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Respiratory Failure & Mechanical Ventilation

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PRVC is based on the concept of adaptive control in which the ventilator automatically adjusts the pressure limit of a breath to meet an operator-set volume target over several breaths. PRVC is a control mode of ventilation with a dual control on the volume and pressure. All breaths are patient- or machine-triggered, volume-controlled with pressure regulation and time-cycled. The breaths delivered at preset tidal volume, minute volume and preset rate during preset inspiratory time. The ventilator automatically adjusts the inspiratory pressure control level to changes in the mechanical properties of the lung/thorax on a breath-by-breath basis. The pressure change is 2-3 cm H2O each time and the pressure dos does not exceed 5 cm H2O below the pressure alarm (limit) level set on the ventilator even if the targeted volume is not achieved, an alarm message is then displayed showing the target volume is not achieved.

The ventilator always uses the lowest possible pressure level to deliver the preset tidal and minute volumes. If an improvement in lung compliance occurred, the same pressure will deliver higher than the target volume, the pressure then will be gradually decreased 2-3 cm H2O each time to achieve the lowest level that assures delivery of target volume. The I:E ratio is controlled, and the inspiratory flow is decelerating (resembling a pressure-controlled breath).

The patient can initiate breaths depending on the sensitivity setting, so it is important to adjust trigger sensitivity appropriately. The patient triggered breaths are delivered using the same preset parameters as the ventilator-initiated breaths. This is a volume targeted (controlled) pressure-limited, time-cycled mode. The purpose of the PRVC mode is to deliver set tidal volumes at the minimum pressure level needed. Regular volume control ventilation has been a conventional mode of ventilation for decades. The main problem associated with regular volume control is the potentially excessive airway pressure that can lead to barotrauma, volutrauma, and adverse hemodynamic effects. Many of these problems can be minimized with PRVC

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