The nurse is reviewing a patient's ABG report. The pH is 7.30, PaCO2 is 50 mmHg, and HCO3 is 24 mEq/L. Based on this, the nurse interprets the results as:

Appeared in: NORCET 7 Prelims -2024

Explanation

The patient's pH of 7.30 is below the normal range of 7.35-7.45, indicating acidosis.
The PaCO2 of 50 mmHg is above the normal range of 35-45 mmHg. Since PaCO2 reflects the respiratory component and is acidic, this high value points to a respiratory cause.
The HCO3− of 24 mEq/L is within the normal range of 22-26 mEq/L, indicating the metabolic system is not the primary cause and has not yet compensated.
The combination of a low pH and a high PaCO2 is the classic sign of respiratory acidosis.

Option A: Metabolic acidosis would present with a low pH (which is present) but also a low HCO3− (below 22 mEq/L). This patient's HCO3− is normal.
Option C: Respiratory alkalosis is characterized by a high pH (above 7.45) and a low PaCO2 (below 35 mmHg). This patient has the opposite: a low pH and a high PaCO2.
Option D: Metabolic alkalosis involves a high pH (above 7.45) and a high HCO3− (above 26 mEq/L). This patient has a low pH and a normal HCO3−.

Clinical Relevance

Nursing practice connection: Knowing Arterial Blood Gas (ABG) interpretation helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Respiratory acidosis is a critical condition caused by hypoventilation, where the lungs fail to eliminate enough CO2. Common causes include COPD, pneumonia, asthma, or overdose of sedatives.
Nurses must promptly recognize signs of respiratory acidosis (e.g., confusion, lethargy, headache, dyspnea) and intervene by improving ventilation, which may involve positioning, encouraging deep breathing, or preparing for mechanical ventilation.
What if the patient's HCO3− was 28 mEq/L? With a pH of 7.30 and PaCO2 of 50 mmHg, a high HCO3− would indicate that the kidneys have started to compensate for the chronic respiratory acidosis by retaining bicarbonate. This would be classified as partially compensated respiratory acidosis.

How to Approach the Question

First, analyze the pH. A value below 7.35 is acidosis; a value above 7.45 is alkalosis.
Second, examine the PaCO2. This is the respiratory parameter. A high PaCO2 (above 45) indicates a respiratory cause for acidosis, while a low PaCO2 (below 35) indicates a respiratory cause for alkalosis.
Third, look at the HCO3−. This is the metabolic parameter. A low HCO3− (below 22) points to metabolic acidosis, and a high HCO3− (above 26) points to metabolic alkalosis.
Finally, determine the primary disorder by matching the parameter (PaCO2 or HCO3−) that corresponds with the pH's direction (acidosis or alkalosis). Use the ROME mnemonic: Respiratory Opposite (pH and PaCO2 move in opposite directions), Metabolic Equal (pH and HCO3− move in the same direction).

Concept Tested & Keywords

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E6 Nursing Fundamentals Taylor p. 785-787

E6 Nursing Fundamentals Potter Perry 12e Part 5 p. 56-58

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 82-84

Practise the full NORCET 7 Prelims -2024

Attempt every question from this paper in a timed mock, then review the full solution for each one.