What is Acid-Base Balance? What is this medical term referring to? If you’re looking for the answer to this question, you’re in the right place, because that is what this study guide is all about.

Acid-Base Balance refers to the degree of acidity or alkalinity in the body. Without the right balance, our organs and systems cannot function properly. In this article, we are going to cover acidosis, alkalosis, and acid-base balance on the pH scale. So if you’re ready, let’s get started.

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What is Acid-Base Balance?

Acid-Base Balance refers to the degree of acidity or alkalinity in the human body. It is measured by the pH scale. The pH scale ranges from 0, which is very acidic, to 14, which is very alkaline.

Blood in the human body is typically slightly more alkaline than acidic. A normal pH ranges from 7.35 to 7.45. The goal of the body is to maintain the blood pH as close to 7.40 as possible.

pH Scale for Acid-Base Balance Vector

How is an Acid-Base Balance Analysis Performed?

An acid-base balance analysis can be performed by looking at the results of an Arterial Blood Gas (ABG). It’s is a test that measures the blood levels of oxygen (PaO2), carbon dioxide (PaCO2), and acid-base balance (pH) in the body.

A sample of blood is collected and the results are used to assess how well oxygen is being distributed throughout the body and how well carbon dioxide is being removed.

This is why ABG Interpretation is a very important skill for Respiratory Therapists and medical professionals.

What are the Normal Values for Acid-Base Balance?

After an arterial blood sample is collected, it should be analyzed and interpreted by the practitioner. The following are the ABG normal values:

  • pH: 7.35-7.45
  • Partial Pressure of Oxygen (PaO2): 75-100 mmHg
  • Partial Pressure of Carbon Dioxide (PaCO2): 35-45 mmHg
  • Bicarbonate (HCO3-): 22-26 mEq/L
  • Oxygen Saturation (SpO2): 94-100%

The human body strives to regulate the amount of carbon dioxide and bicarbonate in the blood in order to keep the pH within the normal range.

What are the Steps for Acid-Base Balance?

  • Step 1 – Collect and Analyze an ABG Sample 
  • Step 2 – Determine if the pH is Alkalosis or Acidosis
  • Step 3 – Determine if the Issue is Respiratory or Metabolic
  • Step 4 – Determine if it’s Compensated or Uncompensated
  • Step 5 – Perform the treatment modalities recommended by the physician

We have an ABG Calculator tool that can help you with this process. With that said, it is best if you learn to perform an ABG Analysis on your own. Our complete guide on Arterial Blood Gases can help.

How Does the Body Maintain Acid-Base Balance?

Acid-Base Balance is controlled by the lungs, kidneys, and buffer systems. The lungs help with ventilation and oxygenation by providing the blood with oxygen and removing carbon dioxide on exhalation.

The kidneys help to regulate blood pH by excreting acids or bases in order to maintain a proper balance. Buffer systems help maintain proper pH balance by guarding against sudden swings in acidity and alkalinity.

What are the Types of Acid-Base Disorders?

There are two types of abnormalities when it comes to maintaining Acid-Base Balance:

  1. Acidosis
  2. Alkalosis

Acidosis means that the blood has either too much acid, or too little bases, which results in a decreased pH. Alkalosis means that the blood has too much base, or too little acid, which results in a decreased pH.

There are also two types of Acid-Base Disorders:

  1. Respiratory
  2. Metabolic

Metabolic acidosis or alkalosis occurs when there is an imbalance in the production of acids or bases that results from a lack of excretion by the kidneys.

Respiratory acidosis or alkalosis occurs when the lungs are removing too much or too little carbon dioxide due to breathing disorders.

Respiratory Acidosis:

  pH PaCO2 HCO3
Acute (Uncompensated) < 7.35 > 45 Normal
Partially Compensated < 7.35 > 45 > 26
Chronic (Fully Compensated) Normal > 45 > 26

Respiratory Alkalosis:





Acute (Uncompensated)

> 7.45

< 35


Partially Compensated

> 7.45

< 35

< 22

Chronic (Fully Compensated)


< 35

< 22

Metabolic Acidosis:





Acute (Uncompensated)

< 7.35


< 22

Partially Compensated

< 7.35

< 35

< 22

Chronic (Fully Compensated)


< 35

< 22

Metabolic Alkalosis:





Acute (Uncompensated)

> 7.45


> 26

Partially Compensated

> 7.45

> 45

> 26

Chronic (Fully Compensated)


> 45

> 26

What is Required for the Body to be in Acid-Base Balance?

