Deciphering the acronyms of noninvasive ventilation (NIV)

BPAP, CPAP, IPAP, EPAP, PEEP, PS? Feeling lost in all the acronyms? Check out our article to learn the essentials!
Last update27th Feb 2021

CPAP, BPAP, IPAP, EPAP, PEEP, PS...with all the acronyms, it’s easy to get lost in the terminology of mechanical ventilation. To help you find your way, let’s take a look at what these acronyms mean and how they relate to one another.

We’ve already covered continuous positive airway pressure (CPAP) and bilevel positive airway pressure (BPAP): CPAP delivers a single pressure during the respiratory cycle, and BPAP delivers two different pressures.

The others—IPAP (inspiratory positive airway pressure), EPAP (expiratory positive airway pressure), PEEP (positive end-expiratory pressure), and PS (pressure support)—are all variables on mechanical ventilators that need to be set by the user.

What is pressure support?

Pressure support (PS) is the variable that often causes initial confusion. It's the pressure that's added to PEEP—and only during inspiration. Keep in mind IPAP does not equal pressure support—IPAP is PEEP plus PS.

That said, there are generally two types of ventilator machines you need to watch out for:

  1. Those that require inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP) to be entered (i.e., initial IPAP / EPAP).
  2. Those—typically in intensive care settings—that require positive end-expiratory pressure (PEEP) and pressure support (PS) values to be set (i.e., initial PEEP / PS).

So let's take a look at how you'll set up CPAP and BPAP on these two types of machines.

CPAP ventilator settings

Remember with continuous positive airway pressure (CPAP) ventilation, constant pressure is delivered over time.

1. Initial IPAP / EPAP

In order to deliver the same pressure over time, IPAP and EPAP must be set to the same value.

Figure 1. To set up a CPAP ventilator where initial IPAP / EPAP settings are required, IPAP and EPAP are set to the same value in order to deliver the same pressure over time.

2. Initial PEEP / PS

To deliver CPAP when PEEP and PS are required, you want to set the PEEP to the amount of continuous pressure desired. Pressure support (PS) is set at zero—since you’re not adding any additional pressure during inspiration.

Figure 2. To set up a CPAP ventilator where initial PS / PEEP settings are required, PEEP is set to the amount of continuous pressure (during inspiration and expiration) desired, and PS is set at zero.

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BPAP ventilator settings

With BPAP two different pressures are delivered, one during inspiration and one during expiration.

1. Initial IPAP / EPAP

On ventilators that use IPAP and EPAP settings, you set IPAP to the inspiratory pressure you desire and EPAP to the expiratory pressure you desire.

Figure 3. To set up a BPAP ventilator where initial IPAP / EPAP settings are required, IPAP and EPAP are independently set to the desired values.

2. Initial PS / PEEP

Setting BPAP on ventilators that use PS and PEEP is different. The PEEP, in this case, is equal to the EPAP and is set at the desired expiratory pressure. The IPAP is equal to the sum of the PEEP plus PS. Therefore, to set the IPAP, you set the PS to a pressure that will be added to the PEEP.

Figure 4. To set up a BPAP ventilator where initial PS / PEEP settings are required, first, PEEP is set to the desired expiratory pressure (and equals EPAP). Then PS is set to a pressure to bring IPAP up to the desired level above PEEP (EPAP).

That’s it for now. If you want to improve your understanding of key concepts in medicine and improve your clinical skills, make sure to register for a free trial account, which will give you access to free videos and downloads. We’ll help you make the right decisions for yourself and your patients.

Recommended reading

  • Garpestad, E, Brennan, J, and Hill, NS. 2007. Noninvasive ventilation. Chest. 132: 711–720. PMID: 17699147
  • Hillberg, RE and Johnson, DC. 1997. Noninvasive ventilation. N Engl J Med. 337: 1746–1752. PMID: 9392701

About the author

Michael Allison, MD
Chief of Critical Care Medicine at the University of Maryland St. Joseph Medical Center, USA.
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