What is continuous positive airway pressure (CPAP)?

Michael Allison, MD
7th Jan 2021

Continuous positive airway pressure (CPAP) is one of two cardinal modes of noninvasive ventilation (bilevel positive airway pressure, or BPAP, is the other).

As the name suggests, CPAP provides continuous pressure throughout the respiratory cycle.

Lungs with the same pressure on inspiration and expiration. Illustration.

Figure 1. Continuous positive airway pressure (CPAP)—one of two cardinal modes of noninvasive ventilation—provides continuous pressure throughout the respiratory cycle.

When a patient on CPAP breathes in, the ventilator machine will provide one constant pressure during the inspiration. When the patient then breathes out, the ventilator will continue that inward pressure during the entire expiration.

Graph with the same pressure on inspiration and expiration.

Figure 2. Continuous positive airway pressure (CPAP) is one of two cardinal modes of noninvasive ventilation. It provides one continuous pressure throughout the respiratory cycle—the pressure is set to the same level for inspiration and expiration.

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Ventilator settings for CPAP

The ventilator settings for CPAP are the following:

  • One single pressure, measured in cm of water (cmH2O)
  • The fraction of inhaled oxygen (FIO2), set between 21% and 100%

Graph with the same pressure on inspiration and expiration.

Figure 3. The ventilator settings for continuous positive airway pressure (CPAP) as visual memory aide: continuous pressure and fraction of inspired oxygen (FIO2) set at 21–100%.

 

Common clinical uses for CPAP

CPAP is commonly used for patients with the following respiratory disorders:

  • Acute pulmonary edema
  • Obstructive sleep apnea
  • Obesity hypoventilation syndrome (Pickwickian syndrome) 

Patients with acute pulmonary edema, obstructive sleep apnea, and obesity hypoventilation syndrome (Pickwickian syndrome). Cartoon.

Figure 4. Visual representation of the common clinical uses for continuous positive airway pressure (CPAP): acute pulmonary edema, obstructive sleep apnea, and obesity hypoventilation syndrome (Pickwickian syndrome).

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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