Risk factors for prolonged invasive mechanical ventilation identified by multivariate logistic regression analysis were the IGS II score on admission superior to 33 (p = 0.016; ORa = 15.08 et IC95% = 1.76–149.36), P/F ratio under 278 mmHg on admission (p = 0.015), CRP level on admission superior to 56 mg/L (p = 0.050; ORa = 7.11 et IC95% = 1.01–50.32) on admission and complications during stay as acute respiratory distress syndrome (ARDS) (p = 0.031; ORa = 16.52 et IC95% = 1.29–210.85) and ventilator-associated pneumonia (VAP) (p = 0.013; ORa = 14.08 et IC95% = 1.76–112.43). This evidence concerns the gene CRP and ventilator-associated pneumonia.