i. Pressure vs. Volume
Pressure advantages
The PIP is lower than on VC mode for the same Vt. The distribution of gas may be
more even in a lung with heterogeneous mechanics (better gas exchange?). It is a
useful mode in air leaks situations because the airway pressure will be maintain
throughout inspiratory cycle. It is more comfortable for the patient (better patient-
ventilator synchrony).
Pressure disadvantages
Changes in compliance will result in changes on minute volume ventilation.
Volume advantages
Clinician could have complete control of minute volume ventilation. Also because of
the “fixed” Vt there is less chance of VALI.
Volume disadvantages.
Because of the constant flow, it could be uncomfortable and therefore there is
higher chance of patient-ventilator asynchrony. PIPs will be higher than in PC for
the same Vt.
- Cycle:
Pressure control: Time cycled – the expiration begins after preset inspiratory time
(Ti) or according to preset I:E
Volume control: Volume cycled – expiration begins after certain Vt was delivered
PRVC (see below): Time cycled - the expiration begins after preset Ti
Pressure and volume support: Breath is flow (usually) cycled, when flow drops
inspiration terminates and expiration starts