Medical questions & health advice by board certified doctors
"Can a patient with chronic bronchitis develop hypoxia without hypercapnia? If so, how?"
I am a Medicine student and I was asked this question on Pathophysiology class
It is possible to develop hypoxia without hypercapnia based on physiological principles. If you are having symptoms of shortness of breath, chronic cough or difficulty breathing, then I recommend that you see your doctor or a healthcare professional. Generally, offloading of carbon dioxide is contingent on minute ventilation; it is a function of air movement, and therefore can be augmented by tidal volume and respiratory rate. In contrast, oxygenation is contingent on two separate factors: FiO2 and peep. CO2 is rapidly diffused across alveolar surfaces, therefore the rate limiting step in CO2 removal is the rate at which it can be removed from the alveoli to support diffusion. In contrast, oxygen is diffusion limited, and is therefore dependent on the diffusion gradient as well as the surface area available for diffusion, hence the FiO2 and peep, respectively. Although less common, there are situations where a patient can offload CO2 but have poor oxygenation. One example is in the setting of poor diffusion states, where patients can actually be hypocapnic due to rapid breathing and increased minute ventilation but decreased oxygenation. Another example is in the setting of carbon monoxide poisoning, where patients develop methemoglobinemia, and lose the capacity to absorb oxygen due to the heme component of hemoglobin being occupied by carbon monoxide. Other possible situations include severe V/Q mismatch with poor alveolar ventilation or states with right to left shunting of blood. Again, please see your doctor or healthcare professional.
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