Ventilatory management of ARDS: can it affect the outcome?

Animal studies have demonstrated that mechanical ventilation with high peak inspiratory pressure (PIP) results in acute lung injury characterised by hyaline membranes, granulocyte infiltration and increased pulmonary and systemic vascular permeability. This can result in progressive respiratory failure and death. In surfactant deficient lungs this occurs with tidal volumes (Vt) as low as 12 ml/kg, and PIP as low as 25 cm H2O, values which are frequently used clinically. The mechanisms resulting in this form of ventilator induced lung injury are not clear, but it appears to result from global or regional overdistension of the lung or terminal airways. It can be prevented or reduced in severity in some animal models by the use of PEEP. It is suggested that the use of high PIP in some patients may result in progressive deterioration of their ARDS, possibly contributing to mortality both from respiratory failure and other causes. It may be very important to limit PIP by reducing Vt even if this results in hypercapnia and a deterioration of oxygenation in the short term.