Fig. 2

Breathing circuit filters. Connections should be tightly fitted to avoid disconnections during movement. Dead space and circuit resistance will increase with the use of filters. a Hydrophobic mechanical filter at the bag-valve-mask interface (black arrow) to reduce dispersion of respiratory droplets during manual ventilation with a positive end expiratory pressure (PEEP) valve (white arrow) to optimise pre-oxygenation. b HEPA (high-efficiency particulate air) filters used on the inspiratory and expiratory ports of mechanical ventilators. c Hydrophobic mechanical filter used before the external expiratory port on a single-limb non-invasive ventilator circuit. d HEPA filters used at the air inlet (solid black arrow) and before the exhalation valve (dashed black arrow) ports of a single-limb transport ventilator circuit. A standard HME (heat and moisture exchanger) (white arrow) is attached at the Y-piece of the breathing circuit. e An alternative combination is the use of HEPA filter at the air inlet and a hydrophobic mechanical HME filter (HMEF) (black arrow) at the Y-piece, nearest to the patient