SCTIMST Staff Nurse - 2016
Medical & Surgical Nursing
Medium
An ABG analysis report shows: pH - 7.20; PCO₂ - 35 mmHg; HCO₃ - 20 mEq/L. These findings are suggestive of?
Appeared in: SCTIMST Staff Nurse - 2016
Explanation
- The primary diagnosis is determined by matching the pH imbalance with the corresponding lab value (PCO₂ or HCO₃).
- A pH of 7.20 is acidic (normal is 7.35-7.45).
- An HCO₃ of 20 mEq/L is low (normal is 22-26 mEq/L) and is consistent with a metabolic cause for acidosis.
- The PCO₂ is within the normal range (35-45 mmHg), ruling out a primary respiratory cause.
- The combination of a low pH and low HCO₃ confirms the diagnosis of metabolic acidosis.
Why Other Options Were Wrong
- Option B: Respiratory alkalosis involves a high pH (alkalosis) and a low PCO₂, which is opposite to the patient's findings of a low pH.
- Option C: Metabolic alkalosis involves a high pH (alkalosis) and a high HCO₃, which is the opposite of the patient's low pH and low HCO₃.
- Option D: Respiratory acidosis involves a low pH but is caused by a high PCO₂ (greater than 45 mmHg) due to hypoventilation. The patient's PCO₂ is normal.
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 to identify acid-base imbalances as background academic context rather than a clinical decision trigger.
- Rapid identification of metabolic acidosis is critical as it can be life-threatening if the pH drops significantly (below 7.2).
- Nurses must monitor for signs of metabolic acidosis, such as Kussmaul respirations (deep, rapid breathing), confusion, and hypotension, and report ABG results promptly.
- Common causes of metabolic acidosis include Diabetic Ketoacidosis (DKA), lactic acidosis (from shock), severe diarrhea (loss of bicarbonate), and renal failure.
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: Analyze the PaCO₂ (respiratory parameter). A high value indicates respiratory acidosis; a low value indicates respiratory alkalosis.
- Step 3: Analyze the HCO₃ (metabolic parameter). A low value indicates metabolic acidosis; a high value indicates metabolic alkalosis.
- Step 4: Match the parameter (PaCO₂ or HCO₃) that corresponds with the pH direction. In this case, the pH is low (acidosis) and the HCO₃ is low (acidosis), so it is metabolic acidosis.
- Step 5: Check for compensation. The parameter that doesn't match the primary problem shows compensation. Here, the PCO₂ is at the low end of normal, indicating the lungs are trying to compensate by blowing off acid (CO₂).
Concept Tested & Keywords
- Concept Tested: Interpretation of Arterial Blood Gas (ABG) results to identify acid-base imbalances.
- Stem keywords: ABG analysis, pH, PCO₂, HCO₃
- Lead-in keywords: suggestive of
- Clinical cues: pH 7.20 indicates acidosis.
- Clinical cues: HCO₃ 20 mEq/L indicates a metabolic component.
Question ID
Q72H5zJFl1L9IslKOnMItS
Reference Book
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 SCTIMST Staff Nurse - 2016
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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