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1 Dept of Geriatric Medicine, University of Tokyo, Tokyo, and 2 Pulmonary Medicine, Yokohama City University, Yokohama, Japan.
To the Editors:
In a recent issue of the European Respiratory Journal, Kostadima et al. 1 reported that early gastrostomy is associated with a lower frequency of ventilator-associated pneumonia (VAP) compared with nasogastric tube (NGT) feeding in patients who are mechanically ventilated due to stroke or head injury. Since VAP is the most frequent and serious intensive care unit (ICU)-acquired infection among patients undergoing mechanical ventilation, and is associated with a 20–30% increase in the risk of death, the preventive strategy for VAP in mechanically ventilated patients is important to reduce the length of an ICU stay and overall mortality 2.
Although the classic theories, including the gastropulmonary hypothesis, are important to understand the mechanisms of VAP, the recent advancement of the pathophysiology of nosocomial pneumonia and aspiration pneumonia are not fully discussed in the paper by Kostadima et al. 1.
There is growing evidence that oropharyngeal dysphagia plays a critical role in aspiration pneumonia and VAP in mechanically ventilated patients 3, 4. Brain injury, severe stroke and unconsciousness, due to sedatives and hypnotics, disturb the swallowing reflex. This results in the development of aspiration pneumonia in humans and animals 5. However, nosocomial pneumonia and aspiration pneumonia are prevented by the improvement of the swallowing reflex after administration of angiotensin-converting enzyme (ACE) inhibitors 6. The elevated levels of bradykinin and substance P by ACE inhibitors play a role in setting the threshold for the cough and swallowing reflex in humans, resulting in the reduction of occurrence of pneumonia. Although Kostadima et al. 1 speculated about the underlying mechanisms of risk of VAP in the patients with NGT feeding, they did not assess the swallowing reflex and cough reflex. We have developed a novel diagnostic test for the risk of aspiration pneumonia 7, 8. The simple swallowing provocation test can be applied for all the ventilated patients as it is very easy and can be performed on bedridden patients without requiring their cooperation. The assessment of the swallowing reflex is the clue to the underlying mechanisms of VAP in critically ill patients. As it has been suggested that nosocomial maxillary sinusitis increases the occurrence of VAP, microaspiration of oropharyngeal materials, including maxillary sinus, is a significant cause of VAP 9.
NGT feeding is known to be a significant cause of aspiration pneumonia in stroke patients 10. Since the NGT bypasses the small amount of gastric contents through to the oropharynx, the materials can be easily aspirated into lower airways in dysphagic patients with stroke. The mechanism is not related to the percutaneous endoscopic gastrostomy (PEG). This evidence supports the fact that NGT feeding, but not PEG, is a significant cause of VAP in critically ill patients. Although feeding via PEG is a very straightforward way to reduce aspiration and aspiration-associated pneumonia, the improvement of the swallowing reflex must be a fundamental approach to reduce VAP in patients. As the PEG procedure using gastroscopic fibre may also be a risk for aspiration in unconscious patients, the indication of early gastrostomy for the patients should be very carefully assessed. The PEG feeding patients with dysphagia may be suffering from aspiration pneumonia 11.
Considered together, we believe that the prevention of aspiration by using oral care, angiotensin-converting enzyme inhibitors and swallowing rehabilitation may be an alternative approach in reducing the risk of ventilator-associated pneumonia in patients.
REFERENCES
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  S. Teramoto, H. Yamamoto, Y. Yamaguchi, Y. Hanaoka, M. Ishii, S. Hibi, H. Kume, and Y. Ouchi Lower respiratory tract infection outcomes are predicted better by an age >80 years than by CURB-65 Eur. Respir. J., February 1, 2008; 31(2): 477 - 478. [Full Text] [PDF]
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S. Teramoto, H. Yamamoto, Y. Yamaguchi, Y. Hanaoka, M. Ishii, S. Hibi, and Y. Ouchi ACE inhibitors prevent aspiration pneumonia in Asian, but not Caucasian, elderly patients with stroke Eur. Respir. J., January 1, 2007; 29(1): 218 - 219. [Full Text] [PDF]
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