The production of hydrogen ions is exactly offset by their loss. This means that, for the body to be in acid-base balance, the level of hydrogen ions must reach equilibrium.

The kidneys maintain acid-base balance by excreting hydrogen ions and generating bicarbonate. This phenomenon maintains blood plasma pH within the normal range.

Which Two Body Systems Contribute to the Acid-Base Balance of Blood?

There are two primary systems in the body that contribute to acid-base balance. They are:

  1. Respiratory System
  2. Urinary System

Each system works simultaneously to maintain a balanced pH within the body.

Acid-Base Balance Practice Questions:

1. What does Acid-base balance mean?
It is the homeostasis of the hydrogen ion concentration in the fluids throughout the body.

2. As a Respiratory Therapist, how do we check the acid-base balance of a patient?
Collect and assess an arterial blood gas (ABG).

3. What is the hydrogen ion concentration determined by?
The ratio of carbonic acid to bicarbonate in the extracellular fluid

4. What are some important sources of acids in the body?
HCl (stomach acid), cellular metabolism, CO2 in plasma- generates H+, skeletal muscle (lactic acid- anaerobic respiration), and fat breakdown (glycogen is broken down into glucose and produces acidic ketones).

5. What is one important base in the body and where is the majority found?
Bicarbonate (HCO3) which has a huge supply found in the intestine. it is produced by the pancreas to neutralize stomach acid.

6. Why is venous blood more acidic than arterial blood?
As the veins carry blood back towards the heart, it contains more acidic gas CO2.

7. Why does pH matter and what is the main element does it affect the most?
The proteins in our body (enzymes and hemoglobin included) are very sensitive to pH changes. A very small change can leave them non-functional. Our body needs to maintain homeostasis.

8. What are the 3 chemical buffer systems in the body?
Protein, Phosphate, and Carbonic Acid/Bicarbonate buffer system.

9. What are the 3 primary ways to control pH?
Chemical buffers, respiration, and kidneys (when respiration isn’t enough).

10. Where is the most water be found in our body?
Intracellular Fluid Compartment (ICF) which is inside the trillions of cells in our body. About 2/3 of all body water is found in the ICF.

11. Why does an increase in breathing rate and depth increases pH?
It is because more CO2 is expelled from the body. This is referred to as hypocapnia wherein the level of CO2 in the body is low and it will avoid acidosis.

12. Why does a decrease in breathing rate and depth decrease pH?
It is because more CO2 is retained. This is called hypercapnia which means there is too much CO2 in the body and can cause acidosis.

13. Where are receptors located which can detect rising CO2 levels and/or rising H+ concentrations?
Medulla oblongata (center of respiratory measures)

14. How can the renal response to pH changes help?
If too acidic, the distal convoluted tubule in the nephron can secrete H+ and reabsorb bicarb while if too basic, it can secrete bicarb into the urine.

15. What happens during respiratory acidosis?
There is an increase in CO2 and an increase in H+.

16. What are some respiratory acidosis conditions?
Emphysema, lung cancer, asthma, pneumonia, and hypoventilation.

17. What happens during respiratory alkalosis?
There is a decrease in CO2 due to hyperventilation. A decrease in H+ can be treated by bag breathing to re-breath CO2.

18. What are the metabolic acidosis symptoms?
Severe diarrhea wherein acid is in intestinal gastric juice and so you lose too much bicarbonate through stool. Another is the kidneys fail to get rid of acid.

19. What are metabolic alkalosis symptoms and what drugs causes this?
Chronic vomiting causes this because of losing HCl makes blood basic. Symptoms of metabolic alkalosis are constipation which is reabsorbing excessive bicarb. Diuretics which increases urine and antacids (Alka Seltzer) are the drugs that causes this.

20. What are the normal Acid-Base values?
pH: 7.35-7.45, PaCO2: 35-45 mm Hg, HCO3: 22 – 26 m Eq/L, and Glucose: 80-120mg/dl.

21. How would you interpret these values: pH below 7.35, PaCO2 above 45 mm Hg, Normal HCO3?
Respiratory acidosis.

22. What is a serious life-threatening condition of diabetes that occurs when your body produces high levels of blood acids called ketones?
Diabetic Ketoacidosis (DKA).

