covers the nose and mouth. It assists patients who can spontaneously breathe. Noninvasive positive pressure ventilation delivers end-expiratory pressure with a volume control setting. There are two ways that noninvasive positive pressure ventilation can be delivered: continuous positive airway pressure or bilevel positive airway pressure. In continuous positive airway pressure, constant pressure is maintained throughout cycles of respiration with no additional inspiratory support. In bilevel positive airway pressure, both expiratory positive airway pressure and inspiratory positive airway pressure are set by the physician. Noninvasive positive pressure ventilation should not be administered to people who are hemodynamically unstable, gastric emptying impaired, bowel obstructed or pregnant. In these circumstances, swallowing large amounts of air will result in vomiting and possibly death. If frequent arrhythmias, myocardial ischemia and shock arrhythmias occur, practitioners should change delivery to endotracheal intubation or conventional mechanical ventilation. People who should not use noninvasive positive pressure ventilation include obtunded patients or ones with secretions. Noninvasive positive pressure ventilation can be used in an outpatient setting for patients with obstructive sleep apnea. See also Crash cart Respiratory failure References External links Medical emergencies Causes of death Symptoms and signs: Respiratory system