Respi physiology: O2-Hb question - 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 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 04-25-2014
USMLE Forums Scout
 
Steps History: Not yet
Posts: 14
Threads: 5
Thanked 0 Times in 0 Posts
Reputation: 10
Post Respi physiology: O2-Hb question

What is the rate of O2 transported to peripheral tissues in a healthy 70-kg patient with Hb conc. of 10mg/dL, PaO2 of 60mmHg , SaO2 of 90% & cardiac output of 5L/min?

My understanding of this question is that I should be using Fick's principle, but I am not sure how to come up with the arterial and mixed venous O2 concentrations.

Much thanks if someone can explain!
Reply With Quote Quick reply to this message



  #2  
Old 04-25-2014
USMLE Forums Scout
 
Steps History: Not yet
Posts: 29
Threads: 13
Thanked 2 Times in 2 Posts
Reputation: 12
Default

Quote:
Originally Posted by philsexy876 View Post
What is the rate of O2 transported to peripheral tissues in a healthy 70-kg patient with Hb conc. of 10mg/dL, PaO2 of 60mmHg , SaO2 of 90% & cardiac output of 5L/min?

My understanding of this question is that I should be using Fick's principle, but I am not sure how to come up with the arterial and mixed venous O2 concentrations.

Much thanks if someone can explain!
haha..phil..dude I dont know what's PaO2 & SaO2 ?
Please if you can tell me.
Reply With Quote Quick reply to this message
  #3  
Old 04-26-2014
USMLE Forums Scout
 
Steps History: Not yet
Posts: 14
Threads: 5
Thanked 0 Times in 0 Posts
Reputation: 10
Default

Quote:
Originally Posted by ANUBHAV View Post
haha..phil..dude I dont know what's PaO2 & SaO2 ?
Please if you can tell me.
Haha sorry.. PaO2: Partial pressure of O2 & SaO2 is Oxygen saturation
Reply With Quote Quick reply to this message
  #4  
Old 04-26-2014
USMLE Forums Addict
 
Steps History: 1+CK+CS+3
Posts: 135
Threads: 21
Thanked 74 Times in 26 Posts
Reputation: 84
Default

Quote:
Originally Posted by philsexy876 View Post
What is the rate of O2 transported to peripheral tissues in a healthy 70-kg patient with Hb conc. of 10mg/dL, PaO2 of 60mmHg , SaO2 of 90% & cardiac output of 5L/min?

My understanding of this question is that I should be using Fick's principle, but I am not sure how to come up with the arterial and mixed venous O2 concentrations.

Much thanks if someone can explain!

where did you find this question

anyway the question asks what is the oxygen delivery to tissues in particular patient. This can be calculated by CO x O2 content in blood

question already tells us what CO value is, 5 L/min, so we have to calculate O2 content of blood.

O2 content of blood = hemoglobin saturation(S O2) x hemoglobin concentration([Hb]) x amount of oxygen per oxyhemoglobin (HBs) + dissolved O2

S O2 in this patient is 0.9

Hb concentration is 10ml/dL

and HBs is a constant value and equals 1.36 ml/dL

all is left, is to calculate dissolved O2, which can be done using Henry's law. Henry's Law states that a gas dissolves in a liquid in direct proportion to its partial pressure and solubility. equation would look like this:

dissolved O2 = ao2(this is solubility coefficient of oxygen in blood) x PaO2

ao2 =0.0031 mL / mmHg of oxygen / dL of blood

so dissolved O2 per dL of blood would be 0.0031 x 60 = 0.186

assuming that 70 kg human would have 5L of blood, dissolved O2 would be 0.186 x 50 (5 L equals 50 dL) = 9.3 ml/dL. the problem is that this patient seems to be anemic and therefore my assumption about 5L of blood could be biased.

now lets's fill in the numbers:

O2 content of blood = 0.9 x 10 x 1.36 + 9.3 = 21.54 ml/dL

O2 delivery to tissues = CO x O2 content of blood = 50 x 21.54 = 1077 ml/dL/min
Reply With Quote Quick reply to this message
The above post was thanked by:
qirkergaard (04-26-2014)
  #5  
Old 04-26-2014
USMLE Forums Scout
 
Steps History: Not yet
Posts: 29
Threads: 13
Thanked 2 Times in 2 Posts
Reputation: 12
Default

Quote:
Originally Posted by icuinwonderland View Post
where did you find this question

Anyway the question asks what is the oxygen delivery to tissues in particular patient. This can be calculated by co x o2 content in blood

question already tells us what co value is, 5 l/min, so we have to calculate o2 content of blood.

O2 content of blood = hemoglobin saturation(s o2) x hemoglobin concentration([hb]) x amount of oxygen per oxyhemoglobin (hbs) + dissolved o2

s o2 in this patient is 0.9

hb concentration is 10ml/dl

and hbs is a constant value and equals 1.36 ml/dl

all is left, is to calculate dissolved o2, which can be done using henry's law. Henry's law states that a gas dissolves in a liquid in direct proportion to its partial pressure and solubility. Equation would look like this:

Dissolved o2 = ao2(this is solubility coefficient of oxygen in blood) x pao2

ao2 =0.0031 ml / mmhg of oxygen / dl of blood

so dissolved o2 per dl of blood would be 0.0031 x 60 = 0.186

assuming that 70 kg human would have 5l of blood, dissolved o2 would be 0.186 x 50 (5 l equals 50 dl) = 9.3 ml/dl. The problem is that this patient seems to be anemic and therefore my assumption about 5l of blood could be biased.

Now lets's fill in the numbers:

O2 content of blood = 0.9 x 10 x 1.36 + 9.3 = 21.54 ml/dl

o2 delivery to tissues = co x o2 content of blood = 50 x 21.54 = 1077 ml/dl/min
ausumn dude !!!!!
Simply ausumnn....!
Reply With Quote Quick reply to this message



Reply

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
Question Membrane Potential - Physiology drpisho USMLE Step 1 Forum 4 02-07-2014 09:28 AM
Physiology question. asioqua USMLE Step 1 Forum 3 05-25-2013 01:55 PM
Atelectasis causes respi acidosis or alkalosis ? tyagee USMLE Step 2 CK Forum 1 09-04-2012 05:05 PM
Renal physiology - tricky question bebix USMLE Step 1 Forum 14 07-26-2011 05:51 AM
Check ur respi knowledge...... shaan.medico USMLE Step 1 Forum 0 03-13-2011 09:51 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)