An unconscious patient is brought into the emergency room. An arterial blood gas (ABG) shows the following results: pH 7.2, pC02 80 mmHg, p02 70 mmHg. Assuming this patient is at sea level and has a respiratory quotient of 1.0, which of the following statements is most consistent with these data?
A) The acid-base disturbance has been present for at least 3 days
B) The patient has been hyperventilating as a result of his acidosis
C) The patient has a metabolic acidosis
D) The patient has ventilation-perfusion mismatch
E) The patient is hypoventilating secondary to a drug overdose
Why cann't it be A ? pH is not that far away from Normal and can be a partially compensated Respiratory Acidosis.
I mean for someone to hypoventilate in RESPONSE to a drug OD means the drug has to be causing metabolic alkalosis which means the pH has to be in the alklotic range in that case which is not the case here. The reason would be the person took a Barbiturate or somthing like that which depresses respiration and is hypoventilating because of that....You can make case for A or C...Bicarb concentration would have been helpful.
Why E then and why not A ?
A....
Okay this might not the best way to go about it but I think it might be A
pH = pKa + log ([HC03-]/[0.0301*pCO2]) <--- This is from Kaplan Physio Page 360
pH = 7.2 (Given)
pKa = 6.10 (Constant for C02 and bicarb system)
pCO2 = 80 (Given)
Do the antilog and solve for HCO3- and you get a HCO3 concentration of 30.21 ... Like I said this should be given and not having to caculate !!!
This means this is a partially compensated Respiratory Acidosis ... ie been there for a while ... 3 days enough time for renal compensation !!
what about assuming this patient is at sea level and has a respiratory quotient of 1.0,
has to be E.
becoz.....clearly acidotic and the pco2 is double what it shud be and I remember in Kap physio it states that the relationship of CO2 is inversely prop to vent rate...so if vent rate must be halved thats why the pco2 is doubled....
also with compensation the pco2 would be much closer to normal...pco2 of 80 is NOWHERE compensated!!!!
resp quotient just tells u there is NO V/Q mismatch....
who says pCO2 has to be compensated ...
its the pH that has to be compensated.....look at the figure in Kaplan Physio page 361 ... look at point B ... see what it says "Partiall compensated respiratory acidosis and pCO2 is 80
pCO2 can be what ever it likes as long as the pH is CLOSE to normal ... thats all compensation looks at !!