Oxygenation
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24 Terms
What drives diffusion of gases in the lungs?
Differences in partial pressures of each gas.
What is the atmospheric pressure at sea level?
760 mmHg
Why is alveolar PO₂ ~100mmHg, not 159mmHg like inspired air?
Due to water vapour (PH₂O = 47 mmHg), CO₂ in alveoli (PCO₂ = 40 mmHg), and the RQ effect.
What is the Alveolar Air Equation?
PAO₂ = FiO₂ × (Patm - PH₂O) - (PaCO₂ / RQ) with RQ usually 0.8.
What is a normal A-a Gradient?
5–10 mmHg
What is the P/F Ratio (PaO₂/FiO₂) range for normal?
400–500
What are the three barriers O₂ must cross to get from alveoli to blood?
- Alveolar epithelium, 2. Interstitial space, 3. Capillary endothelium.
What law governs gas diffusion?
Fick’s First Law.
What are the two ways O₂ is carried in the blood?
Dissolved in plasma and bound to hemoglobin.
How much O₂ dissolves in plasma per 1 mmHg PO₂?
0.003 mL/dL
What is the normal dissolved O₂ at a PaO₂ of 100mmHg?
0.3 mL/dL
How much O₂ does 1g of Hb carry when saturated?
1.34 mL
What is cooperative binding in hemoglobin?
Each O₂ bound increases Hb’s affinity for the next O₂.
What is the normal range for SaO₂?
95%–100%.
What is the clinical importance of keeping PaO₂ > 60 mmHg?
Below this, SaO₂ drops rapidly.
Does 100% SaO₂ always indicate optimal oxygenation?
No, PaO₂ could range from 100 to 600 mmHg with the same SaO₂.
What is the Arterial O₂ content equation (CaO₂)?
CaO₂ = (Hb × 1.34 × SaO₂) + (PaO₂ × 0.003) with normal being 16–20 mL/dL.
What is the mixed venous O₂ content (CvO₂)?
= (Hb × 1.34 × SvO₂) + (PvO₂ × 0.003) with normal being ~15 mL/dL.
What is the normal Ca-vO₂ difference?
5 mL/dL, with 25% of delivered O₂ extracted at rest.
What is the Oxygen Extraction Ratio (O₂ER)?
(CaO₂ - CvO₂) / CaO₂ × 100 with normal being 25%.
What is the formula for O₂ Delivery (DO₂)?
DO₂ = CO × CaO₂ × 10 with normal DO₂ being ~1000 mL/min.
What is the Fick Equation (VO₂)?
VO₂ = CO × (CaO₂ - CvO₂) × 10.
What happens if CaO₂ drops? How is VO₂ maintained?
By increasing CO, increasing O₂ extraction, and vasodilation.
How to estimate VO₂ at rest?
Body Surface Area (BSA) × 130 mL/min.
