2. DEFINITION
• Changes in the ECF bicarbonate concentration
that commonly occur because of a build-up or
loss of hydrogen ion.
3. Acid Base Balance
• Several mechanism helps maintain the pH
of systemic arterial blood between 7.35 &
7.45
• The removal of H+ from the body depend
on the following 3 major mechanism:
a) Buffer system
act quickly to temporarily bind H+,
removing the highly reactive excess H+,
and raising the pH.
4. b) Exhalation of CO2
By increasing the rate and depth of
breathing, more CO2 can be exhaled.
Within minutes this reduces the level of
carbonic acid in blood, which raises the
blood pH ( blood H+ level).
c) Kidney excretion of H+
the slowest mechanism, but the only way
to eliminate acids, through urine.
5. Acidosis & Alkalosis
• A change in blood pH that leads to
acidosis or alkalosis may be encountered
by compensation which response to acid
base imbalance.
• If a person has altered blood pH due to
metabolic causes, hyperventilation of
hypoventilation can help bring the blood
pH back to normal. This form of
compensation, occurs within minutes and
reaches its maximum within hours.
6. Respiratory acid-base imbalance
• If a person altered blood pH due to
respiratory causes, then renal
compensation –changes in secretion of H+
and reabsorption of HCO3- by the kidney
tubules –can help reverse the change.
• Renal compensation may begin in
minutes, but it takes days to reach
maximum effectiveness.
7. • Both respiratory acidosis and alkalosis are
disorders resulting from changes in partial
pressure of CO2 (PCO2) in systemic
arterial blood (35-45 mmHg).
• By contrast, both metabolic acidosis and
alkalosis are disorders resulting from
changes in HCO3- concentration (22-26
mEq/L) in systemic arterial blood.
8. Respiratory Acidosis
• PCO2 level (>45mmHg).
• pH (7.35) if there is no compensation.
Common causes:
• Hypoventilation due to emphysema,
pulmonary edema, trauma to respiratory
center, airway obstruction or dysfunction of
muscles of respiration.
9. Compensatory mechanism:
• Renal:
excretion of H+
reabsorption of HCO3-
Aim of treatment:
• Exhalation of CO2 by providing ventilation
therapy. In addition IV HCO3-
administration may be helpful.
10. Respiratory Alkalosis
• PCO2 level (<35mmHg).
• pH (7.45) if there is no compensation.
Common Cause:
• Hyperventilation due to oxygen deficiency,
pulmonary, pulmonary disease,
cerebrovascular accident (CVA), or severe
anxiety.
11. Compensatory mechanism:
• Renal:
excretion of H+
reabsorption of HCO3-
Aim of treatment:
• Is aimed at increasing level of CO2 in the
body. One simple treatment is to have the
person inhale and exhale into a paper bag
for a short period.
12. Metabolic Acidosis
• HCO3- (<22mEq/L).
• pH (<7.35) if there is no compensation.
Common Cause:
• Loss of bicarbonate ions due to diarrhea,
accumulation of acid (ketosis), renal
dysfunction.
13. Compensatory mechanism:
• Respiratory:
hyperventilation, which increases the loss of
CO2
Aim of treatment:
• If the problem is not too severe,
hyperventilation can help bring blood pH into
the normal range. Treatment consists of
administering IV solution of sodium
bicarbonate and correcting the cause of
acidosis.
14. Metabolic Alkalosis
• HCO3- (>26mEq/L).
• pH (>7.45) if there is no compensation.
Common Cause:
• Loss of acid due to vomiting, gastric
suctioning or use of certain diuretics,
excessive intake of alkaline drugs.
15. Compensatory mechanism:
• Respiratory:
hypoventilation, which increases the loss of
CO2
Aim of treatment:
• If the problem is not too severe,
hyperventilation can help bring blood pH into
the normal range. Treatment consists of
administering IV solution of sodium
bicarbonate and correcting the cause of
acidosis.
16. Diagnosis
• Evaluation of 3 factors in a sample of systemic
arterial blood:
-pH, [HCO3-], PCO2
• Examined in the following 4 step sequence:
1. Note whether the pH is high (alkalosis) or
low(acidosis).
