Understanding Hypercapnia and Respiratory Drives

Educational Pearls:

• Physiologic stimulation of ventilation occurs through changes in levels of:

• Arterial carbon dioxide (PaCO2)

• Arterial oxygen (PaO2)

• Hypercapnia is an elevated level of CO2 in the blood - this primarily drives ventilation

• Hypoxia is a decreased level of O2 in the body's tissues - the backup drive for ventilation

• Patients at risk of hypercapnia should maintain an O2 saturation between 88-92%

• Normal O2 saturation is 95-100%

• In patients who chronically retain CO2, their main drive for ventilation becomes hypoxia

• An audit was performed of SpO2 observations of all patients with a target range of 88–92% at a single hospital over a four-year period

• This found that excessive oxygen administration was more common than insufficient oxygen and is associated with an increased risk of harm

• Individuals at risk of hypercapnia include but are not limited to patients with COPD, hypoventilation syndrome, or altered mental status

References

1. Homayoun Kazemi, Douglas C. Johnson, Respiration, Editor(s): V.S. Ramachandran, Encyclopedia of the Human Brain, Academic Press, 2002, Pages 209-216, ISBN 9780122272103, https://doi.org/10.1016/B0-12-227210-2/00302-2.

2. O'Driscoll BR, Bakerly ND. Are we giving too much oxygen to patients at risk of hypercapnia? Real world data from a large teaching hospital. Respir Med. 2025 Mar;238:107965. doi: 10.1016/j.rmed.2025.107965. Epub 2025 Jan 30. PMID: 39892771.

Summarized by Meg Joyce, MS1 | Edited by Meg Joyce & Jorge Chalit, OMS3

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