A
system for reducing the risk of overventilating a subject in need of ventilation includes a ventilation
assembly comprising a ventilation bag, a patient interface and an automatic flow reduction valve configured to impede flow to a subject wearing the ventilation bag when a pressure or flow rate in a flow path from the bag to the subject exceeds a maximum threshold value. A ventilation sensor positioned in or near to the flow path is configured to measure the pressure or flow rate in the flow path. The ventilation
assembly is configured to communicate via a
user interface or a communicably coupled device with a display at least one
signal related to a maximum
tidal volume determined based on signals from the ventilation sensor.