. aureus, Streptococcus pneumoniae, enteric Gram-negative bacilli including Escherichia coli and Klebsiella, and Pseudomonas. However, because bacterial infection is not a certainty following aspiration, the common practice of presumptive administration of antibiotics should be discontinued. The presence of fever is not an indication for antibiotic therapy after aspiration, because chemical pneumonitis commonly produces fever. Specific therapy should be directed against a Gram stain of an adequate sputum specimen or a specific bacterial isolate.
Prevention of aspiration is undoubtedly the most important aspect of management. Meticulous airway care is essential. The patency of all indwelling nasogastric tubes must be continually confirmed. Careful monitoring of nasogastric tube feeding is extremely important. A bolus of feeding solution should never be given in an attempt to 'catch up' with an infusion that is behind schedule. The use of soft weighted-tip silastic catheters, positioned with the tip in the duodenum, is preferable.
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