Acid-Base Balance- Overview and Practice Questions Illustration

Acid-Base Balance: Overview and Practice Questions (2023)

by | Updated: Oct 17, 2023

Acid-base balance is a critical factor in maintaining homeostasis within the human body. Governed by complex biochemical processes, this balance ensures optimal physiological function by regulating the concentration of hydrogen ions in bodily fluids.

Imbalances can lead to disorders like acidosis or alkalosis, which have serious health implications.

Understanding the mechanisms of acid-base balance and its importance is crucial for medical professionals, as timely diagnosis and intervention are key to mitigating life-threatening conditions.

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What is Acid-Base Balance?

Acid-base balance refers to the regulation of hydrogen ion concentrations in bodily fluids, primarily blood, to maintain a stable internal environment. This balance is crucial for optimal cellular function and metabolic processes. Imbalances can result in conditions like acidosis or alkalosis, which can have severe health implications.

How is Acid-Base Analysis Performed?

Acid-base analysis is most commonly performed through an arterial blood gas (ABG) test. In this test, a small sample of arterial blood is taken, usually from the radial artery in the wrist.

The sample is then analyzed to measure various parameters, including:

  • pH: Indicates the acidity or alkalinity of the blood.
  • Partial pressure of carbon dioxide (PaCO2): Measures the amount of dissolved carbon dioxide, providing insight into the respiratory component of acid-base balance.
  • Bicarbonate (HCO3-): Provides information on the metabolic component of acid-base balance.
  • Partial pressure of oxygen (PaO2): Though not directly related to acid-base balance, this parameter is often included in ABG tests to assess oxygenation.

Additional tests like electrolyte panels may also be conducted to further understand the balance of ions like sodium, potassium, and chloride, which can also affect acid-base status.

The results of these tests are interpreted to diagnose acid-base imbalances such as acidosis (low pH) or alkalosis (high pH) and to determine their respiratory or metabolic origin.

The findings guide clinicians in choosing the appropriate treatment to restore balance, which may include fluid resuscitation, medications, or mechanical ventilation.

Acid-Base Normal Values

Once an arterial blood sample has been obtained, healthcare professionals should promptly analyze and interpret the data.

The following are the standard reference ranges for key acid-base parameters:

  • 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%

Note: The body actively works to regulate levels of carbon dioxide and bicarbonate in the bloodstream to maintain the pH within these optimal ranges.

Regulation of Blood pH

Blood pH is maintained through an intricate interplay between the lungs, kidneys, and buffering systems.

The lungs are responsible for ventilating the blood, taking in oxygen during inhalation, and expelling carbon dioxide during exhalation.

The kidneys contribute by selectively excreting or reabsorbing acids and bases to sustain the desired balance.

Buffer systems serve as a protective mechanism to stabilize pH by counteracting abrupt changes in acidity or alkalinity.

ph-scale-acid-base-balance illustration

Types of Acid-Base Disorders

Acid-base imbalances manifest in two primary forms:

  • Acidosis: Characterized by an excess of acid or a deficiency of bases in the blood, resulting in a lower pH.
  • Alkalosis: Identified by an overabundance of bases or a lack of acids, leading to an elevated pH.

Each disorder can be further categorized into:

  • Respiratory: Occurs when the lungs expel too much or too little carbon dioxide, typically due to underlying lung conditions.
  • Metabolic: Results from an imbalance in acid or base production, often linked to impaired renal function that affects excretion.

Note: Understanding these mechanisms and classifications aids clinicians in diagnosing and treating acid-base imbalances effectively.

Respiratory Acidosis

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

Respiratory Alkalosis

State pH PaCO2 HCO3
Acute (Uncompensated) > 7.45 < 35 Normal
Partially Compensated > 7.45 < 35 < 22
Chronic (Fully Compensated) Normal < 35 < 22

Metabolic Acidosis

State pH PaCO2 HCO3
Acute (Uncompensated) < 7.35 Normal < 22
Partially Compensated < 7.35 < 35 < 22
Chronic (Fully Compensated) Normal < 35 < 22

Metabolic Alkalosis

State pH PaCO2 HCO3
Acute (Uncompensated) > 7.45 Normal > 26
Partially Compensated > 7.45 > 45 > 26
Chronic (Fully Compensated) Normal > 45 > 26


Related: ABG Interpretation Calculator for Acid-Base Analysis

Steps for Analyzing Acid-Base Balance

Analyzing acid-base balance involves a structured approach to ensure accurate diagnosis and effective treatment.

