Strange and Schafermeyer's Pediatric Emergency Medicine, Fourth Edition (Strange, Pediatric Emergency Medicine) 4th Ed.

CHAPTER

4

Respiratory Distress

Joanna S. Cohen

Kathleen M. Brown

HIGH-YIELD FACTS

• Tachypnea, hyperpnea, nasal flaring, and retractions are the key features of respiratory distress.

• Respiratory distress is the most common precipitating cause of cardiopulmonary arrest in children.

• Effective bag-valve-mask (BVM) ventilation is the single most important skill for managing a patient with respiratory failure.

Respiratory distress is one of the most common complaints in children who present to an emergency department (ED). Respiratory distress is characterized by increased respiratory effort, rate, or work of breathing as manifested by tachypnea, hyperpnea, nasal flaring, and inspiratory retractions.

The primary function of respiration is to oxygenate tissues and to remove carbon dioxide produced from metabolism. Respiratory distress can progress to respiratory failure, which is manifested by inadequate oxygenation or ventilation or both. In children, respiratory failure is the most common precipitating cause of cardiopulmonary arrest. Therefore, early recognition and management of respiratory distress is critical for the physician caring for children.

PATHOPHYSIOLOGY

The respiratory system functions primarily to oxygenate the tissues and eliminate carbon dioxide and secondarily to provide immunologic defense and acid–base balance. Control of gas exchange is maintained through a well-coordinated interaction of the respiratory system, the central and peripheral nervous systems, the diaphragm, the chest wall, and the circulatory system.

The respiratory system can be divided into the upper airway which includes the nose, nasopharynx, oropharynx, larynx, trachea, and bronchi and the lower airway consisting of bronchioles, alveoli, and interstitium. Pathology anywhere along this anatomic pathway can produce respiratory distress. For instance, airway obstruction secondary to croup or a foreign body in the larynx produces respiratory distress originating from the upper airway, whereas pulmonary edema, fibrosis, or pneumonia produces respiratory distress originating from the lower airway.

Central nervous system (CNS) control of respiration lies in the respiratory centers of the medulla oblongata. Central chemoreceptors in the medulla respond to CSF pH changes. Peripheral chemoreceptors, located in the aortic and carotid bodies, send afferent signals via the vagus and the glossopharyngeal nerves regarding changes in oxygen, carbon dioxide, and pH in the arterial blood. Disruption of the CNS control of respiration, such as in hydrocephalus or CNS immaturity in the case of premature infants, can produce respiratory distress. The peripheral nervous system provides innervation to the muscles of respiration and can be disrupted in diseases of the peripheral motor nerve, neuromuscular junction, or the muscle itself.

The diaphragm is the principal muscle of inspiration, whereas the intercostal muscles help to lower the ribs. The accessory muscles, such as the sternocleidomastoid, come into play when respiratory effort is increased. In infants, the chest wall is more compliant than in adults so that during inspiration the lower ribs descend rather than elevate. This provides for less-efficient expansion of the lungs, meaning that the diaphragm needs to do more work in children than in adults.1 This predisposes infants to more rapidly progressive and severe respiratory distress.

Oxygen and carbon dioxide exchange at the alveolo-capillary membrane depends on adequate ventilation and perfusion (V/Q) matching. Any process that compromises the delivery of oxygen to the alveoli or blood to the capillaries will cause a V/Q mismatch and lead to respiratory distress. Increased metabolic demands, such as in exercise or illness, can also produce respiratory distress, as can states that affect the blood’s ability to deliver oxygen to the tissues, such as anemia or abnormal hemoglobin states (methemoglobinemia or carboxyhemoglobinemia). Decreased blood flow to the lungs secondary to poor cardiac output or shock can also cause respiratory distress.

CLINICAL PRESENTATION

Children with respiratory distress may present with an altered respiratory rate; increased work of breathing (including the use of accessory muscles); abnormal breath sounds, such as stridor or wheezing; and altered level of consciousness or changes in the color of the skin and mucous membranes. The respiratory rate should be visually evaluated before the patient is physically examined by the provider because anxiety and agitation commonly cause tachypnea. Quiet tachypnea is usually an attempt to increase minute ventilation to blow off carbon dioxide from nonpulmonary diseases such as diabetic ketoacidosis or shock, whereas tachypnea with grunting, stridor, or wheezing suggests respiratory system disease. A slow or irregular respiratory rate may indicate fatigue, CNS depression, or hypothermia. A child in respiratory distress whose respiratory rate goes from rapid to normal may be improving; however, if the child’s level of consciousness is waning, this “improvement” in respiratory rate may actually indicate fatigue and deterioration in the child’s clinical condition.

