2020A Question 12
Using a labeled diagram, describe how a self-inflating bag-valve-mask resuscitation device works.
Expected in the answer was a labelled diagram including mask, valves, self-inflating bag, oxygen input and reservoir bag. Discussion was expected to include the role of each of these parts in the function of the device. A good way to discuss function was to explain the flow of gas through the device in both inspiration and expiration. An understanding of the key role of the non-rebreathing valve in both inspiration and expiration was expected for a pass.
There were a large number of candidates who described a device with a flow inflating bag such as a T-piece or other Mapleson circuits. These circuits are however valveless unlike the BVM device. Lack of understanding of the function of the valves in the BVM was a common reason for a candidate to not pass this question. The bag inlet valve was also frequently omitted. There was additional misunderstanding about the role and location of PEEP valves and APL valves in the device.
A good reference for this material is Understanding Anesthesia Equipment, Dorsch and Dorsch, Chapter 10, 5th Ed.
- Spontaneous ventilation
- Mechanical ventilation
- No power required (hand-compressible, self-expanding bag
- No O2 supply required (air inlet valve opens if subatmospheric)
- Compatible with face mask, LMA, ETT (15mm adaptor)
- Can deliver 100% O2 (2L bag + large reservoir)
- Protection against barotrauma (high pressure relief valve ~30cmH2O)
- Minimal dead space (non-rebreather valve close to patient)
- Relatively low resistance to flow in inspiration
- Minimal waste of fresh gas (one-way refill valve)
- Bulky near patient’s head
- No measurements (pressure, flow, CO2)
- Easy to overventilate + insufflate the stomach (rapidly re-inflating bag)
- Spont vent inspiratory pressure drop of 2cmH2O exceeds recommendation
- Valve malfunction or misassembly can cause barotrauma, failure of oxygenation and ventilation
Fun fact: AMBU = artificial manual breathing unit