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Help with administration of 02 & CODP

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Hi Guys i'm a student Paramedic and having difficulty answering the following question if anyone can help please?


Assume an averaged sized adult patient is breathing oxygen from a non-re-breathing mask is receiving approximately 90% O2.


4.1 What would be the approximate partial pressure of alveolar oxygen be at sea level (760 mmHg)?


This patient begins hypoventilating while receiving 90% O2. Assume that the patient’s tidal volume (Vt) has now decreased to half.


4.2 What is the approximate Vt for this patient at half the normal value?


Assume this patient’s initial SPO2 increased from 83% to 98% following supplemental oxygen therapy.


4.3 Would you expect the patient’s SPO2 to decrease with half the normal VT?

Please explain your answer:


This patient becomes drowsy and begins to lose consciousness although all other observations remain normal.


4.4 What is the most likely cause?

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for the partial pressure question just multiply the percent of the gas (i.e. O2 is 21% so 0.21) by the atmospheric pressure 760mmHg (0.21 x 760mmHg) that gives you the partial pressure in mmHg. Adult tidal volume is around 6L I believe (don't quote me on that) so half of that is about 3L. I don't think their spO2 would decrease, the problem is that your suppressing their respiratory drive by giving high flow O2. This is pretty straight forward, most paramedic schools drive this one home so you should know it. I would highly suggest googling HYPOXIC DRIVE as that is the topic of this question.

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