Lecture 3 Flashcards
What is the difference between hypoxia and Hypoxemia
Hypoxia = inadequate oxygen at tissue level
Hypoxemia =deficient blood oxygen level
When do we assume Hypoxemia
When there is a low PaO2 and low %Hb saturation
When do we assume Hypoxia
When there is low PaO2 and low blood flow
How would you know if a hypoxia is hypoxic or anaemic
A hypoxic hypoxia = decreased PaO2 and an Anaemic hypoxia = a decreased CaO2
Remember CaO2 represents %Hb saturation (with oxygen) and PaO2 represents the 3% dissolved in plasma( besides the % is also less)
What is the difference between stagnant and histotoxic hypoxia
Stagnant hypoxia = and increased a-v difference meaning the problem is low blood flow
Histotoxic hypoxia= a decreased a-v difference meaning the problem is with the cells not being able to extract oxygen from the bloodflow
If a patient has hypoxic hypoxia, how would we know if the cause is diffusion defect or ventilation defect
With ventilation defect - PaO2 is less and PCO2 is greater than normal
With diffusion defect the A-v difference will be increased.
When a patient had :
Decreased haemoglobin concentration (or decreased transport capacity of haemoglobin for oxygen) and CaO2 and or increased Hb affinity for O2 which makes it hard to offload it. What type of hypoxia does this patient have.
Anaemic hypoxia
Mention 3 causes of anaemic hypoxia
Carbon monoxide poisoning
Iron deficiency
Decreased red blood cell production
Why does a patient with histotoxic hypoxia have a decreased (a-v)O2 difference
It is because they have abnormal diffusion or utilisation of O2 in the tissues.
What is the difference between anaemic and stagnant/circulatory hypoxia and why.i n terms of CaO2 and (a-v)O2 difference
Anaemic CaO2 is lesser than normal because there isn’t enough Hb for oxygen to bind and it’s normal in stagnant hypoxia because there is enough blood/Hb to carry the oxygen from the lungs. The difference is that not all the blood available reaches the tissues in stagnant hypoxia hence we have and increased (a-v)O2 difference in stagnant and a normal one in anaemic.
If there isnt enough O2 in the atmosphere what type of hypoxia might result and what other two conditions cause that hypoxia.
Hypoxic hypoxia (low PaO2 and CaO2) It is also caused by abnormal diffusion(gaseous exchange) or abnormal ventilation.
In arterial(or hypoxic )hypoxia how would you know if the problem is a ventilation defect
If there is an increased PaCO2 in the presence of a decreased PaO2
Give the formula for A-a gradient and how does it differ from sea level to Johannesburg
A-a = 150 or 120- (1.25×PaCO2) - PaO2
It’s 150 at sea level and 120 in Johannesburg
What is the Hypoxemia
abnormally low levels of oxygen in the blood
What is the cause of the Hypoxemia if the patient has increased A-a gradient
V/Q mismatch, shunting and diffusion problems