Here are the general steps:

  1. Obtain and Assess an ABG Sample: Collect an arterial blood gas (ABG) sample and analyze its parameters.
  2. Identify pH Levels: Ascertain whether the pH indicates alkalosis or acidosis.
  3. Pinpoint the Origin: Determine if the imbalance is respiratory or metabolic in nature.
  4. Assess Compensation Status: Establish whether the condition is compensated or uncompensated.
  5. Implement Physician-Recommended Treatments: Follow the therapeutic interventions advised by the healthcare provider.

Note: Following these steps systematically will facilitate a comprehensive analysis of acid-base balance and guide healthcare professionals in administering appropriate care.

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Acid-Base Balance Practice Questions

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

2. How can a respiratory therapist check the acid-base balance of a patient?
They collect and assess an arterial blood gas (ABG) sample.

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 it 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 toward the heart, it contains more CO2.

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

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 the kidneys (when respiration isn’t enough).

10. Where is most water found in the body?
Intracellular fluid compartment (ICF)

11. Why does an increase in breathing rate and depth increase pH?
Because more CO2 is expelled from the body, and this is referred to as hypocapnia.

12. Why does a decrease in breathing rate and depth decrease pH?
Because more CO2 is retained, and this is referred to as hypercapnia.

13. Where are receptors located that can detect rising CO2 levels and/or rising H+ concentrations?
Medulla oblongata

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 the conditions associated with respiratory acidosis?
Emphysema, lung cancer, asthma, pneumonia, and hypoventilation.

17. What happens during respiratory alkalosis?
There is a decrease in CO2 due to hyperventilation.

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

19. What maintains bicarbonate levels in the body?
The kidneys

20. What maintains CO2 levels in the body?
The lungs

21. How would you interpret these values: pH < 7.35, PaCO2 > 45 mmHg, 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. Does respiratory acidosis occur when lungs are obstructed and gas exchange is inefficient?
Yes, when the lungs are obstructed, it leads to inefficient gas exchange. This can cause an accumulation of carbon dioxide in the blood, which leads to respiratory acidosis.

24. What are the 3 of the most common parenteral routes?
Intravenous, subcutaneous, and intramuscular

25. How do the lungs compensate for metabolic acidosis?

26. In what two ways can metabolic alkalosis occur?
The loss of fixed acids or the gain of blood buffer base.

27. What is the most complicated acid-base imbalance to treat?
Metabolic alkalosis, which involves fluid and electrolyte imbalances.

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

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

30. What are the common buffers of the body?
HCO3- in extracellular volume, proteins, hemoglobin, and phosphates in cells.

31. What are the two ways the body excretes H+ ions?
Ventilation via CO2 and renal urine excretion via H+.

32. What are some of the causes of metabolic alkalosis?
Vomiting and hypokalemia

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?
The GI tract, kidneys, and brain.

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

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

37. What 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 the cations?
Sodium, potassium, calcium, and magnesium.

44. What are the anions?
Chloride, CO2 (bicarb), phosphorus, sulfate, lactate, and protein.

45. What electrolyte regulates cell electroconductivity and is good for blood clotting?

46. Where is calcium stored?
99% in bone, 0.5% in free form for teeth, muscles, and bone, and the other 0.5% 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?
They regulate the 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 the 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. What is the lab test commonly used in the assessment and treatment of acid–base balance?
Arterial blood gas (ABG)

60. What are the extracellular buffers?
Bicarbonate and carbonic acid

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

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

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

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

65. 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.

