Selective PEEP in Acute Bilateral Lung Disease. Effect on Patients in the Lateral Posture

Seven patients with acute respiratory failure due to diffuse and fairly uniform lung disease were studied during mechanical ventilation in the lateral decubital position with: (a) zero end-expiratory pressure (ZEEP) through a double-lumen oro-bronchial tube to permit a recording of the ventilation to each lung; (b) bilateral positive end-expiratory pressure (PEEP) of 1.2 kPa, with maintenance of ventilation distribution between lungs as observed during ZEEP; (c) selective PEEP of 1.2 kPa, applied to the dependent lung only, with ventilation as during ZEEP; and (d) conventional PEEP of 1.2 kPa applied to both lungs through a single-lumen tube, with free distribution of ventilation between the lungs. During ZEEP, 69% of ventilation was distributed to the nondependent and 31 % to the dependent lung;: cardiac output was 6.5 l×min-1, venous admixture (QS/QT) 40% and arterial oxygen tension (Pao2) 8.3 kPa. With bilateral PEEP, functional residual capacity (FRC) increased by 0.33 1, cardiac output was reduced to 5.1 l×min-1 and venous admixture to 32%. Pao2 increased to 10.1 kPa. With selective PEEP the dependent lung FRC increased by 0.21 1 and the FRC of the non-dependent lung decreased by 0.08 1. Cardiac output increased to 6.1 l×min-1, which was no longer significantly different from that during ZEEP. Venous admixture remained at the same level as with bilateral PEEP. Pao2 increased to 12.0 kPa. Conventional PEEP, applied with a single-lumen tube and with ventilation distribution assumed to be equal between the lungs, gave essentially the same results as bilateral PEEP. It is concluded that selective PEEP improves gas exchange without impeding cardiac output and that this beneficial effect cannot be reproduced by general PEEP whether ventilation is distributed evenly between the lungs or not.