Simple functional diagram of a FLOW-i anesthesia machine

The diagram depicts the machine during the inspiratory phase of a mechanical breath (long-dashed blue arrows, direction of FGF; short-dashed red arrows, gas flow generated by the ventilator; dotted green arrows, drive gas flow) with the inspiratory valve open and the expiratory valve closed. Lightning bolts indicate sites of electronic control. During spontaneous or manual ventilation, excess gas is vented out of the breathing circuit through the APL valve, which is excluded from the system during mechanical ventilation. From the wall outlets or cylinders, pressurized gases (O₂, green; air, yellow; N₂O, blue) pass through external pressure regulators prior to entrance of the anesthesia machine. Fresh gas is delivered via three electronically controlled gas modules with a maximum flow of over 20 L/minute (O₂, green; air, yellow; N₂O, blue), and vapor is added from an electronically controlled vaporizer that injects liquid agent into a heated vaporizing chamber. Exhaled gas is temporarily stored in a long piece of tubing called the volume reflector that takes the place of a bellows. Gas mixing within the volume reflector is minimal. The inspired tidal volume consists of both drive gas from the volume reflector pushed toward the patient by the reflector gas module and fresh gas from its inlet into the breathing circuit. The electronically controlled APL/PEEP valve is closed during mechanical inhalation. During exhalation excess gas is vented from the circuit through the APL/PEEP valve, which contributes no obligatory PEEP.