Which of the following arterial blood gas values is consistent with metabolic acidosis?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2019

Medical Surgical Nursing

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2019

Explanation

Metabolic acidosis is a primary acid-base disorder defined by a decrease in serum bicarbonate (HCO3−) concentration.
The provided value of 15 mEq/L is significantly below the normal range of 22–26 mEq/L, making it the key indicator of this condition.
This loss of base (or gain of acid) leads to a decrease in the blood's pH, causing an acidotic state.
The body attempts to compensate for metabolic acidosis by increasing the respiratory rate to 'blow off' CO2, an acid. This is known as Kussmaul breathing.

Option A: A pH of 7.35 is at the absolute lower limit of the normal range (7.35-7.45). While a pH below this value signifies acidosis, this specific value is technically normal and does not definitively indicate an acidotic state.
Option B: A PaCO2 of 46 mmHg is elevated (normal: 35–45 mmHg). This finding is characteristic of respiratory acidosis, where the lungs fail to eliminate enough CO2.
Option D: A PaO2 of 95 mm Hg is a normal value (normal range: 80–100 mmHg). This parameter measures the oxygen level in the arterial blood and is used to assess for hypoxemia.

Clinical Relevance

Nursing practice connection: Knowing Arterial Blood Gas (ABG) Interpretation: Metabolic Acidosis helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must be able to rapidly identify metabolic acidosis from ABG results to alert the provider and initiate timely interventions, as severe acidosis can be life-threatening.
Key nursing interventions include monitoring vital signs, assessing for signs of respiratory compensation (Kussmaul respirations), administering prescribed treatments like sodium bicarbonate, and addressing the underlying cause (e.g., managing blood sugar in DKA, rehydrating a patient with diarrhea).
What if? - If the PaCO2 was also low (e.g., 30 mmHg) along with the low HCO3−, it would indicate that the respiratory system is actively compensating for the metabolic acidosis by hyperventilating to expel more CO2.

How to Approach the Question

First, identify the question type. This is an analytical question that requires interpreting laboratory values based on knowledge of acid-base balance.
Recall the normal ranges for ABG components: pH (7.35-7.45), PaCO2 (35-45 mmHg), and HCO3− (22-26 mEq/L).
Analyze the term 'metabolic acidosis'. 'Metabolic' points to the kidneys and the HCO3− level. 'Acidosis' points to a low pH (below 7.35).
Apply the ROME mnemonic: 'Metabolic Equal'. This means for a metabolic disorder, the pH and HCO3− will move in the same direction. For metabolic acidosis, both will be low.
Evaluate each option. A pH of 7.35 is low-normal. A PaCO2 of 46 is high (respiratory acidosis). A PaO2 of 95 is normal. An HCO3− of 15 is low, which directly matches the definition of metabolic acidosis.

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