Exam 3 - Blood Gas Flashcards
Describe the behavior of dissolved and atmospheric O2 when in equilibrium?
The atmospheric pressure is pushing O2 into the liquid at the same pressure the dissolved O2 is pushing O2 out
What is the solubility of oxygen?
.003 mL O2 / mmHg O2 / dL soln
How much dissolved oxygen would there be in arterial blood?
Multiply the soubility coefficent by the PaO2 (100mmHg)
How much dissolved oxygen would there be in venous blood?
Multiply the solubility coefficent by the PvO2 (40 mmHg)
Can dissolved oxygen meet metabolic demands?
- No - it only provides 0.3 mL O2/ dL and we require 250 mL O2/min
- This is why we need Hb
How can you calculate the % Hb saturation?
% Hb saturation = (O2 bound to Hb ÷ O2 capacity of Hb) × 100%
O2 bound to Hb = total O2 content - dissolved O2
How much O2 can Hb store?
1.34 mL O2 / g Hb
What would be the amount of O2 in the blood if the Hb were 15 g?
What is this called?
Multiply the Hb by the constant
This is called the carrying capacity
Arterial blood is 20.4 mL O2/ dL - this tells you almost all of our O2 is from Hb
What is the oxygen carrying capacity dependent on?
The Hb saturation
100% = 20 mL O2/ dL
10% = 2 mL O2/ dL
What is a normal Hb for Dr. Schmidt’s A/P?
15 g / dL
Compare adult and fetal Hb?
Adult: tetramer with 2 ⍺ subunits and 2 β subunits; 4 O2 binding sites
Fetal: tertamer with 2 ⍺ subunits and 2 Ɣ subunits; has higher affinity for O2 in order to pull O2 from maternal blood
When is EPO released?
When the medulla of the kidneys are hypoxic
Describe myoglobin’s O2 affinity?
- Myoglobin has a higher affinity for O2 than regular Hb. This is in order to help unload O2 from Hb into the highly metabolic muscles.
- Remember, myoglobin makes muscles red d/t high Fe content from lots of myoglobin
What is a normal oxygen content of arterial blood?
Dissolved O2 + bound O2
.3 mL O2 + 20.1 mL O2 = 20.4 mL O2/ dL
This is if Hb is 15g/dL and sats are 100%
Expalin this portion of the oxy-Hb diss. curve when bound with 50% CO?
- When CO binds to Hb, it increases its affinity for oxygen - preventing it from being released into the tissues (bad)
- Causes a leftward shift
How can you calculate the oxygen content of a blood sample?
carrying capacity × % saturation = content
carrying capacity is calculated based on Hb (Hb × 1.34 mL O2/g Hb)
What is the Hb saturation of venous blood?
What does this do to the oxygen content?
75%
Decreases by 25%
What circulatory bed is the exception to having a venous saturation of 75%?
Why can this be bad?
- Coronary beds have venous saturation of 25% - very effiecent at extracting O2.
- If there is a clot, there is not any excess oxygen to be pulled from bc the other coronaries are using it, and its difficult to pull oxygen off Hb that is only 25% bound.
What are two ways you can think of the affinty between these two curves?
- How much pO2 (x-axis) will it take to attain a certain Hb sat (y-axis); higher affinity = less pressure required to increase sat
- How resistant is the Hb to releasing its O2 (shift left = more resistant)
Describe dissociation curve shifts with high and low PCO2?
- High PCO2 causes O2 to fall off of Hb easier- right shift; highly metabolic tissues produce lots of CO2 and need more O2
- Low PCO2 causes O2 to stay on Hb - left shift; less active tissues produce less CO2 and dont require much oxygen.
This is the Bohr Effect
What is the only form of oxygen that tissues can use?
Dissolved O2 - must be released from Hb in order to diffuse into tissues
Which directions would the dissociation curve shift with acidosis and alkalosis?
Acidosis = right shift
Alkalosis = left shift
What is 2,3-BPG (DPG)?
2,3- Biphosphoglycerate → Biphosphoglyceric Acid
2,3 - Diphosphoglycerate
Byproduct of tissue metabolism
How does 2,3 - BPG effect the dissociation curve?
↑ 2,3-BPG = right shift
↓ 2,3- BPG = left shift
How does temperature effect the dissociation curve?
Hypothermic = left shift
Hyperthermic = right shift
What is the bodies primary goal with a normal dissociation curves?
- For Hb to be able to unload O2 to the the tissues
- For O2 to be able to be loaded onto Hb in the lungs
What would you excpect the dissociation curve to look like between arterial and venous blood?
Why is clinical venous Hb sat lower then what is expected?
- Venous blood has a higher PCO2 and therefore lower pH and is shifted to the right
- Clinically, patients are very sick causing them to have lower pH and higher CO2 than a healthy person - this causes the Hb sat to be decreased
What is a P50 value?
What is normal for arterial blood?
The PO2 required to saturate Hb to 50%
26.5 mmHg - changes with Hb affinity
What are the 3 forms of CO2 found in arterial blood and what percentage do they make up?
Carbamino - 5%
Dissolved - 5%
HCO3- - 90%
How can you calculate the amount of dissolved CO2 in normal arterial blood?
Solubility coefficent of CO2 x pCO2
0.06 mL CO2/mmHg CO2/dL x 40 mmHg = 2.4 mL CO2/dL
How is carbamino formed?
When CO2 knocks of a H+ from terminal amine group, a carbamino compound is created
What is the bicarbonate buffer solution?
What shifts the reaction?
Amount of CO2 in the enviornment directs reaction
Lots of CO2 = right
Less CO2 = left
How much arterial CO2 is there in carbamino, HCO3, and total?
Since we know dissolved is 5% and is 2.4 mL CO2/dL, then we can say that since carbamino is also 5% it has the same CO2 content.
The total CO2 content would be 20 x 2.4 mL CO2/dL = 48 mL CO2/dL
Therefore HCO3 is 48 - 2.4 (2) =43.2 mL CO2/dL
Why is there so much more CO2 content (48 mL/dL) compared to O2 (20.4 mL/dL)?
CO2 is much more soluble
What is the venous CO2 content at a HbO2 saturation of 70%?
52.5 mL CO2/dL
Hb less saturated with O2 = more room for CO2 = higher CO2 content (Bohr Effect)
How does Hb play a role in CO2 carrying capacity of blood?
- Deoxygenated Hb has terminal amine groups that can bind to CO2 and form carbamino compouds
- It can also buffer protons, allowing the bicarb buffer equation to be be pushed further to the right when lots of CO2 is present
Because O2 has fallen off of Hb and it its doing what was mentioned above, it makes it easier for the blood to carry CO2
Less O2 = Higher CO2 carrying capacity
