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Respiratory Failure & Mechanical Ventilation

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Increase Resistance in VCV:

In volume-controlled ventilation, the tidal volume is fixed and any change in the resistance, flow, or compliance on one side of the equation of motion will lead to a change in the pressure on the other side. The increased resistance (red) will result in an increased pressure (green) while the volume is not changing (blue).

↑∆P= ↑R x F + ∆V/Cst

Bronchospasm, secretions in the airways, kinked ETT, or biting on the ETT will lead to increased airway resistance. The pressure scalar will show an increased airway pressure (Paw) and peak inspiratory pressure (PIP) without a change in the plateau pressure (Pplat). The difference between PIP and Pplat will be equivalent to the increased Paw.

The volume will be targeted to the same control level and no change will occur on the inspiratory flow wave. The expiratory phase will show the flow limitation due to increased resistance and increased time constant; and the flow may not return to the zero point before the next breath if the expiratory time is not long enough.

M. Ibrahim
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