"Ideal PEEP" is superior to high dose partial liquid ventilation with low PEEP in experimental acute lung injury

Abstract

Objective: To determine the effects of a high dose partial liquid ventilation (PLV) approximating the amount of the functional residual capacity (FRC) with low levels of positive end-expiratory pressure (PEEP) compared to a lung-protective strategy with volume-controlled mechanical ventilation (vcMV) with a PEEP level above the lower inflection point (LIP) on pulmonary gas exchange, haemodynamics, respiratory mechanics and lung injury in an experimental model of acute lung injury (ALI). Design: Prospective, randomised, controlled study. Methods: Twenty-four anaesthetised, tracheotomised and mechanically ventilated (FIO2 1.0) pigs underwent induction of ALI by repeated saline wash-out of surfactant. Animals were randomly assigned to receive either PLV (PLV, n = 8) with 30 ml/kg of perfluorocarbons (PF 5080, 3M, Germany) and a PEEP level of 5 cmH2O, to receive vcMV with a PEEP level of 1 cmH2O above the LIP (idealPEEP, n = 8), or to receive vcMV with a PEEP level of 5 cmH2O (Controls, n = 8). Measurements and results: Measurements of pulmonary gas exchange, respiratory mechanics and haemodynamics were performed hourly for a 6 h period. In the idealPEEP group, intra-pulmonary shunt (Qs/Qt) decreased from 55 ± 5% after induction of ALI to 10 ± 3% (p < 0.05 versus Controls and versus PLV) and PaO2 increased from 52 ± 4 to 566 ± 19 mmHg after 6 h of treatment (p < 0.05 versus Controls and versus PLV). In the PLV group, Qs/Qt decreased from 50 ± 5% after induction of ALI to 24 ± 3% (p < 0.05 versus Controls) and PaO2 increased from 59 ± 5 to 306 ± 35 mmHg after 6 h of treatment (p < 0.05 versus Controls). In the PLV group and in Controls, mean pulmonary artery pressure (MPAP) was significantly increased from 27 ± 2 to 38 ± 2 mmHg and from 29 ± 1 to 40 ± 1 mmHg, respectively, 6 h after induction of ALI (p < 0.05 versus idealPEEP), while in the idealPEEP group, MPAP was maintained between 26 ± 1 and 31 ± 2 mmHg for 6 h after ALI. Cardiac output (CO) decreased significantly in the idealPEEP group compared to Controls (p < 0.05), while CO did not change in the PLV group and in Controls. The compliance of the respiratory system (CRS) increased in the idealPEEP group after induction of ALI from 11 ± 2 to 22 ± 5 ml/mbar (p < 0.05 versus Controls and versus PLV) and in the PLV group from 10 ± 2 to 13 ± 3 ml/mbar after 6 h of treatment (p < 0.05 versus Controls). On histological examination, the highest total injury scores were found in animals of the PLV group (p < 0.05 versus Controls and versus idealPEEP), while the lowest total lung injury score was found in the dependent lung regions of the idealPEEP group (p < 0.05 versus Controls). Conclusion: In this porcine model of ALI, vcMV with a PEEP level of 1 cmH2O above the LIP was superior to high dose PLV with a PEEP of 5 cmH2O in improving gas exchange and lung mechanics. In terms of lung damage, the treatment in the idealPEEP group resulted in the lowest total lung injury scores.