HMEF Or Bacterial And Viral Filter Which One Belongs In Your Circuit

The Single Question That Decides It

Does the circuit already have active humidification? If it does, a bacterial and viral filter is what you need, because the HMEF would be duplicating a job already done. If it does not, the HMEF earns its place by returning moisture that would otherwise be lost, at 31 mg H2O per litre at a tidal volume of 500 ml on the adult type.

Dead Space Is The Paediatric Constraint

Dead space matters most on small tidal volumes. The adult HMEF carries 45 ml and covers 150 to 1500 ml tidal volumes. The paediatric type drops to 20 ml for 150 to 300 ml. The bacterial and viral filter sits at 32 ml across a 250 to 1500 ml range, which rules it out for the smallest patients.

Filtration Is Comparable Across Both

Both run BFE 99.9 to 99.999 percent and VFE 99 to 99.99 percent depending on grade, so filtration efficiency is rarely the deciding factor. Resistance differs slightly: the BV filter is under 1.2 cmH2O at 30 LPM and under 2.6 cmH2O at 60 LPM at the highest grade.

The Tracheostomy Case Is Different Again

A spontaneously breathing tracheostomy patient does not need a circuit filter, they need something light enough to hang off the tube. The tracheostomy filter weighs 7 g with 15 ml dead space and a 15F connector, with moisture loss of 9.0 mg H2O per litre at 500 ml tidal volume and a recommended tidal volume above 50 ml.

Do Not Combine An HMEF With An Active Humidifier

Putting a heat and moisture exchanger downstream of an active humidifier loads the filter element with condensate and drives resistance up. Pick one humidification strategy per circuit and specify the filter accordingly.