Intraoperative
positive end-expiratory pressure (PEEP) has been proposed to restore lung volumes and improve respiratory function in
obesity. However, the
biological impact of different PEEP levels on the lungs in
obesity remains unknown. We aimed to compare the effects of PEEP = 2 cmH2O versus PEEP = 6 cmH2O during ventilation with low tidal volumes on lung function, histology, and
biological markers in obese and non-obese rats undergoing open abdominal surgery. Forty-two Wistar rats (21 obese, 21 non-obese) were anesthetized and tracheotomized, and
laparotomy was performed with standardized bowel manipulation. Rats were randomly ventilated with protective tidal volume (7 ml/kg) at PEEP = 2 cmH2O or PEEP = 6 cmH2O for 4 h, after which they were euthanized. Lung mechanics and histology, alveolar epithelial cell integrity, and
biological markers associated with
pulmonary inflammation, alveolar stretch, extracellular matrix, and epithelial and endothelial cell damage were analyzed. In obese rats, PEEP = 6 cmH2O compared with PEEP = 2 cmH2O was associated with less alveolar collapse (p = 0.02).
E-cadherin expression was not different between the two PEEP groups. Gene expressions of
interleukin (IL)-6 (p = 0.01) and
type III procollagen (p = 0.004), as well as
protein levels of
tumor necrosis factor-alpha (p = 0.016), were lower at PEEP = 6 cmH2O than at PEEP = 2 cmH2O. In non-obese animals, PEEP = 6 cmH2O compared with PEEP = 2 cmH2O led to increased hyperinflation, reduced
e-cadherin (p = 0.04), and increased gene expression of
IL-6 (p = 0.004) and
protein levels of
tumor necrosis factor-alpha (p-0.029), but no changes in fibrogenesis. In conclusion, PEEP = 6 cmH2O reduced lung damage and
inflammation in an experimental model of
mechanical ventilation for open abdominal surgery, but only in obese animals.