A stethoscope is an invaluable tool in the identification and management of respiratory problems. When listening for breath sounds in a critically ill patient with possible respiratory problems, the clinician should auscultate on either side of the sternum, under the axillae, and on the back.

Upper Airway Obstruction

The upper airway consists of the airways outside the thorax. 

Causes of upper airway obstruction include:

• Foreign-body aspiration
• Allergic reaction
• Infection or abscess formation
• Secretions
• Congenital abnormalities
• The child’s tongue in the presence of a decreased level of consciousness
• Prominent infant occiput with neck flexion when supine
• Poor CNS control

Pediatric patients with upper airway obstruction secondary to foreign-body obstruction, croup, or epiglottitis show abnormal signs during inspiration. Stridor, hoarseness, and a change in voice or cry are significant observations during inspiration that suggest upper airway obstruction. 

Retractions, accessory muscle use, and nasal flaring during the inspiratory phase, are physical signs of upper airway obstruction. Drooling, snoring, or gurgling sounds, poor chest rise, and reduced air entry on auscultation are additional indicators of upper airway obstruction.

Pediatric Patient With Upper Airway Obstruction

Lower Airway Obstruction

The lower airway involves the airways within the thorax, e.g., lower trachea, bronchi, and bronchioles. Lower airway obstruction is often caused by asthma or bronchiolitis in the critically ill pediatric patient. When the lower airway is involved, the clinical signs usually occur in the expiratory phase of respiration. 

Wheezing and a prolonged expiratory period causing increased expiratory effort are frequently present. The child may present with prominent inspiratory retractions because the lower airway obstruction has impaired both inspiration and expiration. The child with a lower airway obstruction will also show signs of decreased air movement on auscultation. 

Status asthmaticus causes significant acute lower airway obstruction. Bronchiolar constriction restricts the movement of air out of the alveoli and causes the patient to work to exhale air. Airway compression leads to air trapping and further expiratory obstruction. The result is lung hyperinflation.

Lung Tissue Disease

Lung tissue disease is caused by:

• Pneumonia
• Cardiogenic or noncardiogenic pulmonary edema
• Trauma
• Allergic reaction
• Toxins
• Vasculitis 
• Infiltrative diseases

Diseases involving the lung tissue usually cause the alveoli to collapse. They may cause pulmonary edema or the accumulation of inflammatory debris in the alveoli. Alveolar collapse results in inadequate gas exchange, which will cause hypoxemia, marked tachypnea, and increased respiratory effort as the patient tries to maintain an elevated end-expiratory pressure to counteract the alveolar collapse.

Conditions involving lung parenchyma cause the lungs to become stiff. Fluid accumulation in the alveoli and interstitium reduces lung compliance and increases respiratory effort. 

In early lung tissue disease, the clinician should expect to see hypoxemia because of alveolar collapse. This can eventually compromise ventilation, causing hypercarbia to appear late in the condition.

Disordered Control of Breathing

Hypoventilation is caused by disordered control of breathing and can lead to hypoxemia and hypercarbia because of the erratic respiratory rate and effort. Periods of increased or decreased respiratory rate and effort ensue. Parents will often describe the child as “breathing funny.” 

Shallow breathing and inadequate effort may be observed in patients with disordered control of breathing. These patients may also have central apnea.

Neurologic conditions such as seizures, head injuries, brain tumors, CNS infections, hydrocephalus, neuromuscular diseases, metabolic abnormalities, and drug overdose can cause disordered control of breathing. The seriously ill child with disordered control of breathing often has an altered mental status.