Add a one-way valve (or ‘check’ valve) on the inspiratory and expiratory limb of each patient. 

These one-way valves are crucial to prevent backflow in the circuits. If they are not inserted on the correct limbs, any pressure difference between patients will yield a flow from regions with higher pressure to regions with lower pressure. This backflow could take place in both inspiratory and expiratory circuits without one-way valves: for example, a difference in individual PEEP could yield a backflow from higher PEEP to lower PEEP through an inspiratory circuit without one-way valves. 

Advice and comments from our contributors

Naturally, it is very important to insert the one-way valves in the correct direction. To avoid errors in urgent situations, it is therefore advisable to use one-way valves that come with a visual indicator of direction, or to mark the correct direction on all the valves beforehand. 

In case there is an extreme shortage of one-way valves, one could use a smaller number of valves in the following situations: 

• if one patient (out of two) will need a higher PIP and PEEP than the other patient for a considerable time, the one-way valve on the expiratory limb of the patient with highest pressure could be left out, and the one-way valve on the inspiratory limb of the patient with lower PIP and PEEP could be left out as well. 
• In principle, a reliable in-line PEEP valve could replace a one-way valve in an expiratory limb. 

Current Status

We’re working on a unified test protocol.