1. Assessment of Hypoxaemia
Dr. Immaculate Kariuki
Consultant Paediatrician
Nairobi, Kenya

2. Intended Learning Outcomes
To understand what hypoxaemia is
To be familiar with assessment of severity of hypoxaemia
To gain an understanding of how to interpret arterial blood gas analysis results

3. What is hypoxaemia? Normal oxygen saturations 94-100% on room air
Hypoxia is defined as saturations below 92 %
Hypoxaemia is defined as a PaO2 <80mmHg calculated from an arterial blood gas (especially necessary for critically ill patients)
A common complication of LRTI present in up to 2/3 of patients admitted with pneumonia

4. Why assess for hypoxaemia?
Uncorrected hypoxaemia and acidosis set the stage for respiratory failure and death
Clinical signs of pneumonia identify hypoxia poorly and cyanosis is a late (terminal) sign
It guides decisions on oxygen therapy before irreversible changes occur and decide on addition of steroids for PCP
Degree of hypoxaemia used to classify PCP severity
WHO recommends use of pulse oximetry to identify hypoxia in patients with pneumonia and manage with oxygen accordingly
Sources:
2. Subhi et al.The prevalence of hypoxaemia among ill children in developing countries: a systematic review
Lancet Infect Dis, 9 (2009), pp. 219–227
3.WHO Pocket book of hospital care for children: guidelines for the management of common illnesses with limited resources (2nd edn.), World Health Organisation, Geneva (201

5. Clinical assessment only: poor predictor of hypoxia
Does this infant have PCP?
(WHO advice)
Mwaniki et al .Bull World Health Organ 2009;87:263–270

6. How to assess for hypoxia: Pulse oximetry

7. Is anything wrong with these scenarios?

8. Where is the problem?

9. Pulse oximetry reduces mortality
Duke Tet al Int. J. Tuberc. Lung Dis ;5: 511–519.
Children .
Oxygen therapy determined using clinical signs only.
703 children. Oxygen therapy determined using pulse oximetry
Mortality
46 (6.5%)
Mortality
26 (10%)
MORTALITY RISK RATIO
0.65 ( ) p=0.07

10. Blood gas analysis NORMAL ARTERIAL BLOOD VALUES Pa O2 : 75-100mmHg
: kPa
Pa CO2: 35-45mmHg
: kPa
pH :
O2 sats: %
HCO3: mEq/L

11. A-a gradient Calculation
Difference between a calculated alveolar PO2 (PAO2) and arterial oxygen levels (PaO2) read from the blood gas analysis.
The calculated PAO2 is derived from:
PAO2    = (Patm - Pwater) FiO2 - PaCO2/ where     
Patm = the atmospheric pressure (760 mm Hg)*
Pwater = the vapor pressure of water at body temp (47 mm Hg)*
FiO2 = the fraction of O2 in the inspired gas (21% on room air)
PaCO2  = the partial pressure of CO2 in arterial blood (from ABG)
O.8    = respiratory quotient
* at sea level

12. Assessment of severity using blood gas analysis
Normal A-a gradient of 5-7mmHg
Mild to moderate PCP
PaO2 above 70mmHg on room air
A-a gradient ≤ 35mmHg
Moderate to severe PCP
PaO2 below 70mmhg on room air
A-a gradient ≥ 35mmHg

13. Summary
Hypoxia is a common and serious complication of PCP in children
Clinical signs alone predict hypoxia poorly
Pulse oximetry helps identify hypoxia and need for oxygen
Where available, blood gas analysis may be used to classify PCP severity