ABG Interpretation

About this course

Arterial blood gas (ABG) analysis is a commonly used diagnostic tool to evaluate the partial pressure of gas in blood and acid-base content. It is especially important for critically ill patients and helps interpret respiratory, circulatory, and metabolic disorders. This course will discuss the step-by-step approach of ABG interpretation for nurses and other healthcare providers.

Learning objectives

• Review normal values for arterial blood gas interpretation.
• Describe indications and contraindications for obtaining an arterial blood gas.
• Identify causes of acidosis and alkalosis.
• Recognize the differences between metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis.
• Interpret an arterial blood gas through worked example.

Course outline

25 sections · finish in any order across devices

1. 1

   Introduction

   ABG (arterial blood gas) interpretation is important for physicians, respiratory therapists, nurses, and other healthcare providers.1 Blood gas analysis is a commonly used diagnostic tool to evaluate the partial pressure of gas in blood and acid-base content.2 It is especially important for critical

   4 min

2. 2

   What Is Arterial Blood Gas

   Analyzing and monitoring the arterial blood gas (ABG) is essential in diagnosing and managing the oxygenation status and acid-base balance of high-risk patients and the care of those who are critically ill.4 Nurses must be able to analyze arterial blood gas competently, determine blood gas exchange

   4 min

3. 3

   Factors That Affect ABG Interpretation

   The following are factors that may make ABG interpretation difficult3:

   4 min

4. 4

   Step 1

   This step involves assessing the internal consistency of the values using the Henderson-Hasselbalch equation1:

   4 min

5. 5

   Step 2

   Next, you need to check if there is alkalemia or acidemia present.1 The normal pH is 7.35-7.45. If a pH is less than 7.40, acidosis may be present. If the pH is greater than 7.40, alkalosis may be present. For example, a pH of 7.37 would be categorized as acidosis, and a pH of 7.42 would be categori

   4 min

6. 6

   Step 3

   Now, you need to determine if the disturbance is respiratory or metabolic.1 For this, you can evaluate the respiratory and metabolic components of the ABG results, the PaCO2 and HCO3, respectively.2

   4 min

7. 7

   Step 4

   Next step is used to determine if there is appropriate compensation for the primary disturbance.1 Usually, compensation does not return the pH to normal (7.35 – 7.45).1 Also, If the observed compensation is not the expected compensation, more than one acid-base disorder is likely present.1

   4 min

8. 8

   Step 5

   Next, if a metabolic acidosis exists, you need to calculate the anion gap.1 A normal anion gap is approximately 12 meq/L, but it can vary in patients with hypoalbuminemia.1 In patients with hypoalbuminemia, the normal anion gap is lower than 12 meq/L; the “normal” anion gap in patients with hypoalbu

   4 min

9. 9

   Step 6

   If an increased anion gap is present, assess the relationship between the increase in the anion gap and the decrease in [HCO3-].1 The ratio of the change should be between 1.0 and 2.0 if an uncomplicated anion gap metabolic acidosis is present.1

   4 min

10. 10

    The Difference Between Arterial Blood Gas and Venous Blood Gas

    Arterial blood gas (ABG) analysis is an important step in assessing the adequacy of oxygenation and ventilation while diagnosing and monitoring acid-base disturbances.7 But an arterial puncture is required for the blood sample. It can lead to complications like pain, hematoma, nerve injury, etc.7 In

    4 min

11. 11

    Respiratory Acidosis

    Respiratory acidosis is caused by inadequate alveolar ventilation leading to CO2 retention.6 Simply put, in this condition, the lungs cannot eliminate enough of the carbon dioxide made by the body.3 As a result, the body excretes the extra hydrogen in the urine and exchanges it for bicarbonate ions.

    4 min

12. 12

    Treatment

    Once the diagnosis has been made, the underlying cause of respiratory acidosis must be treated.8 The hypercapnia should be corrected gradually because rapid alkalization of the cerebrospinal fluid (CSF) may lead to seizures.8

    4 min

13. 13

    Metabolic Acidosis

    Metabolic acidosis is not a benign condition and signifies an underlying disorder that needs immediate attention to minimize morbidity and mortality.9 It can occur because of either increased acid production or acid ingestion, decreased acid excretion, or increased rate of gastrointestinal and renal

    4 min

14. 14

    Causes

    A few conditions can cause metabolic acidosis. For instance, HCO3 loss from diarrhea, shock, renal tubular acidosis, drug intoxication, salicylate poisoning, renal failure, diabetic ketoacidosis, and circulatory failure producing lactic acid can all cause metabolic acidosis.3

    4 min

15. 15

    Respiratory Alkalosis

    Respiratory alkalosis is caused by excessive alveolar ventilation (hyperventilation), resulting in more than normal CO2 exhaling. As a result, PaCO2 is reduced, and pH increases, causing alkalosis.6 It can be acute or chronic and is mainly based on the level of metabolic compensation for the respira

    4 min

16. 16

    Causes

    The primary cause of all respiratory alkalosis etiologies is hyperventilation.10 These include central causes, hypoxemic causes, pulmonary causes, and iatrogenic causes.10

