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ABG interpretation cheat sheet

This ABG cheat sheet gives RT learners a compact interpretation sequence: classify acid-base status, identify the primary driver, assess compensation, evaluate oxygenation, then choose the safest next action.

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Authority page governance

NurseNest Clinical Education Review

Resource reviewed
Review date
May 11, 2026
Updated
May 11, 2026

References

  • Respiratory therapy learning resource governance
  • NurseNest clinical education governance standards
  • Current professional guidance and exam-prep references where applicable

Educational use only. Content supports exam preparation and clinical reasoning practice; it does not replace provider orders, facility policy, scope of practice, or independent clinical judgment.

Editorial policy · Content review policy · Educational disclaimer

ABG sequence

  • Check pH first.
  • Compare PaCO2 and HCO3.
  • Assess compensation.
  • Evaluate PaO2, SpO2, and FiO2 requirement.
  • Connect the result to clinical status.

Clinical cautions

  • Do not treat the number without assessing the patient.
  • Rising PaCO2 plus altered mental status is dangerous.
  • Compensation does not automatically mean no intervention is needed.
ABG quick interpretation table
PatternLikely driverClinical question
Low pH + high PaCO2Respiratory acidosisDoes the patient need ventilatory support?
High pH + low PaCO2Respiratory alkalosisIs pain, anxiety, hypoxemia, or sepsis driving hyperventilation?
Low pH + low HCO3Metabolic acidosisIs shock, renal failure, DKA, or lactic acidosis present?

Use this with active practice

ABG practice questionsOxygen therapy questionsARDS review

Frequently asked questions

What is the first step in ABG interpretation?
Start with pH to determine acidemia or alkalemia, then compare PaCO2 and HCO3 to identify the primary process.
Why include oxygenation after acid-base interpretation?
A correct acid-base label is incomplete if the patient is hypoxemic, tiring, or needs escalation in oxygen or ventilatory support.