Central Institute of Psychiatry - 9 July 2022
Medical & Surgical Nursing
Hard
ABG report of a Patient is: PCO2 - 31 mEq/L, HCO3 - 21, pH - 7.43. What would be the possible acid base imbalance?
Appeared in: Central Institute of Psychiatry - 9 July 2022
Explanation
- The pH of 7.43 is within the normal range (7.35-7.45), indicating a compensated state. Its position on the alkaline side of 7.40 points to a primary alkalosis.
- The PaCO2 is 31 mmHg, which is low (normal: 35-45 mmHg). Low PaCO2 is the hallmark of respiratory alkalosis, caused by hyperventilation.
- The HCO3− is 21 mEq/L, which is low (normal: 22-26 mEq/L). The kidneys have excreted bicarbonate to compensate for the respiratory alkalosis, bringing the pH back to normal.
- The combination of a normal pH, low PaCO2, and low HCO3− is characteristic of fully compensated respiratory alkalosis.
Why Other Options Were Wrong
- Option A: Compensated respiratory acidosis involves a high PaCO2 (acidic) and a high HCO3− (compensatory base), with a pH in the low-normal range (7.35-7.40). The patient's values are the opposite.
- Option C: Uncompensated respiratory alkalosis would have an abnormally high pH (greater than 7.45) because the compensatory mechanism (lowering HCO3−) has not yet occurred or is insufficient. The patient's pH is normal.
- Option D: Uncompensated respiratory acidosis would have an abnormally low pH (less than 7.35) and a high PaCO2. The patient's values are alkalotic, not acidotic.
Related Visual
Clinical Relevance
- Nursing practice connection: Knowing Arterial Blood Gas (ABG) interpretation and identification of acid-base imbalances helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
- ABG analysis is a critical skill for nurses, especially in acute and critical care settings, to assess a patient's oxygenation and acid-base status.
- Respiratory alkalosis is commonly caused by hyperventilation due to anxiety, pain, fever, hypoxia, or mechanical over-ventilation. Nursing interventions focus on treating the underlying cause, such as managing pain or anxiety.
- What if the patient's values were pH 7.48, PaCO2 31, and HCO3− 24? The pH would be high (alkalotic), PaCO2 low (alkalotic), and HCO3− normal. This would indicate Uncompensated Respiratory Alkalosis, as the kidneys have not yet started to compensate.
How to Approach the Question
- First, analyze the pH. A value between 7.35 and 7.45 is normal/compensated. Below 7.35 is acidosis, and above 7.45 is alkalosis. The patient's pH of 7.43 is normal, suggesting compensation.
- Next, determine if the primary problem is respiratory or metabolic. Look at the PaCO2 (respiratory) and HCO3− (metabolic). The patient's PaCO2 is 31 (low/alkalotic) and HCO3− is 21 (low/acidotic).
- Use the ROME mnemonic (Respiratory Opposite, Metabolic Equal) to link the primary cause to the pH. Here, the pH is on the alkaline side, and the PaCO2 is low (alkalotic), which is a respiratory opposite relationship. This confirms the primary problem is respiratory alkalosis.
- Finally, assess for compensation. Since the pH is normal, it is fully compensated. The HCO3− is low, which is the expected metabolic compensation for respiratory alkalosis. Therefore, the diagnosis is Compensated Respiratory Alkalosis.
Concept Tested & Keywords
- Concept Tested: Arterial Blood Gas (ABG) interpretation and identification of acid-base imbalances.
- Stem keywords: ABG report, PCO2, HCO3, pH, acid base imbalance
- Lead-in keywords: What would be the possible
- Clinical cues: pH of 7.43 indicates a compensated state.
- Clinical cues: Low PCO2 of 31 points to a respiratory cause.
Question ID
QWAG0jN0bTuOHo0BNUq1qN
Reference Book
E6 Nursing Fundamentals Taylor p. 785-787
E6 Nursing Fundamentals Potter Perry 12e Part 5 p. 56-58
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