3. Normal value:
pH: 7.4 (7.35 to 7.45)
PaCO2: 40 (35-45) mm of Hg
PO2: 80-90 mm of Hg
HCO3-: 22 (22-26 ) mEq/L
Na+ : 135- 145 mEq/L
K+: 3.5- 5 mEq/L
Cl-: 100-110mEq/L
Anion Gap (AG) = Na – ( Cl +HCO3) = 12 +/- 2 mEq/L
4. • Step 1: Assess the internal consistency of the
values using the Henderseon-Hasselbach
equation:
[H+] = 24(PaCO2)
[HCO3-]
• If the pH and the [H+] are inconsistent, the
ABG is probably not valid.
6. • Step 2: Is there alkalemia or acidemia present?
• pH < 7.35 acidemia
pH > 7.45 alkalemia
• This is usually the primary disorder
• Remember: an acidosis or alkalosis may be
present even if the pH is in the normal range
(7.35 – 7.45)
• You will need to check the PaCO2, HCO3- and
anion gap
7. • Step 3: Is the disturbance respiratory or metabolic?
• What is the relationship between the direction of
change in the pH and the direction of change in the
PaCO2?
• In primary respiratory disorders, the pH and PaCO2
change in opposite directions
• In metabolic disorders the pH and PaCO2 change in
the same direction.
9. Step 4: Is there appropriate compensation for the primary
disturbance? Usually, compensation does not return the pH to
normal (7.35 – 7.45).
Disorder Expected compensation
Metabolic acidosis PaCO2 = (1.5 x [HCO3-]) +8
Acute respiratory acidosis Increase in [HCO3-]= ∆ PaCO2/10
Chronic respiratory acidosis (3-5 days) Increase in [HCO3-]= 3.5(∆ PaCO2/10)
Metabolic alkalosis Increase in PaCO2 = 40 + 0.6(∆HCO3-)
Acute respiratory alkalosis Decrease in [HCO3-]= 2(∆ PaCO2/10)
Chronic respiratory alkalosis Decrease in [HCO3-] = 5(∆ PaCO2/10) to 7(∆
PaCO2/10)
10. • If the observed compensation is not the
expected compensation, it is likely that more
than one acid-base disorder is present.
11. Step 5: Calculate the anion gap
• Step 5: Calculate the anion gap (if a metabolic acidosis
exists):
AG= [Na+]-( [Cl-] + [HCO3-] ) = 12 ± 2
• A normal anion gap is approximately 12 meq/L.
• In patients with hypoalbuminemia, the normal anion
gap is lower than 12 meq/L
• The “normal” anion gap in patients with
hypoalbuminemia is about 2.5 meq/L lower for each 1
gm/dL decrease in the plasma albumin concentration
(for example, a patient with a plasma albumin of 2.0
gm/dL would be approximately 7 meq/L.)
12. • Step 6: If an increased anion gap is present,
assess the relationship between the increase in
the anion gap and the decrease in [HCO3-].
• Assess the ratio of the change in the anion gap
(∆AG ) to the change in [HCO3-] (∆[HCO3-]):
∆AG/∆[HCO3
• This ratio should be between 1.0 and 2.0 if an
uncomplicated anion gap metabolic acidosis is
present.
• If this ratio falls outside of this range, then
another metabolic disorder is present
13. Characteristics of acid-base
disturbances
Disorder pH Primary problem Compensation
Metabolic acidosis ↓ ↓ in HCO3- ↓ in PaCO2
Metabolic alkalosis ↑ ↑ in HCO3- ↑ in PaCO2
Respiratory acidosis ↓ ↑ in PaCO2 ↑ in [HCO3-]
Respiratory alkalosis ↑ ↓ in PaCO2 ↓ in [HCO3-]
14. Disorder Characteristics Selected situations
Respiratory acidosis with
metabolic acidosis
↓in pH
↓ in HCO3
↑ in PaCO2
•Cardiac arrest
•Intoxications
•Multi-organ failure
Respiratory alkalosis with
metabolic alkalosis
↑in pH
↑ in HCO3-
↓ in PaCO2
•Cirrhosis with diuretics
•Pregnancy with vomiting
•Over ventilation of COPD
Respiratory acidosis with
metabolic alkalosis
pH in normal range
↑ in PaCO2,
↑ in HCO3-
•COPD with diuretics, vomiting, NG suction
•Severe hypokalemia
Respiratory alkalosis with
metabolic acidosis
pH in normal range
↓ in PaCO2
↓ in HCO3
•Sepsis
•Salicylate toxicity
•Renal failure with CHF or pneumonia
•Advanced liver disease
Metabolic acidosis with
metabolic alkalosis
pH in normal range
HCO3- normal
•Uremia or ketoacidosis with vomiting, NG
suction, diuretics, etc.
15. Case study 1 Mr. Abc
A 24 year old college student with
history of crohn’s disease and is
complaining of a four day history
of bloody-watery diarrhea. A
blood gas is obtained to assess
acid-base balance:
Ph 7.28
CO2 43
P02 88
HCO3 20
SaO2 96%
What is your
interpretation?
What interventions would
be appropriate?
(PaCO2 = (1.5 x [HCO3-]) +8)
= 38
16. Answer
Pt. has uncompensated metabolic acidosis.
This is due to excessive bicarbonate loss from his diarrhea.
It is interesting to note that he has no compensation.
Normally, the respiratory center compensates quickly for
metabolic disorders.
However, in this case he would have to hyperventilate in
order to compensate.
This may not be possible in his present condition, and should
be evaluated further.
Treatment would consist of control of diarrhea and bowel
rest.
It should not be necessary to administer bicarbonate in his
present condition.