    4 min

17. 17

    Treatment

    Treatment for respiratory alkalosis is focused on treating the underlying problems, such as 10:

    4 min

18. 18

    Metabolic Alkalosis

    Metabolic alkalosis occurs due to decreased hydrogen ion concentration, leading to increased bicarbonate or increased bicarbonate concentrations.6 The kidneys will increase the HCO3 excretion trying to conserve the hydrogen. As a result, the respiratory system will compensate by decreasing ventilati

    4 min

19. 19

    Causes

    Multiple causes and diseases induce metabolic alkalosis.11 In general, the causes can be narrowed down to an intracellular shift of hydrogen ions, gastrointestinal (GI) loss of hydrogen ions, excessive renal hydrogen ion loss, retention or addition of bicarbonate ions, or volume contraction around a

    4 min

20. 20

    Treatment

    Before considering treatment, we need to know the types of metabolic alkalosis. Metabolic alkalosis is split into 2 main categories11:

    4 min

21. 21

    Compensation

    Acid-base disorders are typically associated with a compensatory response that lessens the HCO3/ PaCO2 ratio change and, consequently, the pH.3 Remember that pH is closely controlled in the human body, and there are various mechanisms to maintain it at a constant value.5

    4 min

22. 22

    Metabolic Compensation

    If respiratory acidosis develops, for example, in CO2 retention secondary to COPD, the kidneys will start to retain more HCO3 to correct the pH.5 The result is a low normal pH with a high CO2 and high bicarbonate, and this process can take over days.5

    4 min

23. 23

    Case Reflection

    You are assessing a 60-year-old male in the intensive care unit. He has just arrived from surgery and per the report, he was administered pain medication prior to being transported. The results of the ABG values include pH 7.21, PaCO2 64 mm Hg, HCO3 = 24 mm Hg. What does the ABG reflect?

    4 min

24. 24

    Role of ABG in Trauma Assessment

    The condition of severe trauma is a major global issue as it accounts for one in ten mortalities.12 The pre-hospital resuscitation and monitoring of trauma patients rely on clinical experience and a few basic parameters, including consciousness, breathing quality and rate, heart rate, and blood pres

    4 min

25. 25

    Conclusion

    Arterial blood gas monitoring is the standard for assessing a patient’s oxygenation, ventilation, and acid-base status. Although ABG monitoring has been replaced mainly by non-invasive monitoring, it is still helpful in confirming and calibrating non-invasive monitoring techniques.2

    4 min

This course satisfies

Requirement summaries come from our state requirement records. Always confirm details with your board before you renew.

References and resources

• Kaufman D. American Thoracic Society - Interpretation of Arterial Blood Gases (ABGs). Thoracic.org. Published 2019. https://www.thoracic.org/professionals/clinical-resources/critical-care/clinical-education/ABGs.php
• Castro D, Keenaghan M. Arterial blood gas. National Library of Medicine. Published 2021. https://www.ncbi.nlm.nih.gov/books/NBK536919/
• Edu, N. (2020). ABG interpretation for nurses.‌
• Safwat AM, Khorais AM. Effectiveness of a computer-based learning module on arterial blood gas interpretation among staff nurses in critical care units. International journal of Nursing Didactics. 2018;8(03). doi:10.15520/ijnd.v8i03.2087
• Oxford Medical Education. Arterial Blood Gas (ABG) interpretation for medical students, OSCEs and MRCP. Oxford Medical Education. Published July 29, 2014. https://oxfordmedicaleducation.com/ABGs/ABG-interpretation/
• Zaininger. ABG Interpretation | A guide to understanding ABGs | Geeky Medics. Geeky Medics. Published June 12, 2016. https://geekymedics.com/ABG-interpretation/
• Chong WH, Saha BK, Medarov BI. Comparing Central Venous Blood Gas to Arterial Blood Gas and Determining Its Utility in Critically Ill Patients: Narrative Review. Anesthesia & Analgesia. Published online March 29, 2021. doi:10.1213/ane.0000000000005501
• Shivani Patel, Sandeep Sharma. Physiology, Respiratory Acidosis. Nih.gov. Published June 24, 2021. https://www.ncbi.nlm.nih.gov/books/NBK482430/
• Burger, M., & Schaller, D. J. (2019, June 4). Metabolic Acidosis. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK482146/
• Brinkman, J. E., & Sharma, S. (2019, June 23). Physiology, Respiratory Alkalosis. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK482117/
• Brinkman, J. E., & Sharma, S. (2020). Physiology, Metabolic Alkalosis. PubMed; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK482291/
• Raffee, L. A., Oteir, A. O., Alawneh, K. Z., & Alustath, A. M. (2020). Relationship Between Initial Arterial Blood Gases and Coagulation Profiles – Analyzing the Prognosis and Outcomes in Patients with Multiple Injuries/Trauma. Open Access Emergency Medicine, Volume 12, 87–92. https://doi.org/10.2147/oaem.s244941

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