ABG Interpretation Calculator Tool for Acid Base Balance

ABG Calculator – Acid-Base Analysis (Arterial Blood Gas)

by | Updated: Oct 18, 2023

ABG Interpretation Calculator Tool

ABG Calculator

(Arterial Blood Gas Values)
mm Hg

ABG Calculator

(Arterial Blood Gas Values)
mm Hg

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

ABG Normal Values

ABG interpretation involves learning and understanding the following normal values:

pH 7.35–7.45
PaO2 75–100 mmHg
PaCO2 35–45 mmHg
HCO3- 22–26 mEq/L
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.

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.


  • “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.
  • Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 11th ed., Mosby, 2016.

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