NORCET 2 -2021 (Shift-2)
Medical & Surgical Nursing
Hard
Which value indicates metabolic acidosis with respiratory compensated?
Appeared in: NORCET 2 -2021 (Shift-2)
Explanation
- Metabolic acidosis is the primary disorder, defined by a decreased pH (acidemia) and a decreased bicarbonate (HCO3−) level.
- The body's compensatory mechanism for metabolic acidosis is to increase the respiratory rate and depth (hyperventilation).
- This hyperventilation 'blows off' carbon dioxide (CO2), which is an acid, leading to a decreased partial pressure of arterial CO2 (PaCO2).
- Therefore, the classic signs of metabolic acidosis with respiratory compensation are a decreased pH, decreased HCO3−, and a decreased PaCO2.
Why Other Options Were Wrong
- Option A: A normal arterial CO2 level indicates that there is no respiratory compensation occurring.
- Option C: An increased pH indicates alkalosis, not acidosis. This pattern is the opposite of what is expected.
- Option D: This represents a mixed acid-base disorder. An increased pH (alkalosis) is inconsistent with a decreased bicarbonate and increased CO2 (both of which cause acidosis).
Related Visual
Clinical Relevance
- Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of Arterial Blood Gas (ABG) results for metabolic acidosis with respiratory compensation as background academic context rather than a clinical decision trigger.
- Recognizing ABG patterns is a critical nursing skill for managing acutely ill patients, especially those with conditions like diabetic ketoacidosis (DKA), renal failure, or sepsis, which commonly cause metabolic acidosis.
- Prompt identification of the primary disorder and compensatory state allows for timely and appropriate interventions, such as administering bicarbonate, managing ventilation, or treating the underlying cause.
- What if the PaCO2 was high instead of low, with a low pH and low bicarbonate? This would indicate a severe mixed disorder: combined metabolic and respiratory acidosis. This is a medical emergency as both systems are failing, leading to a rapid drop in pH and requiring immediate, aggressive intervention for both the metabolic and respiratory components.
How to Approach the Question
- First, analyze the pH. A value below 7.35 indicates acidemia (acidosis).
- Next, identify the primary cause. Look at the bicarbonate (HCO3−) and the PaCO2. In this question, the stem specifies 'metabolic acidosis', so you know the primary problem is a low HCO3−.
- Then, determine the compensation. For a metabolic problem, the respiratory system compensates. To counteract acidosis, the lungs will try to eliminate acid (CO2) by hyperventilating.
- This leads to a decrease in PaCO2. Therefore, you are looking for an option with low pH, low HCO3−, and low PaCO2.
- Evaluate each option against this expected pattern to find the correct match.
Concept Tested & Keywords
- Concept Tested: Interpretation of Arterial Blood Gas (ABG) results for metabolic acidosis with respiratory compensation.
- Stem keywords: metabolic acidosis, respiratory compensated, value, pH, bicarbonate, arterial CO2
- Lead-in keywords: Which value indicates
- Negative lead-in flag: false
Question ID
Ql__zF-iTesUGLtw_9Xiv3
Reference Book
E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 78-80
E6 Nelson Textbook of Pediatrics(2024) — Volume 1 pp. 558-560, 662-664
Practise the full NORCET 2 -2021 (Shift-2)
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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