Oxygen In Blood Flashcards
Is the O2 dissolved in plasma enough to supply the body’s requirements?
No, Hb is needed
What is the most important factor that determines whether Hb is in Low Affinity T state or High Affinity R State?
Partial pressure of O2, which determines O2 binding for Hb
What happens to Hb’s affinity for O2 when 1 O2 molecule is released?
It decreases (moves towards low affinity T state)
Does a reduction in Hb affect saturation?
No
At what pO2 is Hb saturated?
Below what pO2 is Hb virtually unsaturated
9-10kPa
1kPa
At what pO2 is Hb half saturated?
What is this called?
3.5-4kPa, called P50 (50% Hb Saturation)
What are 3 things that increase O2 Unloading from Hb (Bohr Shift, moves curve to right)
- Low pH
- Increase in temperature
- Increase in 2,3 DPG (accumulates in RBCs, shifts dissociation curve to right)
Does O2 bound to Hb contribute to PaO2?
No. Arterial partial pressure is only from dissolved O2
What is the minimum required pO2 in capillaries for tissues to be oxygenated?
3kPa
Higher capillary density tissues like heart can utilise a lower pO2, but must still be >3
What are 2 ways of measuring adequacy of oxygenation?
- Oxygen saturation/ Sats/ SaO2
- Arterial Blood Gas (ABG) analysis: measures pO2
How is O2 saturation measured
Using a pulse oximeter
Remember this only measures O2 bound to Hb
What is 1 con of using a standard pulse oximeter?
Can’t distinguish between Normal Hb and Hb bound to CO or Met-Haemoglobins, which both have reduced O2 carrying capacity
What are 2 methods of measuring oxygen saturation using an ABG Analysis?
- Directly measuring Hb saturation using a co-oximeter, that can differentiate between Normal Hb and Hb-CO or Met-Haemoglobins
- Measuring pO2, then using an O2-Hb dissociation curve to calculate saturation