17. Case study 2 Ms. Xyz
Ms. Xyz is a 17 year old with
intractable vomiting. She
has some electrolyte
abnormalities, so a blood
gas is obtained to assess her
acid/base balance:
pH 7.50
C02 36
P02 92
HC03 27
SaO2 97%
What is your
interpretation?
What interventions
would be appropriate
for Ms.Xyz?
Increase in PaCO2
= 40 + 0.6(∆HCO3-)
= 40+ (0.6x5) = 43
18. Answers for Ms. Xyz
Ms. Xyz has an uncompensated metabolic
alkalosis.
This is due to vomiting that results in
excessive loss of stomach acid.
Treatment consists of fluid, antiemetics, and
management of her electrolyte disorders.
19. Case study 3 Mr. Lmn
Mr. Lmn is a 18 year old
comatose, quadriplegic
patient who has the
following abg done as
part of a medical workup:
Ph 7.45
C02 22
P02 96
HCO3 16
Sa02 98%
What is your
interpretation?
What interventions
would be appropriate
for Mr.Lmn?
Decrease in[HCO3-]
=5(∆ PaCO2/10)
=5 (13/10) =6.5
20. Answers for Mr.Lmn
As a result of his neurological condition,
Mr.Lmn has chronic hyperventilation
syndrome. His blood gas shows a fully
compensated respiratory alkalosis.
This is a chronic and stable condition for him
and probably requires no treatment
21. Case study 4 Mr. Cde
Mr. Cde is a 55 year old with
gerd. He takes about 16
antacid tablets a day. An
abg is obtained to assess his
acid/base balance:
Ph 7.46
C02 42
P02 86
HC03 29
Sa02 97%
What is your
interpretation?
What interventions would
be appropriate for Mr.Cde?
Increase in PaCO2
= 40 + 0.6(∆HCO3-)
= 40 + 0.6 (6)
= 43.6
22. Answers for Mr. Cde
Mr. Cde has overmedicated himself with
antacids, effectively absorbing too much
stomach acid.
His abg shows a partially compensated
metabolic alkalosis.
Treatment consists of better control of his gerd,
possibly with H2 blockers or proton-pump
inhibitors
23. Case study 5 Mrs. Rst
Mrs. Rst is found pulseless
and not breathing this
morning. After a couple of
minutes of CPR she responds
with a pulse and starts
breathing on her own. A
blood gas is obtained:
Ph 6.89
C02 70
P02 42
HCO3 13
Sa02 50%
What is your
interpretations?
What interventions
would be appropriate
for Mrs.Rst?
24. Answers for Mrs.Rst
Mrs. Rst has severe metabolic and respiratory
acidosis with hypoxemia.
The metabolic component comes for her
decreased perfusion, and the respiratory
component comes from inadequate ventilation
Treatment would consist of intubation,
mechanical ventilation, blood pressure and
circulatory support.
25. Case study 6 Ms. Uvw
Ms. Uvw was admitted for a
drug overdose. She is being
mechanically ventilated and
a blood gas is obtained to
assess her for weaning. The
results are as follows:
Ph 7.54
C02 19
P02 100
HC03 17
Sa02 98%
What is your
interpretation?
What interventions
would be appropriate
for Ms. Uvw?
Decrease in [HCO3-]
= 5(∆ PaCO2/10)
= 5(16/10)= 8
26. Answer for Ms. Uvw
Ms. Uvw is being over-ventilated which caused a
partially-compensated respiratory alkalosis.
Treatment would consist of decreasing
ventilatory support, or trying other modes of
ventilation to decrease her minute volume.
She will be difficult to wean from the ventilator
in this condition due to the metabolic
compensation.
Therefore attempts should be made to allow her
C02 to increase back to normal before weaning.
27. Case study 7 Mr. Sweet
• Mr. Sweet, a 24-year-old
Type I Diabetic patient
brought to Casualty. He is
drowsy, disoriented and
has shallow hurried
breathing. His breath has a
fruity odour. In report you
learn that his blood
glucose on arrival was 780.
• ABG results are:
pH= 7.33
PaCO2= 25
HCO3=12
PaO2= 89
What is your
interpretation?
What interventions would
be appropriate for Mr.
Sweet? Decrease inPaCO2
= (1.5 x [HCO3-]) +8
=(1.3 x 11) +8
=22.3
Go for Anion Gap
28. Answer for Mr. Sweet
• The pH is acidotic,
• PaCO2 is 25 (low) which should create alkalosis.
• This is a respiratory compensation for the metabolic
acidosis.
• The underlying problem is, of course, a metabolic acidosis.
• Solution:
• Insulin, so the body can use the sugar in the blood and stop
making ketones, which are an acidic by-product of protein
metabolism.
• In the mean time, pH should be maintained near normal so
that oxygenation is not compromised
29. Case study 8 Mr. Tuv
Mr. Tuv is a 80 year old
nursing home resident
admitted with urosepsis.
Over the last 2 hours he has
developed shortness of
breath and is becoming
confused. His abgs shows
the following results:
Ph 7.02
Co2 55
P02 77
Hc03 14
Sa02 89%
What is your
interpretation?
What interventions
would be appropriate
for Mr. Tuv?
30. Answers for Mr. Tuv
Mr. Tuv has metabolic and respiratory acidosis with hypoxemia.
The metabolic acidosis is caused by his sepsis. The respiratory
acidosis is secondary to respiratory failure.
The presentation of sepsis and associated respiratory failure is
consistent with ARDS
Treatment must be aggressive, because is acidosis is severe. He
would probably require mechanical ventilation.
If hypotension exists, aggressive fluid and vasopressor support
would be warranted.
This patient is at high risk for further complications and should be
managed in an ICU.
Bicarbonate should not be administered until the underlying sepsis
and respiratory failure is treated.
