Chapter 6 | Spontaneous Modes and SIMV

We have now overviewed control modes of ventilation and talked about when and how to control a patient’s breathing. Remember in Chapter 3 when we talked about the differences between Control and Spontaneous Modes? We discussed how spontaneous modes allow a patient to be much more in control of their breathing, including how often they breathe and how big a breath they take. In this chapter, we will look more closely at spontaneous modes.

This chapter covers:

  • Spontaneous modes: Overview and description of pressure support ventilation (PSV)
  • When we use PSV
  • PSV settings
  • How we choose the correct settings when initiating PSV
  • What is SIMV, and why it is not a preferred mode


As you have already learned, spontaneous modes are used whenever a patient has an intact drive to breathe because spontaneous ventilation helps to avoid muscle wastage and asynchrony. This chapter will help you to use spontaneous mode effectively, including choosing appropriate ventilator settings. In addition, this chapter describes Synchronized Intermittent Mandatory Ventilation (SIMV), which was once the preferred approach to ventilation, and explains why it should not be used in typical ventilation practice today. Since SIMV is still used by some out-of-date practitioners and healthcare centers, it is important that you are aware of this mode and the reasons that it is no longer used so that you are well positioned to advocate for your patients.

Learning Objectives

At the end of this chapter, you will be able to:

  1. Identify when to use PSV.
  2. Describe typical settings for PSV.
  3. Determine appropriate PSV settings based on assessment of a patient.
  4. Explain why SIMV should not be used as routine practice, in order to advocate effectively for your patient.

Key Terms

  • muscle atrophy
  • weaning
  • Pressure Support Ventilation (PSV)
  • Volume Support Ventilation (VSV)
  • Spontaneous Breathing Trial (SBT)
  • minimal settings
  • extubation
  • Work of Breathing (WOB)
  • Arterial Blood Gas (ABG)
  • Endotracheal Tube (ETT)
  • Synchronized Intermittent Mandatory Ventilation (SIMV)
  • minute volume

Whenever these terms are first introduced in this chapter, they are bolded. However, if you need additional information about a term than what is provided here, you can research it in The Free Dictionary: Medical Dictionary.


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