# Situation: A 24-year-old woman with asthma is brought to the emergency room (ER) with wheezing and breathlessness that began after a viral cold. At home she uses only a salbutamol (albuterol) inhaler, about 6 to 8 times a week. She has no other illness, takes no other medicines, and her oxygen saturation by pulse oximetry (SpO2) is monitored continuously. On arrival her respiratory rate was 32/min, she had loud expiratory wheezes, her SpO2 was 89% on room air, and her arterial carbon dioxide tension (PaCO2) was 30 mmHg (normal 35–45 mmHg). After 1 hour of oxygen and three doses of nebulized salbutamol with ipratropium, the nurse records: respiratory rate 22/min, faint breath sounds with almost no wheezes, SpO2 91% on oxygen, PaCO2 44 mmHg, answers in single words, and eyes that keep closing. How should the nurse interpret these changes?

> source: MyMerci (mymerci.kr)  
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> subject: Nursing Practice III — Care of Clients with Problems in Surgery, Oxygenation, Fluid and Electrolytes, Infectious, Inflammatory and Immunologic Response, Cellular Aberrations

## 문제

Situation: A 24-year-old woman with asthma is brought to the emergency room (ER) with wheezing and breathlessness that began after a viral cold. At home she uses only a salbutamol (albuterol) inhaler, about 6 to 8 times a week. She has no other illness, takes no other medicines, and her oxygen saturation by pulse oximetry (SpO2) is monitored continuously.

On arrival her respiratory rate was 32/min, she had loud expiratory wheezes, her SpO2 was 89% on room air, and her arterial carbon dioxide tension (PaCO2) was 30 mmHg (normal 35–45 mmHg). After 1 hour of oxygen and three doses of nebulized salbutamol with ipratropium, the nurse records: respiratory rate 22/min, faint breath sounds with almost no wheezes, SpO2 91% on oxygen, PaCO2 44 mmHg, answers in single words, and eyes that keep closing. How should the nurse interpret these changes?

## 보기

1. Bronchospasm is easing, so the doses can now be spaced further apart
2. The slower breathing rate shows that her oxygen needs are now met
3. Her early anxiety and hyperventilation have settled with treatment
4. She is tiring, and respiratory failure is developing **✔ 정답**

**정답: 4**

## 해설

Early in an asthma attack, hyperventilation lowers PaCO2, as her first value of 30 mmHg showed. A rise back to a 'normal' 44 mmHg while she speaks in single words, grows drowsy, and has faint breath sounds with few wheezes means airflow is now too low to produce a wheeze (silent chest) and her breathing muscles are tiring. These are signs of impending respiratory failure: the nurse calls the rapid response team and prepares for ventilatory support.

## 심화 해설

Clinical interpretation of changing asthma findings

The transition from the initial presentation to the post-treatment findings is not an improvement. It signals a dangerous shift toward ventilatory failure.

Early in an acute asthma exacerbation, hypoxemia and air hunger drive a strong respiratory drive. The patient hyperventilates, which blows off carbon dioxide and produces a low PaCO₂. The first value of 30 mmHg fits this pattern. At that stage, loud expiratory wheezes mean that air is still moving, albeit through narrowed airways.

After one hour of bronchodilator therapy, the findings have changed in a concerning direction. The respiratory rate has fallen from 32/min to 22/min, and the PaCO₂ has risen to 44 mmHg. On the surface, a PaCO₂ within the normal range of 35–45 mmHg might seem reassuring. However, in a patient who was previously hyperventilating, a return to normal PaCO₂ is not normalization. It represents carbon dioxide retention as airflow becomes critically limited.

The most ominous clues are clinical. The patient now has faint breath sounds with almost no wheezes. Wheezing requires sufficient airflow to vibrate the narrowed airways. When airflow drops severely, the chest becomes quiet—a phenomenon known as silent chest. The absence of wheeze in this context does not mean the bronchospasm has resolved; it means the patient is moving too little air to generate sound [3]. Concurrently, she answers in single words and her eyes keep closing, indicating progressive somnolence. These are signs of fatiguing respiratory muscles and rising CO₂ affecting consciousness.

A rising PaCO₂ toward normal in a previously hypocapnic asthma patient, combined with drowsiness and a quiet chest, indicates impending respiratory failure. The respiratory muscles are no longer able to sustain the work of breathing. This is a pre-arrest situation.

Watch out! Do not interpret the slower respiratory rate or the “normal” PaCO₂ as improvement. In acute asthma, these changes must be read together with mental status and breath sound intensity. A quiet chest plus drowsiness is a late and dangerous sign.

Key point! The nurse should recognize this as respiratory failure and immediately call the rapid response team, prepare for ventilatory support, and continue oxygen while monitoring for further deterioration.

| Finding | Early asthma | Impending respiratory failure |
| --- | --- | --- |
| Respiratory rate | Tachypnea (32/min) | Slowing as muscles fatigue (22/min) |
| PaCO₂ | Low (30 mmHg) from hyperventilation | Rising to normal (44 mmHg) from CO₂ retention |
| Breath sounds | Loud expiratory wheezes | Faint, almost silent chest |
| Mental status | Anxious, alert | Drowsy, single words, eyes closing |
| SpO₂ | 89% on room air | 91% on oxygen, still inadequate |

The underlying physiology aligns with the concept that chemoreflex responses initially drive hyperventilation during hypoxemia and respiratory distress . As the work of breathing overwhelms the respiratory muscles, ventilatory fatigue develops, and the patient can no longer maintain adequate alveolar ventilation . In asthma, this fatigue is compounded by progressive airflow obstruction, leading to CO₂ retention and altered consciousness.

The combination of a quiet chest, drowsiness, and a rising PaCO₂ in acute asthma is a late sign of respiratory muscle fatigue and requires immediate escalation of care. The nurse must not delay intervention while waiting for further blood gas results.References (research sources)

- [3]An Unexpected Case of Perioperative Recurrent Bronchospasm: A Case Report and Review of the Literature.Case reportSaitowitz Z. (2026) · DOI: 10.7759/cureus.109843

## 임상 시나리오

Asthma Deterioration: Recognizing Impending Respiratory FailureWhen normal PaCO2 is not reassuring
Early in acute asthma, hypoxemia and air hunger drive hyperventilation, lowering PaCO2 below 35 mmHg. A rising PaCO2 back into the normal range in a previously hyperventilating patient indicates CO2 retention from critically limited airflow, not improvement.

The most ominous signs are silent chest—faint breath sounds with almost no wheezes—along with single-word speech and drowsiness. Wheezing requires sufficient airflow; its absence here means the patient is moving too little air to generate sound.

CautionDo not interpret a respiratory rate drop from 32/min to 22/min as improvement when accompanied by rising PaCO2 and altered mental status. These are signs of respiratory muscle fatigue and impending ventilatory failure. Activate the rapid response team and prepare for ventilatory support.

## 핵심 개념

- **silent chest** — Severely reduced airflow in severe asthma so little air moves that wheezing disappears, signaling impending respiratory failure
- **PaCO2** — Arterial carbon dioxide tension; low in early asthma hyperventilation, rising toward normal or high indicates fatigue and hypoventilation
- **respiratory failure** — Inability to maintain adequate gas exchange; in asthma, suggested by rising PaCO2, altered mental status, and silent chest
- **bronchospasm** — Airway smooth muscle constriction causing narrowing and wheezing in asthma
- **hyperventilation** — Increased breathing that lowers PaCO2, common early in acute asthma due to hypoxemia and air hunger

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