Causes
Most aspiration events occur in patients with a defective swallowing mechanism, such as a neurological disease or as the result of an injury that directly impairs swallowing or interferes with consciousness. Impaired consciousness can be intentional, such as the use of general anesthesia for surgery. For many types of surgical operations, people preparing for surgery are therefore instructed to take nothing by mouth (nil per os, abbreviated as NPO) for at least four hours before surgery. These conditions enable the entry of bacteria into the lungs, thus allowing the development of an infection. Risk factors
Impaired swallowing: Conditions that cause dysphagia worsen the ability of people to swallow, causing an increased risk of entry of particles from the stomach or mouth into the airways. While swallowing dysfunction is associated with aspiration pneumonia, dysphagia may not be sufficient unless other risk factors are present. Neurologic conditions that can directly impact the nerves involved in the swallow mechanism include stroke, neurodegenerative diseases (such as Parkinsons disease), and multiple sclerosis. Anatomical changes in the chest can also disrupt the swallow mechanism. For example, patients with advanced COPD tend to develop enlarged lungs, resulting in compression of the esophagus and thus regurgitation. Altered mental status: Changes in levels of consciousness affect the swallow mechanism by both disabling the bodys natural protective measures against aspiration as well as possibly causing nausea and vomiting. Altered mental status can be caused by medical conditions such as seizures. However, many other agents can be responsible as well, including general anesthesia and alcohol.
Toxic anterior segment syndrome is an acute, sterile anterior segment inflammation following generally uneventful cataract and anterior segment surgery.One of the main factors in differentiating toxic anterior segment syndrome from an infectious endophthalmitis is the rapid onset. Most patients with toxic anterior segment syndrome will develop symptoms within 12 to 24 hours of the surgery. Common findings on anterior segment slit lamp examination include increased cell and flare with associated fibrin and possible hypopyon formation. Patients may show signs of diffuse corneal edema, and they may also show signs of iris atrophy with pupillary abnormalities and eventual increased intraocular pressure. It is important to differentiate sterile postoperative inflammation from infectious endophthalmitis because the treatments of these patients are markedly different. Patients with toxic anterior segment syndrome will often respond rapidly to treatment with topical corticosteroids, while infectious endophthalmitis must be treated with antibiotics. It is important that the patients be evaluated often to ensure that the inflammation is clearing and that the patients intraocular pressure is under control. The clearing of the inflammation and eventual patient outcome is related to the severity of the toxic insult at the time of surgery. Most patients reported to date are in the category of a moderate toxic inflammation. Toxic anterior segment syndrome may be related to problems with any irrigating solution or other solution placed in the patients eye during surgery, including balanced salt solution or anything added to solutions.