ZONE	READING	DESCRIPTION
Green	71%–100% of the usual or normal peak flow readings	Readings in the green zone indicate that the asthma is under good control.
Yellow	50%–70% of the usual or normal peak flow readings	Indicates caution. Respiratory airways are narrowing and additional medication may be required.
Red	<50% of the usual or normal peak flow readings	Indicates a medical emergency. Severe airway narrowing may be occurring and immediate action needs to be taken.

Data from American Lung Association. (n.d.). Measuring your peak flow rate. Retrieved from http://www.lungusa.org/lung-disease/asthma/living-with-asthma/take-control-of-your-asthma/measuring-your-peak-flow-rate.html

Arterial Blood Gases

Arterial blood gas (ABG) values are useful in assessing respiratory status and acid-base balance; they are a measurement of systemic gas exchange. By comparing the pH, PaCO₂, and HCO₃, the body’s ability to compensate an acid-base imbalance can be assessed; PO₂ values indicate the presence or absence of hypoxemia. Table 18-2 lists normal and abnormal ABG values.

TABLE 18-2 NORMAL AND ABNORMAL VALUES FOR ARTERIAL BLOOD GASES

Interpreting ABG values involves three steps:

• Step 1: Assess the pH to determine the presence of acidosis or alkalosis.

• Step 2: Assess PaCO₂ to determine if the cause of the acid-base imbalance is respiratory or metabolic. If the pH and PaCO₂ are moving in opposite directions (the pH is elevated and the PaCO₂ is decreased, or the pH is decreased and the PaCO₂ is elevated), the imbalance is respiratory in nature.

• Step 3: Assess HCO₃ to determine if the cause of the acid-base imbalance is metabolic. If the pH and the HCO₃ are moving in the same direction (the pH is elevated and the HCO₃ is elevated, or the pH is decreased and the HCO₃ is decreased), the imbalance is metabolic in nature.

When an acid–base imbalance exists, the body will attempt to compensate and normalize the pH. The result of these efforts can be uncompensated, partially compensated, or fully compensated. Table 18-3 defines various acid-base abnormalities based on ABG values.

TABLE 18-3 ACID-BASE ABNORMALITIES DETERMINED BY ARTERIAL BLOOD GAS VALUES

Asthma Exacerbations

Asthma affects millions of adults and children and is considered to be the most prevalent chronic childhood disease. Annually, asthma is responsible for almost 2 million ED visits, 500,000 hospital admissions, 400 deaths, and 100 million days of restricted activity.⁴ Asthma is a chronic disease characterized by airway hyperreactivity, inflammation, and reversible airflow obstruction (bronchospasm). Exacerbations of this common disease can become life-threatening.

Asthma severity is classified as:⁴

• Intermittent

• Symptoms twice a week or less and nighttime symptoms twice a month or less

• Symptoms do not interfere with normal activity

• Use of a short-acting beta-agonist (SABA) inhaler 2 days or less a week

• Mild persistent

• Symptoms more than twice a week but less than once a day with nighttime symptoms three to four times a month

• Minor limitations to normal activities because of symptoms

• Use of SABA inhaler more than 2 days a week but not daily

• Moderate persistent

• Daily symptoms and nighttime symptoms more than once a week but not daily

• Some limitations to normal activity because of symptoms

• Daily use of SABA inhaler

• Severe persistent

• Continual daytime symptoms with frequent nighttime symptoms, often daily

• Extreme limitations to normal activities because of symptoms

• Poor to no control of symptoms

Asthma Triggers

A wide variety of stimulants can precipitate an asthma exacerbation. Specific individuals tend to have particular triggers. Common triggers include:

• Allergies to food or inhalants (e.g., pollen, latex, mold, animal dander)

• Exercise

• Cold exposure (breathing cold air, eating ice cream)

• Tobacco smoke

• Strong smells

• Upper respiratory infections

• Air pollutants

• Sinusitis, rhinitis

• Medications, especially aspirin and nonsteroidal anti-inflammatory drugs

• Food additives

Signs and Symptoms

• Wheezing—most commonly expiratory, but may also be inspiratory or absent

• Cough—may be present without wheezing, especially in children

• Use of accessory muscles of respiration, especially sternocleidomastoid muscles in adults

