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Asthma
ОглавлениеAsthma is a chronic inflammatory lung disorder characterized by acute attacks of airway hyper‐responsiveness with reversible obstruction. Precipitating factors include upper respiratory tract infections, exposure to allergens, high pollution indices, and failure to use preventive and maintenance therapies. The disease affects nearly 25 million individuals (and minority communities disproportionally) in the United States [24]. Although there are hallmark features of an acute exacerbation, assessment of asthma exacerbations can be challenging and potentially misleading (Box 5.2). For example, the absence of wheezing may indicate either severely restricted airflow or clinical improvement following appropriate treatment. A multicomponent guide can help assess the severity and monitor the effectiveness of the treatment of asthma (Table 5.1) [25]. Extreme (both low and high) values of initial prehospital EtCO2 were associated with poor outcomes among adult asthma patients in one study [26].
Oxygen should be provided to relieve hypoxemia and titrated to a SpO2 of 94%‐98%. The initial drug of choice for treatment is a SABA, which acts by relaxing bronchial smooth muscle and increasing mucociliary clearance. Nebulization is the preferred route of administration in the acute setting with either intermittent or continuous delivery. SABAs can also be administered through metered dose inhalers and spacer devices. The use of subcutaneous or intramuscular epinephrine (a nonselective beta‐agonist) has declined with the availability of SABAs, but epinephrine remains useful when the patient is critically ill or when the inhaled SABA cannot be delivered effectively. An anticholinergic bronchodilator agent, such as ipratropium, can be added to the SABA for more severe exacerbations. Patients who fail to respond promptly and completely to inhaled bronchodilators benefit from the administration of systemic corticosteroids. The benefits of prehospital corticosteroid administration have not been proven through randomized controlled clinical trials. Nonrandomized observational studies, however, have shown that EMS delivery of corticosteroids is associated with faster resolution of symptoms and decreased hospital admission rates [27]. It has also been suggested that early use of corticosteroids may enhance the effectiveness of SABAs [28]. Corticosteroid options include prednisone (oral), dexamethasone (oral, IM, IV), and methylprednisolone (IV). Oral steroids as part of an evidence‐based protocol for pediatric asthma were associated with shorter hospital care times, lower hospitalization rates, and less need for critical care in admitted patients [29]. For severe exacerbations that fail to respond to inhaled bronchodilators and systemic corticosteroids, adjunctive therapies, such as IV magnesium sulfate or heliox, if available, should be considered. The beneficial actions of magnesium include smooth muscle relaxation and an anti‐inflammatory effect [30]. A 2014 Cochrane review concluded that a single infusion of 1 or 2 g IV MgSO4 over 15 to 30 minutes reduced hospital admission and improved lung function in adults with acute asthma who had not responded sufficiently to oxygen, nebulized SABAs, and IV corticosteroids in the emergency department [31]. Capnography waveforms in asthma may have a shark fin (Figure 5.2), which can facilitate diagnosis and assessment of response to treatment.
Although NIPPV for acute exacerbations of asthma is traditionally viewed as a last resort due to the fear of worsening air trapping and secondary barotrauma, studies of its use in the emergency department and ICU settings in children and adults have shown benefit [32, 33]. A retrospective study of pediatric patients who were placed on bilevel PAP and given SABAs in the emergency department, with initial disposition plans for ICU admission, found that 22% of the patients tolerated bilevel PAP and were able to be downgraded to ward admission [34]. None required subsequent ICU admission. All of these patients had improved SpO2 levels as well as respiratory rates, and there were no bilevel PAP–related adverse events [33].
Table 5.1 Asthma severity guide
Source: Based on National Heart, Lung and Blood Institute, National Institutes of Health. Guidelines for the diagnosis and management of asthma (EPR‐3). 2007. National Heart, Lung, and Blood Institute; National Institutes of Health; US Department of Health and Human Services.
| Parameter | Mild | Moderate | Severe |
|---|---|---|---|
| Shortness of breath | Walking | Talking | At rest |
| Ability to speak | Full sentences | Phrases | Words |
| Accessory muscle use | Rare | Common | Always |
| Mental status | Agitation (variable) | Agitated (usually) | Agitated to somnolent |
| Heart rate (bpm) | 100 | 100‐120 | >120 |
| Respiratory rate | Increased | Increased | >30 |
| EtCO2 (mmHg) | 20‐30 | 30‐40 | >40 |
| Lung sounds | End expiratory wheezing | Full expiratory wheezing | Absent or biphasic wheezing |
bpm, beats per minute; EtCO2, end‐tidal CO2
Figure 5.2 A capnogram depicting bronchospasm with a characteristic “shark fin” appearance.
Source: Based on Egleston CV, Ben Aslam H, Lambert MA. Capnography for monitoring non‐intubated spontaneously breathing patients in an emergency room setting. J Accid Emerg Med. 1997; 14:222–4.
If rapid sequence intubation is necessary for an asthma patient, the preferred induction agent is ketamine due to its inherent bronchodilator properties. Once intubated, ventilation should be provided at reduced volumes and rates to prevent air trapping and secondary barotrauma. The inspiratory‐to‐expiratory ratios should be adjusted to provide a prolonged expiratory phase. Permissive hypercarbia is generally well‐tolerated in these individuals. All NIPPV and intubated asthma patients should be monitored closely for signs of secondary barotrauma, such as tension pneumothorax and pneumomediastinum.
