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4 Cards in this Set
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- Back
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How do you know whether something is respiratory or metabolic?
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Step 1: Is the pH acid or basic?
Step 2: Look at the directions that the PaCO2 and the HCO3 are pointing. They should be pointing in the same direction if the problem isn't a mixed disturbance. Example: If you have an acidosis and both the PaCO2 and the HCO3 are elevated, then it MUST be the PaCO2 that is driving the acidosis, this is a RESPIRATORY ACIDOSIS. If you have an acidosis and the PaCO2 and the HCO3 are both decreased, then the acidosis MUST be due to the decrease in bicarb (a low PaCO2 would not make you acidotic) |
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What is the relationship between PaCO2 and HCO3 in the setting of a non-mixed acid-base disturbance?
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Here's the basic equation (basically a shortened Henderson- Hasselbhach formula)
H+ = 24 * (LUNGS/KIDNEYS) H+ = 24 * (PaCO2/HCO3) So, in order to keep the pH of your blood constant (your body really wants to do this) you need to keep the RATIO of PaCO2 to HCO3 the same. Thus, if PaCO2 falls, HCO3 also has to fall to maintain the ratio. If HCO3 rises, PaCO2 must also rise. |
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A person with a history of athsma is sitting upright, is diaphoretic, and has tachypnea, stulted speach. What are you thinking about? What are going to be the stages of his disease?
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Patient might have athsma.
Ex: pH = 7.41/ PaCO2 = 25/PaO2 = 35/HCO3 = 15 1) pH acid or base? Base so is alkalosis. 2) Which way is PaCO2 and HCO3 pointing? Both are low, so this has to be a RESPIRATORY alkalosis (low HCO3 would not give you an alkalosis). In asthmatics, pts often hyperventilate until their muscles get tired --> then their pH starts to normalize BUT there is STILL an elevated A-a gradient --> eventually this patient will become ACIDOTIC with an elevated A-a gradient. |
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What is a quick way to calculate the A-a gradient?
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The A-a gradient is
[((Patm - PH2O) * FiO2) - (PaCO2/R)] - PaO2 Usually on room air (Patm - PH2O) * FiO2 = 150, so 150 - (PaCO2/0.8) is the simplified version. Note that (PaCO2/0.8) is the same as (1.25 * PaCO2), so an easy way to do this calculation is to do this: Ex: PaCO2 = 40 40/2 = 20 20/2 = 10 (this is 0.25 of 40) Add 10 to 40 = 50 1.25 * 40 = 50 150 - 50 = 100 100 - PaO2 gives you your A-a gradient |