• Chest tightness and hyperresonance on percussion (resulting from hyperinflation)

• Anxiety or restlessness

• Halting speech (inability to speak in full sentences)

Diagnostic Procedures

• Routine laboratory tests and chest radiograph not usually necessary; do not delay initiation of treatment to obtain these ⁵

• Arterial blood gases to determine degree of hypoxemia

• Peak expiratory flow rate less than 50% of predicted value

• As a measure of airflow limitation, PEFR is a more reliable indicator of severity of exacerbation than degree of symptoms ⁶

• Pulse oximetry—value less than 92% indicates probable need for hospitalization ⁵

Therapeutic Interventions

• Allow the patient to maintain a position of comfort.

• Assess duration and severity of symptoms; document medications already taken in an attempt to manage the exacerbation.

• Obtain intravenous access for medication administration and hydration; dehydration can contribute to mucus plugging and catecholamine release.⁷

• Provide continuous cardiac and pulse oximetry monitoring.

• Administer supplemental oxygen to keep pulse oximetry greater than 90%.

• Administer inhaled SABA such as albuterol (Proventil) via nebulizer or metered dose inhaler (MDI), preferably with a spacer.

• Anticholinergics such as ipratropium bromide (Atrovent) are frequently combined with SABA.

• Measure PEFR before and after interventions. Serially measure PEFR as long as the patient is able to cooperate. A patient’s inability to perform PEFR testing is an indicator of severe disease.

• Corticosteroids may be given to treat the inflammatory component of asthma.

• Magnesium sulfate may be considered if other interventions are ineffective; magnesium relaxes bronchial smooth muscles by an uncertain mechanism.⁵

• Heliox, a mixture of helium and oxygen, may improve gas exchange because of the low density of helium.

• Endotracheal intubation and intensive care unit admission is often necessary with imminent respiratory failure or arrest.

Status asthmaticus is a severe asthma exacerbation that does not respond to therapy. Ominous signs indicating a need for endotracheal intubation include:

• “Silent chest,” indicating minimal airflow

• Fatigue and decreasing level of consciousness

• Hypoxemia, hypercapnia, or metabolic acidosis

Acute Bronchitis

Acute bronchitis is a self-limiting respiratory infection characterized by cough with or without sputum production.⁸ It is most often the result of a virus such as influenza A or B or the respiratory syncytial virus (RSV); less than 10% of cases are bacterial in nature.⁸ The diagnosis of acute bronchitis is made after ruling out other causes of cough such as:

Signs and Symptoms

• Cough is always the predominant symptom and may last up to 3 weeks

• Sputum may or may not be present

• Wheezing

• Pleuritic chest pain

• Cold-like symptoms

Diagnostic Procedures

• Diagnosis is based on clinical presentation and history

• No acute findings on chest radiograph

Therapeutic Interventions

• Symptomatic treatment, including rest and oral hydration.

• Dextromethorphan (Benylin, Delsym) or codeine may be given for short-term relief from coughing.

• Bronchodilators may be useful if wheezing is present.

• Research does not support the use of expectorants or mucolytics.⁸

• Antibiotics are not effective or appropriate for treating acute bronchitis. Patient education related to overuse of antibiotics and the development of antibiotic-resistant organisms is an important aspect of care for these patients.

Acute Exacerbation of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease is defined as a preventable and treatable disease, characterized by progressive airflow limitation. It is associated with an abnormal inflammatory response of the lungs that is not fully reversible.¹⁰ Traditionally, COPD is described as consisting of chronic bronchitis (defined as cough and sputum production for at least 3 months during 2 consecutive years) or emphysema (which involves destruction of the alveoli); most patients have some degree of both components. Asthma is characterized by reversible airflow limitations and is not included in the definition of COPD.

Chronic obstructive pulmonary disease is a progressive and irreversible disease; there is no cure and the goal is to manage the symptoms and limit disease progression. Patients often present to the ED with acute exacerbations or when their current level of therapy is no longer adequate.