Components of a mechanically delivered breath

Among the several modes of ventilation, there are several key features in how they determine when to deliver a mechanical breath (triggering) and how they deliver it (targeting and cycling).


  1. Time cycle
  2. Pressure-trigger
  3. Flow-trigger

Limit variable

Gas flow rate (i.e. volume control)

Pressure (i.e. pressure control/support)

Cycling target

  1. Volume of gas delivered
  2. Pressure
  3. Time
  4. Decrease in inspiratory flow


Passive expiration

Ventilator Basics 101

This excellent and practical tutorial is brought to by American Thoracic Society.

This scheme can be made even simpler. The TAG scheme or taxonomic attributes grouping helps break down every mode of ventilation into 3 attributes. See reference below for details.

Control variable



Breath sequence

Continuous mandatory ventilation

Intermittent mandatory ventilation

Continuous spontaneous ventilation

Targeting scheme

Set point(s): all targets set by operator

Dual (d) vent switches between PC and VC within a breath

Bio-variable (b) inspiratory pressures varies randomly

Servo (r) inspiratory pressure proportional to patient insp effort

Adaptive (a) vent adjusts pressures to meet Vt target

Optimal (o) adaptive target to minimize WOB

Inteliigent (i) uses tools of artificial intelligence

Below is an example of how this schema is broken down. The major benefit of this scheme is it is vendor agnostic!

The consequences of positive pressure ventilation


Mireles-Cabodevila E, Siuba MT, Chatburn RL. A Taxonomy for Patient-Ventilator Interactions and a Method to Read Ventilator Waveforms. Respiratory care. 2021;(July). doi:10.4187/respcare.09316