SPONTANEOUS BREATHING MODE
In spontaneous breathing, unit operation is controlled entirely by the patient's
inhalation and exhalation efforts. Gases flow from the oxygen blender, are filtered in the
inlet manifold, and delivered to the functional components of the unit.
a. During the inspiratory phase of the spontaneous breathing mode (figure 1-12)
a constant flow of gas is provided from the inlet manifold to the pressure gauge and to
the flow regulator. The flow gauge indicates the flow of gases in lpm before delivery to
the patient airway. As gas leaves the flow regulator, it flows in two paths: one is
directed to the nebulization control and the other to the by-pass valve.
b. As gas flows into the 500cc nebulizer, any liquids within are nebulized. Gas
flows from the nebulizer to the top flapper of the shuttle valve and to the overpressure
governor. Gas also flows through the bifurcation fitting, through the large green hose
and the water trap to the patient-airway connection. Overpressure-governor reed valves
are set at 30cmH2O. Pressures in the inspiratory lines will build up to the preset level. If
there is an obstruction of outflow gases, the overpressure governor will open at
30cmH2O and relieve this pressure to the atmosphere.
c. At the mechanical airway connection, some of the gas flows into the red
expiratory line along with the patient's exhaled gases. Expiratory gases are directed
through the water trap and the expiratory valve in the shuttle-valve assembly. Exhaled
gases leave the shuttle valve through the master tee and flow over the top surface of the
airBird non-rebreathing-valve diaphragm through the outflow valve to the atmosphere.
The outflow valve pressure is indicated on the proximal airway gauge.
d. During the expiratory phase (figure 1-13), gas flows through the inspiratory-
interrupter cartridge and the expiratory flow-gradient control to the venturi in the shuttle