DIAGNOSTIC STUDIES

The use of diagnostic studies is limited in the evaluation of

a patient with an asthma exacerbation. However, certain

diagnostic modalities may be indicated, depending on the

clinical situation.

...... Laboratory

An arterial blood gas (ABG) may demonstrate an increased

pC02 level, indicating ventilatory failure and need for

admission to the intensive care unit (ICU). However, the

patient's clinical condition is more important than an ABG

to predict outcome or the need for intubation. Electrolytes

and renal function may be helpful if the patient has comorbidities that make metabolic derangements more likely. An

elevated white blood cell count may aid in the diagnosis of

concomitant pulmonary infection.

..... Imaging

Hyperinflation of the lungs is seen in moderate to severe

exacerbations and may be reflected on the chest x-ray ( CXR)

as an increased anterior-posterior diameter and flattening

of the diaphragm muscles. A CXR should be considered in

patients not responding to treatment, those with fevers,

and those requiring hospitalization or intubation. About

15% of these patients have unsuspected pneumonia, CHF,

pneumothorax, or pneumomediastinum.

...... Electrocardiogram

The electrocardiogram (ECG) is not routinely useful and

often demonstrates sinus tachycardia. In severe asthma

exacerbations, a right ventricular strain pattern that nor ­

malizes with improvement of airflow may be seen.

Dysrhythmias and ischemia may occur in older patients

with coexistent heart disease.

PROCEDURES

...... Peak Expiratory Flow Rate

Forced expiratory volume in 1 second (FEV1) and peak expiratory flow rate (PEFR) are objective measurements of the

degree of airway obstruction that can be performed at the

bedside (Figures 21-1 and 21-2). These aid the physician in

monitoring the progression of treatment and determination

of patient disposition. Predicted values for FEV1 and PEFR

are based on the patient's age, sex, and height and c ompared

with a standardized chart or by using the percent of the

patient's personal best peak flow. PEFRs <25% predicted

indicate a life-threatening exacerbation and require aggressive

management. The severity of asthma can be determined by

the percentage PEFR and categorized as mild ( > 70%), moder ­

ate ( 40-69% ), or severe ( <40%) and will guide further ther ­

apy. PEFR values at 1 hour from presentation and beyond are

useful to determine need for hospitalization. Either FEV1 or

PEFR can be used in acute exacerbations.

Figure 21-1. FEV1 meter.

� Nebulizer

The components of a nebulizer treatment include the

mouthpiece, medication reservoir, 02 tubing, and "accordion" extension tube. The albuterol is placed within the

reservoir, and the components are fastened together. The

extension tube provides a reservoir of "trapped" 0 2 and

nebulized albuterol that can be inhaled with each breath.

The 02 tubing is hooked up to the green wall 02 port and

turned to 6 L/min because the yellow wall port only delivers air (21% Fi02

). The patient holds the nebulizer during

the treatment (Figure 21-3). If the patient is unable to hold

the treatment, a facemask is used instead.

MEDICAL DECISION MAKING

The diagnosis o f a n asthma exacerbation in the ED is

relatively straightforward. Any patient who has a history

of asthma and presents with wheezing, cough, and dyspnea likely has asthma as the underlying cause. However,

there are several situations in which wheezing may not be

asthma.