Understanding your equipment... The BVM

Oxygen delivery using a Manual Resuscitator (aka bag-valve mask/BVM device) is commonly performed during resuscitation efforts. As the name implies it is assumes manually delivering breaths by squeezing the bag. Others have assumed that since it is a 'closed' system that as long as there is a good seal it can also passively deliver high concentrations of oxygen in the spontaneously breathing patient. This is often not the case and depends on the type of BVM device you have and other factors. This is the first of a series of videos on understanding your airway equipment.

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.


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