17. 2. Then check whether which value PCO2 or
HCO3- is out of the normal range and could be
the cause of the pH change. For example,
elevated pH could be caused by low PCO2 or
high HCO3-.
3. If the cause is a change in pH PCO2, the
problem is respiratory; if the case is a change
in HCO3-, the problem is metabolic.
18. Homework
• Summarize respiratory and metabolic acidosis
and alkalosis (in form of table).
• *note: definition, common cause and
compensatory mechanism
19. • Question 1
A patient was admitted at the A&E department in hospital due
to ethylene glycol poisoning. Following are the arterial blood
diagnosis:
Laboratory findings Patient Normal
pH 5.3 7.4 + 0.05
pCO2 40 mmHg 40mmHg
HCO3 15mmHg 20mmHg
What is the diagnosis for the above condition? (1m)
What is the compensatory action occurs in the body of the
above patient? (1m)
Explain on one of the common cause of the above condition.
(1m)
20. • Question 2
A patient was admitted at the A&E department in hospital.
Following are the arterial blood diagnosis:
Laboratory findings Patient Normal
pH 7.85 7.4 + 0.05
pCO2 20mmHg 40mmHg
What is the diagnosis for the above condition? (1m)
What is the 2 compensatory action occurs in the body of the
above patient? (2m)
Explain on one of the common cause of the above condition.
(1m)
21. • Question 3
A patient was presented at the A&E department in hospital with the
symptoms of vomiting.
Estimate the probable arterial blood diagnosis. (2m)
What is the diagnosis for the above condition? (1m)
Write down the pathophysiology that lead to the above condition
starting from the ABG test. (2m)
What is the compensatory action occurs in the body of the above
patient? (1m)
What are the other common cause that lead to the above condition.
(2m)
22. • Question 4
A patient was admitted at the A&E department in
hospital. Following are the arterial blood diagnosis:
Laboratory findings Patient Normal
pH 7.2 7.4 + 0.05
pCO2 60mmHg 40mmHg
Justify the above condition? (2m)
What is the 2 compensatory action occurs in the
body of the above patient? (2m)
Explain on one of the common cause of the above
condition. (1m)
23. • Question 5
HCO3- level is decreased, the compensatory
mechanism shows high PCO2
What would be the probable value of pH?
(1m)
Interpret the above value and how does it
lead to the above condition? (2m)
Suggest one possible clinical condition that
lead to the above disorder. (1m)
24. • Question 6
PCO2 increased, the compensatory
mechanism shows increased HCO3-
What would be the probable value of pH?
(1m)
Where does the compensatory action took
place? (1m)
What is another result of compensatory
action? (1m)
Suggest one possible clinical condition that
lead to the above disorder. (1m)
25. • Question 7
PCO2 decreased, the compensatory
mechanism shows decreased HCO3-
What would be the probable value of pH?
(1m)
Where does the compensatory action took
place? (1m)
What is another result of compensatory
action? (1m)
Suggest one possible clinical condition that
lead to the above disorder. (1m)
26. • Question 8
A patient was presented at the A&E department in
hospital diagnosed with hypoxia or raised intracranial
pressure.
Estimate the probable arterial blood diagnosis. (2m)
What is the diagnosis for the above condition? (1m)
Explain the compensatory mechanism. (2m)
Where does the compensatory action took place? (1m)
27. • Question 9
A patient was presented at the A&E department in
hospital diagnosed with acute exacerbation asthma.
Estimate the probable arterial blood diagnosis. (2m)
What is the diagnosis for the above condition? (1m)
Explain the compensatory mechanism. (2m)
Where does the compensatory action took place?
(1m)
28. • Question 10
A patient was presented at the A&E department in
hospital diagnosed with renal failure with bicarbonate
being lost in the urine.
Estimate the probable arterial blood diagnosis. (2m)
What is the diagnosis for the above condition? (1m)
Explain the compensatory mechanism. (2m)
Where does the compensatory action took place?
(1m)
29. • Question 11
A patient was presented at the A&E department in
hospital diagnosed with extremely high ingestion of
sodium bicarbonate.
Estimate the probable arterial blood diagnosis. (2m)
What is the diagnosis for the above condition? (1m)
Explain the compensatory mechanism. (2m)
Where does the compensatory action took place?
(1m)
