Basics of Oxygenation

1. OXYGENATION
Dr Ajay Prakaash
Senior resident
Neonatology
KIMS, Trivandrum

2. Components of respiration
 Oxygenation
 Ventilation

3. OXYGENATION
Transfer of oxygen across pulmonary capillaries for
transport & delivery to tissues

4. •FiO2
•PAO2
•PaO2
•CaO2
•PAco2
•Oxygen transport
•Hemoglobin
•Circulation

5. PAo2 = [(Barometric pressure – Partial pressure of water vapor) x Fio2 – (PaCo2/RQ)]
Sea level
Barometric pressure 760
Partial pressure of water vapor 47
Fio2 0.21
PaCo2 40
RQ 0.8 – 1 (Depends on the diet)
Respiratory quotient is the ratio of CO2 excreted to O2 uptake
Carbohydrate diet increases CO2 production

6. PAo2 = [(Barometric pressure – Partial pressure of water vapor) x Fio2 – (PaCo2/RQ)]
At sea level, with normal Paco2 (40mmhg) and respiratory quotient of 0.8
PAo2 = [(760 – 47) x 0.21 – (40/0.8)] = 150 – 50 = 100mmhg

7. Altitude
Barometric pressure
Barometric pressure varies with weather and altitude

8. PAo2 = [(Barometric pressure – Partial pressure of water vapor) x Fio2 – (PaCo2/RQ)]
At high altitude, (5800ft above sea leave)
PAo2 = [(600 – 42) x 0.21 – (40/0.8)] = 117 – 50 = 67mmhg
Barometric pressure is approximately 600mmHg &
Partial pressure of water vapor also decreases to 42mmHg

9. Oxygen transport to the tissues depends on the
oxygen-carrying capacity of the blood and the rate of
blood flow

10. Oxygen transport
• During inspiration oxygen enters the
alveoli
• Oxygen diffuses through the
alveolar membrane and binds to the
hemoglobin to form oxyhemoglobin

11. Haldane effect and Bohr effect
Tissue
Oxygen delivery
Haldane effect: Oxygen affects the
affinity Hb for oxygen
Hypoxic (more Co2&H+)
Bohr effect: Co2 / H+ affect the
affinity of Hb for oxygen
%HbSaturation
Po2

12. Pulmonary arterial blood passes through the lung capillary
Co2 released  This rises the local PH
Increases oxygen affinity and more O2 bound to hemoglobin
Systemic arterial blood passes through the tissue capillary
Co2 level picks up   PH reduces
Release of O2 to tissue

13. Factors affecting haemoglobin affinity for oxygen

14. Saturation (SpO2)
• SpO2 is very useful for minute to minute measurement of oxygenation
• Spo2 is clinically monitored with pulse oximetry
• It shows the percentage of haemoglobin saturated with oxygen
• It acts by the principle of spectrometry
• Based on the fact that oxygenated Hb and deoxygenated Hb have
different absorption spectra

15. Ventilation perfusion mismatch

16. Oxygen content (CaO2)
The amount of oxygen in arterial blood
Each gram of haemoglobin will bind 1.34 mL of O2
when fully saturated with oxygen
0.003 represents the amount of oxygen dissolved in
plasma
CaO2 = (1.34 × Hb × SaO2) + (0.003 × PaO2)

17. Clinical indicators of disease severity from blood gas
1. Arterial-alveolar O2 tension ratio  Should be close to 1, A value
less than 0.3 indicates severe compromise of oxygen transfer
2. Alveolar-arterial O2 gradient (AaDO2 = PAO2 – PaO2)  Should be
less than 20 in room air
3. Oxygenation index = (MAP x FiO2 x100)/PaO2  more than 15 is
severe respiratory compromise. OI more than 40 is indication for
ECMO
FiO2

18. Determinants of oxygenation during Ventilation
Oxygenation
Mean
Airway
pressure
FiO2
PIP
PEEP I:E
Flow

19.  In HFO the I:E ratio is very short, therefore to maintain adequate MAP
PEEP should be raised by 2 to 4cmH2O

20. Thank you!!