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  #1  
Old 07-13-2011
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Drug Aspirin Toxicity; Acid Base disturbance

Which of the following is most likely to be found in Aspirin overdose:

a. pH 7.55 pCO2 50 HCO3 24
b. pH 7.25 pCO2 62 HCO3 38
c. pH 7.46 pCO2 22 HCO3 16
d. pH 7.35 pCO2 32 HCO3 20


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i think, b. pH 7.25 pCO2 62 HCO3 38
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Quote:
Originally Posted by dryogi View Post
i think, b. pH 7.25 pCO2 62 HCO3 38
We know Aspirin overdose will cause metabolic acidosis. However the body will compensate by hyperventilation (respiratory alkalosis) so one will expect the pCO2 to be low

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in this case, i think then the best answer could be given well..if we could also know the ingested toxic dose of aspirin .
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Quote:
Originally Posted by dryogi View Post
in this case, i think then the best answer could be given well..if we could also know the ingested toxic dose of aspirin .
unfortunately we don't have the ingested dose of Aspirin.

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Old 07-13-2011
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asprin overdose = hyperventilation = decrease co2 lvls this leads to an alkaline state(co2= acid) this is the initial effect of asprin , later there is a metabolic acidosis due to the increase lactic acid production what we have to look for is a low co2 combined with a acidosis ph value


d. pH 7.35 pCO2 32 HCO3 20
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Old 07-13-2011
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The correct answer is C. if you have Master the Board the last edition it is on page 536.
Myself i thought it is D. I don't get it why we have pH 7.46.

Anyone please help,

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i think aspirin overdose leads to respiratory alkalosis so c
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Quote:
Originally Posted by nano View Post
The correct answer is C. if you have Master the Board the last edition it is on page 536.
Myself i thought it is D. I don't get it why we have pH 7.46.

Anyone please help,

Thanks


Ok, there is a trick for this ABG

The first thing you should know is that aspirin toxicity manifests as a concomitant Respiratory alkalosis and Metabolic acidosis, the respiratory alkalosis is related to the aspirin toxicity itself because aspirin stimulates the respiratory center. Therefore the first thing you will see is Respiratory alkalosis as primary disorder associated with metabolic acidosis as you can see in the option C, where you have:

1. Alkalemia pH= 7.46
1. Respiratory alkalosis, with a VERY low PCO2 (22) which points to the primary defect.
2. Respiratory acidosis, with a low HCO3 (16)

Hope you find this useful!
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Old 07-13-2011
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I would have thought D too but I see why C sort of makes sense - Does it matter if the ASA ingestion is recent vs a few hours ago?
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Old 07-13-2011
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C-PH7.46 alkalosis first w/asa tox
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Every place i read about aspirin poisoning says the same thing initially there is a alkalosis due to hyperventilation but then due to the build up of lactic acid the alkalosis becomes a acidosis that was the reason why i chose D and now that u mentioned it remeber it from the book and remember even then i didnt agree with it fully but heres how i explained it to myself in 3 questions

for example pH 7.35 pCO2 32 HCO3 20
1) pH what is it? acidotic or alkalotic (acidotic)

2) Which value would make this acidosis/alkalosis pH? (since its acidosis the HCO3 is the culprit - making these values a metabolic acidosis)

3) whats the other value doing ie is it counteracting it or not this tells us is the initial problem being compensated or not , ( in this case he pCO2 is decreased and this will make him alkalotic ie its compensating the metabolic acidosis)


Now looking at the option C pH 7.46 pCO2 22 HCO3 16

1) Its an alkalosis
2) Causitive agent is the pCO2 ( ie metabolic alkalosis)
3) The HCO3 is making it acidotic thereby compensating the alkalosis

Now my understanding with Asprin is that it has seperate effects on 2 different centers ie its causing a hyperventilation ie alkalosis so yeah the HCO3 would decrease to counteract that BUT at the same time its building up Lactic Acid this would soon over come the alkalosis and make it into a acidotic state. Atleast thats how i understood it
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Also if any of u have done first aid do u remeber the acidosis / alkalosis chart



Remember MUDPILES S being salicylates??

so according to this ph less than 7.4 ie acidosis
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Old 07-14-2011
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The answer is C.
Here is the WHY from UpToDate
A variety of acid-base disturbances can occur with salicylate intoxication. Salicylates stimulate the respiratory center directly, resulting in an early fall in the PCO2 and respiratory alkalosis. An anion-gap metabolic acidosis then FOLLOWS, due primarily to the accumulation of organic acids, including lactic acid and ketoacids.
The net effect of these changes is that most adults have either a respiratory alkalosis or a mixed respiratory alkalosis-metabolic acidosis; pure metabolic acidosis is unusual in adults, but it may be seen in children who are brought to medical care soon after ingestion . Acute respiratory acidosis is rare in the early stages of aspirin toxicity, but it may be seen in later stages of profound poisoning. Respiratory acidosis that occurs early in the course of aspirin poisoning should suggest coingestion with a respiratory depressant. Approximately one-third of adults who self-poison ingest one or more other medications, many of which are respiratory depressants

