Effects Of Neurally Adjusted Ventilatory Assit On Air Distribution And Dead Space In Patients With Acute Exacerbation Of Chronic Obstructive Pulmonary Disease

Objective:To evaluate the effects of neurally adjusted ventilatory assit on air distribution and dead space in patients with acute exacerbation of chronic obstructive pulmonary disease.Methods:Fifteen mechanically ventilated patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) were included in the study. The initial PSV levels were set to 10 cmH2O (PSV 100), and the patients were ventilated for 10 minutes. Thereafter, the ventilator mode was changed to NAVA, and the electrical activity of the diaphragm (EAdi) during pressure support(PSV 100) was used to titrate to the coresponding initial NAVA gain (NAVA100), and the patients were ventilated with this mode for 10 minutes. Then, the patients were ventilated with pressure support in 5 cmH2O (PSV 50) and NAVA 50 (NAVA level was set to half of NAVA 100), pressure support in 15 cmH2O (PSV 150) and NAVA 150 (NAVA level was set to 1.5-fold of NAVA 100) respectly for 10 minutes. Air distribution, regional ventilation-delay and regional impedance compliance were collected by EIT and ventilator waveform was recorded by Servo Tracker. Two miniutes before changing ventilator mode, diaphragm activity was measured by B-mode ultrasonography and expiratory air was collected by Douglas bag. PeCO2 of the gas collected in Douglas bag was measured with a blood gas analyzer and Vd/Vt was calculated by PeCO2 and PaCO2. After each ventilator mode, arterial blood gas analysis was measured to get P/F, PaO2 and PaCO2.Results:Fifteen AECOPD patients were recruited in the study from Jan 2014 to Febr 2015. The age was 78.6, APACHE Ⅱ was 18.4, and PEEPi was 4.17cmH2O. (1)Effects of NAVA on P/F and PaCO2:There was no difference between NAVA and PSV in P/F and PaCO2. (2)Changes of respiratory mechanics indices during NAVA:When assist level increased during NAVA and PSV, Pmean, VE and Vti also increased. But in NAVA 100 and NAVA 150, VE and Vti were significantly lower than in PSV (p<0.05). (3)Effects of NAVA on air distribution: ①Compared with PSV, NAVA could improve regional ventilation-delay and regional impedance compliance in the near-diaphragm lung region. ②Ventilation contribution of the near- diaphragm lung region increased during NAVA when compared to PSV. (4)Effects of NAVA on dead space:Vd/Vt decreased significantly during NAVA when compared to PSV.Conclusions:NAVA could increase air distribution in the near-diaphragm lung region, decrease Vd/Vt in AECOPD patients and improve pulmonary ventilation homogeneity.