Recommendations
Key Recommendations
Objective assessment of the severity of the exacerbation requires measurement of oxygen saturation and other vital observations together with assessment of decline in pulmonary function. Arterial blood gases (ABGs) are measured in severe exacerbations. Symptoms and signs of respiratory distress are noted.
The patient's usual medication regimen is established, along with any changes that they have made in response to the exacerbation after following their self-management plan. Risk factors for asthma-related death are also established.
Clinical evaluation
A focused clinical assessment should be performed whilst initiating timely and appropriate therapy (see Management Approach).[1]
Many patients with asthma are poor perceivers of the severity of their asthma and therefore objective assessment of lung function correlates more accurately with the severity of an asthma exacerbation than patient self-assessment.
Pulse oximetry to measure oxygen saturation is performed immediately (ideally before starting supplemental oxygen, depending on clinical urgency). Significant hypoxemia with an oxygen saturation (SpO₂) <90% is infrequent during asthma exacerbations and, if present, represents severe airflow limitation. SpO₂ <90% indicates a need for aggressive therapy.[1]
Key components of the history include the time of onset, possible causes of the presenting exacerbation, and severity and duration of symptoms. Consider:
Progressive worsening of cough. An increase in cough may be the first symptom of an exacerbation.
Wheezing. Typically worsens progressively during an exacerbation. A patient with asthma in extremis without wheezing is likely to be on the verge of respiratory failure.
Chest tightness.
Ability to speak. The inability to complete a sentence owing to dyspnea is an indicator of severe airflow obstruction and impending respiratory failure.
Shortness of breath. Degree of breathlessness is a pointer to the severity of the exacerbation.
Exercise limitation.
Asthma and smoking history.
Recent viral or bacterial respiratory infection.
Sleep disturbance.
Details of medications taken before the presenting exacerbation are recorded, including dose prescribed, dose usually taken, any recent changes to treatment, dose taken in response to the deterioration, and patient response to this therapy. Ask about the patient’s use of any other medications that could have triggered the exacerbation (e.g., use of nonsteroidal anti-inflammatory drugs [NSAIDs], aspirin, and beta-blockers).[1]
Anaphylaxis is an important alternative or complicating diagnosis to consider (especially if the patient has a history of suspected or confirmed anaphylaxis, which is a risk factor for asthma-related death).[1] Food-induced anaphylaxis commonly presents as a life-threatening asthma exacerbation.[1]
Risk factors for asthma-related death are also established. Factors include:[1]
A history of near-fatal asthma requiring intubation and mechanical ventilation
Hospitalization or emergency care visit for asthma in the past year
Currently using or having recently stopped oral corticosteroids
Not currently using inhaled corticosteroids (ICS)
Overuse of short-acting beta-2 agonists, especially use of one or more inhalers of albuterol (or equivalent) monthly on average, or use of nebulized short-acting beta-2 agonist
Poor adherence to ICS-containing medications and/or poor adherence to (or lack of) a written asthma action plan
A history of psychiatric disease or psychosocial problems
Food allergy (or anaphylaxis) in a patient with asthma
Comorbidities including pneumonia, diabetes, and arrhythmias.
Physical exam
Key components include:
Measurement of blood pressure, pulse, oxygen saturation, respiratory rate, temperature, and assessment of conscious level. A respiratory rate of >30 breaths/minute and/or a heart rate of >120 bpm suggests a severe exacerbation.[1] Confusion or drowsiness may be caused by hypoxia and/or hypercapnia; altered consciousness is an indication of a life-threatening exacerbation.[1]
Assessment for presence of stridor or cyanosis.
Objective assessment of respiratory distress and accessory muscle use. Use of accessory muscles, including the scalene, parasternal, and sternocleidomastoid muscles, is a sign of severe asthma exacerbation.[1]
Auscultation of the lung fields. In a severe exacerbation, the absence of wheezing (i.e., "silent chest") indicates severely reduced air exchange and is a sign of a life-threatening exacerbation.[1]
Decline in pulmonary function can be assessed using peak expiratory flow rate or forced expiratory volume in 1 second (FEV₁).[1] FEV₁ is a valid measure of airway caliber, but peak expiratory flow is considered more clinically useful and is more readily available in acute care.[45] In acute settings, these lung function measurements may be more reliable than symptoms for determining exacerbation severity, and if possible, should be performed before initiation of acute treatment (but without inappropriately delaying management).[1]
Additionally, assess for the presence of complicating factors such as anaphylaxis, pneumonia, atelectasis, pneumothorax and pneumomediastinum, and consider whether there are signs of alternative causes of acute breathlessness (e.g., pulmonary embolism, heart failure).[1]
Laboratory evaluation
ABGs should be considered in patients with severely impaired lung function (e.g., peak expiratory flow rate or FEV₁ <50% predicted), and in those who do not respond to initial treatment, or when there is concern regarding deterioration.[1]
Respiratory alkalosis from increased work of breathing is a common finding and therefore it is important to recognize that a normal or elevated partial pressure of carbon dioxide (PaCO₂) (≥45 mmHg, 6 kPa) or increasing PaCO₂ from a previous ABG is frequently an indication of impending respiratory failure with potential need for airway intervention (as is a partial pressure of oxygen [PaO₂] <60 mmHg [8 kPa]).[1]
Complete blood count is indicated in acute exacerbations when complicating factors (e.g., pneumonia) are suspected from the history and exam. Electrolyte abnormalities may need to be monitored (e.g., for patients requiring intravenous fluid rehydration).[45]
Other investigations
A chest x-ray is not routinely necessary. It should be considered if a complicating or alternative pulmonary pathology is suspected or for patients who are not responding to treatment to rule out a pneumothorax if difficult to diagnose clinically.[1][46]
Exhaled nitric oxide is a biomarker that may have a role in the management of chronic asthma but has no value in the management of acute exacerbations.
How to use a peak flow meter to obtain a peak expiratory flow rate measurement.
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