Diagnosis of Acid Base Disturbance - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 2 CK Forum

USMLE Step 2 CK Forum USMLE Step 2 CK Discussion Forum: Let's talk about anything related to USMLE Step 2 CK exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 08-21-2012
tyagee's Avatar
USMLE Forums Master
 
Steps History: ---
Posts: 1,365
Threads: 648
Thanked 588 Times in 354 Posts
Reputation: 598
Question Diagnosis of Acid Base Disturbance

A 55-year-old woman is found in an alleyway by paramedics. She is obtunded, hypotensive and tachycardic. Her breath smells of alcohol.
Electrolytes
Sodium 135 meq/L (135 mmol/L)
Chloride 92 meq/L (92 mmol/L)
Potassium 3.8 meq/L (3.8 mmol/L)
Carbon dioxide 12 meq/L (12 mmol/L)
Blood gases
pH 7.08
PCO2 42 mm Hg (5.6 kPa)

Which of the following acid-base disorders is most likely present?

(A) Metabolic acidosis, metabolic alkalosis, and respiratory acidosis
(B) Metabolic acidosis and respiratory alkalosis
(C) Metabolic alkalosis and respiratory acidosis
(D) Respiratory acidosis and metabolic acidosis
(E) Simple metabolic acidosis

please give reason along
Reply With Quote Quick reply to this message



  #2  
Old 08-21-2012
dr_mhm's Avatar
USMLE Forums Guru
 
Steps History: 1+CK+CS
Posts: 460
Threads: 100
Thanked 235 Times in 147 Posts
Reputation: 245
Default

There must be a typo.... you say CO2 12 and then pCO2 42, I want to assume that the 12 is actually the HCO3, right? Then, it would be:

E. Metabolic acidosis.
ph low ---> acidemia
bicarb low --> metabolic (Co2 is actually normal so it's NOT respiratory)

On top of that, the anion gap is high: metabolic acidosis with elevated anion gap. Probably due to alcohol intoxic!
Reply With Quote Quick reply to this message
  #3  
Old 08-21-2012
Hitman's Avatar
USMLE Forums Master
 
Steps History: Not yet
Posts: 928
Threads: 17
Thanked 539 Times in 375 Posts
Reputation: 549
Default

yes its not Co2 its HCO3 = 12 and paco2 = 42

so patient has anion gap metabolic acidosis but she should be having resp compensation and paco2 should be less than 40 but it s above 40 showing resp acidosis so the ans is D = Resp acidosis + anion gap metabolic acidosis its a mixed disorder not simple metabolic acidosis ..........
Reply With Quote Quick reply to this message
 
  #4  
Old 08-21-2012
tyagee's Avatar
USMLE Forums Master
 
Steps History: ---
Posts: 1,365
Threads: 648
Thanked 588 Times in 354 Posts
Reputation: 598
Default

guys, ans is A. yes, A. and source is damn authentic. anyone, who knows why a?
Reply With Quote Quick reply to this message
  #5  
Old 08-21-2012
Hitman's Avatar
USMLE Forums Master
 
Steps History: Not yet
Posts: 928
Threads: 17
Thanked 539 Times in 375 Posts
Reputation: 549
Default

Quote:
Originally Posted by tyagee View Post
guys, ans is A. yes, A. and source is damn authentic. anyone, who knows why a?

metabolic alkalosis with acidosis ??

HCO3 is 12 right
Reply With Quote Quick reply to this message
  #6  
Old 08-21-2012
koolkiller88's Avatar
USMLE Forums Master
 
Steps History: Step 1 Only
Posts: 864
Threads: 62
Thanked 372 Times in 224 Posts
Reputation: 382
Default

Ya ph is 7.08 so, either it can be A or E. but don't know why it's A. Just posting to follow this question. Seems like a good concept.


