6.4 Types of Spontaneous Modes

Just like control modes, there are several spontaneous modes available on the market, but unlike control modes, one has gained more popularity over other, and it is mainly used in current practice. Pressure Support Ventilation (PSV) is by far the most common support mode utilized in critical care. Volume Support Ventilation (VSV) does exist, but it is not often used—most likely due to physiologic variability in volumes being a cornerstone of spontaneous breathing. We will focus on Pressure Support Ventilation as the main spontaneous mode.

We already discussed modes such as Synchronized Intermittent Mandatory Ventilation (SIMV), and Adaptive Support Ventilation, considered “mixed” modes—control and spontaneous.

Another spontaneous mode that is up-and-coming in the respiratory world is Proportional Assist Ventilation (PAV). PAV is still a relatively “new” mode, but a lot of ongoing research is increasing its use in the critical care world. PAV utilizes unique breath-initiation and breath-delivery software that has promising implications for how patients breathe on a ventilator.
A clinician completed paperwork in the ICU, with ventilated patients in the background.
The COVID-19 pandemic saw a massive increase in ventilated patients, with make-shift ICUs and new clinicians recruited to meet the need. Photo by Mohsen Atayi via Wikimedia Commons, CC-BY 4.0

Pressure Support Ventilation (PSV)

In PSV, every time a patient initiates a breath, the ventilator will push air to reach a set pressure into the patient’s lungs while they spontaneously inhale. The patient plays the only role in deciding how often to breathe and can also vary their volumes based on what they need—for example, if they want to take a long and large breath, they can do this at any point. They can also breathe at a more rapid pace with smaller breaths if desired. The only fixed setting that will not change is the amount of support given to them by the ventilator. They cannot get more than the set “help pressure” unless the clinician comes and changes it.

PSV Basic Settings:

  • Pressure Support (PS)
  • PEEP (every ventilator, every time)
  • FiO2 (every ventilator, every time)

What is NOT set:

  • [latex]RR[/latex] (patients must trigger all breaths)
  • Flow or I-time (patients can take air in at whatever speed they want and end the breath when they want to. The vent will sense when inspiration and expiration start)

FiO2 and PEEP are set on every ventilator—it is no different in spontaneous modes. In addition, in PSV, the amount of pressure support (PS) is the singular central setting that a clinician must set. The pressure support should be set at an amount that will allow the patient’s work of breathing to remain within normal limits. If they are getting worse, then they are “failing” and may need more support or a change back to a control mode of ventilation.

During pressure support ventilation, each breath will be patient triggered, pressure limited and flow cycled. When we observe the waveforms in pressure support ventilation, notice some similarities with pressure control ventilation. The difference is that every breath in pressure support is patient triggered and the cycle variable is flow, as opposed to time as in pressure control.

A Pressure Support Ventilation Diagram is shown with diagrams for pressure, flow, and volume.
Figure 6.4.1: “Pressure Support Ventilation Diagram” by Freddy Vale, CC BY-NC-SA 4.0

Key Takeaway

Any time you connect a patient to a ventilator, you always set FiO2 and PEEP. In a spontaneous mode, the patient is in control of how often they breathe, therefore no [latex]RR[/latex] is set. In PSV, you set a “helping” pressure that is delivered with every patient-triggered breath. A volume is not set: the patient pulls whatever volume they want/can based on their strength and pathophysiology. Under-support can cause high respiratory rates and small volumes. Over-support can cause low respiratory rates and high volumes.
Watch this short video for summary of features and graphics Pressure Support Ventilation.

 

Video: “Pressure Support Ventilation Curves” By The Critical Care Practitioner [2:30] Transcript Available

“Types of Spontaneous Modes” from Basic Principles of Mechanical Ventilation by Melody Bishop, © Sault College is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

License

Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Breathe Easy: RT Student Resource for Mechanical Ventilation Copyright © 2023 by Fanshawe College is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

Share This Book