Can I Cover The MDM Inspiratory Valve?

February 9, 2021

A community dental team recently asked this question.  They have been covering the MDM Flowmeter with a large clear plastic bag to protect it during procedures.  A query arose as to whether the air entrainment valve should be left uncovered.

The air entrainment valve is part of the machine’s hypoxic guard.  It will only open, to allow fresh room air into the bag tee of the flowmeter, if the oxygen exhausts and the nitrous oxide cut-off engages.  Normally it is closed, not allowing any passage of air. 

In normal use, with good cylinder management, this will never happen.  However, it is a valid point as to whether it is allowable to cover the valve area or not.  If the air entrainment valve did engage due to lack of oxygen from the cylinders, then there would still be enough air flow from around the flowmeter and the underside of the plastic bag to allow room air to flow sufficiently into the breathing system.

It is vital to ensure that all sedation procedures are commenced with an ‘in-use’ cylinder with sufficient contents for the procedure.  It is also important to have a ‘full’ cylinder in reserve.  This obviously only applies to a flowmeter mounted on a mobile 4 cylinder stand – piped systems operate differently.  In the UK it is mandatory to have four cylinders in use at all times for this type of equipment.

For any further queries on this topic, please email