Arterial Blood Gas Analysis
OSCE IN PEDIATRICS
FOR PEDIATRICS PRACTICAL EXAMINATION
ABG report – Ph – 7.60 / PaCo2 – 30 / PaO2 – 54 mmHg / Bicarb 30.3
Na 120 , K 4 , Blood sugar 180 mg % , BUN 3 , Osmolality - 300
Ques 1 - Interpret this blood gas
Ques 2 – What change in Paco2 you expect if there is rise in bicarb by 1 mm ?
Ques 3 - Above mentioned ABG was taken when patient was inspiring 60% Fio2 . Choose the
correct option to describe oxygen status of the patient
Under corrected Hypoxemia
Over corrected hypoxemia
Ques 4 What will be the PaCo2 level ( assuming normal PaCo2 level of 40 ) if Bicarb decreases by 10
in metabolic acidosis ( give maximum and minimum value )
Ques 5 What is osmolar gap in this patient
SPOT 1 ANS
Ans 1 ) Metabolic alkalosis with metabolic alkalosis
Ans2 ) Increase in PaCo2 by 0.5-1 mm H
Ans 3 ) b
Ans 4 ) 30-25 mmHg
Ans 5 ) 49
Which patient is more hypoxemic, and why?
• Patient A:
PaCO2 34 mm Hg
PaO2 85 mm Hg
Hemoglobin 7 gm%
• Patient B:
PaCO2 74 mm Hg
PaO255 mm Hg
Hemoglobin 15 gm%
The body needs oxygen molecules, so oxygen content
takes precedence over partial pressure in determining
degree of hypoxemia. In this problem the amount of
oxygen molecules contributed by the dissolved fraction is
negligible and will not affect the answer. Also, the PaCO2
and pH are not needed to answer the question.
• Patient A: Arterial oxygen content = .95 x
7 x 1.34 = 8.9 ml O2/dl
• Patient B: Arterial oxygen content = .85 x
15 x 1.34 = 17.1 ml O2/dl
• Patient A, with the higher PaO2 but the
lower hemoglobin content, is more
Calculate Oxygen content in given blood gas
Hb 8 gm%
• 11 ml O2/dl
(1.34 X HB X SPO2/100)+.003 x PaO2
True or False:
The pO2 in a cup of water open to the
atmosphere is always higher than the
arterial pO2 in a healthy person (breathing
room air) who is holding the cup
• The PO2 in the cup of water is always higher. This is for
several reasons. First, there is no barrier to oxygen
diffusing into the water; thus the PO2 in the cup will be
the same as the atmosphere, at sea level approximately
160 mm Hg.
• Second, there is no CO2 coming from the cup to dilute
the oxygen, as there is in people.
• Third, there is no V-Q inequality or shunt; even healthy
people have a difference between alveolar PO2 and
arterial PO2 for this reason. Thus a healthy person and a
cup of water exposed to the atmosphere at sea level
would have PO2 values of about 100 mm Hg and 160
mm Hg, respectively.
State which of the following situations would
be expected to lower a patient's arterial pO2.
There may be none, one, or more than one
b) Carbon monoxide poisoning
c) An abnormal hemoglobin that holds oxygen
with half the affinity of normal hemoglobin
d) An abnormal hemoglobin that holds oxygen
with twice the affinity of normal hemoglobin
e) Lung disease with intra-pulmonary shunting.
Only e) lung disease. . .
a) affects only content, not oxygen
saturation or PO2.
b) through d) affect only oxygen saturation
and content, not PO2.
What is the pH of a blood sample with
HCO3- 24 mEq/L and PaCO2 80 mm
This is a simple calculation from the
Henderson-Hasselbalch equation; the
answer is 7.1. Even without doing the
calculation, it should be apparent that a
very high PaCO2 and normal bicarbonate
will give a very acidic pH, and that 7.10 is
the closest fit.
• A patient is admitted to the ICU with the
following lab values:
• BLOOD GASES under room air
• pH: 7.199
• ELECTROLYTES, BUN & CREATININE
• Na: 131
• 5 year male child recently diagnosed as a case of AML .
TLC 57000. Chest Xray normal. Hemodynamically stable
with RR of 23/min. Normotensive Pulse oximetry showed
SpO2 of 98%. ABG report
• pH – 7.43
• PaCO2 – 34
• PaO2 – 47.6 mmHg
• Bicarb 24 .
• Above mentioned ABG was taken when patient was
inspiring at room air.