Differential ventilation in acute respiratory failure. Indications and outcome.

Acute respiratory failure (ARF) is a life-threatening condition which frequently requires ventilatory support. Many patients die of hypoxaemia despite a high inspired oxygen concentration and application of general positive end-expiratory pressure (PEEP). Differential ventilation has been used in selected patients with unilateral lung disease or with large inequalities in pathology between the two lungs. An important contributor to the hypoxaemia is a vertical inequality in the ventilation-perfusion (V/Q) matching. This can be compensated for by placing the patient in the lateral position, ventilating each lung separately in proportion to its assumed blood flow, and applying PEEP selectively to the dependent lung to counteract airway closure and alveolar collapse and thus improve the gas distribution within that lung. This ventilatory regime should promote V/Q matching better than general PEEP, and will not impede cardiac output. Major improvement in gas exchange has been achieved in short-term experiments and in prolonged ventilator treatment of patients with ARF.