Measurement of arterial blood gas shows pH 7.2, PaCO2, 70 mmHg, HCO3, 27 mmol/L and PaO2 59 mmHg Interpret th… - HPSSC Staff Nurse - 2021

HPSSC Staff Nurse - 2021

Medical & Surgical Nursing

Hard

Appeared in: HPSSC Staff Nurse - 2021

Explanation

The primary disturbance is respiratory acidosis, identified by a low pH (7.2) and a high PaCO₂ (70 mmHg).
This condition arises from alveolar hypoventilation, where the lungs fail to eliminate enough CO₂, causing it to build up in the blood as carbonic acid.
The bicarbonate (HCO₃⁻) level is slightly elevated at 27 mmol/L, indicating that the kidneys have started to compensate by retaining bicarbonate to buffer the excess acid.
The low PaO₂ of 59 mmHg signifies concurrent hypoxemia, a common finding with respiratory depression or failure.

Option B: Respiratory alkalosis is characterized by a high pH (greater than 7.45) and a low PaCO₂ (less than 35 mmHg), which is the opposite of the patient's values.
Option C: Metabolic acidosis involves a low pH (less than 7.35) but is primarily caused by a low bicarbonate level (less than 22 mmol/L). This patient's bicarbonate is slightly high.
Option D: Metabolic alkalosis is defined by a high pH (greater than 7.45) and a high bicarbonate level (greater than 26 mmol/L). This patient has acidosis, not alkalosis.

Clinical Relevance

Nursing practice connection: Knowing Arterial Blood Gas (ABG) Interpretation helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Respiratory acidosis is a life-threatening condition that requires immediate nursing intervention to improve ventilation and oxygenation.
Common causes include COPD exacerbation, opioid overdose, pneumonia, and neuromuscular diseases that impair breathing.
Nurses must closely monitor respiratory rate, oxygen saturation, and level of consciousness, and be prepared for interventions like administering oxygen, bronchodilators, or initiating mechanical ventilation.

How to Approach the Question

First, look at the pH. Classify it as acidosis (less than 7.35), normal (7.35-7.45), or alkalosis (greater than 7.45). In this case, 7.2 is acidosis.
Second, examine the PaCO₂ (the respiratory component). Determine if it explains the pH change. A high PaCO₂ causes acidosis. Here, PaCO₂ is 70 mmHg (high), which aligns with the acidosis.
Third, check the HCO₃⁻ (the metabolic component). A low HCO₃⁻ causes acidosis. Here, HCO₃⁻ is 27 mmol/L (slightly high), which does not explain the acidosis. Instead, it shows the metabolic system is trying to compensate.
Finally, synthesize the findings. Since the respiratory value (PaCO₂) matches the pH direction (acidosis), the primary problem is respiratory acidosis. The opposing metabolic value (HCO₃⁻) indicates partial compensation.

Concept Tested & Keywords

Concept Tested: Arterial Blood Gas (ABG) Interpretation
Stem keywords: arterial blood gas, pH 7.2, PaCO2 70 mmHg, HCO3 27 mmol/L, PaO2 59 mmHg
Lead-in keywords: Interpret
Clinical cues: Low pH indicates acidosis.
Clinical cues: High PaCO2 indicates a respiratory problem.

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