SUPERIMPOSING POSITIVE END-EXPIRATORY PRESSURE DURING PARTIAL LIQUID VENTILATION IN EXPERIMENTAL LUNG INJURY

This study was undertaken to determine the effects of superimposing in cremental levels of positive end-expiratory pressure (PEEP) during par tial liquid ventilation (PLS') on gas exchange, respiratory mechanics and morphological changes in experimental acute lung injury (ALI). In a prospective trial, sis pigs weighing 30+/-5 kg (mean+/-SD) were trac heotomized, submitted to pressure-controlled mechanical ventilation (p c-CR ni) and depleted of surfactant by lung lavage, Animals were then mechanically ventilated with three levels of PEEP: 0.5, 1.0 and 15 kPa , PLV was then initiated by intratracheal instillation of 30 mL.kg(-1) perfluorocarbon, followed by pc-CMV with PEEP 0.5, 1.0 and 15 kPa, Co mputed tomography (CT)-based analyses of lung volumes and density were obtained after lung lavage, in PLV and during the combined applicatio n of PLV and PEEP. Simultaneously, haemodynamics, gas exchange, dynami c compliance (C-dyn) and dynamic resistance (R-dyn) were determined. S tatistical analysis was performed using multivariate analyses of varia nce for repeated measures (p<0.05), In ALI and before PLV, the applica tion of PEEP significantly reduced cardiac output and intrapulmonary s hunt. Arterial oxygen tension (Pa,O-2) was increased from 6.9 kPa (52 (42, 54) mmHg) (median, (25th and 75th percentile)) to 8.6 kPa (65 (52 , 133) mmHg (PEEP 1.0 kPa) and 15.6 kPa (117 (90, 195) mmHg) (PEEP 15 kPa) (p<0.05), The lung volume obtained by CT increased, CT density wa s reduced (p<0.05), C-dyn tended to increase and Rdyn to decrease (non significant). PLV increased arterial carbon dioxide tension and reduce d pH (p<0.05), CT lung volume and lung density were increased (p<0.05) . Superimposing PEEP on PLV increased Pa,O-2 from 9.3 kPa (70 (52, 124 ) mmHg) (PEEP 0.5 kPa) to 12.9 kPa (97 (55, 233) mmHg) (PEEP 1.0 kPa) and 40.3 kPa (303 (64, 426) mmHg) (PEEP 1.5 kPa) (p<0.05), but had no significant effect on CT lung volume and density. It was concluded tha t in experimental lung injury, positive end-expiratory pressure provid ed alveolar recruitment. The combined application of positive end-expi ratory pressure and partial liquid ventilation significantly augmented oxygenation and might eventually allow either a reduction in the volu mes of perfluorocarbons required, or a reduction in positive end-expir atory pressure necessary to maintain pulmonary gas exchange in acute l ung injury.