Arterial blood gases look complicated, but you only need three numbers and one memory trick: ROME, which stands for Respiratory Opposite, Metabolic Equal.
The three numbers
| Value | Normal | Tells you |
|---|---|---|
| pH | 7.35 to 7.45 | Acid (below 7.35) or base (above 7.45) |
| PaCO2 | 35 to 45 mm Hg | The lungs (respiratory) |
| HCO3 | 22 to 26 mEq/L | The kidneys (metabolic) |
Five steps
- Look at the pH. Low means acidosis. High means alkalosis.
- Look at the PaCO2. If it moves the opposite way from the pH (pH down, CO2 up), the problem is respiratory.
- Look at the HCO3. If it moves the same way as the pH (pH down, HCO3 down), the problem is metabolic.
- Name it. For example, respiratory acidosis.
- Check compensation. If the other value is normal, it is uncompensated. If the other value is abnormal and the pH is still abnormal, it is partially compensated. If the pH is back to normal, it is fully compensated.
Practice
pH 7.30, PaCO2 50, HCO3 24
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Uncompensated respiratory acidosis. The pH is low and the CO2 is high (opposite), and the HCO3 is normal.
pH 7.48, PaCO2 40, HCO3 30
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Uncompensated metabolic alkalosis. The pH and HCO3 are both high (equal), and the CO2 is normal.
pH 7.32, PaCO2 30, HCO3 16
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Partially compensated metabolic acidosis. The pH and HCO3 are both low, and the lungs are blowing off CO2 to help, but the pH is not back to normal yet.
Common causes
| Problem | Common causes |
|---|---|
| Respiratory acidosis | Slow or shallow breathing: COPD, opioid overdose, sedation |
| Respiratory alkalosis | Breathing too fast: anxiety, pain, early sepsis |
| Metabolic acidosis | DKA, diarrhea, kidney failure, lactic acidosis |
| Metabolic alkalosis | Vomiting, NG suction, some diuretics, too many antacids |
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Quick answers
What does ROME stand for in ABGs?
Respiratory Opposite, Metabolic Equal. In respiratory problems, pH and PaCO2 move in opposite directions. In metabolic problems, pH and HCO3 move in the same direction.
What are normal ABG values?
pH 7.35 to 7.45, PaCO2 35 to 45 mm Hg, HCO3 22 to 26 mEq/L, and PaO2 80 to 100 mm Hg.
Evidence & Clinical Sources
- MedlinePlus lab tests
- Hinkle & Cheever, Brunner & Suddarth's Textbook of Medical-Surgical Nursing, Wolters Kluwer
Reviewed against current guidelines and drug labels. Always follow your program, a current drug reference, and facility policy. Our sources policy
For learning only. Lab ranges and policies vary. Always follow your nursing program, a current drug reference, and your facility's policies.