Figure 70-12 Monaghan 225 ventilator modified for use in a hyperbaric chamber. A gas-mixing system with two ball rotameters has been added to provide the inspired gas, which enters the ventilator through a conduit attached to the air intake. The FIO₂ setting has been permanently set at 21% to force the ventilator to use the externally mixed gas as the breathing gas. The FIO₂ adjustment knob has been removed. A 5-L reservoir bag is attached to the patient gas circuit. A reservoir relief valve prevents overpressurization of the reservoir bag. A subambient pressure relief valve allows entrainment of room air if insufficient gas is provided to the reservoir bag. (From Moon RE, Bergquist LV, Conklin B, Miller JN: Monaghan 225 ventilator use under hyperbaric conditions. Chest 89:846, 1986.)