What is Autoflow? AutoFlow, only found on the Drager, is an adjunct to volume-controlled ventilation mode. Autoflow is like Drager’s version of Pressure Regulated Volume Control (Check out Dr. Siuba’s review of PRVC HERE.) Autoflow regulates inspiratory flow and inspiratory pressure delivering the set tidal volume at the lowest possible inspiratory pressure. This allows for lung protection.
How it works
When AutoFlow is turned on, the inspiratory flow pattern changes from the constant flow associated with volume control to a decelerating flow pattern associated with pressure-controlled ventilation. The ventilator will use the plateau pressure as the starting inspiratory pressure and adjusts to 75% of the starting pressure to achieve set tidal volume delivery. Inspiratory pressure of each breath is adjusted to meet an averaged tidal volume. The minimum inspiratory pressure for mandatory breaths is 3cmH2O above PEEP and 0.1cmH2O above PEEP for spontaneous breaths.
Autoflow is an averaged tidal volume guaranteed with adjusted flow and inspiratory pressure. The flow and pressure tend to be regulated by compliance and controlled by alarm settings. To keep a patient from hyper/hypoventilating, you must set the Vt High appropriately along with the Pmax. The Pmax alarm regulates the inspiratory pressure control. Autoflow allows for spontaneous breathing throughout the inspiratory and expiratory phases of the mechanical ventilation breath, improving synchrony. Allowing for too much volume or pressure could result in overinflation, and a low setting could result in collapse or hypoventilation. Common alarms associated with Autoflow are pressure limited volume not reached and Vt high minimum pressure. These alarms could indicate a change of mode is necessary.
Should Autoflow always be on?
No. Autoflow can allow for overinflation in the lungs when a rapid change in compliance occurs. Autoflow should not be used with inverse ratios, as it may increase your intrinsic PEEP. The pressure alarms regulate the inspiratory pressure used on mandatory breaths; therefore, when ventilating with uncuffed tubes, Autoflow is not recommended as it will autocycle.
For the most part, Autoflow is safe, but it is not a set-and-forget adjunct. Autoflow has been studied for efficacy and improvement in ventilation with little results. Most studies with Autoflow only showed a decrease in alarm activation.
- Reduces high airway pressures while enhancing spontaneous breathing
- Is the combination of pressure control and volume control ventilation
- Improves ventilator synchrony
Peyne, T., & Rutten, F. (2012, October). Autoflow. https://www.draeger.com/Products/Content/autoflow-bk-9066357-en.pdf
When used in conjunction with active leak compensation, the Drager v500 rarely has issues with auto-cycling even with leaks >50% and low flow trigger (even as low as 0.2 L/min).
The Drager also seems to adapt and compensate well for volume lost due to ETT air leaks making it ideal for volume targeted ventilation compared to other ventilator which target VTinsp.