POSITIVE END EXPIRATORY PRESSURE - Positive end expiratory pressure or PEEP, is a respiratory treatment modality commonly used in association with assisted mechanical ventilation. This technique involves the application of airway pressure greater than atmospheric pressure by the introduction of mechanical impedance to exhalation. PEEP is effective in helping to keep the alveoli of the lungs open so they can play an active role in respiratory exchange. PEEP is useful in the treatment of a variety of pulmonary conditions including ARDS, pulmonary contusion, pneumonia, and congestive heart failure. A common side effect in the application of PEEP is a direct effect on lung compliance and an increased risk for pneumothorax due to over-pressurization. Airway pressures and lung compliance are closely monitored by a respiratory therapist during the administration of PEEP.