Medical Disclaimer: This calculator is for educational purposes only and should not be used to diagnose or treat any type of medical condition. This calculator should only be used for practicing ABG interpretation. It is not meant for clinical use.

ABG Interpretation Calculator

ABG Calculator

(Arterial Blood Gas Values)
pH
mm Hg
mEq/L

ABG Calculator

(Arterial Blood Gas Values)
pH
mm Hg
mEq/L

ABG Normal Values

ABG interpretation involves learning and understanding the following 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%

Each of these values is important in the assessment of how well a patient is taking in oxygen while removing carbon dioxide.

What is an Arterial Blood Gas?

An arterial blood gas (ABG) is a blood test that measures the levels of oxygen, carbon dioxide, and bicarbonate in the blood. It also measures the pH of the blood, which provides an assessment of the acid-base balance within the body.

The test results are used by medical professionals to assess how well oxygen is being distributed throughout the body and how well carbon dioxide is being removed.

Steps for Performing an ABG Analysis

In order to properly interpret an ABG, there are a few steps that need to be taken:

  • Step 1 – Obtain and run an arterial blood 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 the results are compensated or uncompensated

By following these steps, you will be able to perform an ABG analysis and determine the best treatment method for the patient.

What is Acid-Base Balance?

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

Human blood is typically slightly more alkaline than acidic, and a normal pH ranges from 7.35 to 7.45. Our body strives to maintain the blood pH as close to 7.40 as possible.

pH scale acid-base balance

Medical professionals are able to evaluate a patient’s acid-base balance by performing a test to measure the levels of carbon dioxide and bicarbonate in arterial blood.

This test is called an Arterial Blood Gas (ABG).

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 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.

Types of Acid-Base Disorders

There are four primary types of acid-base disorders:

  1. Respiratory acidosis
  2. Respiratory alkalosis
  3. Metabolic acidosis
  4. Metabolic alkalosis

Each one is caused by a different imbalance within the body and requires different treatment methods.

Respiratory Acidosis

Respiratory acidosis occurs when the lungs are not able to remove enough carbon dioxide from the blood. This can be caused by a number of different respiratory disorders, such as COPD, bronchitis, or pneumonia.

Treatment for respiratory acidosis typically involves increasing ventilation in order to remove more carbon dioxide from the blood. This can be done with mechanical ventilation by increasing the respiratory rate or tidal volume.

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

Respiratory Alkalosis

Respiratory alkalosis occurs when the lungs remove too much carbon dioxide from the blood. This is typically caused by hyperventilation.

Treatment for respiratory alkalosis involves decreasing ventilation in order to retain more carbon dioxide in the blood. This can be done with mechanical ventilation by decreasing the respiratory rate or tidal volume.

 

pH

PaCO2

HCO3

Acute (Uncompensated)

> 7.45

< 35

Normal

Partially Compensated

> 7.45

< 35

< 22

Chronic (Fully Compensated)

Normal

< 35

< 22

Metabolic Acidosis

Metabolic acidosis occurs when there is an accumulation of acids in the blood. This can be caused by renal failure, diabetic ketoacidosis, or lactic acidosis.

Treatment for metabolic acidosis typically involves using intravenous fluids to correct the fluid and electrolyte imbalance. Medications, such as bicarbonate, may also be given to help neutralize the acids in the blood.

 

pH

PaCO2

HCO3

Acute (Uncompensated)

< 7.35

Normal

< 22

Partially Compensated

< 7.35

< 35

< 22

Chronic (Fully Compensated)

Normal

< 35

< 22

Metabolic Alkalosis

Metabolic alkalosis occurs when there is a lack of acids in the blood. This can be caused by vomiting or the use of diuretics.

Treatment for metabolic alkalosis typically involves correcting the fluid and electrolyte imbalance with intravenous fluids. Medications, such as potassium chloride, may also be given to help replenish the body’s acid stores.

 

pH

PaCO2

HCO3

Acute (Uncompensated)

> 7.45

Normal

> 26

Partially Compensated

> 7.45

> 45

> 26

Chronic (Fully Compensated)

Normal

> 45

> 26

Final Thoughts

ABG interpretation is a vital skill for any medical professional. By understanding the normal values and steps for performing an ABG analysis, you will be able to effectively assess and treat acid-base disorders.

An ABG calculator is a tool that provides an easy way to determine the acid-base status by inputting the pH, PaCO2, and HCO3- values. However, it is important to note that the ABG calculator should not be used as a substitute for clinical judgment.

Check out our full ABG interpretation guide if you want to learn more. Thanks for reading and, as always, breathe easy, my friend.

Medical Disclaimer: This content is for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you read in this article. We strive for 100% accuracy, but errors may occur, and medications, protocols, and treatment methods may change over time.

References

The following are the sources that were used while doing research for this article:

  • “Interpretation of Arterial Blood Gas.” PubMed Central (PMC), Apr. 2010, www.ncbi.nlm.nih.gov/pmc/articles/PMC2936733.
  • “Diagnosing Metabolic Acidosis in the Critically Ill: Bridging the Anion Gap, Stewart, and Base Excess Methods.” PubMed, 1 Mar. 2009, pubmed.ncbi.nlm.nih.gov/19247746.
  • Rose, Burton, and Theodore Post. Clinical Physiology of Acid-Base and Electrolyte Disorders (Clinical Physiology of Acid Base & Electrolyte Disorders). 5th ed., McGraw-Hill Education / Medical, 2001. [Link]
  • Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 11th ed., Mosby, 2016. [Link]

Disclosure: The links to the textbooks are affiliate links which means, at no additional cost to you, we will earn a commission if you click through and make a purchase.