| Objective: Chronic Obstructive Pulmonary Disease (COPD) is a preventable and treatable disease with some significant extra-pulmonary effects that may contribute to the severity in individual patients. Its pulmonary component is characterized by airflow limitation that is not fully reversible and usually progressive and associated with an abnormal inflammatory response of the lung to noxious particles or gases. Pathological changes characteristic of COPD are found in the proximal airways, peripheral airways, lung parenchyma, and pulmonary vasculature. The mainly pathology include chronic inflammation and structural reform resulting from repeated injury and repair. The chronic airflow limitation characteristic of COPD is caused by a mixture of small airway disease (obstructive bronchiolitis) and parenchymal destruction (emphysema). Airway infection is the most common cause of COPD exacerbation, which present with severe occlusion of airway. As an important therapeutic method, mechanical ventilation has been widely used for the patients with acute exacerbation of COPD and respiratory failure.The strategy of mechanical ventilation need to be adjusted due to the changes in the pathophysiology such as the increases of lung compliance ,airway resistance and physiologic dead space as well as powerless of respiratory muscle in the patients with COPD, in which, there are some differences with other diseases. The respiratory muscle must to be unloaded fully while atrophy should be obviated; and the alveolar ventilation delivered must to be sufficient to guarantee the effective gas exchange while a series of complication such as hyperventilation should be avoided.At present, synchronized intermittent mandatory ventilation plus pressure support mode(SIMV + PSV)has already been extensively applicated clinically ,but the clinical application and observation of adaptive support ventilation mode (ASV) is still very limited ,particular in COPD patients .The purpose of this study is to reveal the differences between the two modes (SIMV+PSV vs ASV) in the respects of mechanics of breathing ,hemodynamics,and gas exchange in the patients tolerating mechanical ventilation because of an acute exacerbation of COPD and to provide guidance to clinicians.Method: The patients who need to be treated with invasive mechanical ventilation because of an acute exacerbation of COPD were all given tracheal intubation through nose or mouth and convention drug treatment. They were ventilated with SIMV+PSV or ASV mode randomly when the circulation and respiration condition were stable and consciousness was recovered. Artery blood gas analysis (ABG) was performed after 2 hours and then the mode was changed into the other with the same minute ventilation for the next 2 hours .The ABG would be rechecked at the end of the observation .Using the function of tendency looking back on ventilator ,all the parameters were recorded every 10 minutes including respiratory rate (RR),tidal volume (VT),peak airway pressure (Ppeak), mean airway pressure (Pmean), inspiratory ,airway occlusion pressure (P0.1), static compliance (C), intrinsic positive end expiratory pressure(PEEPi)et cetera. All the parameters of hemodynamics including heart rate(HR),mean arterial pressure (MAP),and arterial blood pressure (BP)were obtained by the record of the ECG monitor every 15 minutes. The average of every parameter was calculated. Base on the average parameters, the statistic analysis was done for the two modes.Statistical analysis: Using SPSS11.0 for statistical analysis. Measurement data were expressed as mean±standard deviation. Paired T was applied in comparison of mean between two groups. Wlicoxon rank sum test was applied in comparison of bias data. Significant difference was defined as P<0.05.Results: 1.The parameters of respiratory pattern: compared with SIMV+PSV,Vt increased (P<0.01) and ftot decreased (P<0.01) during ASV, with significant difference. However, MV remained unchangedbetween ASV and SIMV+PSV (P>0.05) . The fspont increased (P<0.01) and fcontrol decreased (P<0.01) during ASV compared with SIMV+PSV.2. The parameters of mechanics of breathing: compared with SIMV+PSV. Ppeak (P<0.01) and Pmean greatly decreased (P<0.05)during ASV while the level of pressure support increased (P<0.01) significantly . In ASV, The Fins increased (P<0.05) but the Fexp remain the same as SIMV+PSV (P>0.05).The Csat increased during ASV(P<0.01).3. PEEPi was significantly decreased during ASV compared to SIMV+PSV (P<0.05).4. Compared with SIMV+PSV, the value of I/E is lower in ASV(P<0.05).5. P0.1, the index of respiratory muscle work, greatly decreased while in ASV (P<0.01).6. There was no significant difference in Bp, MAP and HR between the two modes (P>0.05).7. There was no difference in the parameters of gas exchange. (P>0.05).8. During the whole period of experiment , no ventilator associated lung injury was discovered. Conclusions: 1. ASV can markedly reduce airway pressure and improve the respiration pattern.2. ASV can reserve and support the spontaneously breathing to the utmost when the MV is guaranteed;3. ASV can decrease inspiratory load and patients'effort. The I/E can be adjusted automatically, the PEEPi can be reduced significantly.4. No differences in the hemodynamics and gas exchange was observed between the two modes.5. ASV is an effective and safe mode for COPD patients, it should be used widely.
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