Controlled ventilation with best positive end-expiratory pressure (PEEP) and high level PEEP in acute respiratory failure (ARF)

We assessed hemodynamics, total lung and chest wall compliance (CT) and gas exchange using two different levels of PEEP during controlled ventilation in two different groups of patients with ARF; in the first group (Group 1, 12 patients) chest X-Rays showed a symmetrical pattern of bilateral alveolar infiltrates; in the second group (Group 2, 5 patients) chest X-Rays showed an asymmetrical pattern with unilateral lobar consolidation. A first level of PEEP (best PEEP=9±3 cm H₂O) produced an improvement in CT and in gas exchange with a slight decrease in cardiac index in both groups; but improvement in PaO₂ (from 64±33 to 122±76 torr, p<0.001 in Group 1, and from 76±39 to 91±33 torr, p<0.05 in Group 2) and decrease in QS/QT were not as well marked in Group 2 as in Group 1. A second level of PEEP (high level PEEP: 20±4 cm H₂O) produced a sharp decrease in CT and required hemodynamic support in each case (blood volume expansion with or without Dopamine infusion) to maintain cardiac index within a normal range. In Group 1 this high level PEEP produced a greater improvement in gas exchange (PaO₂ increased from 122±76 to 194±76, p<0.01) but in Group 2 it had a deleterious effect, producing a decrease in PaO₂ (from 91±33 to 76±41 torr, p<0.05), and an increase in; with this higher PEEP we also noted an increase of alveolar dead space in Group 2.This study demonstrates the efficiency of high levels of PEEP to reduce in ARF but also shows its limitations: namely reduction in cardiac performance and in efficiency if the damage to one lung is significantly more pronounced than that to the other lung.Supported in part by a grant of the U.E.R. Paris-Ouest