Respiratory Distress

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3 Respiratory Distress

Shirley D. Viteri, Esther Maria Sampayo

Respiratory distress is defined as an alteration in the normal biomechanical and physiologic mechanisms of respiration. Respiratory distress is manifested by complaints of difficulty breathing and a variety of findings on physical examination showing increased respiratory effort. The degree of these findings can vary from mild to severe. Respiratory distress is one of the most common conditions for which children present for acute care. In contrast to adults, children experience significant morbidity and mortality as a result of respiratory conditions because of their different anatomy and physiology as well as decreased pulmonary reserve. Rapid assessment and appropriate management of children with respiratory distress is imperative, given that patients who cannot be adequately managed in the acute setting may progress to acute cardiopulmonary failure and ultimately death.

Etiology and Pathogenesis

The main function of the respiratory system is to supply sufficient oxygen to meet metabolic demands and to remove carbon dioxide. A variety of processes, including ventilation (gas delivery to and from the lungs), perfusion (amount of venous blood brought to the pulmonary bed), and diffusion (the movement of gases across the alveolar membrane), are involved in tissue oxygenation and carbon dioxide removal. Abnormalities in any one of these mechanisms, including hypoventilation, diffusion impairment, intrapulmonary shunt (when alveoli are perfused but not ventilated), and ventilation/perfusion mismatch (a disparity between gas delivery and pulmonary venous blood delivery), can lead to respiratory failure.

Respiratory distress can either be a manifestation of a primary respiratory problem or a secondary effect resulting from the disruption of another organ system. The pathogenesis and resultant signs and symptoms are directly linked to the underlying cause. In general, causes of respiratory distress may be classified as involving (1) the airway; (2) the lungs, chest wall, or both; (3) the central nervous system (CNS) respiratory drive or control; or (4) the neuromuscular system. Alternatively, the respiratory system may be compromised by dysfunction in other organ systems (i.e., cardiovascular, gastrointestinal, endocrine, hematologic) that affect respiratory function or trigger respiratory compensatory mechanisms.

Observed manifestations of distress reflect attempts by the patient to address the underlying inadequacies of their current respiratory status. Several core principles can explain these manifestations depending on the underlying cause:

1. Inadequate minute ventilation: Hypoxemia or hypercarbia can lead to increased minute ventilation by increasing tidal volume, respiratory rate, or both, as is seen in pneumonia with hypoxemia and resultant tachypnea.
2. Disordered regulatory system: Interference with the normal signal pathways of respiration by either depression (e.g., narcotic overdose) or stimulation of the drive to breathe (e.g., metabolic acidosis).
3. Disorders of mechanical structures: Disruption of the normal physical mechanisms of breathing, as in airway obstruction or muscular disorders.

Clinical Presentation

Initial Assessment

The evaluation of a child with acute respiratory distress includes determining the severity as well as the underlying cause. Given that respiratory distress may range in severity from mild to severe, the clinical presentation can be quite varied. In all cases, the first key to the assessment is to ensure the patency of the airway, adequate breathing, and intact circulation (see Chapter 1). After these basic life support principles have been addressed, the physical examination may proceed.

History

A thorough history, including existing medical problems and recent events leading to the current presentation, provides important clues to the underlying cause (Table 3-1). For example, a patient with a foreign body obstruction or anaphylaxis may have an acute presentation of severe respiratory distress compared with a child with an infectious cause in whom the presentation may be more gradual.

Table 3-1 Focused History for a Patient with Respiratory Distress

Component Comments and Examples
Onset, duration, and chronicity
• Abrupt onset: suggests upper airway conditions such as foreign body, allergy, or irritant exposure
• Gradual onset: more consistent with process such as infection or heart failure

Alleviating and provoking factors
• A child with respiratory distress caused by upper airway obstruction may have some degree of relief by assuming the “sniffing position” to maximize airway patency

Treatment attempted
• A child with wheezing secondary to asthma may respond readily to inhaled bronchodilators, but a child with wheezing caused by foreign body aspiration may continue to show symptoms after treatment
Respiratory symptoms
• Cold symptoms: may indicate viral upper respiratory infection
• Cough: “seal-like” or “barky” cough is commonly heard in patients with croup
• Eliciting descriptions of the difficulty breathing may provide clues to the underlying cause (e.g., supraclavicular or suprasternal retractions point to upper airway obstruction)
• Color change: pallor may indicate anemia; cyanosis is indicative of decreased oxygen content in the blood, as seen in some forms of congenital heart disease and in methemoglobinemia
• Respiratory effort: poor effort may be seen in patients with underlying muscular dystrophies
• Change in voice: whereas muffled or hoarse voice points to upper airway pathology, lower airway disease does not typically change the character of the voice
Systemic or associated symptoms
• Fever: presence suggests an infectious cause
• Hydration status, including intake and output (urine, emesis, diarrhea, excessive perspiration, or high respiratory rate)
• Weight loss or failure to gain weight: may indicate systemic process (e.g., inborn error of metabolism) or the severity of respiratory distress is impairing growth (as seen in congestive heart failure)
• Abdominal pain: may suggest abdominal pathology such as obstruction or appendicitis or may represent referred pain from diaphragmatic irritation (as in basilar pneumonia)
Past medical history
• Underlying disorders may predispose patients to certain conditions: for example, a patient with sickle cell disease and respiratory distress may be exhibiting signs of acute chest syndrome; a patient with known gastroesophageal reflux and coarse lung findings on examination could have an aspiration pneumonia
Exposures or environmental factors
• For example, a patient involved in a fire may not only be affected by thermal injury to the airways but also systemic toxins such as carbon monoxide and cyanide
• A patient with allergy and a potential exposure to the allergen could be showing signs of anaphylaxis
Trauma
• History of trauma suggests diagnoses such as pneumothorax, flail chest, cardiac tamponade, or abdominal injury
Immunization status
• Children with incomplete or lack of immunization against Haemophilus influenzae type B are at increased risk for this form of epiglottitis
Last oral intake
• If advanced airway management becomes necessary (e.g., positive-pressure ventilation), the presence of stomach contents may increase the risk of pulmonary aspiration

Physical Examination

Vital Signs

Vital signs, including temperature, heart rate, blood pressure, respiratory rate, and pain score, should be promptly obtained in all patients with respiratory distress. Pulse oximetry, although not classically part of the vital signs, should also be noted to detect hypoxia. Tachypnea (rapid breathing) is one of the most consistent findings among children with respiratory distress and may be caused by fever, hypoxemia, hypercarbia, metabolic acidosis, pain, or anxiety (Table 3-2). However, many children with significant respiratory disease may have normal respiratory rates. Bradypnea may also occur in response to hypoxia in younger infants or from respiratory fatigue, CNS depression, or increased intracranial pressure. Pulsus paradoxus, an exaggeration of the normal decrease in blood pressure during inspiration, of greater than 10 mm Hg correlates well with the degree of airway obstruction but is very difficult to assess in children and therefore not routinely measured.

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