This document discusses acid-base balance and imbalance. It defines key terms like pH, acids, and bases. The body regulates acid-base balance through buffering systems, respiratory compensation, and renal compensation. Acid-base imbalance can be diagnosed using arterial blood gases and anion gap tests. The main types of imbalance are respiratory acidosis and alkalosis from lung issues, and metabolic acidosis and alkalosis from kidney or production problems. Causes, signs, and compensation methods are described for each type.

1. Acid- Base balance &Imbalance
By
Dr.Nahla Shaaban Khalil
Critical Care And Emergency Nursing Department
Faculty of Nursing
Cairo university
2018

2. Objectives:
At the end of this lecture all students will be able to:
Define PH ,acid and base.
Discuss how the body regulates acid- base balance.
Identify the main diagnostic tests used to assess acid- base
imbalance.
Identify ABG parameters.
Differentiate between the respiratory and metabolic imbalances
regarding their causes, and clinical manifestations.

3. Outlines:
Definitions of PH,acid and base.
Regulation of acid-base balance.
Diagnosing acid- base imbalance.
-Arterial blood gases interpretation.
-Anion gap.
Acid base imbalance:
-Respiratory acidosis and alkalosis.
- Metabolic acidosis and alkalosis.

4. Definitions:
Acids:-are substances that dissociate or lose
ions.
Bases:-are substances capable of accepting
ions.
Buffer :-is substance that reacts with acids and
bases to maintain neutral environment of stable
PH.
PH:-represent the free hydrogen ions
concentration.

5. Acid base balance :
Equilibrium between the acid and base elements of the
blood and body fluids.
Co2+H20  H2CO3  H+HCO3
One
part
acid
20part
base
=

7. :Regulation of acid-base balance
The body has three mechanisms to maintain
acid-base balance:
1- Buffering mechanism.
2- The respiratory compensation mechanism.
3-The metabolic or renal compensation
mechanism.

9. Buffering mechanism:
Acid-base buffer is defined as a solution
containing two or more chemical compounds
that prevent marked change in hydrogen ions.
Buffers act immediately to
trap( H+)temporarily until respiratory and renal
mechanism act. they only minimize the change
in(H+)concentration.

10. Types of buffer system:-
1- Bicarbonate buffer system.
2- Phosphate buffer system.
3- Protein buffer system.
a- Plasma proteins.
b- Hemoglobin.
C -Tissue proteins.

11. Protein buffer system:
The plasma proteins in general and hemoglobin in
particular constitute an important buffer system.
It plays an important role in buffering co2
There are about 700gm of hemoglobin in the blood of
an adult person.
Deoxy hemoglobin is better buffer than oxy
hemoglobin.
Co2+H20  H2CO3  H+HCO3

13. Respiratory regulation of acid- base balance
The lungs regulate blood levels of co2 that combine with
H2O to form H2CO3 .
Chemo receptors in the medulla of the brain sense those
PH changes and vary the rate and depth of breathing to
compensate.
Breathing faster or deeper(Hyperventilation)
Eliminate more co2 leading to increase PH.
Slow and shallow breathing(Hypoventilation)
Lead to accumulation of co2 decrease PH.

14. Renal regulation of acid-base balance
Kidneys make long- term adjustment to PH.
They reabsorb acids and bases or excrete them into
urine, and can also produce HCO3to replenish lost
supply.
Such adjustment to PH take the kidneys days
to weeks to complete. If the blood contains too
much acids or not enough base, the PH drops
and the kidneys in response reabsorb NaHCO3
and excrete (H+) leading to normalization of PH.

16. Diagnosis of acid base imbalance:
1-Arterial Blood Gases(ABG).
2-Anion gap estimation.

17. ABG parameters:
pH [H+
]
PCO2 Partial pressure CO2
PO2 Partial pressure O2
HCO3 Bicarbonate
BE Base excess
SaO2 Oxygen Saturation

18. Normal values:
Parameters Normal values
PH 7.35-7.45
PaCO2 35-45
HCO3 22-26
Pao2 80-100
Sao2 %More than 95
B/E ( -/+2(

19. Base excess(B/E(:
The base excess indicates the amount of excess or
insufficient level of bicarbonate in the system.
The normal range is –2 to +2 mEq/liter.
(A negative base excess indicates a base deficit in the
blood).

