A patient's ABG report shows the following values: pH = 7.10, HCO₃⁻ = 8 mEq/L, PaCO₂ = 22 mmHg. What is the most likely acid-base disturbance?

Appeared in: JIPMER Nursing Officer-2024

Explanation

The patient's pH of 7.10 is below the normal range of 7.35-7.45, indicating a state of acidosis.
The bicarbonate (HCO₃⁻) level of 8 mEq/L is significantly below the normal range of 22-26 mEq/L, which is the primary indicator of a metabolic problem.
In metabolic acidosis, both the pH and the HCO₃⁻ levels decrease, following the 'Metabolic Equal' rule of the ROME mnemonic.
The low PaCO₂ level (22 mmHg) signifies that the respiratory system is compensating by increasing the rate and depth of breathing (hyperventilation) to expel more CO₂ and counteract the acidosis.

Option A: This condition is characterized by a low pH and a high PaCO₂ (above 45 mmHg) due to hypoventilation. The patient's PaCO₂ is low, not high.
Option B: This involves a high pH (above 7.45) and a low PaCO₂ (below 35 mmHg). The patient's pH is low, indicating acidosis, not alkalosis.
Option D: This is defined by a high pH (above 7.45) and a high HCO₃⁻ (above 26 mEq/L). The patient's values for both pH and HCO₃⁻ are low.

Visual 1: Flowchart - A step-by-step flowchart for ABG interpretation, starting with pH, then checking PaCO₂ and HCO₃⁻ to determine the primary disorder and compensation.
Visual 2: Diagram - A ROME (Respiratory Opposite, Metabolic Equal) mnemonic chart showing the directional relationship between pH, PaCO₂, and HCO₃⁻ for each acid-base disorder.

Clinical Relevance

Nursing practice connection: Knowing Arterial Blood Gas (ABG) interpretation for acid-base balance helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses are often the first to receive and interpret ABG results, requiring prompt identification of life-threatening conditions like severe acidosis to initiate timely interventions.
Monitoring for signs of respiratory compensation (e.g., Kussmaul respirations - deep, rapid breathing) is a key nursing assessment in patients with metabolic acidosis.
What if? - If the patient's PaCO₂ was normal (e.g., 40 mmHg) with the same low pH and HCO₃⁻, it would indicate an uncompensated metabolic acidosis, suggesting an acute problem or failure of the respiratory system to respond.

How to Approach the Question

Step 1: Analyze the pH. A value below 7.35 indicates acidosis. A value above 7.45 indicates alkalosis.
Step 2: Determine the primary cause by comparing the direction of change in PaCO₂ and HCO₃⁻ with the pH.
Step 3: Use the ROME mnemonic: Respiratory Opposite (pH and PaCO₂ move in opposite directions), Metabolic Equal (pH and HCO₃⁻ move in the same/equal direction).
Step 4: In this case, pH is low (acidosis) and HCO₃⁻ is also low. Since they move in the same direction, the primary disorder is metabolic acidosis.
Step 5: Check for compensation. The PaCO₂ is low, which is the expected respiratory compensation for metabolic acidosis. The body tries to 'blow off' acid (CO₂) to correct the pH.

Concept Tested & Keywords

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