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d. pH 7.35 pCO2 32 HCO3 20

the answer because normal ph appear in aspirin poisoning (resp alkalosis with metabolic acidosis ) with decrease hco3 and pco2 decrease

from my uw notes

but seems mtb say deffrent d. pH 7.35 pCO2 32 HCO3 20 is for sepsis and uremia dka

Last edited by USMLE-Syndrome; 07-14-2011 at 03:52 AM.
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The net effect is usually toward an alkalosis. See UpTodate above
Quote:
Originally Posted by miss patho View Post
d. pH 7.35 pCO2 32 HCO3 20

the answer because normal ph appear in aspirin poisoning (resp alkalosis with metabolic acidosis ) with decrease hco3 and pco2 decrease

from my uw notes

but seems mtb say deffrent d. pH 7.35 pCO2 32 HCO3 20 is for sepsis and uremia dka
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Old 07-15-2011
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Default Damn it to hell !!

Just did a question in uworld about aspirin toxicity i brought it down to 2 options

1)7.45 co2 = 30 hco3 = 20
2) 7.36 co2 =22 hco3 =12

now if i hadnt went thru this thread i would have chosen the 2nd one ie 7.36

BUT because of the conclusion i drew from that article ( that most aspirin poisioning show a alkalosis net effect) i chose the first 1 ie 7.45 ( even though according to my general calculations the hco3 should have been even lower to reflect the metabolic acidosis due to lactic acid accumulation )

on checking answers i again was wrong with it being #2 ie 7.36

why cant they make up their mind and give us a specific value ? i know its mixed but if ur going to ask questions u have to make it so that 1 answer is superior to another answer by a big difference , not somthing that is nitpicking small and that can be argued either way
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Old 07-15-2011
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Quote:
Originally Posted by docnas View Post
Just did a question in uworld about aspirin toxicity i brought it down to 2 options

1)7.45 co2 = 30 hco3 = 20
2) 7.36 co2 =22 hco3 =12

now if i hadnt went thru this thread i would have chosen the 2nd one ie 7.36

BUT because of the conclusion i drew from that article ( that most aspirin poisioning show a alkalosis net effect) i chose the first 1 ie 7.45 ( even though according to my general calculations the hco3 should have been even lower to reflect the metabolic acidosis due to lactic acid accumulation )

on checking answers i again was wrong with it being #2 ie 7.36

why cant they make up their mind and give us a specific value ? i know its mixed but if ur going to ask questions u have to make it so that 1 answer is superior to another answer by a big difference , not somthing that is nitpicking small and that can be argued either way

Hey, yeah I understand it is a little tricky but there is a reasoning for this one:

1)7.45 co2 = 30 hco3 = 20
2) 7.36 co2 =22 hco3 =12 <----------

pH tell you the amount of acid in the blood.
PCO2: Points towards a respiratory disorder
HCO3: Points towards a metabolic disorder.

As we were discussing earlier in this topic, Aspirin overdose stimulates the respiratory center inducing respiratory alkalosis, but also produces metabolic acidosis.

These questions are so tricky but you can figure out in many ways. In the first question you had we could figure out that the answer was option C because it had a slight alkalosis and a very low values of PCO2 and low values of HCO3, this is essential!

In the first option, you have a pH of 7.45 but, PCO3 and HCO3 are not too low.

Now if you compare both ABGs, the option C of the first question(pH 7.46 pCO2 22 HCO3 16
) and number 2 of this question (7.36 co2 =22 hco3 =12) you can see that a very low PCO2 is the key to recognize the primary disorder because the PCO2 is very low....
HCO3 will be low, in the latter case, is too low so it turned pH from a slighty alkalotic to a normal (7.36)

I have to admit that this sort of questions are very hard, indeed. But I hope you get the idea of what you have to look in an ABG, so you can use these ideas when you need them.

I hope you find this useful.
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Allright im giving up on getting a 100% understanding of the pH in asprin and just simply stick with the fact of severe resp alkalosis( thanks saddalsud for pointing out the severe part of that) and a high metablic acidosis and ta hell with the pH value.

EDIT - Just noticed another aspirin question in uworld values were 7.43, 25 and 16
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Quote:
Originally Posted by docnas View Post
Allright im giving up on getting a 100% understanding of the pH in asprin and just simply stick with the fact of severe resp alkalosis( thanks saddalsud for pointing out the severe part of that) and a high metablic acidosis and ta hell with the pH value.

EDIT - Just noticed another aspirin question in uworld values were 7.43, 25 and 16
You are welcome, by the way, in this new question you can see again that you have a very low PCO2, which is compatible with respiratory alkalosis and similar to the other questions we were reviewing.
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