Sent from my iPad using Tapatalk HD
__________________
One day i will infect these microbes and they will search for "Anti-MEbiotic"....
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message
  #7  
Old 08-21-2012
MedicalExaminer's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 824
Threads: 66
Thanked 463 Times in 298 Posts
Reputation: 473
Default

Increased anion gap metabolic acidosis without respiratory compensation (co2 is in normal range)

E
__________________
Everything is possible for him who believes (MARK 9:23)
245/247/passed on 1st attempt/223/2mos Obsie /3 US LORS/visa not needed/2008 grad
Reply With Quote Quick reply to this message
  #8  
Old 08-21-2012
Hitman's Avatar
USMLE Forums Master
 
Steps History: Not yet
Posts: 928
Threads: 17
Thanked 539 Times in 375 Posts
Reputation: 549
Default

Quote:
Originally Posted by MedicalExaminer View Post
Increased anion gap metabolic acidosis without respiratory compensation (co2 is in normal range)

E

well resp compensation is mostly there if not its a mixed disorder ...... plus its 42 indicates resp acidosis ...... so ans should be D or A

but dont know why A ....... would be interesting to see the explanation .....
Reply With Quote Quick reply to this message
  #9  
Old 08-21-2012
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 791
Threads: 76
Thanked 673 Times in 317 Posts
Reputation: 691
Default

I think the answer is D.......very low pH with low bicarbonate and high normal CO2 indicates mixed acidosis

tyagee...can u specify the source of this question....??????
Reply With Quote Quick reply to this message
  #10  
Old 08-22-2012
XpaezX's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,216
Threads: 41
Thanked 1,327 Times in 711 Posts
Reputation: 1342
Default

Its Anion Gap Metabolic acidosis because of the Alcohol and the pH (remember the mnemonic MUDPILES)
Its respiratory acidosis because the PCO2 if normal and it should be low because of compensation (remember respiratory compensation is immediate)

What I dont get is why is it metabolic alkalosis.... I already tried calculations and all that, maybe if they have said the patient was full of vomit then yeah.. I would think on that... or maybe because of the chloride but now im just guessing...

This is what I found as the possible reason.

When to suspect a mixed acid base disorder:
  1. The expected compensatory response does not occur
  2. Compensatory response occurs, but level of compensation is inadequate or too extreme
  3. Whenever the PCO2 and [HCO3-] becomes abnormal in the opposite direction. (i.e. one is elevated while the other is reduced). In simple acid base disorders, the direction of the compensatory response is always the same as the direction of the initial abnormal change.
  4. pH is normal but PCO2 or HCO3- is abnormal
  5. In anion gap metabolic acidosis, if the change in bicarbonate level is not proportional to the change of the anion gap. More specifically, if the delta ratio is greater than 2 or less than 1.
  6. In simple acid base disorders, the compensatory response should never return the pH to normal. If that happens, suspect a mixed disorder.

  1. Anion Gap Acidosis and Metabolic Alkalosis
    This mixed acid base disorder is identified in patients with a delta ratio greater than 1, which signifies a reduction in bicarbonate less than it should be, relative to the change in the anion gap. This suggests the presence of another process functioning to increase the bicarbonate level without affecting the anion gap, i.e. metabolic alkalosis.
    Examples:
    • Lactic acidosis, uremia, or DKA in a patient who is actively vomiting or who requires nasogastric suction.
    • Patient with lactic acidosis or DKA given sodium bicarbonate therapy
From the University of Connecticut webpage

Last edited by XpaezX; 08-22-2012 at 08:35 AM. Reason: :)
Reply With Quote Quick reply to this message
The above post was thanked by:
heartbeat (08-24-2012), Hitman (08-22-2012), koolkiller88 (08-23-2012), MedicalExaminer (08-22-2012), venky2600 (08-23-2012)
  #11  
Old 08-22-2012
Hitman's Avatar
USMLE Forums Master
 
Steps History: Not yet
Posts: 928
Threads: 17
Thanked 539 Times in 375 Posts
Reputation: 549
Default

Quote:
Originally Posted by XpaezX View Post
Its Anion Gap Metabolic acidosis because of the Alcohol and the pH (remember the mnemonic MUDPILES)
Its respiratory acidosis because the PCO2 if normal and it should be low because of compensation (remember respiratory compensation is immediate)

What I dont get is why is it metabolic alkalosis.... I already tried calculations and all that, maybe if they have said the patient was full of vomit then yeah.. I would think on that... or maybe because of the chloride but now im just guessing...

This is what I found as the possible reason.

When to suspect a mixed acid base disorder:
  1. The expected compensatory response does not occur
  2. Compensatory response occurs, but level of compensation is inadequate or too extreme
  3. Whenever the PCO2 and [HCO3-] becomes abnormal in the opposite direction. (i.e. one is elevated while the other is reduced). In simple acid base disorders, the direction of the compensatory response is always the same as the direction of the initial abnormal change.
  4. pH is normal but PCO2 or HCO3- is abnormal
  5. In anion gap metabolic acidosis, if the change in bicarbonate level is not proportional to the change of the anion gap. More specifically, if the delta ratio is greater than 2 or less than 1.
  6. In simple acid base disorders, the compensatory response should never return the pH to normal. If that happens, suspect a mixed disorder.

