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Oxygenation -Understanding your BVM Device 2

Understanding the mechanics of oxygen delivery using BVM requires an appreciation of its component valves. The first BVM Device has 5 valves, 3 at the rear and 2 in the front. The forward duckbill valve is a one way valve allowing flow to the patient. A second expiratory disc valve is what differentiates this set up from others. It is a one way valve sitting below the duckbill allowing expired gas to exit while preventing room air entrainment. In contrast the second BVM (a 4 valve device) has a single forward duckbill valve with an expiratory port below it on the side the distal elbow connector. This port allows bidirectional flow. If the patients minute ventilation exceeds the flow to the mask air will be entrained and dilute delivered oxygen (FDO2). This can be managed by placing a PEEP valve over this port which creates a one way exit for expired gas (and allows for the application of PEEP). All of this applies to passively oxygenating the spontaneously breathing patient ie. not squeezing the bag.