A nurse is analyzing arterial blood gas (ABG) results for a patient with asthma exacerbation. The results show: pH 7.48, PaCO2 30 mmHg, HCO3- 24 mEq/L, PaO2 85 mmHg. What is the nurse's priority assessment based on these findings?
1Assess the patient's respiratory rate, depth, and use of accessory muscles✓ 정답
2Check the patient's urine output and kidney function tests
3Monitor the patient's cardiac rhythm and heart rate
4Evaluate the patient's neurological status and level of consciousness
해설
The ABG indicates respiratory alkalosis (pH 7.48, PaCO2 30 mmHg, HCO3- 24 mEq/L) without compensation, requiring immediate focus on respiratory status to assess for hyperventilation. Assessing respiratory rate, depth, and accessory muscle use directly evaluates ventilation effectiveness. Urine output, cardiac rhythm, and neurological status are important but secondary in this acute setting.
The first step in analyzing this clinical scenario is interpreting the arterial blood gas (ABG) values. The results show a pH of 7.48, which is above the normal range of 7.35–7.45, indicating alkalosis. The PaCO2 is 30 mmHg, which is below the normal range of 35–45 mmHg, representing a respiratory alkalosis. The HCO3- is 24 mEq/L, which is within the normal range of 22–26 mEq/L, confirming that there is no metabolic compensation occurring. This pattern—elevated pH and decreased PaCO2 with a normal HCO3-—is the classic presentation of an uncompensated respiratory alkalosis.
Pathophysiology in Asthma Exacerbation
In a patient with an asthma exacerbation, this ABG picture is a critical finding. Asthma is characterized by variable airflow limitation, which can become life-threatening during a severe exacerbation [1]. Early in an acute exacerbation, the patient’s respiratory drive is stimulated, leading to hyperventilation. The patient breathes faster and deeper to compensate for the sensation of dyspnea and to maintain oxygenation, which "blows off" carbon dioxide (CO2). This results in a low PaCO2 and a subsequent rise in pH, creating a state of acute respiratory alkalosis. The airway epithelial dysfunction central to asthma pathogenesis contributes to this airflow obstruction and the resulting ventilation-perfusion mismatch [3].
Clinical Priority and Nursing Assessment
The presence of a respiratory alkalosis in an asthma exacerbation is a warning sign that should direct the nurse's immediate assessment. It indicates that the patient is working very hard to breathe and is in the early, hyperventilation phase of respiratory distress. The priority is to perform a focused respiratory assessment to determine the patient's current level of work of breathing and the potential for rapid deterioration. Assessing the respiratory rate, depth, and use of accessory muscles directly evaluates the patient's ventilatory effort and the severity of the airflow limitation. A patient in this state is at high risk for impending respiratory muscle fatigue. If the patient tires and can no longer maintain the hyperventilation, the PaCO2 will begin to rise, "normalizing" to 40 mmHg or higher. A "normal" or rising PaCO2 in a tachypneic asthmatic patient is an ominous sign of impending respiratory failure, as it indicates the patient is no longer able to compensate. This clinical trajectory is precisely why non-invasive ventilation (NIV) strategies are considered a cornerstone in managing acute respiratory failure to prevent the need for intubation . The nurse's bedside assessment of work of breathing is the most direct and immediate indicator of whether the patient is improving, stable, or progressing toward respiratory collapse.
References (research sources)
[1]
Epidemiology and Immunopathogenesis of Virus Associated Asthma Exacerbations.Research articleBakakos A, Sotiropoulou Z, Vontetsianos A, Zaneli S, Papaioannou AI, Bakakos P. (2023) · DOI: 10.2147/jaa.s277455
[3]
Airway epithelial dysfunction in asthma pathogenesis: epigenetic mechanisms, inflammatory crosstalk, and therapeutic opportunities.Research articleZhang B, Song G, Sun M, Zhang Y, Ren M. (2026) · DOI: 10.3389/falgy.2026.1839974
Clinical Priority in Uncompensated Respiratory Alkalosis
Pathophysiology and ABG Interpretation
In an acute asthma exacerbation, airway inflammation and bronchoconstriction increase the work of breathing. The patient's initial compensatory response is hyperventilation, which lowers PaCO2 and raises pH, producing an uncompensated respiratory alkalosis (pH >7.45, PaCO2 <35 mmHg, normal HCO3-). This finding indicates that the patient is still able to maintain gas exchange but is under significant respiratory stress.
Nursing Assessment and Rationale
The priority assessment is a focused respiratory evaluation. The nurse must immediately assess the patient's respiratory rate, depth, and use of accessory muscles. This data provides real-time information on the patient's work of breathing and helps detect early signs of impending respiratory muscle fatigue. A patient in this state is at high risk for decompensation; if respiratory muscles tire, hyperventilation will cease, PaCO2 will begin to rise, and the ABG will transition from alkalosis to a normal or acidotic pH—a dangerous sign of impending respiratory failure.
Clinical Implications and Monitoring
While other assessments (cardiac rhythm, neurological status, renal function) are part of a comprehensive evaluation, they are secondary to the immediate respiratory threat. The nurse should monitor for a declining respiratory rate, decreased breath sounds, or a change in mental status, which signal exhaustion. Serial ABGs or continuous capnography may be indicated to track PaCO2 trends. The goal is to intervene with bronchodilators, corticosteroids, and oxygen therapy before the patient decompensates.
Respiratory Alkalosis — An acid-base disorder characterized by elevated blood pH (>7.45) and decreased PaCO2 (<35 mmHg) due to hyperventilation.
Uncompensated ABG — An arterial blood gas result where the pH is abnormal and either the respiratory or metabolic component is abnormal, but the other system has not yet responded to normalize the pH.
Asthma Exacerbation — An acute or subacute episode of progressive worsening of asthma symptoms, including shortness of breath, wheezing, and cough, associated with variable expiratory airflow limitation.
Hyperventilation — Rapid or deep breathing that leads to excessive exhalation of carbon dioxide, resulting in a decreased PaCO2 and respiratory alkalosis.