In this blog, we will discuss ABGs which is an abbreviation for Arterial Blood Gases, the components of ABGs, normal ABG values, and more. But, before that, it is important to understand what ABG is? and why it is required.
What is an ABG (Arterial Blood Gas)?
This test checks the patient’s lungs and how well they can move oxygen and remove carbon dioxide from the blood. It is a blood test that measures the oxygen and carbon dioxide levels, pH levels, and levels of acidity in blood.
It is an important skill for nurses, physicians, and other healthcare workers to learn. This test is commonly performed in the ER or ICU. First, let us discuss how and which vein draws ABGs.
Veins that are used to draw ABG (Arterial Blood Gasses)
The most commonly used vein to draw ABG is the radial artery. The femoral artery or Brachial Artery can also draw blood samples. A small amount of blood is required for this test, generally 1ml3 which is then sent to the labs for testing.
Components of ABGs measured.
- pH: The PH of blood means the measurement of acidity or alkalinity in blood and is determined by the concentration of hydrogen ions.
- PaO2 (Partial Pressure of Oxygen): It measures the pressure of oxygen dissolved in the blood and how well oxygen is moving from the lungs to into the blood.
- PaCO2 (Partial pressure of carbon dioxide): Measurement of pressure exerted by carbon dioxide in the blood and how well it moves out of the body.
- HCO3 (Bicarbonate): Helps maintain acid-base balance by regulating the pH of the blood. You can calculate it by using the measured values of pH and PACO2.
- O2 Sat (Oxygen saturation): measurement of how much hemoglobin is transported by blood’s hemoglobin.
- O2 CT (Oxygen content): measurement of the amount of oxygen in your blood.
- Hemoglobin: determines the amount of hemoglobin in your blood.
Normal ABG values (Arterial Blood Gas values)
Here is the chart of normal ABG values.
pH
The normal range of pH in blood is 7.35-7.45.
Below 7.35 is acidic.
Above 7.45 is alkaline.
PaO2
The normal range for PaO2 is 75-100 mmHg.
Below 75mmHg indicates hypoxemia.
Above 100mmHg can lead to oxygen toxicity
PaCO2
Normal level for PaO2 is 35-45 mmHg.
Below 35mmHg indicates hypocapnia.
Above 45mmHg indicates Hypercapnia.
HCO3- (Bicarbonate)
The normal level for HCO3- or Bicarbonate is 22-26mEq/L.
Below 22mEq/L indicates metabolic acidosis.
Above 26mEq/L indicates metabolic alkalosis.
O2 Sat (Oxygen Saturation)
The normal range for Oxygen Saturation is 95-100%.
Below 95 % indicate hypoxemia which means low oxygen level in blood.
Above 100% is rare and can be caused by pulse oximetry due to supplemental oxygen or other factors.
How to interpret ABGs values?
Here is an easy way to interpret ABG (Arterial Blood Gas) values. The “ROME” mnemonic is used for interpreting Arterial Blood Gas results quickly.
Respiratory Opposite: (Respiratory Disorders)
The inverse relationship between pH and PaCO2. This indicated Respiratory Disorders. In Respiratory Opposite, pH and PaCO2 move in opposite directions.
- Respiratory Acidosis: pH ↓ PaCO2 ↑
- Respiratory Alkalosis: pH ↑ PaCO2 ↓
Metabolic Equal: (Metabolic Disorders)
It is the direct relationship between pH and HCO3-. This indicates Metabolic Disorders. In Metabolic Equal pH and HCO3- move in the same direction.
- Metabolic Acidosis: pH ↓ HCO3 ↓
- Metabolic Alkalosis: pH ↑ HCO3 ↑
Compensation consideration
Partial compensation: The opposite system (respiratory for metabolic or metabolic for respiratory) is adjusting but has not completely normalized the pH.
Full compensation: The opposite system has adjusted sufficiently to bring the pH back into the normal range, but the primary disturbance (PaCO₂ or HCO₃⁻) remains abnormal.
Step-by-step interpretation of ABGs (Arterial Blood Gas)
- Assess the pH and find if it is acidosis or alkalosis.
- Determine the primary disturbance whether it is respiratory or metabolic.
- Check for compensation and determine whether it is partial or full compensation.
Examples of Common Conditions and ABGs Patterns
Respiratory Acidosis:
Low pH level and elevated PaCO2.
- COPD
- Hypoventilation
Respiratory Alkalosis:
High pH level and Low PaCO2.
- Anxiety
- Hyperventilation
Metabolic Acidosis:
Low pH and Low HCO3-
- Renal failure
- Diabatic ketoacidosis
Metabolic Alkalosis:
High pH level and High HCO3- level.
- Vomiting
- Dehydration
Importance of Arterial Blood Gasses (ABGs)
ABGs or Arterial Blood Gases provide information about the patient respiratory and metabolic status. The key reasons why ABGs are important are as follows:
- Determine acid-base balance.
- Helps in the evaluation of oxygen.
- Helps diagnose respiratory-related problems such as asthma, pneumonia, COPD, etc.
- Helps healthcare providers to monitor disease progression in patients.
- It can help in diagnosing kidney disorders.
What is ABG vs VBG?
ABG stands for Arterial blood Gas whereas VBG stands for Venous Blood Gas. Both are blood tests used to measure the level of oxygen and carbon dioxide in blood. The main difference is that in ABG blood is from the artery and in VBG the blood is actually from Vein.
Risks associated with ABGs
Risks related to ABGs are exceedingly rare, but it includes:
- Infection
- Bleeding
- Bruising
- Fainting
- Nerve damage
There may be some other risks, too. It is important to note that the patients cannot lift heavy objects for 24 hours after the test.
Conclusion
Healthcare professionals need to understand ABG or Arterial Blood Gas. Mastering this skill can help to assess the respiratory and metabolic condition of the patients. In this blog we have provided you the information about ABG, what components are measured in ABG, tricks, and tips to remember ABGs.
