The document discusses acid-base balance and imbalances in the human body. It explains that the body tightly regulates blood pH between 7.35-7.45 through buffer systems, respiration, and kidney function. When pH falls below or rises above this range, acidosis or alkalosis occurs respectively. Various conditions can cause respiratory or metabolic acidosis/alkalosis by affecting carbon dioxide or bicarbonate levels. The body attempts to compensate for imbalances through opposing respiratory or renal responses depending on the underlying cause. Diagnosis involves determining if the pH, carbon dioxide, or bicarbonate levels are abnormal and whether compensation is partial or complete.

1. XIANG ZHUXING
Acid and Base Imbalance
xiangz@unifiji.ac.fj

2. The Body and pH
 Homeostasis of pH is tightly controlled
 Blood = 7.35 – 7.45
 < 6.8 or > 8.0 death occurs
 Acidosis (acidemia) below 7.35
 Alkalosis (alkalemia) above 7.45

3.  The body produces more acids than bases
 Acids take in with foods
 Acids produced by metabolism of lipids and proteins
 Cellular metabolism produces CO2.
 CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3
-

4. Control of Acids: Buffer systems
1. Bicarbonate buffer (ECF)
• Take up H+ or release H+ as conditions
change
• Buffer pairs – weak acid and a base
• Exchange a strong acid or base for a weak
one
• Results in a much smaller pH change

5. Phosphate buffer
 Major intracellular buffer
 H+ + HPO4
2- ↔ H2PO4-
 OH- + H2PO4
- ↔ H2O + HPO4
2-

6. Protein Buffers
 Includes hemoglobin, work in blood
and ICF
 Carboxyl group gives up H+
 Amino Group accepts H+
 Side chains that can buffer H+ are
present on 27 amino acids.

7. 2. Respiratory mechanisms
 Exhalation of carbon dioxide
 Powerful, but only works with volatile
acids (CO2)
 Doesn’t affect fixed acids like lactic acid
 CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3
-
 Body pH can be adjusted by changing rate
and depth of breathing

8. 3. Kidney excretion
 Can eliminate large amounts of acid
 Can also excrete base
 Can conserve and produce bicarb ions
 Most effective regulator of pH
 If kidneys fail, pH balance fails

9. Rates of Correction
 Chemical buffers function almost
instantaneously
 Respiratory mechanisms take several
minutes to hours
 Renal mechanisms may take several hours
to days

11. Acid-Base Imbalances
 pH< 7.35 acidosis
 pH > 7.45 alkalosis
 The body response to acid-base imbalance is
called compensation
 May be complete if brought back within
normal limits
 Partial compensation if range is still
outside norms.

12. Compensation
 If underlying problem is metabolic,
hyperventilation or hypoventilation can help :
respiratory compensation.
 If problem is respiratory, renal mechanisms can
bring about metabolic compensation.
NORMAL RANGE:
HCO3- = 22 - 26 mEq / L
pCO2 = 35 – 45 mm Hg

14. Respiratory Acidosis
 Carbonic acid excess
PCO2 > 45mm Hg (hypercapnia)
 pH < 7.35
 Primary cause: hypoventilation

15. Respiratory Acidosis
 Chronic conditions:
 Depression of respiratory center in brain that controls
breathing rate – drugs or head trauma
 Paralysis of respiratory or chest muscles
 Emphysema
 Acute conditons:
 Adult Respiratory Distress Syndrome
 Pulmonary edema
 Pneumothorax

16. Compensation for Respiratory Acidosis
Kidneys eliminate hydrogen ion
and retain HCO3-

17. 17

18. Respiratory Alkalosis
 Carbonic acid deficit
PCO2 < 35 mm Hg (hypocapnia)
 pH > 7.45
 Most common acid-base imbalance
 Primary cause is hyperventilation

19. Respiratory Alkalosis
 Conditions that stimulate respiratory center:
 Oxygen deficiency at high altitudes
 Pulmonary disease and Congestive heart failure –
caused by hypoxia
 Acute anxiety
 Fever, anemia
 Early salicylate intoxication
 Cirrhosis
 Gram-negative sepsis

20. Compensation of Respiratory Alkalosis
Kidneys conserve hydrogen ion and
eliminate HCO3-

21. 21

22. Metabolic Acidosis
 Bicarbonate deficit
 HCO3- < 22mEq/L
 pH < 7.35
 Causes: Gain of strong acid; Loss of base
 Accumulation of acids (lactic acid or ketones)
 Failure of kidneys to excrete H+
 Loss of bicarbonate through diarrhea or renal
dysfunction

23. Compensation for Metabolic Acidosis
 Increased ventilation
 Renal excretion of hydrogen ions if
possible

24. 24

25. Metabolic Alkalosis
 Bicarbonate excess
 HCO3- > 26 mEq/L
 pH > 7.45
 Causes: (more base; less acid)
 Excess vomiting = loss of stomach acid
 Excessive use of alkaline drugs
 Certain diuretics
 Endocrine disorders
 Heavy ingestion of antacids
 Severe dehydration

26. Compensation for Metabolic Alkalosis
 Alkalosis most commonly occurs with
renal dysfunction, so can’t count on
kidneys
 Respiratory compensation difficult –
hypoventilation limited by hypoxemia
PO2: 80-100 mmHg
O2 sat: 95%-100%

27. 27

28. Diagnosis of Acid-Base Imbalances
1. Note whether the pH is low (acidosis) or
high (alkalosis)
1. Decide which value, pCO2 or HCO3
- , is
outside the normal range and could be the
cause of the problem. If the cause is a
change in pCO2, the problem is
respiratory. If the cause is HCO3
- the
problem is metabolic.

29. 3. Look at the value that doesn’t
correspond to the observed pH change. If
it is inside the normal range, there is no
compensation occurring. If it is outside the
normal range, the body is partially
compensating for the problem.
Diagnosis of Acid-Base Imbalances

30. Example
 A patient is in intensive care because he
suffered a severe myocardial infarction 3
days ago. The lab reports the following
values from an arterial blood sample:
 pH = 7.3
 HCO3- = 20 mEq / L ( 22 - 26)
 pCO2 = 32 mm Hg (35 - 45)

32. Diagnosis
Metabolic acidosis
With compensation

33. 7.
7.35
35
7.45

34. Cheat Sheet
• Increase pH – alkalosis
• Decrease pH – acidosis
• Respiratory – CO2
• Metabolic(kidneys)– HCO3-
• CO2 has an inverse relationship with pH
• When pH goes down, CO2 goes up
• HCO3 follows pH, If pH goes up so does HCO3-
• CO2 increases, pH decreases – resp. acidosis
• CO2 decreases, pH increases – resp. alkalosis
• HCO3 increases, pH increases – metabolic alkalosis
• HCO3 decreases, pH decreases – metabolic acidosis

35. Practice : Analyzing ABG
6 7.5 51 35
7 7.29 49 32

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 https://www.slideshare.net/nikhilnanjappa1/acid-base-balance-and-imbalance