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The remainder of the physical exam should focus on

localizing the underlying source of distress, especially if

there is no evidence of airway disease. Poor respiratory

effort or apnea with depressed airway reflexes suggests

central nervous system disease. Congestive heart failure

can present with diminished heart sounds, a murmur or

gallop, venous distension, or hepatosplenomegaly. Pallor

or cyanosis suggests anemia. Consider sepsis or metabolic

acidosis with isolated tachypnea. Look for any signs of

ingestion or inhalation injury, such as burns or soot in the

oropharynx or nares.

DIAGNOSTIC STUDIES

...... Laboratory

The majority of causes of respiratory distress can be determined with a careful history and physical exam, and clinical appearance always supersedes lab studies. Arterial

blood gas (ABG) analysis may be useful for moderate/

severe respiratory distress, diabetic ketoacidosis, or other

metabolic disorders. It is important to note that a "normal"

ABG in severe respiratory distress is actually quite worrisome, because this may indicate that the patient is starting

to tire out and retain more C02

, thus normalizing the C02

and pH but heading toward impending respiratory failure.

Respiratory failure can be defined as PaO 2 <60 mmHg

despite supplemental 02 of 60% or PaC02 >60 mmHg.

The complete blood count identifies anemia and provides

supportive evidence of an infectious process when leukocytosis or a left shift is present. Electrolytes may be useful if

the suspected cause of distress is metabolic in origin. RSV

and influenza testing are rarely helpful in the ED setting .

..... Imaging

Chest x-ray may reveal an infiltrate, pleural e ffusion, hyperinflation, atelectasis, pneumothorax, pneumomediastinum,

foreign body, or cardiomegaly. The location (esophagus vs.

trachea) of an aspirated coin in a child can be determined

by the orientation of the coin on the radiograph. When the

coin is in the esophagus, it lies in the frontal (coronal) plane

and is round on posteroanterior view (Figure 49-1). The

opposite is true when the coin is in the trachea. It appears

round on the lateral radiograph. This is because the incom ­

plete cartilaginous rings of the trachea open posteriorly.

The majority of aspirated foreign bodies are radiolucent

(eg, peanut), but radiographs may still provide clues to its

presence. Complete bronchial obstruction produces

resorption atelectasis distally. Pulmonary infiltrates may be

seen because of an inflammatory reaction to the foreign

body. Partial obstruction in a bronchus is identified on an

expiratory film when there is air trapping and limited

Figure 49-1. A, B. Coin in the esophagus of a

1 0-month-old infant who presented with wheezing.

Note the airway compression on the lateral view (arrow).

expiration on the affected side. In young children it is very

difficult to get the patient to cooperate for expiratory films,

so if there is a suspicion of air trapping, bilateral lateral

decubitus films can be very useful instead (Figure 49-2).