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.
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- ↓ < 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
- Anxiety, pain, hyperventilation
- High altitude
- DKA, lactic acidosis
- Diarrhea, renal failure
- Vomiting / NG suction
- Loop diuretics, antacids
- Hypoventilation
- Somnolence (CO₂ narcosis)
- Rapid breathing (tachypnea)
- Lightheaded
- Tingling, tetany (↓ ionized Ca²⁺)
- Kussmaul respirations
- Fruity breath (DKA)
- Slow shallow breathing
- Tingling, tetany (↓ ionized Ca²⁺)
- Support ventilation
- Hold sedatives/opioids
- Slow the breathing
- Treat anxiety/pain
- Treat cause (insulin, fluids)
- Watch K⁺ drop as insulin acts
- Replace K⁺/Cl⁻
- Stop NG suction
- Hyperkalemia
- Hypokalemia
- Hyperkalemia
- Hypokalemia
- pH ↓ + CO₂ ↑ (opposite = respiratory)
- pH ↑ + CO₂ ↓ (opposite = respiratory)
- pH ↓ + HCO₃⁻ ↓ (equal = metabolic)
- pH ↑ + HCO₃⁻ ↑ (equal = metabolic)
- pH 7.24 / CO₂ 58 / HCO₃ 24
- pH 7.50 / CO₂ 30 / HCO₃ 24
- pH 7.25 / CO₂ 40 / HCO₃ 17
- 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
- Anxiety, pain, hyperventilation
- High altitude
Respiratory Acidosis
- Hypoventilation
- Somnolence (CO₂ narcosis)
Respiratory Alkalosis
- Rapid breathing (tachypnea)
- Lightheaded
- Tingling, tetany (↓ ionized Ca²⁺)
Respiratory Acidosis
- Support ventilation
- Hold sedatives/opioids
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 7.24 / CO₂ 58 / HCO₃ 24
Respiratory Alkalosis
- pH 7.50 / CO₂ 30 / HCO₃ 24
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ROME: Respiratory = Opposite (pH and CO2), Metabolic = Equal (pH and HCO3 move together).
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- SimulatorAcid–Base & ABG SimulatorBuild a gas. Watch compensation happen. Move CO₂ or bicarbonate, then read the gas in three calls: pH, cause, compensation.
- SimulatorFluid & Electrolyte SimulatorChange one lab. Watch the whole patient respond. Sodium, potassium, calcium, magnesium, pH and volume, all linked — with a live ECG and an IV pole where every bag runs.
- GuideRespiratory vs Metabolic Acidosis and Alkalosis: The 4 Disorders With Causes, Findings and What the Nurse DoesTwo organs, two directions. Respiratory disorders are CO₂ problems that belong to the lungs and happen in minutes; metabolic disorders show up in the bicarbonate and come from everywhere else. Each of the four with its causes, what you see, what the nurse does and what the provider orders — in a table, then patient by patient, with each one loaded in a live gas.
- TopicMetabolic AcidosisWhen pH drops and bicarbonate is the culprit, the cause matters as much as the numbers — because DKA and renal failure demand very different nursing responses.