Airway Pressure Release Ventilation (APRV) Compared to ARDSnet Ventilation

Traditional modes of ventilation have failed to improve patient survival. Subsequent observations that elevated airway pressures observed in traditional forms of ventilation resulted in barotrauma and extension of ALI lead to the evolution of low volume cycled ventilation as a potentially better ventilatory modality for ARDS. Recent multicenter trials by the NIH-ARDS network have confirmed that low volume ventilation increases the number of ventilatory free days and improves overall patient survival. While reducing mean airway pressure has reduced barotrauma and improved patient survival, it has impaired attempts to improve alveolar recruitment. Alveolar recruitment is important as it improves V/Q mismatch, allows reduction in FIO2 earlier, and decreases the risk of oxygen toxicity. Airway pressure release ventilation (APRV) is a novel ventilatory modality that utilizes controlled positive airway pressure to maximize alveolar recruitment while minimizing barotrauma. In APRV, tidal ventilation occurs between the increase in lung volumes established by the application of CPAP and the relaxation of lung tissue following pressure release. Preliminary studies have suggested that APRV recruits collapsed alveoli and improves oxygenation through a restoration of pulmonary mechanics, but there are no studies indicating the potential overall benefit of APRV in recovery form ALI/ADRS.

Low volume ventilation may increase number of ventilatory free days and may improve overall patient survival. While reducing mean airway pressure has reduced barotrauma and improved patient survival, it has impaired attempts to improve alveolar recruitment. Alveolar recruitment is important as it improves V/Q mismatch, allows reduction in FIO2 earlier, and decreases the risk of oxygen toxicity. Airway pressure release ventilation (APRV) is a novel ventilatory modality that utilizes controlled positive airway pressure to maximize alveolar recruitment while minimizing barotrauma. In APRV, tidal ventilation occurs between the increase in lung volumes established by the application of CPAP and the relaxation of lung tissue following pressure release. Preliminary studies have suggested that APRV recruits collapsed alveoli and improves oxygenation through a restoration of pulmonary mechanics, but there are no studies indicating the potential overall benefit of APRV in recovery form ALI/ADRS.

Eligibility Criteria:
Inclusion Criteria:

* All patients admitted to the Internal Medicine service at the Baroness Erlanger Hospital of the University of Tennessee College of Medicine with hypoxia (O2 saturation \< 93%) and pulmonary distress, will be screened for study participation.
* Patients displaying all the following clinical criteria: acute onset of respiratory failure; hypoxia defined as a PaO2/FiO2 ratio of \< 300 Torr; pulmonary capillary wedge pressure less or equal than 18 mm Hg, and/or no clinical evidence of left sided heart failure; and chest x-ray with diffuse bilateral pulmonary infiltrates.

Exclusion Criteria:

* Patients receiving conventional volume ventilation with or without PEEP for \> 6 hours prior to study enrollment
* Patient's family or surrogate unwilling to give informed consent
* Patients requiring sedation or paralysis for effective ventilation
* Patients known pulmonary embolus within 72 hours of study enrollment
* Patients with close head injuries or evidence of increased intracranial pressure
* Patients with burns over 30% of total body surface area
* Pulmonary capillary wedge pressure greater than 18 mm Hg
* CVP \> 15 cm H2O
* Patients with B type Naturetic peptide levels \> 1000
* Patients with prior history of dilated cardiomyopathy with EF \< 25%
* Patients receiving chronic outpatient peritoneal or hemodialysis
* Patients with severe liver disease (as defined by Child-Pugh class C)
* AIDS patients