23. True or False: Proteins within the body help to maintain fluid balance but not acid-base balance?

24. What are the 3 of the most common parenteral routes?
Intravenous (I.V.) route is the most common, Subcutaneous (sub-Q) route, and Intramuscular (I.M.) route.

25. How can excessive blood loss be countered and still maintain normal osmolarity?
Saline (isotonic, 0.9% NaCl) and requires a very large volume because much of the saline escapes blood and enters interstitial fluid compartment. It can induce hypernatremia (plasma Na+ concentration too high) or hyperchloremia.

26. What is acidemia?
It is too many H+ ions and state caused by acidosis of the body.

27. What is alkalemia?
It is lack of adequate H+ ions and is a state cause by alkalosis of the body.

28. What are the issues with pH in the body?
Cells function in a range of H+ ions and thus if the range leaves the ideal value, cells will not be able to function, and proteins may denature.

29. What is the normal range of pH for our body?
7.45 (low) – 7.34 (higher end).

30. What are the common buffers the body uses as a first-line of defense in response to an increase in pH?
HCO3- in extracellular volume, proteins, hemoglobin, and phosphates in cells, phosphates, ammonia in urine.

31. What are the two ways the body excretes H+ ions
Ventilation via Co2 and renal urine excretion via H+.

32. What are buffers?
It minimizes the changes in pH when acid or base is added to a solution. Hemoglobin and proteins are found intracellularly. Extracellularly we have bicarbonate, phosphate, and ammonia.

33. What is the largest single component of the body that is essential for all body tissues?

34. What organs are included in the homeostasis of water?
GI tract, kidneys, and brain.

35. Where is most water in the body stored?
It is in the intracellular (in the cells).

36. Which age group most commonly has fluid, electrolyte, and acid-base balance issues?

37. Which of the following helps prevent changes in the acid-base balance of body fluids?
Proteins and some minerals.

38. The skeletal system helps maintain acid-base balance by doing what?
By absorbing or releasing alkaline phosphate and carbonate salts.

39. What two organs play an important role in maintaining acid-base balance?
The lungs and kidneys.

40. What organ is the chief regulator of the body’s acid-base balance?
The kidneys.

41. Which of the following is not a cause of metabolic disturbances of acid-base balance?
A high-fiber diet.

42. When the body experiences alkalosis, how do proteins help restore the acid-base balance?
Proteins release hydrogen into the blood.

43. What are your cations (more acidic, positive charged electrolytes)?
Sodium, potassium, calcium, and magnesium

44. What are your anions (more basic and negative charged electrolytes)?
Chloride, CO2 (bicarb), phosphorus, sulfate, lactate, and protein.

45. What electrolyte regulates cell electroconductivity and is good for blood clotting (with vitamin K)?

46. Where is calcium stored?
99% in bone and .5% in free form for teeth, muscles, and bone and the other .5% is bound to albumin.

47. How much calcium from the diet is absorbed?

48. How much calcium is excreted by the kidneys?
100-200 mg

49. What is the body’s base?

50. What is the major cation of extracellular fluid?

51. What is the job of sodium and chloride?
It regulates ECF and plasma volume, nerve impulses, and muscle contraction.

52. What hormone balances sodium?
Aldosterone from the adrenal cortex which is stimulated by ACTH that comes from anterior pituitary.

53. What is the body’s acid?

54. What is the major cation of intracellular fluid?

55. What does potassium help you stay protected from?
High blood pressure

56. What is the job of potassium?
Water balance osmotic equilibrium, acid-base balance, neuromuscular activity, and cell growth.

57. What electrolyte is a major buffer?

58. What is the role of phosphorus?
Energy metabolism of ATP (in phosphorylation reactions).

59. How to determine acid-base balance?

60. What is the lab test commonly used in the assessment and treatment of acid–base balance?
Arterial Blood Gas (ABG)

61. What are your extracellular buffers?
Bicarbonate and carbonic acid

62. What metabolic changes would you check to see for acid-base balance?
Changes in bicarbonate levels.

63. What respiratory changes would you look for to see for acid-base balance?
Changes in dissolved PCO2 level.

64. What is having high levels of carbonic acid from having too much CO2 considered?
Respiratory acidosis.

65. What could cause respiratory acidosis and what conditions/diseases can cause it?
It is caused by an increased CO2. The conditions are decreased lung surface area, such as emphysema (damaged air sacs making it hard to breath), obstructive lung disease (asthma), and neuromuscular disease in which respiratory function is impaired (MS, ALS).