Increased respiratory effort, as with nasal flaring, retractions, and use of accessory muscles, increases oxygen demand of the respiratory muscles and produces more carbon dioxide. Stridor is a high-pitched inspiratory noise that suggests an extrathoracic airway obstructing mechanism, such as foreign body or croup, whereas wheezing during exhalation suggests an intrathoracic airway obstruction etiology, such as asthma. Grunting occurs during expiration and is an effort to increase airway pressure and maintain patency of the small airways and alveoli during collapse that can occur with pulmonary edema, pneumonia, or atelectasis. Decreased breath sounds suggest airflow obstruction, parenchymal lung disease, or poor respiratory effort. Seesaw respiration or abdominal breathing with chest wall retractions and abdominal expansion during diaphragmatic contraction during inspiration indicate upper airway obstruction.2

LABORATORY AND RADIOGRAPHIC FINDINGS

Pulse oximetry uses changes in the absorption of two different wavelengths of light to estimate relative oxygen tissue saturation. The accuracy of pulse oximetry can be affected by movement, temperature, probe position, and poor tissue perfusion. End-tidal carbon dioxide monitoring can help assess ventilation. Capnography is a graphic display of exhaled carbon dioxide that can be measured by the placement of a probe in the nostril of a spontaneously breathing patient or in line with an endotracheal tube in the intubated patient. Capnography is used for endotracheal tube confirmation, moderate sedation, trauma, and acid–base disturbances.3 An arterial blood gas can be used to assess blood gas exchange in the lungs, the acid–base balance of the body, and electrolyte levels. A basic metabolic panel to calculate the anion gap in a patient with a metabolic acidosis aids in diagnosis. An elevated anion gap in a patient with a metabolic acidosis could be indicative of diarrheal dehydration, diabetic ketoacidosis, an inborn error of metabolism, sepsis, or toxin ingestion (see Chapter 112), whereas a metabolic acidosis with a normal anion gap is more likely to be from hypernatremic dehydration, renal tubular acidosis, or rapid volume expansion. An evaluation of ammonia level may also be useful diagnostically for a patient with metabolic acidosis when a metabolic or hepatic disease is in the differential diagnosis. A bedside dextrose test should be obtained in patients with altered mental status.

The chest radiograph is the most frequently ordered test in patients with respiratory distress. Usually, a routine chest radiograph consists of two images: a posteroanterior (PA) frontal view and a left lateral view. In the case of respiratory distress, a chest radiograph may show the presence of a radiopaque foreign body, lobar pneumonia, pneumothorax, atelectasis, hyperinflation, or cardiac enlargement, in addition to a number of other indicators that may help with the diagnosis.

Other radiographic studies may be helpful in certain situations. A lateral neck radiograph should be considered in patients with signs of upper airway pathology such as stridor or prolonged inspiration. In children with a suspected pulmonary foreign body who cannot cooperate for inspiratory and expiratory radiographs, lateral decubitis films may demonstrate air trapping consistent with a foreign body. Foreign bodies may also be identified on fluoroscopy or computed tomography (CT). Although the best method to diagnose pulmonary embolism in children has not been established, CT scan, MRA, and V/Q scans have all been used.4 Imaging studies of other organ systems may be useful depending on the clinical evaluation. For instance, an echocardiogram will identify patients with myocarditis, and a creatinine phosphokinase level is useful to screen for suspected muscle diseases.

DIFFERENTIAL DIAGNOSIS

A differential diagnosis for respiratory distress can be organized by age and the anatomic location of the source of the distress. It is useful to think of the respiratory system as consisting of an upper airway and a lower airway. In addition to originating directly from the respiratory system, respiratory distress can be caused by problems in the muscles that perform the work of breathing or the central or peripheral nervous system which controls respiration. Metabolic, cardiac, gastrointestinal, and hematologic causes must also be considered (Tables 4-1 and 4-2). Figure 4-1 is an algorithmic description of the differential diagnosis of the obstructed airway in children.

TABLE 4-1

Major Causes of Respiratory Distress in Newborns

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TABLE 4-2

Major Causes of Respiratory Distress in Infants and Children

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FIGURE 4-1. Differential diagnosis of the obstructed airway in children.

