Example: (2)
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| ABG Report of the patient |
A patient of constrictive pericarditis, who had breathlessness on slight movement from one month admitted in stuporosed condition in emergency department of DMCH on 15/01/15.
ABG was done on 15/01/15 at 9.39 PM.
There is slight left shift of the oxygen dissociation curve, most probably due to decrease in temperature.
Step:2
Step:5
Expected cause of Acid-Base change in simple.
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ABG Analysis:
(i) Gas Analysis
Step:1
PaO2 – 49.8 mm of Hg – Moderate hypoxemia
SPo2 – 70.5 % - Severe hypoxemia
There is slight left shift of the oxygen dissociation curve, most probably due to decrease in temperature.
Step:2
PAO2
- 49.8 mm Hg – low
So, either
Fio2 low or PaCo2 high.
Step:3
P(A-a)O2 =
(49.8 – 49.8) mm Hg.
= 0 mm of Hg – normal
Step:4
PaCo2 –
122.5 – Hypercapnea – hypoventilation
So, the
patient has hypoxemia with Hypercapnea
i.e. Type
2 Respiratory failure.
Due to
advanced stage of LVF.
Step:5
Here PaCo2
is increased, and P(A-a)O2 is not increased , so the cause is hypoventilation
alone and since the patient had no neuromuscular
disease , so it is due to decreased respiratory drive due to critical illness.
Step:6
P/F index
or hypoxemia index = 237.3
x-ray
finding does not suggest progressive diffuse pulmonary infiltration , feature
of
pneumonia
. So it can be due to heart failure or arterial hypoxemia.
Step:7
There is
slight mismatch in the relation between SPo2 and PaO2.
Cause of
mismatch is left shift of the oxygen dissociation curve most probably due to
low temperature.
Step:8
Hemoglobin
and HCT value are high indicating polycythaemia mosr probably due to
hypercapnea . we calculate arterial oxygen content
CaO2=
16.4X10(gm/L) X 1.34 X 70.5 / 100 + 0.003 X 49.8
= 154.93 + 0.149
= 155.08 ml/L
Expected CaO2 in a 70 Kg person is 194.44 ml/L.
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(ii) Electrolyte Analysis
S.Na+ -
130.7 mmol/L – low
S.Cl- - 86.5
mmol/l – low
S.iCa –
0.915 mmol/L – normal
S.K+ - 5.31
mmol/L – high
Decrease
level of s.Na+ and Cl-is due to fluid retention.high
level of K+ matches with the change in
pH due to acidosis.
Anion Gap :-
AG =
[130.7]-[86.5+43.4]
= 130.7-129.9
= 0.8 mmol/l
Derived AG is 6.1 mmol/L
This increased level of AG is due to increased in
unmeasured anion.
Delta Gap :-
= 6.1-12
= -5.9
Delta gap + HCo3 = -5.9+43.4
= 37.5 – metabolic alkalosis.
Gap-Gap Ratio :-
= -5.9
/(24-43.4)
= -5.9/-19.4
= 0.30
<1
BE :-
BE= 43.4 –
24=19.4
So,metabolic
alkalosis.
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(iii) Acid Base Analysis
Step:1
Step:2
Hco3 –
43.4 mmol/L – Metabolic alkalosis
Step:3
PaCo2-
122.5 – Respiratory acidosis
Step:4
Step:5
Expected cause of Acid-Base change in simple.
So, respiratory acidosis with compensated metabolic
alkalosis.
Compensation of Hco3 In chronic condition
= 2.62 X 122.5/7.50 kpa=42.79
So,
expected value of Hco3 = 24+42.79=66.70
Compensation of Hco3 In acute condition
=
0.75X 122.5/7.5 = 12.25
So,
expected value of Hco3 = 24+12.25=36.25
So,respiratory acidosis with chronic compensated metabolic
alkalosis.
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Final diagnosis
Respiratory acidosis with chronic compensated metabolic
alkalosis with hypoxemia and dilutional huponatremia
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Causes of Respiratory Acidosis
In this case it is ventilatory
failure due to decreased respiratory drive or due to respiratory muscle
weakness.
