# A nurse is analyzing arterial blood gas (ABG) results for a patient admitted with chronic obstructive pulmonary disease (COPD) exacerbation. The ABG results show: pH 7.25, PaCO2 65 mmHg, HCO3- 30 mEq/L, PaO2 55 mmHg. What is the nurse's priority assessment finding to monitor?

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## 문제

A nurse is analyzing arterial blood gas (ABG) results for a patient admitted with chronic obstructive pulmonary disease (COPD) exacerbation. The ABG results show: pH 7.25, PaCO2 65 mmHg, HCO3- 30 mEq/L, PaO2 55 mmHg. What is the nurse's priority assessment finding to monitor?

## 보기

1. Respiratory rate and breathing pattern changes **✔ 정답**
2. Serum potassium levels and cardiac rhythm
3. Blood pressure and peripheral perfusion
4. Level of consciousness and neurological status

**정답: 1**

## 해설

The ABG shows respiratory acidosis with partial compensation. The priority is monitoring respiratory rate and pattern as the primary problem is inadequate ventilation requiring immediate intervention. Other assessments (potassium, blood pressure, consciousness) are important but secondary.

## 심화 해설

Analysis of ABG Results

The patient’s ABG reveals a pH of 7.25 (acidosis), a PaCO₂ of 65 mmHg (elevated), and an HCO₃⁻ of 30 mEq/L (elevated). This pattern indicates a primary respiratory acidosis with partial metabolic compensation, a classic finding in acute exacerbation of chronic obstructive pulmonary disease (COPD). The PaO₂ of 55 mmHg confirms significant hypoxemia. In COPD exacerbation, alveolar hypoventilation leads to CO₂ retention, which shifts the equilibrium of the bicarbonate buffer system, increasing hydrogen ion concentration and lowering pH. The kidneys retain bicarbonate over time to compensate, but in an acute-on-chronic presentation, this compensation is often incomplete .

Priority Assessment Rationale

The priority assessment is to monitor respiratory rate and breathing pattern changes. The ABG demonstrates hypercapnic acute respiratory failure (ARF), a life-threatening condition that is a leading cause of hospital admission in COPD exacerbation [3]. The primary pathophysiological problem is ventilatory failure—the inability to effectively eliminate CO₂. This is driven by worsening airflow obstruction, increased dead space ventilation, and respiratory muscle fatigue. The most direct clinical indicators of worsening ventilatory failure are changes in respiratory mechanics: a rapid, shallow breathing pattern, use of accessory muscles, paradoxical abdominal movement, and a declining respiratory rate in a previously tachypneic patient, which can signal impending respiratory arrest. While non-invasive ventilation (NIV) is the first-line strategy for this condition, its failure can be precipitated by worsening ARF, patient-ventilator asynchrony, or interface intolerance [3]. Therefore, continuous assessment of breathing pattern and rate is the most immediate and sensitive way to detect deterioration and the need for escalation of ventilatory support [3].

Why Other Options Are Not the Priority

Monitoring serum potassium levels and cardiac rhythm is important because acidosis can cause an extracellular shift of potassium, leading to hyperkalemia and risk of cardiac arrhythmias. However, this is a secondary effect of the acid-base disturbance. The immediate threat to life is the progressive respiratory failure itself, which requires direct monitoring of the respiratory system . Assessing blood pressure and peripheral perfusion addresses cardiovascular stability, which can be compromised by dynamic hyperinflation and increased intrathoracic pressure. While relevant, it is not the most direct measure of the primary problem: CO₂ retention [3]. Monitoring level of consciousness and neurological status is critical because severe hypercapnia causes CO₂ narcosis, leading to somnolence, confusion, and coma. However, a change in neurological status is a late sign of decompensation. By the time consciousness is altered, respiratory failure is already advanced. Subtle changes in respiratory rate and pattern serve as earlier, more sensitive indicators of impending ventilatory collapse, allowing for timely intervention before neurological deterioration occurs .References (research sources)

- [3]Management of hypercapnic acute respiratory failure with high-flow nasal cannula therapy: A narrative review.Research articleGirault C, Artaud-Macari E, Declercq PL, Frat JP, Ricard JD, Thille AW, Béduneau G. (2026) · DOI: 10.1016/j.aicoj.2026.100053

## 임상 시나리오

Clinical Guide: Monitoring COPD Exacerbation with Respiratory Acidosis

This guide outlines evidence-based clinical assessment for a patient with ABG-confirmed acute-on-chronic respiratory acidosis, focusing on early detection of ventilatory failure.

1. Pathophysiology & ABG Interpretation

The ABG (pH 7.25, PaCO2 65 mmHg, HCO3- 30 mEq/L) indicates a **primary respiratory acidosis with partial metabolic compensation**. The elevated PaCO2 confirms alveolar hypoventilation, the hallmark of acute exacerbation of COPD. The slightly elevated HCO3- reflects renal compensation from chronic CO2 retention, but the pH remains acidotic, signifying an acute-on-chronic process. The PaO2 of 55 mmHg indicates significant hypoxemia requiring controlled oxygen therapy to avoid suppressing the hypoxic respiratory drive.

2. Priority Assessment: Respiratory Mechanics

The primary problem is **ventilatory failure**. The nurse must continuously assess:

- **Respiratory Rate and Rhythm:** A rapid, shallow pattern indicates increased dead space ventilation and muscle fatigue. A sudden drop in rate in a previously tachypneic patient is an ominous sign of impending respiratory arrest.

- **Breathing Pattern:** Look for paradoxical abdominal movement (inward abdominal motion on inspiration), which signals diaphragmatic fatigue.

- **Accessory Muscle Use:** Observe for sternocleidomastoid contraction, supraclavicular retractions, and intercostal indrawing. This indicates high work of breathing.

- **Auscultation:** Monitor for diminished breath sounds or a silent chest, which suggests severe airflow obstruction and exhaustion.

3. Secondary Assessments & Rationale

While respiratory mechanics are the priority, these assessments provide critical context:

- **Level of Consciousness:** Rising PaCO2 causes CO2 narcosis, manifesting as somnolence, confusion, or coma. This is a late sign requiring immediate intervention.

- **Cardiac Rhythm:** Hypoxemia and acidosis can precipitate dysrhythmias. Monitor for sinus tachycardia and ventricular ectopy.

- **Oxygen Saturation (SpO2):** Titrate oxygen to a target SpO2 of 88-92% to balance hypoxemia correction with the risk of CO2 retention.

4. Clinical Red Flags & Escalation

Immediately report these findings to the provider and prepare for non-invasive ventilation (NIV) or intubation:

- Worsening respiratory acidosis on repeat ABG despite therapy.

- Altered mental status (GCS drop of 2 or more points).

- Hemodynamic instability (new-onset hypotension, bradycardia).

- Severe dyspnea with inability to speak in full sentences.

## 핵심 개념

- **Respiratory Acidosis** — A condition of decreased blood pH caused by alveolar hypoventilation leading to CO2 retention, common in COPD exacerbation.
- **Ventilatory Failure** — The inability of the respiratory system to maintain adequate gas exchange, resulting in hypercapnia and hypoxemia.
- **Hypercapnia** — An abnormally elevated level of carbon dioxide (PaCO2) in the arterial blood, indicating inadequate alveolar ventilation.
- **Metabolic Compensation** — The renal response to chronic respiratory acidosis, involving increased bicarbonate (HCO3-) retention to buffer excess acid.
- **Accessory Muscle Use** — Recruitment of neck, shoulder, and chest wall muscles during breathing, signaling increased work of breathing and impending respiratory failure.

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