  1. Anion Gap Acidosis and Metabolic Alkalosis
    This mixed acid base disorder is identified in patients with a delta ratio greater than 1, which signifies a reduction in bicarbonate less than it should be, relative to the change in the anion gap. This suggests the presence of another process functioning to increase the bicarbonate level without affecting the anion gap, i.e. metabolic alkalosis.
    Examples:
    • Lactic acidosis, uremia, or DKA in a patient who is actively vomiting or who requires nasogastric suction.
    • Patient with lactic acidosis or DKA given sodium bicarbonate therapy
From the University of Connecticut webpage

great post buddy , thanks never new about the delta ratio

but still the ratio is less than 1 ..... meets the mixed acid base criteria but still metabolic alkalosis not fitting in ........

Tyagee pl post the explanation and where is the qs from ???
Reply With Quote Quick reply to this message
  #12  
Old 08-23-2012
tyagee's Avatar
USMLE Forums Master
 
Steps History: ---
Posts: 1,365
Threads: 648
Thanked 588 Times in 354 Posts
Reputation: 598
Default

Quote:
Originally Posted by Hitman View Post
great post buddy , thanks never new about the delta ratio

but still the ratio is less than 1 ..... meets the mixed acid base criteria but still metabolic alkalosis not fitting in ........

Tyagee pl post the explanation and where is the qs from ???
The most likely acid-base disorder is metabolic acidosis, metabolic alkalosis, and respiratory
acidosis. The low pH defines acidosis; the finding of a low carbon dioxide level further defines
the acidosis as metabolic acidosis. The increased anion gap categorizes the metabolic acidosis
as an increased anion-gap acidosis. The PCO2 measurement determines if respiratory
compensation is appropriate for the degree of metabolic acidosis. The adequacy of respiratory
compensation can be checked using Winter formula:
Expected PCO2 = (1.5 [HCO3
-] + 8) 2 = 24 2
This formula confirms the measured PCO2 is elevated for the degree of metabolic acidosis,
establishing the diagnosis of respiratory acidosis. Finally, the corrected carbon dioxide level is
calculated to determine if a complicating metabolic disturbance is present:
Corrected [HCO3
-] = measured [HCO3
-] + (measured anion gap - 12)
Using this formula, the corrected carbon dioxide level (the expected carbon dioxide
concentration if no other acid-base disturbances were present) is 31 meq/L (31 mmol/L),
establishing the diagnosis of a complicating metabolic alkalosis.

***
can any 1 make something out of it. i cant get still why ans includes metabolic alk
Reply With Quote Quick reply to this message
  #13  
Old 08-23-2012
USMLE Forums Scout
 
Steps History: 1+CK+CS+3
Posts: 16
Threads: 2
Thanked 8 Times in 8 Posts
Reputation: 18
Default

i think your meaured bicarb(the expected one) is not correct it should be...(measured anion gap-normal anion gap)-measured bicarb..therefore the expected bicar is (31-12)-12=7...which more less than the measured one..so it should be a concurrent metabolic alkalosis that causes an increase in bicarb...
also you can use the delta ratio to come up with the same conclusion..
delta ratio=delta AG/delta bicarb=31-12/24-12=19/12=1.6>>1 so there a concomittente metabolic alkalosis.....
check out this video for more explaination..check the end of this video..there is a discussion about the case.....

Reply With Quote Quick reply to this message
The above post was thanked by:
eriqaly (11-11-2015)



Reply

Tags
Acid-Base-, Step-2-Questions, Videos-Animations

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
The cause of Acid Base Disturbance? mosallam USMLE Step 2 CK Forum 15 09-11-2014 08:54 PM
Metabolic alkalosis & Acid-base disturbance heights USMLE Step 1 Bits & Pieces 2 04-15-2014 02:59 AM
Try this Easy Acid-Base Disturbance problem II Dr.NickRiviera USMLE Step 1 Forum 2 04-28-2012 09:18 AM
Try this easy Acid-Base Disturbance problem. Dr.NickRiviera USMLE Step 1 Forum 4 04-28-2012 08:56 AM
Aspirin Toxicity; Acid Base disturbance nano USMLE Step 2 CK Forum 19 07-15-2011 07:49 PM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)