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CO2 Retention In the normal individual, central chemoreceptors (in the brainstem) are controlled by the blood pH (affected by amount of PaCO2). The peripheral chemoreceptors (in the carotid and aortic bodies) are controlled by the amount of PaO2 in the blood. In patients with chronic lung disease ("CO2 retainers"), the central chemoreceptors are inactivated due to the chronically high PaCO2. In this case, the peripheral chemoreceptors take over, which means PaO2 of the blood is in control of how fast and deep the patient breathes. It's important to remember that the peripheral chemoreceptors are only stimulated when the PaO2 is low. Chronic lung disease patients also have chronically low PaO2 ... that the peripheral chemoreceptors have gotten used to. Adding too much supplemental oxygen can fool the body of the chronic lung disease patient ("CO2 retainer") into believing that the patient no longer needs to breathe because he or she has "enough" oxygen in the blood. This brings on apnea, with possible respiratory failure requiring mechanical ventilation. Degrees of Hypoxia:
Credit: Shawna Strickland, MEd, RRT-NPS, AE-C |
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