Comparison of Optimal PEEP ventilation vs Prone position ventilation on changes in Regional Lung Ventilation in Patients with Acute Respiratory Distress Syndrome - A Randomized Clinical Trial

Mechanical ventilation is frequently required in patients with acute  respiratory failure, even though being life saving, positive pressure ventilation  has many   detrimental effects   like    adverse effects on hemodynamics and ventilator induced lung injury (VILI). Lung protective ventilation which includes avoiding high tidal volume, high inspiratory pressures along with optimal positive end expiratory pressure (PEEP) selection is being followed to prevent VILI and improve oxygenation in patients with Acute Respiratory Distress Syndrome (ARDS). The optimal PEEP selection remains a difficult task even though a standardized approach to adjust PEEP is available in terms of PEEP/ FiO2 table as per ARDS network guidelines, and other PEEP titration methods guided by lung mechanics. These methods probably consider the global lung mechanics, and do not take into consideration the regional lung ventilation with varying PEEP levels. Prone ventilation is another ventilatory strategy in ARDS, where it is used as rescue therapy in severe ARDS, by which it helps in homogenisation of ventral- dorsal transpulmonary pressure difference, reduces dorsal lung compression and improves oxygenation. Moreover the effect on regional ventilation in use of optimal PEEP ventilation strategy in supine position when compared to prone ventilation is not well explored.

PEEP selection and titration are usually performed by assessing lung mechanics, and variables of lung mechanics are assessed considering the lung as a single unit, hence, the effects on regional lung ventilation are not apparent. Electrical impedance tomography is a non invasive, non-radioactive, bedside imaging tool, providing functional images with a high temporal resolution. Images obtained are also dynamic, allowing us to follow the response of the lungs to any therapeutic intervention. Regional overdistension and alveolar collapse can be visualized using EIT. Hence, it can be used to assess the status of regional lung ventilation with optimal PEEP ventilation as well as prone ventilation. As the regional lung ventilation in terms of regional overdistension and alveolar collapse can be visualized dynamically breath by breath using EIT, the effect of Optimal PEEP ventilation after PEEP titration and the effect of prone position ventilation on regional ventilation can be assessed in better certainty with EIT. By ventilating patients with Optimal PEEP, as identified by PEEP titration method, the regional lung ventilation achieved may be comparable to regional lung ventilation achieved by prone ventilation in patients with ARDS.

If comparable results are found, Optimal PEEP ventilation with PEEP titration can be used instead of Prone ventilation strategy.

Study Hypothesis : Regional lung ventilation (TIV dorsal /TIV total) between Optimal PEEP ventilation method and Prone position ventilation are comparable.