Bypass Circuit (“Bias Flow”)

The bypass circuit is an extra ‘short circuit’ between the inspiration and expiration channels. This stabilizes the working of the ventilator and makes the system more reliable.

Add an extra splitter to the inspiratory and expiratory channels of the ventilator, insert one-way valves in the correct directions, and connect inspiratory and expiratory channels directly with a short tube.

The bypass circuit is an optional component: a working setup can also be realized without adding a short circuit that directly connects inspiratory with expiratory channels. In that case one needs to make sure there is at least one patient circuit with a low resistance, meaning at least in one circuit the inspiratory flow is not (heavily) restricted by a flow restrictor or peep valve.  In a circuit without bypass circuit, the acceptable limits of flow restriction are dependent on the ventilator type and the flow restrictor used.

Example setup with a bypass circuit (shaded circuit) directly connecting inspiration to expiration. Picture by Steven Roy, MD.

The International Workgroup on Differential Multiventilation

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