This study will examine the impact of acute illness on sequential airway IgA levels in intensive care patients who will require prolonged intubation. Infections are the most common cause of late deaths in non-head injured trauma patients and a frequent cause of morbidity and mortality in hospitalized patients, especially intubated Intensive Care Unit (ICU) patients. Nosocomial pneumonia is the most common of these infections, and its incidence in defined populations of critically injured patients is responsive to route and type of nutrition. This study will focus on the mechanisms of specific immune mucosal defenses in intestinal and extraintestinal sites and link enteral feeding (or lack of it) with maintenance (or deterioration) of respiratory mucosal defenses.