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#1
04-28-2012
 USMLE Forums Master Steps History: --- Posts: 1,365 Threads: 648 Thanked 591 Times in 355 Posts Reputation: 601
Carbon Dioxide Production To Oxygen Uptake Ratio!

This is a question from USMLE World.

An 85-year-old male is placed on mechanical ventilation after a complicated elective hernia repair. After five days of endotracheal intubation with mechanical ventilation, the ratio of the rate of carbon dioxide produced to the rate of oxygen uptake is 1.05. What is the best explanation for these findings?
A. Sepsis
B. High-protein tube feeding
C. Carbohydrate excess in the diet
D. High inspired oxygen fraction
E. Pulmonary atelectasis

 The above post was thanked by: doc_study (04-28-2012)

#2
04-28-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 735 Threads: 89 Thanked 289 Times in 191 Posts Reputation: 301

I am between A and E....Since c and d could not cause above finings...sepsis causes metabolic acidosis and build up of lactic acid..so compensatory response should hyperventilate so co2 should decrease.

So i think E is the answer as diffusion is getting effected in atelectasis.
#3
04-28-2012
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 246 Threads: 18 Thanked 142 Times in 86 Posts Reputation: 152

ANS : c
RQ = co2 production/o2 consumption (per unit time) its like rate of waste production to energy consumption, it's used to assess metabolism in body.
this ratio depend on MAJOR FUEL being used (oxidized) for energy production.

RQ close to 1 --> carbohydrate as main fuel
RQ = 0.8 --> protein
RQ = 0.7 --> lipid

finally this all bla bla bla is used to assess readiness of the pt to be weaned from mechanical ventilation as over feeding --> excess co2 production makes weaning more challenging ??? (why; ?? idon't know)

No an explanation for that
 The above post was thanked by: Brainiac (05-29-2013), dryogi (04-28-2012), Novobiocin (04-28-2012), usmledee (04-28-2012)

#4
04-28-2012
 USMLE Forums Veteran Steps History: Step 1 Only Posts: 239 Threads: 3 Thanked 48 Times in 37 Posts Reputation: 58

Bisho, Thnx .. u have clear it very well.
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#5
04-28-2012
 USMLE Forums Master Steps History: --- Posts: 1,365 Threads: 648 Thanked 591 Times in 355 Posts Reputation: 601

Quote:
 Originally Posted by dryogi Bisho, Thnx .. u have clear it very well.
m still confused...help!
#6
04-28-2012
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 246 Threads: 18 Thanked 142 Times in 86 Posts Reputation: 152

i know it a very vague concept & i think its highly unlikely to be test on exam. but i will try to explain more.
we knew the fact that fat provide more energy than carbohydrate at the same amount ( i think 1g of fat --> 9 kcal, while 1g of carbo --> 4kcal)
-RQ of Carbo = 1 & RQ=co2 pro/o2 cons-
WHAT DO I THINK ''BUT DON'T KNOW IF CORRECT'' is if increasing carbo in diet this will lead to a ratio more than one.

when pt on mechanical ventilation if fed excessive carbohydrate --> this will lead to excessive production of co2 --> increase amount of minute ventilation required to reach equilibrium (remember the pt is mechanically ventilated & we are controlling his breath) --> much hard weaning bcuz of acid-base abnormalites which the pt will develop (cuz of accumulating co2)

Hope this make things better
 The above post was thanked by: geo82 (12-19-2012), Novobiocin (04-28-2012), step_enhancer (09-19-2012)
#7
04-28-2012
 USMLE Forums Scout Steps History: Not yet Posts: 45 Threads: 3 Thanked 29 Times in 22 Posts Reputation: 39

RQ can also be used to check if the patient is being fed adequately... cho being the main fuel and prot and fat indicating starvation...
 The above post was thanked by: tyagee (04-29-2012)
#8
04-29-2012
 USMLE Forums Master Steps History: --- Posts: 1,365 Threads: 648 Thanked 591 Times in 355 Posts Reputation: 601

Quote:
 Assessment of the RQ is important when attempting to wean patients from mechanical ventilation, as overfeeding, especially with carbohydrates, can cause excessive C02 production and make weaning more challenging.

uworld in explan mention above lines. i cant understand them.anyone? i dont have even slightest of the idea what they want us to understand
#9
04-29-2012
 USMLE Forums Scout Steps History: Not yet Posts: 45 Threads: 3 Thanked 29 Times in 22 Posts Reputation: 39

Quote:
 Originally Posted by tyagee uworld in explan mention above lines. i cant understand them.anyone? i dont have even slightest of the idea what they want us to understand
it means that if the patient is overfed (carbs in general) this ratio will go above 1... it shud be 1 ideally.... if more carbs are fed, more co2 is monitored... now if more co2 is monitored, thn the patient has to be kept on the respirator... even when his respiration becomes normal.

in short, u cannot assess if the patient is hypercarbic due to respi problem or overfeeding... so u may assess this situation falsely and still keep him on respirator even when he does not need it....

hope u get this...
 The above post was thanked by: geo82 (12-19-2012), tyagee (04-29-2012)
#10
09-19-2012
 USMLE Forums Newbie Steps History: Not yet Posts: 1 Threads: 0 Thanked 0 Times in 0 Posts Reputation: 10

The Oxygen should be maintained in perfect levels with out fail for the proper breathing and safe living of any one. The levels of oxygen should not either increase or decrease. It should be maintained perfectly, If the levels are in low ratio, then the Oxygen should be provided through a oxygen concentrator or with any other system or if it is higher in the ratio, then the sufficient corbondioxide should be supplied to make the condition of the patient safe. There are many systems introduced to fulfill the requirement.
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#11
09-19-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 851 Threads: 88 Thanked 710 Times in 380 Posts Reputation: 720

Quote:
 Originally Posted by elaxrawn The Oxygen should be maintained in perfect levels with out fail for the proper breathing and safe living of any one. The levels of oxygen should not either increase or decrease. It should be maintained perfectly, If the levels are in low ratio, then the Oxygen should be provided through a oxygen concentrator or with any other system or if it is higher in the ratio, then the sufficient corbondioxide should be supplied to make the condition of the patient safe. There are many systems introduced to fulfill the requirement.
WTF is this ..............
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#12
10-03-2012
 USMLE Forums Newbie Steps History: Not yet Posts: 1 Threads: 0 Thanked 0 Times in 0 Posts Reputation: 10

The Oxygen is the most required gas for any person, which out this, the life cannot be possible. The masks regarding the oxygen provision are very important and I would like to know about the details regarding these Masks. Could you please produce some attachments links regarding my requirement.
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#13
12-19-2012
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I came across this through one of my friends but not having complete idea regarding the task. Could any one please produce some more attachments regarding this. Thanks in advance.
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#14
05-29-2013
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I had gone through the site. It was very interesting. I would like to have complete details regarding this. Can any one please produce me the details in the name of a post. Thanks in advance.
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 Tags Physiology-, Respiratory-, Step-2-Questions

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