Volume Support or Assist-control Ventilation (VSV or ACV)

Created on Tue, 06/16/2015 - 18:05
Last updated on Tue, 06/16/2015 - 18:27

ACV: Assist Control Ventilation

  • Volume Controlled (but could be pressure controlled)
  • Flow-Triggered (but could be anything-triggered)

..typically, there is a backup mode, which is time triggered. In case the patient forgets to breathe.

  • Volume- limited, Flow-limited   (but doesn't have to be flow-limited)
  • Time-Cycled  ((but it can be volume-cycled if you don’t want inspiratory pauses)
The key feature is, EACH BREATH IS THE SAME.  The patient can decide on their own respiratory rate- but the tidal volume is controlled, and each breath is time-cycled or volume cycled.

The volume-controlled ACV gives you limited control over your minute volume. The patient may take as many breaths as he damn well please. With volume-controlled ACV you can control the tidal volume, at least. There is also Pressure-controlled ACV, which is discussed later, and for some reason called PCV (Pressure Controlled Ventilation).

This is slightly better for the partially sedated patient; however, it is still uncomfortable to have the same volume of air rigidly pushed into you.

The workload of breathing is not reduced greatly especially if the flow limit is low. The respiratory muscles continue to contract throughout much of the breath. This was confirmed by an 1986 study which discovered that in some cases patient work-per-litre-of-tidal-volume (WP) was greater with mechanical ventilation than with spontaneous breathing!

In short, its possible that what you are doing is not helpful.



Most of this information comes from only two textbooks. With "Basic Assessment and Support in Intensive Care" by Gomersall et al (as well as whatever I picked up during the BASIC course) as a foundation, I built using the humongous and canonical "Principles and Practice of Mechanical Ventilation" by Tobins et al – the 1442 page 2nd edition.

Marini JJ, Rodriguez M, Lamb V. The inspiratory workload of patient-initiated mechanical ventilation. Am Rev Respir Dis 1986; 134: 902–9.