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  • Pneumonia in the critically ill hospitalized patient: part 8

Reduced gastric acid in the intubated intensive care unit patients may result from intrinsic disease of gastric acid production or from the use of antacids or histamine type 2-blockers which neutralize or block gastric acid secretion. Correlation between levels of bacteria in the gastric juice and treatment of patients with peptic ulcer disease with cimetidine was reported by Ruddell et al. du Moulin et al described gastric overgrowth with Gram-negative bacilli in mechanically ventilated pa­tients and related these finding to increasing the gastric pH. These observations have been corroborated by other investigators. The level of gastric overgrowth noted in critically ill ventilated patients is a concern. Some patients with high gastric pH had colonization with Gram-negative bacilli that reached 100 million organisms/ml. Colonization was usually considerably lower when the pH was less than 3.5. Gastric over­growth with aerobic Gram-negative bacilli was most common, but high numbers of Gram-positive bacteria and fungi may occur as well.

Several investigators have studied the time se­quence of colonization. du Moulin et al showed that 52 of 58 post-surgical patients with respiratory failure had gastric and/or tracheal coloni­zation with Gram-negative bacilli and a clear sequence of transmission could be demonstrated in 17 of 52 patients. In 11 (65 percent of the patients), gastric colonization preceded tracheal colonization. In a sim­ilar study, using pharyngeal and gastric specimens from 40 medical and surgical patients, Goularte et al showed a clear sequence of colonization in ten patients in whom four (40 percent) had gastric colonization that preceded colonization of the pharynx. Daschner et al reported retrograde colonization of the trachea from the stomach in 32 percent of 142 patients who were receiving stress ulcer prophylaxis and mechani­cal ventilation. When a nasogastric tube is in place, it may facilitate the transfer of bacteria from a colonized stomach to the oropharynx and organisms may then be aspirated into the lung.
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The possible role of gastric colonization in the pathogenesis of pneumonia was supported in our prospective study of risk factors for pneumonia in mechanically ventilated patients. Overall, 21 percent of the 233 patients receiving mechanical ventilation developed pneumonia. Pneumonia occurred in 38 percent of 18 patients who received antacids and cimetidine, 36 percent of 48 patients who received cimetidine alone, and in 18 percent of 135 patients who received antacids alone. Although the numbers of patients with pneumonia in each group were small, H2-blockers with and without antacids were inde­pendently associated with the development of pneu­monia (p = .01).

In a study of 153 critical care patients receiving antacids and/or cimetidine therapy, Donowitz et al showed that 59 percent of gastric cultures with a pH of were positive for Gram-negative bacilli. In contrast, only 14 percent of gastric cultures at a pH ^4 were positive for these organisms (p <.001). As gastric pH increased, the proportion of specimens with Gram-negative bacilli rose, and those with normal flora decreased.

A more recent report of nosocomial pneumonia in mechanically ventilated patients receiving prophylaxis against stress bleeding concluded that rates of pneu­monia directly correlated with increasing gastric pH. In patients whose gastric pH was <3.4, the rate of pneumonia was 41 percent compared to a rate of 69 percent in patients who had a pH >5.0.

Tube feeding and aspiration is particularly common in critically ill patients. Enteral feeding and prepara­tions have a pH range from 6.4 to 7.0. Pingleton et al demonstrated gastric colonization in 100 percent of ventilated patients receiving enteral feeding without antacid or H2-blocker therapy, and 11 (63 percent) subsequently developed nosocomial pneumonia.
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