Oxygen concentrations at the rear and front of the bag in bag valve mask devices during oxygenation of neonates

Abstract

Objective: To study the concentration of oxygen flowing passively from the front and the rear parts of different brands of self-inflating bag valve mask ventilation devices at different oxygen flows and that flowing actively from the front part at different ventilation rates. Methods: Two devices were tested, the Ambu device in which the added oxygen enters at a right angle to the axis of the bag and the VBM in which the oxygen enters parallel to the axis of the bag and faces either a hole or a ridge in the intake valve. An oxygen analyzer was used to measure the oxygen concentration at different oxygen flow rates (2, 4, 6, 8 and 10 L/min) supplied by a 100% oxygen source. This was measured in both devices from the front and rear parts as step one. With active ventilation compressing the bag, oxygen concentration was measured from the front part. This was done at ventilation rates of 30 and 60 min −1. Results: Passive flow oxygenation. With the Ambu device, the oxygen concentration measured at the front part of the bag was 21% and that measured from the rear part was 100%, at all oxygen flow rates. With the VBM brand, in the first position with the oxygen source facing a hole (VBM-hole), the oxygen concentration was high at low flow rates and decreased with increased flow. Similar findings happened when measuring oxygen concentration from its rear part. With the oxygen source facing a ridge (VBM-ridge), the oxygen concentration measured from the front was directly proportional to the oxygen flow rate i.e. it increased with increasing flow. From the rear part, the oxygen concentration was near 100% at all flow rates. Active ventilation. Using the Ambu device, the oxygen concentration increased with increasing flow rate and reached 100% at 10 L/min flow. With VBM-hole, the oxygen concentration increased gradually with increasing flow but never reached 100%. With VBM-ridge, the performance was comparable to the Ambu. In all the situations, the oxygen concentration was higher when the ventilation was done at 30 min −1 than at 60 min −1. Conclusion: The Ambu device can provide 100% oxygen from its rear part even at low flow rates and 100% oxygen during active ventilation provided at least 10 L/min oxygen is used. The VBM is at a disadvantage when the oxygen source faces a hole; as the jet flowing in the bag causes a Venturi effect; which sucks air in from outside and dilutes the oxygen concentration provided. The ridge type does not have this problem. Ventilation at a rate of 30 min −1 produced a higher oxygen concentration. The operator should be aware of the limitations of the device used.