In COPD, the arterial blood gas (ABG) imbalance commonly shows:

NORCET 9 Mains - 2025

Medical Surgical Nursing

Hard

Appeared in: NORCET 9 Mains - 2025

Explanation

Chronic Obstructive Pulmonary Disease (COPD) is characterized by airflow limitation, which impairs the body's ability to effectively exhale carbon dioxide (CO₂).
This leads to CO₂ retention, a state known as alveolar hypoventilation, causing an increase in the partial pressure of arterial CO₂ (PaCO₂).
Since CO₂ functions as an acid in the blood (forming carbonic acid), the elevated PaCO₂ lowers the blood pH below 7.35.
An acid-base imbalance caused by a primary increase in PaCO₂ is defined as respiratory acidosis.

Option A: Respiratory alkalosis is caused by hyperventilation, where too much CO₂ is exhaled. This is the opposite of what occurs in COPD, which involves hypoventilation and CO₂ retention.
Option C: Metabolic alkalosis is a primary increase in bicarbonate (HCO₃⁻) or loss of metabolic acids, which is not the primary problem in COPD. While bicarbonate levels do rise in chronic COPD, it is a compensatory response to the primary respiratory acidosis, not the initial imbalance.
Option D: Metabolic acidosis results from an excess of metabolic acids or a deficit of bicarbonate. The primary issue in COPD is respiratory, related to CO₂ management, not metabolic acid production or bicarbonate loss.

Visual 1: Flowchart - A flowchart illustrating the progression: COPD → Impaired Exhalation → CO₂ Retention (Hypercapnia) → Increased PaCO₂ → Decreased Blood pH → Respiratory Acidosis.
Visual 2: Chart - An ABG interpretation chart (like a ROME or tic-tac-toe grid) showing how to diagnose the four primary acid-base imbalances based on pH, PaCO₂, and HCO₃⁻ values.

Clinical Relevance

Nursing practice connection: Knowing Pathophysiology of COPD and Arterial Blood Gas (ABG) Interpretation helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
A key nursing responsibility is the cautious administration of oxygen to COPD patients. Over-oxygenation can diminish the hypoxic drive to breathe and worsen V/Q mismatch, leading to increased CO₂ retention and severe acidosis (CO₂ narcosis).
The target oxygen saturation (SpO₂) for most patients with chronic CO₂ retention is typically lower, around 88-92%, to prevent this complication.
Nurses must monitor for signs of worsening respiratory acidosis, such as headache, confusion, lethargy, drowsiness, and eventually coma. Any change in mental status requires immediate assessment and intervention.

How to Approach the Question

First, identify the core pathophysiology of the disease mentioned in the stem. For COPD, the key issue is impaired airflow and gas exchange, specifically difficulty with exhalation.
Next, connect this pathophysiology to its effect on blood gases. Difficulty exhaling means the body retains carbon dioxide (CO₂).
Recall the acid-base properties of blood gases. CO₂ is an acid. Therefore, retaining CO₂ will make the blood more acidic.
Determine the origin of the problem. Since the issue stems from the lungs (respiration), the primary imbalance is 'respiratory'.
Combine the findings: an acidic state caused by a respiratory problem is 'respiratory acidosis'.
Finally, evaluate the other options to confirm they are incorrect. Alkalosis is the opposite of what's expected, and metabolic issues have different root causes (kidneys, metabolism) not directly related to COPD's primary defect.

Concept Tested & Keywords

Concept Tested: Pathophysiology of COPD and Arterial Blood Gas (ABG) Interpretation
Stem keywords: COPD, arterial blood gas, ABG imbalance
Lead-in keywords: commonly shows

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