The Significance Of Volume Controlled Ventilation Assisted With Autoflow On Model Lung

BackgroundVolume controlled ventilation (VCV) and pressure controlled ventilation (PCV) are different control variables within one ventilatory mode. Each of these two methods has its advantages and disadvantages. The main advantage of VCV is the assurance of the constant tidal volume, while PCV shows better effects in decreasing risk of barotraumas, improving patient-ventilator synchrony, reducing work of breath, promoting gas distribution in lung and perfusion-ventilation ratio. Dual control mode is a new technique that combines the beneficial characteristics of both VCV and PCV. Autoflow is one of them designed in Drager Evita ventilator. Comparing the difference of dual control mode and traditional constant flow of VCV or PCV, some investigations summarized the advantages of dual control mode. It helps to avoid mismatch of patient need and constant inspiratory flow of VCV and thus improve the patient-ventilator synchrony while assuring a pre-set tidal volume (Vt), lower work of breathing (WOB), reduce airway pressure and promote gas exchange. It is especially suitable for respiratory instable patients. However, there's few research comparing the changing of respiratory mechanical parameters including airway pressure, flow velocity after being assisted with Autoflow.Model lung is an ideal tool to study the respiratory mechanical features, on which certain degrees of compliance, airway resistance and inspiratory flow can be set respectively.Patient respiratory style and other clinical conditions can be excluded on model lung. The experimental repetition is good theoretically.The goal of our study is to compare the variables of Vt, peak inspiratory pressure (PIP) and mean airway pressure (MAP) in IPPV mode with different inspiratory flow on Drager Evita 4 ventilator before and after assisted with Autoflow under different pre-set compliance and resistance simulated on model lung. The correlated factor of PIP, MAP, peak inspiratory flow velocity (Pflow) and mean inspiratory flow velocity (Mflow) after being assisted with Autoflow will also be discussed. Materials and methods1. Materials1.1 Drager Evita 4 Ventilator (Drager Medical AG & Co., Germany)1.2 2601i adult/infant model lung (Michigan Instruments, Inc., US)1.3 Ventview inspect software (Drager Medical AG & Co., Germany)2. Methods2.1 Apply self-examination of Drager Evita 4 ventilator and make sure it works properly.2.2 Randomize one pre-set compliance on 260H adult model lung.2.3 Randomize one pre-set resistance on 2601i adult model lung.2.4 Test the model lung and ensure it work accurately and no gas leakage is found.2.5 Measure the compliance and resistance of the system with Ventview inspect software.2.6 Connect Drager Evita 4 Ventilator with 2601i adult model lung and set the following basic parameter: IPPV mode, Vt 500 ml, inspiratory time 1.7s, respiratory rate 12/min and PEEP 5 cmH2O.2.7 Choose one of the following flow velocity randomly: 30, 35, 40, 45, 50, 55L/min.2.8 Record waveform of airway pressure, flow and volume vs. time after 3-5 minute working of the ventilator. Measure and record inspiratory Vt, PIP and MAP.2.9 After assisted with Autoflow for 3-5 minutes, record waveform of airway pressure,flow and volume vs. time. Measure and record inspiratory Vt, PIP, MAP, Pflow and inspiratory time (Ti) (duration of which inspiratory flow velocity above 0) and calculate Mflow by Vt and Ti.2.10 Repeat steps 2.7-2.92.11 Repeat steps 2.3-2.102.12 Repeat steps 2.2-2.11 3. Statistical analysisThe variables were expressed as mean ± SE. Student's t test and linear regression analysis were performed. A P value <0.05 was regarded statistically significant. SPSS 10.0 software was used for statistical analysis. Results1. After assisted with Autoflow, accelerating-pressure waveform turns into square-pressure waveform while inspiratory square-flow waveform turns into decelerating-flow waveform.2. No change of Vt...