Mechanism by which a sustained inflation can worsen oxygenation in acute lung injury
ABSTRACT Sustained lung inflations (recruitment maneuvers [RMs]) are occasionally used during mechanical ventilation of patients with acute lung injury to restore aeration to atelectatic alveoli. However, RMs do not improve, and may even worsen, gas exchange in a fraction of these patients. In this study, the authors sought to determine the mechanism by which an RM can impair gas exchange in acute lung injury.
The authors selected a model of acute lung injury that was unlikely to exhibit sustained recruitment in response to a lung inflation. In five sheep, lung injury was induced by lavage with 0.2% polysorbate 80 in saline. Positron emission tomography and [13N]nitrogen were used to assess regional lung function in dependent, middle, and nondependent lung regions. Physiologic data and positron emission scans were collected before and 5 min after a sustained inflation (continuous positive airway pressure of 50 cm H2O for 30 s).
All animals showed greater loss of aeration and higher perfusion and shunting blood flow in the dependent region. After the RM, Pao2 decreased in all animals by 35 +/- 22 mmHg (P < 0.05). This decrease in Pao2 was associated with redistribution of pulmonary blood flow from the middle, more aerated region to the dependent, less aerated region (P < 0.05) and with an increase in the fraction of pulmonary blood flow that was shunted in the dependent region (P < 0.05). Neither respiratory compliance nor aeration of the dependent region improved after the RM.
When a sustained inflation does not restore aeration to atelectatic regions, it can worsen oxygenation by increasing the fraction of pulmonary blood flow that is shunted in nonaerated regions.
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ABSTRACT: One-lung ventilation (OLV) with normal tidal volumes (10ml/kg) may result in biotrauma of the ventilated lung which is characterized by increased concentrations of proinflammatory cytokines in the bronchoalveolar lavage fluid . The effects of inhalational or intravenous anesthetic drugs on the immunological response to OLV are unclear. A prospective, randomized experimental study was performed to analyze systemic and pulmonary immunological parameters prior to and after OLV. The animal study had been approved by the Animal Care and Use Committee of the Uppsala University. 12 Yorkshire/Swedish land pigs were used in the study. The pigs were randomized to receive either 6mg/kg•h propofol (group P, n=6) or 6.3±1.0Vol % desflurane (group D, n=6) anesthesia. After tracheotomy and insertion of an ID 8.5mm single lumen tube, the pigs were mechanically ventilated (VT=10ml/kg). After insertion of a left sided bronchusblocker, OLV was started with VT=10ml/kg, FiO2=0.40, PEEP=5cmH2O) for 60min and a typical left-sided thoracotomy was performed. Cardiopulmonary and respiratory data were recorded continuously. Fiberoptic, bronchoalveolar lavage (BAL) of both lungs and serum samples were achieved before (t1), 20min after OLV (t2) and 90min after OLV (t3). In BAL fluids and serum samples, pro-inflammatory (TNFα, IL8) and anti-inflammatory cytokines (IL10), in BAL additionally number of cells and protein concentrations were determined. Data were analyzed by Friedman and post-hoc Wilcoxon test. In the ventilated lung (VL) intraalveolar cells, protein and proinflammatory cytokines (IL8, TNFα) were significantly increased over time. A proinflammatory response was also detected in the non-ventilated lung (NVL). In contrast to propofol anesthesia, alveolar IL8 concentrations in pigs receiving desflurane anesthesia were significantly smaller in both lungs 90min after OLV. Serum concentrations of IL8, TNFα and IL10 were significantly decreased in the desflurane group. Our results indicate that OLV using a tidal volume of 10ml/kg initiates epithelial damage and proinflammatory effects in the alveolar compartment of the ventilated lung. Likewise, an immune response was detected in the non-ventilated lung and systemically. The immunologic reactions were influenced by the type of general anesthesia, and desflurane markedly decreased the pulmonary and systemic pro-inflammatory response in this animal model of thoracic surgery.ASA 2006; 10/2006
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ABSTRACT: Acute lung injury occurs in a third of patients with smoke inhalation injury. Its clinical manifestations usually do not appear until 48-72 h after inhalation. Identifying inflammatory changes that occur in pulmonary parenchyma earlier than that could provide insight into the pathogenesis of smoke-induced acute lung injury. Furthermore, noninvasive measurement of such changes might lead to earlier diagnosis and treatment. Because glucose is the main source of energy for pulmonary inflammatory cells, the authors hypothesized that its pulmonary metabolism is increased shortly after smoke inhalation, when classic manifestations of acute lung injury are not yet expected. In five sheep, the authors induced unilateral injury with 48 breaths of cotton smoke while the contralateral lung served as control. The authors used positron emission tomography with: (1) [F]fluorodeoxyglucose to measure metabolic activity of pulmonary inflammatory cells; and (2) [N]nitrogen in saline to measure shunt and ventilation-perfusion distributions separately in the smoke-exposed and control lungs. The pulmonary [F]fluorodeoxyglucose uptake rate was increased at 4 h after smoke inhalation (mean ± SD: 0.0031 ± 0.0013 vs. 0.0026 ± 0.0010 min; P < 0.05) mainly as a result of increased glucose phosphorylation. At this stage, there was no worsening in lung aeration or shunt. However, there was a shift of perfusion toward units with lower ventilation-to-perfusion ratio (mean ratio ± SD: 0.82 ± 0.10 vs. 1.12 ± 0.02; P < 0.05) and increased heterogeneity of the ventilation-perfusion distribution (mean ± SD: 0.21 ± 0.07 vs. 0.13 ± 0.01; P < 0 .05). Using noninvasive imaging, the authors demonstrated that increased pulmonary [F]fluorodeoxyglucose uptake and ventilation-perfusion mismatch occur early after smoke inhalation.Anesthesiology 09/2013; 120(3). DOI:10.1097/01.anes.0000435742.04859.e8 · 6.17 Impact Factor
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ABSTRACT: Direct comparison of the relative efficacy of different recruitment maneuvers (RMs) for patients with acute respiratory distress syndrome (ARDS) via clinical trials is difficult, due to the heterogeneity of patient populations and disease states, as well as a variety of practical issues. There is also significant uncertainty regarding the minimum values of positive end expiratory pressure (PEEP) required to ensure maintenance of effective lung recruitment using RMs. We used patient-specific computational simulation to analyze how three different RMs act to improve physiological responses, and investigate how different levels of PEEP contribute to maintaining effective lung recruitment.Critical Care 01/2015; 19(8). DOI:10.1186/s13054-014-0723-6 · 5.04 Impact Factor