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Pressure-regulated volume control

Introduction to pressure regulated volume control mode for junior ICU trainees and nurses

Readers should have an understanding of basic mechanical ventilation before reading this page

  • form of assist-control ventilation. Breaths can be:
    • ventilator initiated (control breath)
    • patient initiated (assist breath)
  • constant pressure applied throughout inspiration (like pressure control), regardless of whether breath is a control breath or an assist breath
    • improved oxygenation due to decelerating inspiratory flow pattern (consequence of constant pressure)
  • ventilator adjusts pressure from breath to breath, as patient's airway resistance and respiratory system compliance changes, in order to deliver the set tidal volume
    • ventilator monitors each breath and compares the delivered tidal volume with the set tidal volume. If the delivered volume is too low it increases the inspiratory pressure on the next breath. If it is too high it decreases the pressure
    • the maximum allowed inspiratory pressure is 5 cm H2O below the upper pressure alarm limit
  • the duration of inspiration is determined by the respiratory rate and the I:E ratio or inspiratory time (ie this is a time-cycled mode of ventilation)
    • longer inspiratory time is associated with improved oxygenation and lower inspiratory pressure but a higher risk of gas trapping and development of intrinsic PEEP
  • not recommended for severe asthma or COPD

Settings

  • minimum respiratory rate
    • patient’s spontaneous respiratory rate < set rate ̃ ventilator gives additional control breaths to make up difference

    • patients spontaneous rate > set rate ̃ no control breaths

  • target tidal volume

    • initial setting: 8 ml/kg predicted body weight based on height

  • upper pressure limit

    • ventilator delivers pressure of up to 5 cm H2O below upper pressure alarm limit

    • set to 35-40 cm H2O to ensure "safe" pressures

    • do not exceed this setting without consulting an ICU specialist

  • inspired oxygen concentration

    • initial setting 100%

  • I:E ratio

    • initial setting: 1:2 (=inspiratory time of 33%)

    • consider longer inspiratory time if there is no intrinsic PEEP, no bronchospasm and oxygenation is poor

  • PEEP

    • initial setting 5-10 cm H2O

  • Rise time

    • 5% of inspiratory time usually satisfactory

Advantages

  • decelerating inspiratory flow pattern with automatic adjustment of the inspiratory pressure for changes in compliance and resistance resulting in a guaranteed tidal volume

    • decreased

    • decreased

 Disadvantages

  • pressure delivered is dependent on the tidal volume achieved on the last breath. If the patient intermittently makes a significant inspiratory effort this will result in very variable tidal volumes with both high and low volumes being delivered .

Download

Click here to download PRVC tutorial

 

©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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