Arterial blood gas analysis is a laboratory test to know the patient’s acid-base balance. This laboratory test is also used to determine the extent of the buffer system in compensating, and includes the measurements of the following:
- acidity (pH), levels of oxygen
- carbon dioxide
- bicarbonate or HCO3
Arterial Blood Gas
- pH
- PaCO2 or the Partial Pressure of Carbon Dioxide
- PaO2 of Partial Pressure of Oxygen
- SO2 or Oxygen Saturation
- HCO3 or Bicarbonate
- BE or Base Excess
Arterial Blood Gas or ABG is taken from an artery; commonly on radial or brachial arteries. ABG interpretation will help us identify if the patient is having respiratory/metabolic alkalosis/acidosis. Interpreting ABG will also allow us to differentiate these acid-base conditions, and if the body is compensating or not. It has been a struggle for nurses to interpret ABG but there is a fun way to do so—the Tic Tac Toe Method.
Things to take note of when interpreting ABG:
| Normal | Acid | Base | |
| pH | 7.35 – 7.45 | less than 7.35 | over 7.45 |
| PCo2 | 35 – 45 | over 45 | less than 35 |
| HCO3 | 22 – 26 | less than 22 | over 26 |
Note:
- CO2: 35-45 (CO2 lab value ALWAYS indicates a RESPIRATORY issue)
- HCO3: 22-26 (HCO3 lab value ALWAYS indicates a METABOLIC issue)
Let’s start playing Tic Tac Toe and learn to interpret ABGs in a fun and easy way.
1. Make sure you memorize the normal values of pH, PaCO2, and HCO3.
2. Prepare your Tic Tac Toe layout.
| Acid | Normal | Base |
3. When given the values, analyze the following:
- PH
- PCO2
- HCO3
4. Keep in mind the normal values, acidic value, and alkalotic value. Check if the values are under normal, acidosis, or alkalosis.
5. If the pH is less than 7.35, place it under Acid, if it is over 7.45, you should place it under Base.
6. If the PCO2 is over 45, it should be placed under Acid and if less than 35, then it should be under Base.
7. For HCO3, when the given value is less than 22, then it should be placed under Acid, and when it’s over 26, then it is considered alkalotic.
8. Play for Acidosis or Alkalosis.
9. Play for Metabolic or Respiratory.
10. Play for Compensation.
In reference to number 10, how do we say if it’s fully compensated, partially compensated, or uncompensated? Let’s see here:
| Fully Compensated | pH is normal |
| Partially Compensated | all three (3) values are not normal |
| Uncompensated | PaCO2 or HCO3 is normal and yet the other is not normal |
Tic Tac Toe
We are all aware that in Tic Tac Toe, we would need to cross out one line, might it be vertical, horizontal, or diagonal.
To better understand the concept of Tic Tac Toe in interpreting ABG, we’ll use an example. Let’s have scenario no. 1:
pH – 7.24
PCo2 – 49
Hc03 – 31
| Acid | Normal | Base |
| pH | HC03 | |
| CO2 |
Interpretation: Respiratory Acidosis. The body is Partially Compensating.
The explanation for the interpretation: Let’s take a look at our Tic Tac Toe grid. Acid is crossed out which means this is ACIDOSIS. How did we know it’s Respiratory? Since CO2 is the representation of your breathing. This makes it Respiratory, and since both pH and CO2 are crossed out under acid. This is why our interpretation is Respiratory Acidosis.
Now how do we know that the body is compensating? In the example, the body is partially compensating because looking at it, the body is trying to reach a homeostatic environment by trying to balance the metabolic system. That makes it partially compensating.
Examples of abnormal ABG results:
- Respiratory Acidosis, compensation: there are uncompensated, partially compensated, or fully compensated
- Respiratory Alkalosis, compensation: there are uncompensated, partially compensated, or fully compensated
- Metabolic Acidosis, compensation: there are uncompensated, partially compensated, or fully compensated
- Metabolic Alkalosis, compensation: there are uncompensated, partially compensated, or fully compensated
Nursing Management for Patients With Abnormal ABG Results:
- Respiratory Acidosis, compensation: there are uncompensated, partially compensated, or fully compensated
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- Achieve homeostasis
- Prevent/minimize complications
- Provide information about condition/prognosis and treatment needs as appropriate
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- Respiratory Alkalosis, compensation: there are uncompensated, partially compensated, or fully compensated
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- Monitor respiratory rate
- Encourage breathing slowly and deeply
- Assess the level of awareness
- Provide comfort
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- Metabolic Acidosis, compensation: there are uncompensated, partially compensated, or fully compensated
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- Prepare sodium bicarbonate ampules (for emergency)
- Make sure to monitor vital signs
- Monitor laboratory results
- Assess the level of consciousness frequently
- Pay close attention to signs of decreasing levels of consciousness
- Properly document a patient’s intake and output, making sure it is taken accurately (to monitor renal function)
- Prevent aspiration for patients that are vomiting
- Watch out for possible seizures
- Make sure to provide oral hygiene
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- Metabolic Alkalosis, compensation: there are uncompensated, partially compensated, or fully compensated
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- Monitor respiratory rate, rhythm, and depth
- Assess the level of consciousness
- Monitor heart rate and rhythm
- Monitor and record output plus the source
- Make sure to monitor intake and patients daily weight
- Restrict oral intake and reduce noxious environment stimuli
- Intake of high potassium and high calcium food
- Religiously take medication
- No excessive sodium bicarbonate intake
- Identify other underlying disorder
- Monitor laboratory results
- Prepare supplemental O2
- Prepare for possible dialysis
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Helping the patient’s body attain a homeostatic environment to avoid complications is the main goal of care for those with abnormal ABG results.
