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25 Cards in this Set
- Front
- Back
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What exactly does the Oxyhemoglobin curve describe?
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It describes the relationship between the O2 available and the amount of O2 carried by hemoglobin (Hb).
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What are the functions of the horizontal and vertical axes respectively?
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The horizontal axis is PaO2,(partial pressure of O2) or the quantity of O2 available.
The vertical axis is denoted as SaO2,(Hb saturation) or the quantity of Hb that is saturated with O2. |
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Once the PaO2 is at 60mm Hg, what does the curve look like?
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It is almost flat. This means that there is little change in saturation above this point.
A PaO2 of 60 mm/Hg is considered sufficient. |
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What does the curve look like, if the PaO2 (horizontal) is less than 60mm/Hg?
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The curve appears very steep. Small changes in the PaO2 greatly reduces the SaO2.
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What is suggested by the term "affinity"?
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It is used to describe O2s attraction to Hb at its binding sites.
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List 4 variables that potentially change affinity.
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Temperature
pH change or variation CO2 2,3 DPG (diphosphoglycerate) |
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What is 2,3 DPG?
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It is a by product of metabolism which may compete with O2 for its binding sites.
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What are the normal values at the start of the curve?
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The pH is at about 7.4
PaCO2 is at 40mm/Hg Temperature is at 37 Centigrade When any of these values are altered, this is referred to as a shift. |
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What is meant when the curve shifts from left or right?
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The Y axis or vertical region tends to move to the left or the right.
In fact, a left shift tends to increase O2 affinity for Hb. A shift to the right will decrease O2 affinity for Hb. |
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Considering a left shift, list 2 conditions that might cause this to happen?
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Alkalosis
Hypothermia. O2 will have an increased affinity for Hb. |
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in a left shift, what will happen to SaO2?
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Sao2 will increase at a given or set PaO2. However, more of it will remain on the Hg and be carried back to the lungs without being consumed. This may result in tissue hypoxia, despite there being adequate O2 in the blood.
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List 2 conditions that might cause a right shift.
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Acidosis
Fever. At this stage, O2 will have a lower affinity for Hb. Blood will tend to release the O2 more willingly. More O2 will be available to cells. However, less O2 will be carried from the lungs. |
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In a strict sense, changes between these 2 values do not significantly affect the percentage of saturation of Hb. True/False
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True. Technically, the very steep part of the curve occurs after the partial pressure of O2 tends to fall below 60mm/Hg.
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How is Hb affected with a shift to the left?
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Hb will have an increased affinity for O2 and will therefore release less to the tissues.
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List several conditions that will result in a left shift.
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Acute alkalosis
Decreased PCO2 Decreased temperature Low levels of 2,3 DPG, carboxyhemoglobin, methemoglobin, and abnormal Hb. |
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In a shift to the left, it is easier to load O2, but more difficult to unload it. True/False
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True.
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List severasl conditions that will result in a shift to the right.
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Acute acidosis
High PCO2 increased temperature High levels of 2,3 DPG, and abnormal Hb. |
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In a right shift, it is conversely difficult to load the O2, and easier to unload it. True/False
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True.
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Under standard conditions, (pH at 7.4), at a PaO2 of 60, what would be the SaO2?
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It would be a n SAO2 of about 93.
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In a standard right shift, pH decrease, increase PaCO2, increased temperature and an increase in 2,3 DPG, what would the SaO2 be with a PaO2 of 60mm/Hg.
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It would be about 75. It is less than 93 hypothetically, because a right shift lets go of more O2. Logically, this would decrease the SaO2. More O2 would be available to tissues in these listed conditions.
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In a hypothetical left shift, what would the SaO2 be with a PaO2 of 60? (pH increase, decrease PaCO2,decrease in temperature, decrease 2,3 DPG)
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It would be almost 100% Left shifts tend to hold on to O2 at Hb sites. There would be less O2 available to tissues in these stated conditions.
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At higher saturation levels, above 90%, the curve is flat. Why is this?
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Because Hb is considered nearly saturated, and will not take on more O2 molecules.
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In the end it is the O2 content of the blood that is more critical than the partial pressure of O2. True/False
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True.
A reduction in the Hb concentration from 15-10g/dl reduces the arterial oxygen content (CaO2) by as much as a reduction in PaO2 from 100mm/Hg to 40mm/Hg. |
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A small drop in SaO2 may represent a large drop in PaO2 due to the shape of the Oxyhemoglobin dissociation curve. True/False
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True. When Hb is 50% saturated, the PaO2 is 28mm/Hg.
At 75%, the PaO2 is about 40mm/Hg (mixed venous blood). |
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What is FiO2?
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The air around us is made up of 78.1% nitrogen, 20.9% oxygen, 0.9% argon and 0.1% carbon dioxide and other gases. Therefore, your FiO2 is 0.21 (21%). If someone in the hospital is on a breathing machine that is delivering pure 100% oxygen, then his/her FiO2 would be 1.00 (100%).
They named it such because, as you point out, it stands for "fraction of inspired oxygen". In other words, it is the "fraction" of the "inspired" air (inspire means to breathe in) that is made up of "oxygen", O2. |