66. What leads to a decrease in carbonic acid from excessive expiration of CO2 and water?
Respiratory alkalosis.

67. What happens with respiratory alkalosis and what causes it?
It causes losing too much CO2 and water from excessive breathing which decreases carbonic acid. The conditions: Early sepsis (blood poisoning), anxiety reactions, can be caused from intense exercise.

68. Phosphorus is critical to the acid-base balance in cells because of its role in:
Creating buffers to maintain the correct pH.

69. What does it mean when there’s an increase in hydrogen ions (decreased pH) from increased production, increased ingestion, or increased retention or decreased bicarbonate from extracellular fluid?
Metabolic acidosis

70. How do you get metabolic acidosis and what conditions are associated with it?
Cause: Decreased pH (increased H+) or decreased bicarb from extracellular fluid. Conditions: Diarrhea (loss water and bicarb), uremia (increased NH4), ketoacidosis from diabetes mellitus (type 1), high fat-low carb diet, and drugs (diuretics).

71. How do you get metabolic alkalosis and what conditions, or diseases are associated?
Decrease in H+ (increase pH), or increased bicarbonate from retention of base in ECF cause: Diuretics (thiazide), increased ingestion of alkali (fruit), loss of chloride, and vomiting (loss of stomach acid).

72. What is the normal blood pH?

73. What is the normal PCO2 level?
35-45 mm Hg

74. What is the normal PO2?
80-100 mm Hg

75. What is the normal HCO3-?
22-26 mEq/L

76. What is the normal oxygen saturation?

77. What does it mean when there’s an increased PCO2?
Respiratory acidosis

78. What does it mean when there is a decreased HCO3-?
Metabolic acidosis

79. What does it mean if there is a decrease in PCO2?
Respiratory alkalosis

80. What does it mean if there’s an increase in HCO3-?
Metabolic alkalosis

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81. How does the body compensate for respiratory acidosis?
It increases renal excretion of acids resulting in increasing serum bicarb.

82. How does the body compensate for respiratory alkalosis?
It decreases renal excretion of acid resulting in decreased serum bicarb.

83. how does the body compensate for metabolic acidosis?
Hyperventilation with resulting low PCO2.

84. How does the body compensate for metabolic alkalosis?
Hypoventilation with resulting increase in PCO2.

85. Hyperkalemia or hyponatremia could lead to?
Metabolic acidosis (K is an acid).

86. What will be the effect of hypokalemia or hypernatremia?
Metabolic alkalosis (sodium is a base).

87. What is the medical treatment aimed at with Respiratory Acidosis?
Improving ventilation and Correcting the primary condition responsible for the imbalance.

88. What is the state called in which arterial blood is more acidic than normal?

89. What is the difference called between the normal buffer base and the actual buffer base in a whole blood sample?
Base excess (BE).

90. The most important renal mechanism for regulating acid-base balance of the blood involves what?
Maintaining HCO3- balance.

91. How is BE expressed?

92. What is the normal BE?
+2 mEq/L

93. What is the buffer base?
The total blood buffer capable of binding hydrogen ions.

94. What is the normal blood buffer base range?
48–52 mEq/L

95. What is a titrable, nonvolatile acid called?
Fixed acid.

96. What does a fixed acid represent?
The by-product of protein catabolism.

97. What is hypercapnia?
Excess amounts of CO2 in the blood (PaCO2).

98. What is the presence of lower than normal amounts of CO2 in the blood (PaCO2) called?

99. What is the definition of metabolic acidosis?
A non-respiratory process resulting in acidemia.

100. What is called when non-respiratory processes, such as losing fixed acid or gaining HCO3-, result in alkalemia?
Metabolic alkalosis.

101. What is the definition of respiratory acidosis?
Hypoventilation, the loss of HCO3- or gaining fixed acids resulting in acidemia.

102. What is the definition of respiratory alkalosis?
Hyperventilation, resulting in alkalemia.

103. The plasma concentration of HCO3- that exists if PCO2 is normal is known as what?
Standard bicarbonate.

104. How is standard bicarbonate expressed?

105. What is the PCO2 baseline for standard bicarbonate?
40 mm Hg

106. What is an acid that can be excreted in its gaseous form called?
Volatile acid.

107. What is a physiological example of a volatile acid?
Carbonic acid.

108. How much CO2 does normal ventilation eliminate every day?
24,000 mmol/L total 13,000 mmol/L of volatile.

109. What continuously generates H+?
Normal metabolism.

110. What property of H+ is the reason for the need to regulate its concentration?
It reacts readily with the protein molecules of vital cellular catalytic enzymes.