20. Arterial Blood Gases Interpretation:.

22. Anion Gap in Plasma
The difference between measured major positive and negative
charges.
[Na+
] -[Cl-
] - [HCO3-
]
The normal value is (8-14) mEq/L
The sum of measured cations is grater than of measured anions
due to the presence of unmeasured anions (proteins
,phosphates, sulfates, and organic acids as lactic acids, and
ketones acids).
An increased anion gap may be the only clue that metabolic
acidosis is present in a mixed acid-base disorder.

24. Acid –base imbalance:
Respiratory acidosis.
Respiratory alkalosis.
Metabolic acidosis.
Metabolic alkalosis.

25. 25

26. 1-Respiratory Acidosis
It occur with any mechanism that decreases the rate of
alveolar ventilation.
It is characterized by:
PH< 7.35
PaCO2 > 45 mmHg
compensatory increase in HCO3
-

27. Causes of respiratory acidosis:
Depression of respiratory centre:
 Narcotics / over sedation.
 Anesthesia.
 Respiratory arrest.
 Paralysis of respiratory muscles
 Impaired ventilation.
 Airway obstruction:
Foreign body.

28. Signs and Symptoms associated with Acidosis:
Decrease excitability of CNS:
 Restlessness,
 Headache,
 Drowsiness,
 Disorientation,
 Coma,
Cardiovascular:
 Dysrhythmias,
 Decreased cardiac contractility
 Hypotension.

29. Increase electrolytes :
-Hyperkalemia
-Hyper calcemia

30. Compensation of respiratory acidosis:
Renal compensation:
 Increased the plasma HCO3concentration .
 The increased PaCO2acts as a stimulus to increase the
formation of H and HCO3 from CO2+ H2O in the renal
tubular cells.
 The renal H is secreted and the new HCO3 is returned
to the plasma.

31. Respiratory Alkalosis:
It is defined as a decrease in PaCo2 caused by increase
alveolar ventilation.
It is characterized by:
 PH > 7.45
 PaCO2 < 35 mmHg
 compensatory decrease in HCO3

32. Causes of Respiratory Alkalosis:
Hyperventilation:
o Hypoxemia
o Anemia
o Fever
o Psychological dyspnea
o Early in exercises
o Angry

33. :Signs and Symptoms associated with Alkalosis
Increase excitability of CNS:
o Light headedness,
o Numbness,
o Tingling,
o Confusion,
o Inability to concentrate
o Blurred vision.
• Decrease electrolytes:
Hypokalemia
Hypertension

34. Compensation of respiratory alkalosis
Renal compensation:
The kidneys decrease plasma [ HCO3 ]:
 Decrease reabsorption of the filtered HCO3.
 The decreased CO2 decreases the generation of H by the
tubular epithelial cells.

37. Metabolic acidosis:
It is defined as a primary decrease in plasma
bicarbonate concentration(HCO3).
It is characterized by:
 PH < 7.35
 HCO3 < 22 mEq/ L
 Compensatory decrease in PaCO2

38. Causes of metabolic acidosis:
1)Loss of HCO3:
 Prolonged severe diarrhea
2)Decreased elimination of acids:
 Renal failure
3)Excess production of Acids:
 Starvation - Shock
 Cardiac arrest - Alcoholic Ketoacidosis
 Tissue hypoxia
 Sepsis
 Diabetic Ketoacidosis

39. Metabolic alkalosis:
It results from an increase in bicarbonate in ECF.
It is characterized by:
 PH > 7.45
 HCO3 > 26 mEq/ L
 Compensatory increase in PaCO2

40. Causes of metabolic alkalosis:
Excess of base /loss of acid.
Acute H ion loss:
 Vomiting,
 Gastric suction.
 diuretics as: Frusemide.
Excess intake of Alkali
Diet rich H in fruits and vegetables.
IV NaHCO3administration.