MANAGEMENT

The goals of treating respiratory distress are to provide adequate ventilation and oxygenation. Each child in respiratory distress must first be evaluated for impending respiratory failure. Airway, breathing, and circulation should be assessed rapidly and conditions requiring immediate lifesaving interventions, such as upper airway obstruction, tension pneumothorax, cardiac tamponade, and respiratory failure, must be identified and treated. Airway patency must be established. A patient with complete upper airway obstruction will have no air movement and may present with gagging or choking. With partial airway obstruction, the patient may present with stridor. An alert child will assume a position of comfort and agitation should be minimized, since it increases minute ventilation and often worsens upper airway obstruction. A child who is obtunded may have soft tissue obstruction of the airway, which can be relieved by positioning the airway with a chin-lift or jaw thrust. The mouth and nose should be suctioned and any foreign body that is visualized should be removed. An oropharyngeal airway or nasopharyngeal airway may be indicated to maintain patency of the airway. In extreme cases, a surgical airway may be needed.

In the pediatric trauma patient with respiratory distress, the differential diagnosis of upper airway obstruction should include blunt or penetrating injury to the trachea. Endotracheal intubation or cricothyrotomy may be required and the most skilled provider available should manage the airway. Trauma patients might also have respiratory distress secondary to a tension pneumothorax, which requires immediate decompression via needle thoracentesis.

Once an airway is established, attention should be turned to breathing. For patients with severe respiratory distress or impending failure, high-concentration humidified oxygen should be delivered to maintain cerebral and myocardial oxygenation. Effective bag-valve-mask (BVM) ventilation is still the single most important intervention in managing a patient with respiratory failure. Children with out-of-hospital respiratory arrest who received BVM and endotracheal tube placement did not have better outcomes than those who received BVM alone.5 However, in the ED, endotracheal intubation is indicated for impending respiratory failure, inability to maintain the airway or ongoing cardiopulmonary arrest.

Medications to address specific causes of respiratory distress should be given if the cause can be identified or if there is a suspicion based on the history. Croup can be treated with nebulized epinephrine and dexamethasone. Anaphylaxis is treated with intramuscular epinephrine, an antihistamine, H2-blockers, methylprednisolone, and an isotonic crystalloid fluid bolus. Albuterol and steroids should be given for asthma. Management of specific diseases is described in detail in subsequent corresponding chapters.

DISPOSITION/OUTCOME

Many children presenting to the ED with respiratory distress can be treated and discharged. Examples include successfully treated asthma exacerbations, foreign-body removal, and patients with intoxication that has resolved.

Indications for admission to the hospital include, but are not limited to, a persistent increased work of breathing, hypoxia requiring oxygen administration, persistent hypercarbia, concern for recurrence (e.g., anaphylaxis), and patients who require further investigation. Children requiring endotracheal intubation or those having severe respiratory distress with impending respiratory failure should be admitted to an intensive care unit.

Respiratory distress can lead to respiratory failure. Fortunately, pediatric cardiopulmonary arrest is a rare event. However, outcome studies describing inpatient pediatric cardiopulmonary resuscitation show 24-hour survival rates around 35%.6,7 In children, respiratory distress is the most common cause of cardiopulmonary arrest and is associated with better 24-hour survival when compared to shock, the second most common cause of cardiopulmonary arrest.7 For this reason, a thorough understanding and ability to manage respiratory distress in children is critical to the emergency medicine provider.

REFERENCES

1. Heulitt MJ, Ouellet P. Pediatric critical care medicine. In: Slonim AD, Pollack MM, eds. Respiratory System Physiology. Philadelphia, PA: Lippincott Williams & Wilkins; 2006:264.

2. Ralston M, Hazinski MF, Zaritsky AL, et al., eds. Pediatric Advanced Life Support Provider Manual (Chapter 2). Dallas, TX: American Heart Association, Subcommittee on Pediatric Resuscitation; 2006.

3. Langhan ML, Chen L. Current utilization of continuous end-tidal carbon dioxide monitoring in pediatric emergency departments. Pediatr Emerg Care. 2008;24(4):211–213.

4. Chn AK, Deveber G, Monagle P, et al. Venous thrombosis in children. J Thromb Haemost. 2003;1(7):1143–1155.

5. Gausche M, Lewis RJ, Stratton SJ, et al. Effect of out-of-hospital pediatric endotracheal intubation on survival and neurological outcome: a controlled clinical trial. JAMA. 2000;283(6):783–790.

6. Torres A Jr, Pickert CB, Firestone J, et al. Long-term functional outcome of inpatient pediatric cardiopulmonary resuscitation. Pediatr Emerg Care. 1997;13:369–373.

7. Reis AG, Nadkarni V, Perondi MB, et al. A prospective investigation into the epidemiology of in-hospital pediatric cardopulmonary resuscitation using the international Utstein reporting style. Pediatrics. 2002;109:200–209.