A nurse cares for a patient who is hyperventilating which arterial blood gas should the nurse expect

Arterial blood gases (ABG's) is a blood test which is used to give an indication of ventilation, gas exchange and acid-base status and is taken from an arterial blood supply[1]. The arterial blood gas test is one of the most common tests performed on patients in intensive care units. At other levels of care, pulse oximetry plus transcutaneous carbon dioxide measurement is a less invasive alternative method of obtaining similar information.[2]

To perform this test, blood is collected from a specific artery, usually the radial artery of the wrist. This blood sample allows an accurate determination of the amount of oxygen that passes from the lungs to the blood. This test is the one most commonly performed to diagnose cases of respiratory failure[3].
Arterial blood gas test results can show if:

• Lungs are getting enough oxygen.
• Lungs are removing enough carbon dioxide.
• Kidneys are working properly.[2]

Uses[edit | edit source]

ABGs are very useful for detecting conditions that cause respiratory failure. Including: Lung Failure; Acute respiratory distress syndrome (ARDS); Sepsis; Diabetic ketoacidosis (DKA); Cystic fibrosis; Pneumonia; Emphysema; Hypovolemic shock; Acute heart failure; Cardiac arrest; Kidney Failure; Septic Shock; Trauma; Chronic vomiting; Uncontrolled diabetes; Asthma ; Chronic Obstructive Pulmonary Disease (COPD); Hemorrhage; Drug Overdose; Metabolic Disease; Chemical Poisoning; To check if lung condition treatments are working.[4]

[3]

Measurements[edit | edit source]

The key components to an ABG are:

1. pH - This measures the balance of acids and bases in the blood.
2. Partial pressure of oxygen (PaO2) - This measures the pressure of oxygen dissolved in the blood.
3. Partial pressure of carbon dioxide (PaCO2) - This measures the amount of carbon dioxide in the blood and how well carbon dioxide can move out of the lungs.
4. Bicarbonate (HCO3) - This is calculated using the measured values of pH and PaCO2 to determine the amount of the basic compound made from carbon dioxide (CO2.)
5. Oxygen saturation (O2 Sat) - This measures how much hemoglobin in the blood is carrying oxygen.
6. Oxygen content (O2CT) - This measures the amount of oxygen in the blood.
7. Hemoglobin - This measures the amount of hemoglobin in the blood.

Normative Values[edit | edit source]

According to the National Institute of Health, typical normal values are:

• pH: 7.35-7.45
• Partial pressure of oxygen (PaO2): 75 to 100 mmHg
• Partial pressure of carbon dioxide (PaCO2): 35-45 mmHg
• Bicarbonate (HCO3): 22-26 mEq/L
• Oxygen saturation (O2 Sat): 94-100%[4]

Interpretation of ABGs[edit | edit source]

1. Look at the pH
   • Increased = Alkalosis
   • Decreased = Acidosis
2. Look at the PaCO2
   • Increased = Respiratory Acidosis
   • Decreased = Respiratory Alkalosis
3. Look at the HCO3
   • Increased = Metabolic Alkalosis
   • Decreased = Metabolic Acidosis
4. Identify if there is a compensation
   • Full compensation if the pH is within the normal range
   • Partial compensation if either the PaCO2 or HCO3 value is wavering to compensate for the primary acid-base disturbance; but, the pH is still not within the normal physiologic range.
5. Look at the O2
   

The results should always be read and compared in reference to the patients previous ABG (if available) as you will then be able to assess a trend and make a more accurate assessment on whether you should treat or if your treatment has be successful or not.

Primary Acid-base disturbances[edit | edit source]

They are:

1. Uncompensated Respiratory Acidosis: This occurs when there is an increase in the PaCO2 level without a resultant alteration (increase) of the HCO3 value. Thus, there will an acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs).
2. Partially compensated Respiratory Acidosis: This occurs when there is an increase in the PaCO2 level with a resultant alteration (increase) of the HCO3 value; but, the pH is still not within the normal range. Thus, there will still be an acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs).
3. Fully compensated Respiratory Acidosis: This occurs when there is an increase in the PaCO2 level with a resultant alteration (increase) of the HCO3 value; thereby, balancing the pH within the normal range. Thus, there will a compensation of the acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs) with metabolic alkalosis.
4. Uncompensated Respiratory Alkalosis: This occurs when there is a decrease in the PaCO2 level without a resultant alteration (decrease) of the HCO3 value. Thus, there will an alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood).
5. Partially compensated Respiratory Alkalosis: This occurs when there is a decrease in the PaCO2 level with a resultant alteration (decrease) of the HCO3 value; ; but, the pH is still not within the normal range. Thus, there will an alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood).
6. Fully compensated Respiratory Alkalosis: This occurs when there is a decrease in the PaCO2 level with a resultant alteration (decrease) of the HCO3 value; thereby, balancing the pH within the normal range. Thus, there will a compensation of the alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood) with metabolic acidosis.
7. Uncompensated Metabolic Acidosis: This occurs when there is an decrease in the HCO3 level without a resultant alteration (decrease) of the PaCO2 value. Thus, there will an acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate).
8. Partially compensated Metabolic Acidosis: This occurs when there is an decrease in the HCO3 level with a resultant alteration (decrease) of the PaCO2 value; but, the pH is still not within the normal range. Thus, there will still be an acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate).
9. Fully compensated Metabolic Acidosis: This occurs when there is an decrease in the HCO3 level with a resultant alteration (decrease) of the PaCO2 value; thereby, balancing the pH within the normal range. Thus, there will a compensation of the acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate) with respiratory alkalosis.
10. Uncompensated Metabolic Alkalosis: This occurs when there is a increase in the HCO3 level without a resultant alteration (increase) of the PaCO2 value. Thus, there will an alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate).
11. Partially compensated Metabolic Alkalosis: This occurs when there is a increase in the HCO3 level with a resultant alteration (increase) of the PaCO2 value; ; but, the pH is still not within the normal range. Thus, there will an alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate).
12. Fully compensated Metabolic Alkalosis: This occurs when there is a increase in the HCO3 level with a resultant alteration (increase) of the PaCO2 value; thereby, balancing the pH within the normal range. Thus, there will a compensation of the alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate) with respiratory acidosis.
13. Mixed Acid-Base disturbances: This occurs when there is either both metabolic and respiratory acidosis present or metabolic and respiratory alkalosis present at the same time of analysing arterial blood gases

Tutorials[edit | edit source]

Useful Resources[edit | edit source]

ABG Calculator

ABG's at altitude

Acid-Base Questions

ABG Interpretation Quiz

 References[edit | edit source]