pH below 7.20 or above 7.60 is life-threatening and must be reported immediately.
Before you read
Test yourself first: 5 questions
Question 1 of 5
A client on long-term phenytoin for seizures has a level of 28 mcg/mL and reports nystagmus, slurred speech, and an unsteady gait. Which is the correct interpretation?
Answer: C. The therapeutic phenytoin range is 10 to 20 mcg/mL; 28 mcg/mL is toxic. Classic signs of phenytoin toxicity include nystagmus, ataxia, slurred speech, and confusion. The nurse holds the drug and notifies the provider.
Question 2 of 5
A client on theophylline has a level of 25 mcg/mL and reports tachycardia, tremor, and nausea. Which interpretation is correct?
Answer: B. The therapeutic theophylline range is 10 to 20 mcg/mL; a level of 25 mcg/mL indicates toxicity. Early signs include tachycardia, nausea, tremor, and restlessness; severe toxicity can cause seizures and dysrhythmias. The nurse holds the drug and notifies the provider.
Question 3 of 5
The nurse is reviewing normal arterial blood gas reference ranges with a new graduate. Which value represents the normal range for arterial pH?
Answer: A. The normal arterial pH range is 7.35 to 7.45. A value below 7.35 indicates acidosis and a value above 7.45 indicates alkalosis. The other ranges listed correspond to PaCO2 (35-45 mmHg), HCO3 (22-26 mEq/L), and an abnormal acidotic value.
Question 4 of 5
A nurse interprets an arterial blood gas during a cardiac arrest: pH 7.18, PaCO2 30, HCO3 12. Which interpretation is correct?
Answer: A. A low pH with a low bicarbonate and a compensatory low PaCO2 indicates metabolic acidosis with respiratory compensation. During cardiac arrest, tissue hypoperfusion produces lactic acidosis. The primary treatment is restoring perfusion through effective CPR rather than routine bicarbonate.
Question 5 of 5
A client is admitted with pneumonia and worsening hypoxemia. The nurse anticipates that pulse oximetry corresponds best to which arterial blood gas value?
Answer: A. Pulse oximetry (SpO2) estimates the oxygen saturation of hemoglobin, which corresponds to the PaO2 on the arterial blood gas through the oxyhemoglobin dissociation curve. It assesses oxygenation, not acid-base status; pH, PaCO2, and HCO3 reflect acid-base balance rather than oxygen saturation.
Keep the streak going with more questions like these, each with a full rationale.
What is arterial blood gas interpretation?
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).
Key points to remember
- 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.
Nursing priorities
- 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.
Labs & values
Patient teaching
- 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.
Red flags: report now
- 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.
References
Clinical references for this topic
