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The pressure is on! The danger of a broken blow off valve on a bag valve mask
  1. S B Ainsworth,
  2. R Humphreys,
  3. L Stewart
  1. Neonatal Unit, Directorate of Women & Children’s Health, Forth Park Hospital, Kirkcaldy KY2 5AH, Scotland, UK
  1. Correspondence to:
    Dr Ainsworth

Statistics from

We would like to draw the reader’s attention to a potentially dangerous occurrence with bag valve mask systems when repair and reassembly is carried out incorrectly. Bag valve masks are in common use in neonatal and paediatric resuscitations1,2 and incorporate a pressure relief valve to prevent excessive pressures being delivered.

In this case, checking of a Laerdal paediatric (500 ml) resuscitator (catalogue number 86005033) before use revealed that the blow off valve was not working despite the initial cursory inspection failing to detect any problem (fig 1). Closer inspection revealed that the yellow over-ride button had been broken off and the device reassembled in such a way that the button was placed inside the valve the wrong way round (fig 1 inset). The resuscitator was taken out of use and subjected to further testing. The problem was then brought to the attention of the manufacturer.

Figure 1

 The “odd” appearance of the spring loaded blow off valve. Inset: the spring loaded pressure regulator assembly shown as it was reassembled with top of the yellow part reversed.

As in other reports of problems with bag valve mask systems used in adults and children, the fault was not immediately apparent.3,4 In this case the reassembled device did not look so different from the normal functioning valve (fig 2 and inset), yet by connecting it to a manometer we could generate pressures of 70 cm H2O even with gentle manual ventilation.

Figure 2

 The spring loaded blow off valve of the Laerdal silicone paediatric resuscitator as it should normally appear. Inset: the spring loaded pressure regulator assembly, unscrewed to show the normal configuration.

Although it seems likely that the blow off valve was reassembled by an inexperienced person, we feel that this could have been prevented had the button been too large to fit within the valve body. This design fault is not unique to Laerdal resuscitators and should merit a review by all manufacturers. This event also highlights to clinicians that equipment should always be checked before use and that visual inspection alone cannot be relied on to reveal any potential problems.


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  • Competing interests: none declared

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