Which type of acid base imbalance is most commonly seen in patients with Chronic Obstructive Pulmonary Diseas… - RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

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Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Explanation

Chronic Obstructive Pulmonary Disease (COPD) impairs alveolar gas exchange, leading to the retention of carbon dioxide (CO2).
This condition, known as alveolar hypoventilation, causes the partial pressure of CO2 (PaCO2) in the blood to rise.
Elevated PaCO2 leads to an excess of carbonic acid (H2CO3) in the blood, which lowers the pH, resulting in respiratory acidosis.
In chronic COPD, the kidneys compensate by retaining bicarbonate (HCO3−) to buffer the excess acid, often bringing the pH back toward a normal range.

Option A: Metabolic acidosis is caused by an increase in metabolic acids or a loss of bicarbonate, which is not the primary mechanism in COPD.
Option B: Metabolic alkalosis results from a loss of acid (e.g., from vomiting) or an excess of bicarbonate. While it can occur concurrently due to diuretic use in COPD patients, it is not the primary imbalance.
Option D: Respiratory alkalosis is caused by hyperventilation (blowing off too much CO2), which is the opposite of the gas exchange impairment seen in COPD.

Clinical Relevance

Nursing practice connection: Knowing Pathophysiology of acid-base imbalance in COPD helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must carefully monitor Arterial Blood Gas (ABG) results in COPD patients to guide treatment, especially during acute exacerbations, and to assess the adequacy of ventilation.
A critical nursing intervention is the cautious administration of oxygen. In patients with chronic CO2 retention, the primary stimulus to breathe can become hypoxia (low oxygen) rather than high CO2. Giving too much oxygen can suppress this hypoxic drive, leading to further CO2 retention, severe acidosis, and CO2 narcosis (lethargy, confusion, coma).
What if? If a patient with chronic respiratory acidosis from COPD also develops severe diarrhea, they could lose significant bicarbonate. This would result in a mixed acid-base disorder (respiratory acidosis and metabolic acidosis), leading to a dangerously low pH that is difficult to manage.

How to Approach the Question

First, identify the core disease process mentioned in the question: Chronic Obstructive Pulmonary Disease (COPD).
Next, recall the primary pathophysiological defect of COPD, which is impaired gas exchange and alveolar hypoventilation.
Then, determine the effect of hypoventilation on blood gases. The lungs cannot effectively eliminate carbon dioxide (CO2), causing it to accumulate in the blood.
Connect this change in blood gas to the acid-base balance. CO2 is an acidic substance in the blood. Its retention leads to an increase in carbonic acid, which lowers the blood pH.
Finally, classify the imbalance based on these findings. A low pH caused by a primary respiratory problem (high CO2) is defined as respiratory acidosis.

Concept Tested & Keywords

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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