The biological effects of higher and lower positive end-expiratory pressure in pulmonary and extrapulmonary acute lung injury with intra-abdominal hypertension.

INTRODUCTION: Mechanical ventilation with high positive end-expiratory pressure (PEEP) has been used in patients with acute respiratory distress syndrome (ARDS) and intra-abdominal hypertension (IAH), but the role of PEEP in minimizing lung injury remains controversial. We hypothesized that in the presence of acute lung injury (ALI) with IAH: 1) higher PEEP levels improve pulmonary morphofunction and minimize lung injury; and 2) the biological effects of higher PEEP are more effective in extrapulmonary (exp) than pulmonary (p) ALI. METHODS: In 48 adult male Wistar rats, ALIp and ALIexp were induced by Escherichia coli lipopolysaccharide intratracheally and intraperitoneally, respectively. After 24 hours, animals were anesthetized and mechanically ventilated (tidal volume of 6 mL/kg). IAH (15 mmHg) was induced and rats randomly assigned to PEEP of 5 (PEEP5), 7 (PEEP7) or 10 (PEEP10) cmH2O for 1 hour. RESULTS: In both ALIp and ALIexp, higher PEEP levels improved oxygenation. PEEP10 increased alveolar hyperinflation and epithelial cell damage compared to PEEP5, independent of ALI etiology. In ALIp, PEEP7 and PEEP10 increased lung elastance compared to PEEP5 (4.3 ± 0.7 and 4.3 ± 0.9 versus 3.1 ± 0.3 cmH2O/mL, respectively, P <0.01), without changes in alveolar collapse, interleukin-6, caspase-3, type III procollagen, receptor for advanced glycation end-products, and vascular cell adhesion molecule-1 expressions. Moreover, PEEP10 increased diaphragmatic injury compared to PEEP5. In ALIexp, PEEP7 decreased lung elastance and alveolar collapse compared to PEEP5 (2.3 ± 0.5 versus 3.6 ± 0.7 cmH2O/mL, P <0.02, and 27.2 (24.7 to 36.8) versus 44.2 (39.7 to 56.9)%, P <0.05, respectively), while PEEP7 and PEEP10 increased interleukin-6 and type III procollagen expressions, as well as type II epithelial cell damage compared to PEEP5. CONCLUSIONS: In the current models of ALI with IAH, in contrast to our primary hypothesis, higher PEEP is more effective in ALIp than ALIexp as demonstrated by the activation of biological markers. Therefore, higher PEEP should be used cautiously in the presence of IAH and ALI, mainly in ALIexp.

Lung perfusion during cardiac surgery with cardiopulmonary bypass: is it necessary?

Thirty-two pigs were randomized into group I (aortic cross clamping, antegrade cardioplegia, moderate hypothermia) and group II (normothermia, beating empty heart). Groups were subdivided into subgroups A, B and C, receiving no lung perfusion, perfusion with arterial blood and perfusion with venous blood. Swan-Ganz catheter was used to take mean pulmonary artery pressure which would be used as lung perfusion pressure. Cardiopulmonary bypass (CPB) was established through cannulating aorta and double venae cavae, mechanical ventilation was interrupted and lung perfusion was carried out for 30 min. Blood samples and pulmonary specimens were withdrawn pre- and postoperatively for gasometrical, histological and genic analyses. Postoperative comparison revealed that pulmonary vascular resistance was lower in IC than IA (P=0.01) and it was lower in IIC than IIA (P=0.005). Subgroup IIB had increasing venous oxygen tension (P=0.01) as well as arterial and venous oxygen saturation (P=0.01) compared to IIA. Arterial oxygen saturation was decreased in IIC vs. IIA (P=0.006). Histological differences were observed between subgroups A and B as well as A and C (P=0.003). Lung perfusion during CPB may improve pulmonary hemodynamic performance, optimize gas exchange and maintain cellular integrity.