When atelectasis occurs in acute respiratory distress syndrome (ARDS) patients, it can be difficult to figure out how to resolve the refractory hypoxemia that results. In this video from our Mechanical Ventilation Essentials course, you'll learn about the relationship between oxygenation status and ARDS severity and why supplemental oxygen won't help ARDS patients.
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[00:00:00] Some of the patients you will encounter may develop acute respiratory distress syndrome, also known as ARDS. In ARDS, the affected part of the lung is not the airways, rather, the affected part of the lung is at the alveolar level. ARDS is caused by leaking of fluids into the tiny alveolar sacs of the lungs. So, for example, here is one magnified alveolus. And normally, oxygen that is inhaled into the alveolus
[00:00:30] is supposed to diffuse into the blood, so that the blood can deliver the oxygen to the body. But in ARDS fluids fill the air sac. The integrity of some of the alveoli will be compromised, often leading to alveolar collapse or atelectasis. And this will ultimately compromise gas exchange. So, as a result of the few alveolar collapse, the lung will appear to shrink on a chest x-ray film. Collapsed alveoli may also result in refractory
[00:01:00] hypoxemia. Refractory hypoxemia is hypoxemia that does not correct with the administration of supplemental oxygen. In other words, you can try to administer high levels of FiO2 but because the alveolus is collapsed and compromised, oxygen concentration alone will not correct the hypoxemia. Correcting refractory hypoxemia will require a recruitment of the alveolus, which is a reopening or a
[00:01:30] restabilizing of the collapsed alveolus. The oxygenation status of the patient is also one of the ways in which we classify the severity of ARDS. So, to determine the oxygenation status, the clinician should perform the P / F ratio, which is simply the PaO2 divided by the FiO2 of the patient. Here, you can see the classification of the severity of ARDS as well as the mortality risk. So,
[00:02:00] improving oxygenation will be one of the challenges in treating ARDS. But how can we get oxygen in if patients with ARDS have a difficult time getting volume into their lungs, due to the fact that the alveoli are collapsed? Reopening collapsed alveoli will require an immense amount of patient effort. Additionally, the lung will tend to recoil upon inhalation. In other words, even if the patient does inhale volume, the lung will
[00:02:30] immediately want to recoil at exhale. This ultimately leads to shallow and rapid breathing. So, that begs the question, what are some strategies in modifying our ventilator settings in treating patients with ARDS? And the answer to this question is coming up in the next lessons. So, stay tuned.