The alveolar ventilation controls CO 2 homeostasis according to the alveolar ventilation equation : Mathematically, V̇ A is total ventilation minus anatomical dead space ventilation. Its calculation requires exclusion of ventilation occurring in the anatomical dead space. in a passive mechanically ventilated patient on volume control (VC) mode, V̇ E = V T x RR.Īlveolar ventilation ( V̇ A the subscript ‘A’ denotes ‘alveolar’) is the amount of ventilation occurring in the alveoli in one minute. Minute ventilation ( V̇ E the subscript ‘E’ denotes ‘exhaled’) is the total ventilation in one minute (units: L/min). At this point, it is helpful to define minute ventilation and alveolar ventilation : V D /V T is a common way to quantify dead space. The fraction of the tidal volume that does not contribute to gas exchange is known as dead space fraction (V D /V T where V T = tidal volume and V D = dead space volume). A certain amount of dead space is normally present in every person (this is known as anatomical dead space: see below). This concept can be extended to include factors that cause a dead space effect. Uworld says this is v/q mismatch but that gets me confused cause why wouldn't a vent defect give v/q mismatch.Simply put, dead space represents the volume of ventilated air that does not participate in gas exchange. That's why you will see a drop in PaO2 in PE(minor). So this one is tougher but: Let's assume you have a well ventilated alveoli, when there is poor oxygen content, vasculature will constrict and redistribute this blood to other alveolar however it will overwhelm the capacity of extracting oxygen into blood - so adding oxygen will help. Dead space/physiologic dead space/V/Q mismatch to inifinty.I remember total pulm shunt as if pulm art partial pressure = pulm vein partial pressure, shunted, basically just bypassed lungs. These alveolar are already extracting maximum oxygen, adding more would not help. Lets assume this kid have some alveoli that are working. pulm shunting - ventilation defect V/Q 0, perfusion intact.So this is my understanding of the topic and I might be wrong so please correct me if thats the case:
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