Multi-valve system with gas storage
A self-inflating bag provides an alternative that enables the resuscitator to venti-late the patient’s lungs with room air or, if oxygen is available, with air enriched with oxygen. For the latter to succeed, the self-inflating bag must have a reservoir in which oxygen can accumulate during inspiration (see Fig. 8.5).
Without a self-inflating bag, gas has to be admitted to the breathing system under pressure. Figure 8.6shows a simple arrangement. We incorporate a bag and two valves. Now the fresh gas accumulates in the bag during exhalation when the inspiratory valve closes and the expiratory valve opens (venting CO2-laden gas to the atmosphere). During inspiration the valves swap roles: the inspiratory valve opens and the expiratory one closes. Such valves have little resistance, perhaps 1 or 2 cm H2O, and thus will easily open during the respiratory cycle. This works for a patient breathing spontaneously. Again, an adjustable pressure-limiting valve on top of the expiratory limb enables us to ventilate the patient’s lungs.