[The study of AutoFlow role in volume controlled ventilation].

OBJECTIVE: To evaluate the efficacy and safety of automatic variable flow rate (AutoFlow) for volume control ventilation through monitoring the number of ventilator alarm. METHODS: Forty-eight adult patients receiving the Drager Evita 4 ventilator with an expectation of more than 2 days duration were divided into two groups by randomly digital methods, each n=24. The patients in control group were received routinely mode with synchronized intermittent mandatory ventilation (SIMV), and the others in observation group were given SIMV and assist with AutoFlow. The midazolam and fentanyl was given to retain the Ramsay score 2-3 by continuous micro-pump. The ventilator alarm, blood gas analysis and respiratory function were recorded. RESULTS: There were no significant differences in respiratory rate (RR), tidal volume (VT), positive end-expiratory pressure (PEEP), fraction of inspired oxygen (FiO2), pH, arterial partial pressure of carbon dioxide (PaCO2), arterial partial pressure of oxygen (PaO2), oxygenation index (PaO2/FiO2), as well as sedative dose and time between two groups within 5 days of mechanical ventilation. Duration of mechanical ventilation in all patients was 164 days (3756 hours), and 78 days (1812 hours) in control group, 86 days (1944 hours) in observation group. The duration of mechanical ventilation in observation group was longer than that in control group [3 (1-15) days vs. 2 (1-28) days, P>0.05]. A total of 23 843 alarms were recorded, approximately 6 times/h, and 17 386 alarms in control group, averagely 9.6 times/h, 6457 alarms in the observation group, averagely 3.3 times/h. The number of ventilator alarm in observation group was less than that in control group (P<0.01). The number of airway pressure alarm in observation group was less than that in the control group [122 (8-1068) vs. 565 (13-1898), P<0.01]. There was no significant difference in sequential organ failure assessment (SOFA) score within 5 days between the two sets of mechanical ventilation. In the observation group ventilator-associated pneumonia (VAP) was occurred in 4 cases, and no pneumothorax happened, while in the control group there were 8 cases and 2 cases respectively. The mortality rate in intensive care unit (ICU) in observation group was lower than that in control group, but there was no statistical difference (25.0% vs. 37.5%, P>0.05). CONCLUSIONS: AutoFlow is confirmed be safe for volume control ventilation mode, and could significantly reduce the alarm of ventilator.