Chest
Volume 95, Issue 1, January 1989, Pages 155-161
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Clinical Investigations in Critical Care
Patterns and Routes of Tracheobronchial Colonization in Mechanically Ventilated Patients: The Role of Nutritional Status in Colonization of the Lower Airway by Pseudomonas Species

https://doi.org/10.1378/chest.95.1.155Get rights and content

Tracheobronchial colonization by Gram-negative bacteria is common in mechanically ventilated patients. Pseudomonas sp are commonly isolated from the lower airways. We hypothesized that Pseudomonas sp would preferentially colonize the lower airway and would be more common in patients with poor nutritional status. We serially collected 75 pairs of upper and lower respiratory tract cultures from 14 patients treated with mechanical ventilation for at least one week, examined patterns of airway colonization and routes of bacterial entry for Pseudomonas sp and other enteric Gram-negative bacteria (EGNB), and related these findings to host-associated factors, including nutritional status. Pseudomonas sp were the most common species isolates taken from the lower airway, found in nine of 14 patients and in 41.3 percent of all cultures. In contrast to other EGNB, Pseudomonas sp were found significantly (p≤0.05) more often in the tracheobronchial tree (31 of 75 cultures) than in the oropharynx (18 of 75 cultures). Primary colonization of the lower airway by Pseudomonas sp was found in four patients, while other EGNB never followed this pattern when subjects were studied with cultures taken every third day. A host-related factor related to lower airway colonization by Pseudomonas species was poor nutritional status, assessed by a multifactorial index (p≤0.01). We conclude that in mechanically ventilated patients, Pseudomonas sp colonize the lower airway in a different pattern and by a different route from those of other EGNB. The findings that Pseudomonas sp preferentially colonize the tracheobronchial tree may be important for the design of strategies to prevent airway colonization. The recognition that poor nutritional status, a potentially modifiable host-related factor, favors lower airway growth of Pseudomonas sp suggests one direction for future infection-control efforts. (Chest 1989; 95:155-61)

Section snippets

Patients

Patients admitted to the medical intensive care unit at Winthrop-University Hospital were eligible for this study if they required endotracheal intubation and mechanical ventilation for the treatment of respiratory, neuromuscular, or cardiovascular disease. To be included in the study, patients had to give informed consent and to remain on mechanical ventilation for a minimum of one week. Individuals were excluded if, at the time of endotracheal intubation, they had a diagnosis of an acute

Frequency of Colonization at the Two Respiratory Tract Sites

A total of 75 sets of paired cultures were collected simultaneously and serially from both the buccal mucosa and tracheobronchial tree of the 14 subjects. Enteric Gram-negative bacteria (EGNB) were present in the initial lower respiratory tract culture in three of the 14 subjects. EGNB were found at least once in the tracheobronchial cultures of 11 subjects, while three subjects were never colonized during the study. In nine of these 11 colonized individuals, Pseudomonas sp were present, while

DISCUSSION

Respiratory tract colonization is common in hospitalized patients, with a frequency that parallels the degree of underlying illness in a given individual.12 Among critically ill patients treated with endotracheal intubation and mechanical ventilation, such colonization becomes more prominent as time in the intensive care unit increases and frequently culminates in the development of nosocomial pneumonia.3,6 In studies of critically ill patients, tracheobronchial colonization by enteric

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Assistant Professor of Medicine, SUNY, Stony Brook.

Instructor in Medicine, SUNY, Stony Brook.

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Associate Professor of Medicine, SUNY, Stony Brook.

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