ABG Interpretation: Metabolic vs Respiratory Acidosis vs Alkalosis — The 4-Pattern Matrix
An NCLEX question gives you pH 7.28, CO2 55, HCO3 26 — you have about 30 seconds to name the pattern and pick the right intervention. Mixing up the CO2 and HCO3 directions flips your answer to the wrong disorder and the wrong nursing action.
Comparison
- ↓ < 7.35
- ↑ > 7.45
- ↓ < 7.35
- ↑ > 7.45
- ★↑ > 45 (primary problem)
- ★↓ < 35 (primary problem)
- Normal or ↓ (compensating)
- Normal or ↑ (compensating)
- Normal or ↑ (compensating)
- Normal or ↓ (compensating)
- ★↓ < 22 (primary problem)
- ★↑ > 26 (primary problem)
- COPD, opioid OD, airway obstruction
- Hyperventilation, anxiety/pain, high altitude
- DKA, lactic acidosis, diarrhea, renal failure
- Vomiting / NG suction, loop diuretics, antacids
- Hypoventilation; lethargy/confusion
- Lightheaded; perioral tingling
- Kussmaul respirations; fruity breath (DKA)
- Slow shallow breathing; tetany/cramps
- Support ventilation; hold sedatives
- Slow the breathing; treat anxiety/pain
- Treat cause (insulin, fluids); watch K⁺
- Replace K⁺/Cl⁻; stop NG suction
- Hyperkalemia
- Hypokalemia
- Hyperkalemia
- Hypokalemia
- pH ↓ + CO₂ ↑ → opposite = respiratory
- pH ↑ + CO₂ ↓ → opposite = respiratory
- pH ↓ + HCO₃⁻ ↓ → same = metabolic
- pH ↑ + HCO₃⁻ ↑ → same = metabolic
- pH 7.28 / CO₂ 58 / HCO₃ 24
- pH 7.50 / CO₂ 30 / HCO₃ 24
- pH 7.30 / CO₂ 40 / HCO₃ 16
- pH 7.50 / CO₂ 42 / HCO₃ 32
Respiratory Acidosis
- ↓ < 7.35
Respiratory Alkalosis
- ↑ > 7.45
Respiratory Acidosis
- ★↑ > 45 (primary problem)
Respiratory Alkalosis
- ★↓ < 35 (primary problem)
Respiratory Acidosis
- Normal or ↑ (compensating)
Respiratory Alkalosis
- Normal or ↓ (compensating)
Respiratory Acidosis
- COPD, opioid OD, airway obstruction
Respiratory Alkalosis
- Hyperventilation, anxiety/pain, high altitude
Respiratory Acidosis
- Hypoventilation; lethargy/confusion
Respiratory Alkalosis
- Lightheaded; perioral tingling
Respiratory Acidosis
- Support ventilation; hold sedatives
Respiratory Alkalosis
- Slow the breathing; treat anxiety/pain
Respiratory Acidosis
- Hyperkalemia
Respiratory Alkalosis
- Hypokalemia
Respiratory Acidosis
- pH ↓ + CO₂ ↑ → opposite = respiratory
Respiratory Alkalosis
- pH ↑ + CO₂ ↓ → opposite = respiratory
Respiratory Acidosis
- pH 7.28 / CO₂ 58 / HCO₃ 24
Respiratory Alkalosis
- pH 7.50 / CO₂ 30 / HCO₃ 24
★ marks the fact that sets a column apart.
Clinical Pearl
ROME: Respiratory = Opposite (pH and CO2), Metabolic = Equal (pH and HCO3 move together).
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