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: The effects of prolonged recruitment manoeuvre (PRM) were compared with sustained inflation (SI) in paraquat-induced mild acute lung injury (ALI) in rats. Twenty-four hours after ALI induction, rats were anesthetized and mechanically ventilated with VT=6 ml/kg and positive end-expiratory pressure (PEEP)=5 cmH(2)O for 1h. SI was performed with an instantaneous pressure increase of 40 cmH(2)O that was sustained for 40s, while PRM was done by a step-wise increase in positive inspiratory pressure (PIP) of 15-20-25 cmH(2)O above a PEEP of 15 cm H(2)O (maximal PIP=40 cmH(2)O), with interposed periods of PIP=10 cmH(2)O above a PEEP=15 cmH(2)O. Lung static elastance and the amount of alveolar collapse were more reduced with PRM than SI, yielding improved oxygenation. Additionally, tumour necrosis factor-alpha, interleukin-6, interferon-gamma, and type III procollagen mRNA expressions in lung tissue and lung epithelial cell apoptosis decreased more in PRM. In conclusion, PRM improved lung function, with less damage to alveolar epithelium, resulting in reduced pulmonary injury.Respiratory Physiology & Neurobiology 10/2009; 169(3):271-81. DOI:10.1016/j.resp.2009.10.002 · 1.97 Impact Factor
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ABSTRACT: Rationale: There are limited data on the safety and efficacy of recruitment maneuvers (RMs) in acute lung injury (ALI)patients. OBJECTIVE: To evaluate the frequency, timing, and risk factors for complications from RMs in adult ALI patients. METHODS: Secondary analysis of data from a randomized controlled trial of a lung open ventilation strategy that included sustained inflation RMs. Measurements and Main Results: Respiratory (e.g., desaturation) and cardiovascular (e.g., hypotension) complications from recruitment maneuvers were common (22% of all patients receiving RMs) and the majority occurred within seven days of enrollment. New air leak through an existing chest tube was uncommon (<5%).As compared to patients receiving 1 or fewer RMs, the number of RMs received was associated with increased risk in both younger (age < 56) and older patients (age > 56): 2 RMs, odds ratio [OR] 6.92 (95% CI 1.70-28.2);≥3 RMs,OR 15.4 (95% CI 4.77-49.6)) and 2 RMs, OR 5.43 (95% CI 1.76-16.8); ≥3 RMs, OR 4.93 (95% CI 1.78-13.7)), respectively. Patients with extrapulmonary ALI had decreased odds of developing complications (OR 0.42; 95% CI 0.22-0.80). CONCLUSIONS: Complications in adult ALI patients receiving RMs were common, but serious complications (e.g., new air leak through an existing chest tube) were infrequent. There is a significant association between the number of RMs received and complications, even after controlling for illness severity and duration. Given their uncertain benefit in ALI patients, and the potential for complications with repeated application, the routine use of sustained inflation RMs is not justified.Respiratory care 05/2012; 57(11). DOI:10.4187/respcare.01684 · 1.84 Impact Factor
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ABSTRACT: Aspiration-induced lung injury can decrease gas exchange and increase mortality. Acute lung injury following acid aspiration is characterized by elevated pulmonary blood flow (PBF) in damaged lung areas in the early inflammation stage. Knowledge of PBF patterns after acid aspiration is important for targeting intravenous treatments. We examined PBF in an experimental model at a later stage (2 hours after injury). Anesthetized Wistar-Unilever rats (n = 5) underwent unilateral endobronchial instillation of hydrochloric acid. The PBF distribution was compared between injured and uninjured sides and with that of untreated control animals (n = 6). Changes in lung density after injury were measured using computed tomography (CT). Regional PBF distribution was determined quantitatively in vivo 2 hours after acid instillation by measuring the concentration of [(68)Ga]-radiolabeled microspheres using positron emission tomography. CT scans revealed increased lung density in areas of acid aspiration. Lung injury was accompanied by impaired gas exchange. Acid aspiration decreased the arterial pressure of oxygen from 157 mmHg [139;165] to 74 mmHg [67;86] at 20 minutes and tended toward restoration to 109 mmHg [69;114] at 110 minutes (P < 0.001). The PBF ratio of the middle region of the injured versus uninjured lungs of the aspiration group (0.86 [0.7;0.9], median [25%;75%]) was significantly lower than the PBF ratio in the left versus right lung of the control group (1.02 [1.0;1.05]; P = 0.016). The PBF pattern 2 hours after aspiration-induced lung injury showed a redistribution of PBF away from injured regions that was likely responsible for the partial recovery from hypoxemia over time. Treatments given intravenously 2 hours after acid-induced lung injury may not preferentially reach the injured lung regions, contrary to what occurs during the first hour of inflammation. Please see related article: http://dx.doi.org/10.1186/s12871-015-0014-z.BMC Anesthesiology 12/2015; 15(1):36. DOI:10.1186/s12871-015-0013-0 · 1.33 Impact Factor