111. Why can H+ be dangerous?
It’s reactions with proteins can change their physical contour, rendering the enzyme inactive

112. What gas is carbonic acid (H2CO3) in equilibrium with?
Dissolved CO2.

113. What would be the results of an ABG if the patient is hyperventilating?
The pH would be greater than 7.45, the PaCO2 would be less than 35, and the HCO3 would be 22-26. The interpretation would be respiratory alkalosis.

114. What are the two major mechanisms responsible for maintaining a stable pH despite CO2 production?
Isohydric buffering and ventilation.

115. What disease can increase fixed acid production?

116. How does the respiratory system compensate for increased fixed and volatile acid production?

117. How do the kidneys compensate for respiratory acidosis?
By reabsorbing HCO3 back into the blood.

118. What can be done to correct respiratory acidosis and improve alveolar ventilation?
Bronchial hygiene, lung expansion, non-invasive positive pressure ventilation, intubation, and mechanical ventilation.

119. What are some signs of respiratory alkalosis?
Paresthesia, dizziness, headache, and hyperventilation.

120. How do the kidneys compensate for respiratory alkalosis?
By excreting HCO3 in the urine.

121. What is a buffer solution?
A mixture of acids and bases that resist changes in pH when an acid or a base gets added to it.

122. How are blood buffers classified?
They are classified as either bicarbonate (open) or non-bicarbonate (closed) buffer systems.

123. What can be done to correct respiratory alkalosis?
Oxygen therapy.

124. What acids does a closed buffer system buffer?
Volatile and fixed acids.

125. What acids does an open buffer system buffer?
Fixed, only when ventilation is not impaired, plus any individual H+ regardless of origin.

126. What are the two ways that metabolic acidosis can occur?
Acid accumulation in the blood or excessive loss of HCO3.

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127. What is the normal anion gap range?

128. What does the buffering of a fixed acid produce?

129. What is the most important non-bicarbonate buffer system?
Hemoglobin because it is the most abundant.

130. What is the common blood fluid compartment that both open and closed buffer systems function?
Blood plasma.

131. What are the primary acid excreting organs?
The lungs and kidneys.

132. Which is faster at removing acid, the lungs or the kidneys?
The lungs.

133. Why is CO2 elimination crucial?
It reacts with H2O to form large quantities of H2CO3.

134. What is the anion gap?
It is the calculation of 4 electrolytes (Na+, Cl-, K+, and HCO3-).

135. What is the purpose of using the anion gap?
To eliminate the effects of respiratory involvement; i.e. to see what’s going on at the metabolic level.

136. What is indicated by an anion gap greater than 16?
Metabolic acidosis.

137. What are some of the symptoms of metabolic acidosis?
Dyspnea, hyperpnea, Kussmaul’s breathing, lethargy, and coma.

138. At what pH are severe cardiac arrhythmias likely?
Below 7.2.

139. How do the lungs compensate for metabolic acidosis?

140. What factor determines how much H+ is removed by the kidneys?
Blood pH.

141. How much fixed acid is excreted per day by the kidneys?
Less than 100 mEg

142. In what 2 ways can metabolic alkalosis occur?
Loss of fixed acids or gain of blood buffer base; either one increases plasma HCO3.

143. What is the most complicated acid-base imbalance to treat?
Metabolic alkalosis; it involves fluid and electrolyte imbalances.

144. What is the goal of secreting less H+?
To increase the amount of HCO3- in the urine; increase the amount of H+ in the blood.

145. What is the goal of secreting more H+?
To increase the amount of HCO3- in the blood; decrease the amount of H+ in the blood.

146. What are some of the causes of metabolic alkalosis?
Vomiting, hypokalemia.

147. How do the lungs compensate for metabolic alkalosis?
By hypoventilating.

148. What maintains bicarbonate levels?
The kidneys.

149. What maintains CO2 levels?
The lungs.

150. pH changes caused by PaCO2 are referred to as what?
Primary respiratory disturbances.

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Final Thoughts

So there you have it.

Acid-Base Balance uses the pH scale to measure the amount of acidity or alkalinity in the human body. Once you understand this concept, it makes the learning process much easier. Hopefully you found this study guide (and the practice questions that were included) to be helpful.

Thank you so much for reading and as always, breathe easy my friend.


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