Pulse Oximetry Flashcards
How many hemoglobin molecules in one RBC?
There are ≈300 million hemoglobin molecules inside each red blood cell (RBC)
Each of the 4 subunits can bind one oxygen molecule, which means that each hemoglobin can bine 4 oxygen molecules, which means that each RBC can contain over 1 billion O2 molecules!
What is hematocrit? Normal male/female values?
Hematocrit refers to the PERCENTAGE of blood that is red blood cells
–Normal male Hct ≈ 45%
–Normal female Hct ≈ 39%
What is in blood?
- Plasma
- White blood cells/thrombocytes
- Red blood cells (RBCs)
What does hemoglobin and hematocrit look like on a lab test?
On lab results, hematocrit is a percentage, and hemoglobin is a concentration
–The hematocrit is usually ≈ 3x the Hb
How can you define anemia?
Anemia can be defined as a decrease in hemoglobin and/or a decrease in hematocrit
What are causes of anemia?
1. Blood loss
–Because hemoglobin molecules are lost
2. Fluid administration
–Because it dilutes the hemoglobin concentration
3. Lysed RBCs
–Because hemoglobin is destroyed
4. Decreased production of RBCs
–Happens with decreased erythropoietin (EPO) production, which is common in patients with renal insufficiency/failure
What are PAO2, PaO2, & SaO2
PAO2 refers to the partial pressure of oxygen in the ALVEOLI
PaO2 refers to the partial pressure of oxygen in the ARTERIES
SaO2 refers to the percentage of hemoglobin that is saturated with oxygen
What determines PA02?
- FiO2
High FiO2 = High PAO2; low FiO2 = Low PAO2 - Barometric pressure
- High elevation (low barometric pressure) = lower PAO2
- Low elevation (high barometric pressure) = higher PAO2
What is normal PA02?
–70-100mmHg on room air
≈5x the FiO2 in healthy patients
What decreases PA02?
PAO2 decreases with age
How does PA02 affect Pa02?
The higher the PAO2, the higher the rate of diffusion into the blood, and the higher the PaO2
What is the A-a gradient? What are normal values?
The difference in PAO2 and PaO2 is referred to as the A-a gradient
A normal A-a gradient is:
5-15mmHg on room air
10-110mmHg on 100% FiO2
What can increase (widen) the A-a gradient?
If patients have lung disease, oxygen will not have a problem getting into the alveoli (PAO2 shouldn’t change much), but the amount of oxygen that is able to get into the blood will be decreased (because of impaired alveolar capillary diffusion), which means PaO2 will be decreased
How are Pa02 and Sa02 related?
SaO2 is PRIMARILY determined by PaO2
–The analogy is that hemoglobin is like a sponge
It soaks up oxygen from the blood until it is maximally saturated (100%)
PaO2 of 60mmHg =
SaO2 of 90%
“Below a PaO2 of 60mmHg, cerebral blood flow increases rapidly.”
PaO2 of 27mmHg =
SaO2 of 50% (in adults)
SaO2 can ALSO (but to a lesser degree) be affected by these 7 other things:
- pH
- CO2
- Temperature
- Anemia
- 2,3 DPG
- Carboxyhemoglobin levels
- Methemoglobin levels
All of these factors alter the way hemoglobin “soaks up” oxygen