Influence Of Mechanical Ventilation On Local And Systemic Inflammatory Responses

Mechanical ventilation is an important therapeutic technique for patients with respiratory failure. Whereas, it may lead to complications, such as ventilation-induced lung injury (VILI). Both clinical and basic research have demonstrated that excessive tidal volume and/or end-inspiratory lung volume is the main determinant of ventilator-induced lung injury. More recently, attention has focused on the roles and implication in the pathogenesis of ventilator-induced lung injury of inflammatorycells and mediators that may be activated and released either in the alveolar space or in the systemic circulation because of the rupture of the alveolar-capillary barrier and on the cellular response to mechanical stress.Interleukin-6 (IL-6) is a pleiotropic cytokine that is commonly produced at local tissue sites and released into circulation in almost all situations of homeostatic perturbation typically including trauma, endotoxic lung, and acute infections. IL-6 is induced often together with the proinflammatory cytokines (TNF-a and IL-1) in many alarm conditions, and circulating IL-6 plays an important role in the induction of acute phase reactions.ObjectiveThe purpose of this study was to investigate the effect of different mechanical ventilation strategies on pulmonary and systemic inflammatory responses.Materials and MethodsFifteen healthy pigs (male, mean weight is 26.2 ?1.0 kg)were randomly divided into three groups: group A (VT=7 ml/kg, PEEP=8cmH2O); group B (VT=7 ml/kg, PEEP=16cm H20), andgroup C (VT=15 ml/kg, PEEP=0).General anesthesia was induced with IV diprivan, 2 mg/kg; fentanyl, 0.05mg/kg; scoline, 50mg. The trachea was intubated with a 7.5-8mm inner-diameter tube, and mechanical ventilation was started. Anesthesia was maintained by continuous inhalation isoflurane. Additional fentanyl and vecuronium were administered if needed. ECG, SpO2, ABP, PETCO2, et al were recorded continually.Peripheral blood were drawn at 0h,1h,3h following ventilation. After 3hrs' ventilation, the pigs were killed and lung biopsy specimens were obtained. Plasma levels of IL-6 were determined using ELISA. The alteration of pulmonary histopathology were observed as well.ResultsThere is a significant histological change (alveolar congestion, thickness of the alveolar wall, and leukocyte infiltration) in group B (VT=7 ml/kg, PEEP-16cm H2O) and C (VT=15 ml/kg, PEEP=0), whereas no significant alteration in group A (VT=7 ml/kg, PEEP=8cmH2O). The plasma levels of IL-6 in group Band C increased significantly at 1h and 3h following ventilation compared to the baseline. However, there is no significant elevation of plasma IL-6 concentration in group A following ventilation.ConclusionsMechanical ventilation either with high PEEP or with large volume strategy would induce local and systemic inflammatory responses, overwhelming inflammation may play an important role in the VILI.