Physiology of the aerodigestive system and aberrations in that system resulting in aspiration.

Background: Aspiration pneumonia remains a significant and often devastating problem in critically ill patients. It is unclear whether aspiration pneumonia occurs because of problems in the handling of oropharyngeal secretions or if the reflux of gastric contents is the major etiological factor. Additionally, the obvious breakdown of upper aerodigestive protective mechanisms in the critically ill patient population is largely unstudied. Finally, the impact and contribution of tubes, both endotracheal and nasoenteral, on aspiration pneumonia is unclear.

Methods: A Medline literature search on scientific and review articles concerning the normal physiology of the aerodigestive tract and factors that compromised normal physiology was undertaken. Readings were supplemented by expert outside opinion from researchers in these fields and from the combined expertise from a multidisciplinary panel of experts assembled at a recent summit on aspiration pneumonia.

Results: Changes in the normal physiology of the aerodigestive tract are vast and varied and dependent on the response to injury, iatrogenic interventions, and the use of nasoenteral and endotracheal tubes. The effects on gastric and esophageal motility are likely dynamic and represent an ongoing but changing risk of reflux for the patient. Nasoenteral and endotracheal tubes likely compromise upper aerodigestive protective mechanisms.

Conclusions: More research is needed on the functioning of the aerodigestive protective mechanisms in critically ill patients. Understanding of the dynamic changes in gastrointestinal motility will also be an important factor to decrease the incidence of aspiration pneumonia in this patient population.