👤 By the CinnaRN Clinical Content Team🕐 Updated 2026-08-23🏷️ Physiological Adaptation🔖 Free to read, print, and share
Also known as: ABG · blood gas · arterial gas · acid-base
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Use this quick-reference guide to spot, treat, and prevent Arterial Blood Gas Interpretation on the NCLEX. Keep it handy during review and on exam day!
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📒 The 1-minute cheat sheet
🧪 Values
pH 7.35-7.45
PaCO2 35-45 mmHg (lungs)
HCO3 22-26 mEq/L (kidneys)
📌 Rome
Respiratory Opposite: pH↑ CO2↓
Metabolic Equal: pH↑ HCO3↑
📌 Acid
pH <7.35 = acidosis
Resp acid: ↑CO2 (hypovent, COPD)
Metab acid: DKA, diarrhea, renal
📌 Alk
pH >7.45 = alkalosis
Resp alk: hyperventilation/anxiety
Metab alk: vomiting, antacids
📚 Arterial Blood Gas Interpretation — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
An ABG measures blood pH, CO2, and bicarbonate to classify acid-base disturbances as respiratory or metabolic, and acidosis or alkalosis. The lungs control CO2 (acid) and the kidneys control bicarbonate (base). Use the ROME memory aid: Respiratory Opposite (pH and CO2 move opposite directions), Metabolic Equal (pH and HCO3 move the same direction).
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Key points
Understand these first
Normal pH is 7.35-7.45; below 7.35 is acidosis, above 7.45 is alkalosis.
CO2 is the respiratory component; HCO3 (bicarbonate) is the metabolic component.
High CO2 with low pH equals respiratory acidosis; common with hypoventilation, COPD, and opioid overdose.
Low CO2 with high pH equals respiratory alkalosis; common with hyperventilation and anxiety.
Low HCO3 with low pH equals metabolic acidosis; seen in DKA, shock, and prolonged diarrhea.
Compensation is full when pH returns to normal range; partial when pH is still abnormal but the opposing system has shifted.
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Nursing priorities
What to do, in order
Assess airway, breathing, and the respiratory pattern first since gas exchange drives most ABG changes.
Determine which system is the primary cause and which is compensating before reporting.
Correlate the ABG with the patient's clinical picture, oxygen saturation, and mental status.
Apply pressure to the puncture site for at least 5 minutes (longer if anticoagulated) to prevent arterial bleeding.
Place the sample on ice and transport promptly so results are not falsely altered.
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Red flags — report now
Escalate immediately
pH below 7.20 or above 7.60 is life-threatening and must be reported immediately.
Falling pH with rising CO2 and decreasing level of consciousness signals impending respiratory failure.
Never delay airway intervention while waiting for ABG results in a decompensating patient.
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Labs & values
Numbers to know
pH 7.35-7.45
PaCO2 35-45 mmHg
HCO3 22-26 mEq/L
PaO2 80-100 mmHg
SaO2 95-100%
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Patient teaching
What patients must know
Report dizziness, numbness, or tingling around the mouth, which can signal hyperventilation.
Use prescribed breathing techniques or pursed-lip breathing to help control CO2 levels.
❓ Arterial Blood Gas Interpretation: NCLEX FAQs
What are the priority nursing interventions for Arterial Blood Gas Interpretation?
Assess airway, breathing, and the respiratory pattern first since gas exchange drives most ABG changes. Determine which system is the primary cause and which is compensating before reporting. Correlate the ABG with the patient's clinical picture, oxygen saturation, and mental status. Apply pressure to the puncture site for at least 5 minutes (longer if anticoagulated) to prevent arterial bleeding.
What are the warning signs of Arterial Blood Gas Interpretation a nurse must report?
pH below 7.20 or above 7.60 is life-threatening and must be reported immediately. Falling pH with rising CO2 and decreasing level of consciousness signals impending respiratory failure. Never delay airway intervention while waiting for ABG results in a decompensating patient.
What do I need to know about Arterial Blood Gas Interpretation for the NCLEX?
Normal pH is 7.35-7.45; below 7.35 is acidosis, above 7.45 is alkalosis. CO2 is the respiratory component; HCO3 (bicarbonate) is the metabolic component. High CO2 with low pH equals respiratory acidosis; common with hypoventilation, COPD, and opioid overdose. Low CO2 with high pH equals respiratory alkalosis; common with hyperventilation and anxiety.
What patient teaching is important for Arterial Blood Gas Interpretation?
Report dizziness, numbness, or tingling around the mouth, which can signal hyperventilation. Use prescribed breathing techniques or pursed-lip breathing to help control CO2 levels.
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Quick Tip
Normal pH is 7.35-7.45; below 7.35 is acidosis, above 7.45 is alkalosis.