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

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

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

69. Having high levels of carbonic acid from having too much CO2 is known as what?
Respiratory acidosis

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

71. Why is phosphorus critical to the acid-base balance of cells?
It creates a buffer to maintain the correct pH.

72. What is the normal blood pH?

73. What is the normal PaCO2 level?
35-45 mmHg

74. What is the normal PaO2?
80-100 mmHg

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

76. What is the normal oxygen saturation?
> 95%

77. What does it mean when there’s an increased PaCO2?
Respiratory acidosis

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

79. What does it mean if there’s a decreased PaCO2?
Respiratory alkalosis

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

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

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

83. how does the body compensate for metabolic acidosis?

84. How does the body compensate for metabolic alkalosis?

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

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

87. What is the treatment for respiratory acidosis?
The goal of treatment is to improve ventilation and correct 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 between the normal buffer base and the actual buffer base in a blood sample?
Base excess (BE)

90. The most important renal mechanism for regulating the 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 a buffer base?
The total blood buffer capable of binding hydrogen ions.

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

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

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

97. The plasma concentration of HCO3- that exists if the PaCO2 is normal is known as what?
Standard bicarbonate

98. What is the PaCO2 baseline for standard bicarbonate?
40 mmHg

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

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

101. What continuously generates H+?
Normal metabolism

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

103. What would the results of an ABG be 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.

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

105. What disease can increase fixed acid production?

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

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

108. 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.

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

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

FAQs About Acid-Base Balance

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

For the body to achieve acid-base balance, the production and loss of hydrogen ions must be precisely offset, reaching a state of equilibrium.

The kidneys play a pivotal role in this balance by excreting hydrogen ions and generating bicarbonate, which helps maintain the blood plasma pH within a normal range.

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

The respiratory and renal systems are the two primary body systems that contribute to maintaining acid-base balance.

The respiratory system is responsible for modulating blood pH by expelling carbon dioxide, whereas the renal system removes acids and other waste products from the blood.

Which Age Group Most Commonly Has Fluid, Electrolyte, and Acid-Base Balance Issues?

The elderly are most susceptible to fluid, electrolyte, and acid-base imbalances. Age-related changes, such as a decrease in renal function, make this group more vulnerable.

Additionally, the elderly are often on medications that can further disrupt these balances.

What is the Lab Test Commonly Used in the Assessment and Treatment of Acid-Base Balance?

The arterial blood gas (ABG) test is the standard lab test used for evaluating a patient’s acid-base status.

This test measures levels of oxygen, carbon dioxide, bicarbonate, and provides an overall assessment of acid-base balance in the blood.

Which of the Following Helps Prevent Changes in the Acid-Base Balance of Body Fluids?

Protein and mineral salts in the diet serve as buffers that help prevent fluctuations in the acid-base balance of body fluids.

These nutrients assist in stabilizing blood pH within its normal range.

How Do the Kidneys Regulate Acid-Base Balance?

The kidneys contribute to acid-base balance by excreting hydrogen ions and generating bicarbonate ions.

This action aids in maintaining the blood pH within a normal range.

How Do the Lungs Regulate Acid-Base Balance?

The lungs assist in regulating acid-base balance by eliminating carbon dioxide, a waste product that can acidify the blood.

By removing carbon dioxide, the lungs help to keep the blood pH within a normal range.

What Organ is the Chief Regulator of the Body’s Acid-Base Balance?

The kidneys serve as the principal regulators of the body’s acid-base balance.

Through the excretion of hydrogen ions and the generation of bicarbonate, they help to maintain blood pH within a normal range.

Final Thoughts

The regulation of acid-base balance is a cornerstone in sustaining overall health and biological function. When this balance is disrupted, it can lead to detrimental health conditions that demand immediate attention.

Early detection through diagnostic tests, coupled with effective treatments, can mitigate risks and restore equilibrium.

For respiratory therapists and healthcare providers, comprehending the intricacies of acid-base balance is not just academic but a clinical imperative for patient care.

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


  • Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
  • “Understanding Acid-Base Disorders.” PubMed Central (PMC), 1 Sept. 2017.
  • “Acid-Base Balance.” National Center for Biotechnology Information, 1972.
  • “Interpretation of Arterial Blood Gas.” PubMed Central (PMC), Apr. 2010.

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