Volume vs Pressure controlled ventilation (VCV vs PCV)






Volume controlled ventilation (VCV)

The constant variable is tidal volume. Peak inspiratory pressure is variable.
Peak inspiratory pressure varies with compliance and resistance.
Flow pattern is set by clinician. Wave form will impact pressures
Breathes delivered at clinician set parameters:  tidal volume, flow rate and pattern and set RR. Machine initiated breathes or patient initiated breathes are all delivered at these parameters.
Volume delivery is constant, inspiratory pressure varies, inspiratory flow is constant, inspiratory time determined by set flow and rate.
Advantages of volume ventilation. Delivers constant tidal volume, this ensures a consistent level of alveolar ventilation.

Disadvantages of volume ventilation:
Peak pressures may change rapidly and harmfully with changes in pip.
Flow pattern and flow rate are fixed and may not meet patients demands.




Pressure controlled ventilation (PCV)

Peak inspiratory pressure is the constant variable. Tidal volume is the variable.
Peak inspiratory pressure is the constant variable, tidal volume varies with impedance.
Flow pattern is determined by demand( the patient). Pressure and resistance and compliance will have an affect on flow. Flow rate decreases as inspiratory time increases.
Flow varies according to patient demand, clinician sets I time or I:E ratio and RR. Tidal volume varies with changes in compliance and resistance. Flow delivery is decelerating.
Volume delivery varies, inspiratory pressure in constant, inspiratory flow varies, inspiratory time set by clinician.
Pressure ventilation advantages
Pip and peak pressures are maintained at a constant level.
Flow varies with patient demand.
Disadvantages with pressure ventilation:
Tidal volume changes with patient compliance and resistance and increases the chance of harmful alteration of blood gases.






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