Chapter 35: Respiratory Distress

BACKGROUND

Respiratory distress is one of the most common reasons for a child to present to the emergency department or a practitioner’s office. Respiratory distress can result from disorders in the respiratory system or in organ systems that control or influence respiration. Young children have an increased risk for respiratory distress because of their anatomy and physiology. Nearly 20% of all emergency department visits for children younger than 2 years are for respiratory disease.¹ The causes of respiratory distress are vast, and practitioners caring for children should have a systematic approach to its diagnosis and management. Cardiopulmonary arrest in children is largely due to respiratory failure (in adults, cardiac causes are most common). Rapid evaluation and management of severe pediatric respiratory disease may be necessary to prevent respiratory failure.

PATHOPHYSIOLOGY

Understanding respiratory physiology can aid the practitioner in diagnosing the cause of respiratory symptoms. The main goals of respiration are oxygen uptake and elimination of carbon dioxide. Secondary goals include acid–base buffering, hormonal regulation, and host defense. To achieve the goals of respiration, three main functional components of the respiratory system are used: (1) mechanical structures (including chest wall, respiratory muscles, and pulmonary circulation), (2) membrane gas exchanger (interface between airspace and pulmonary circulation), and (3) regulatory system (network of chemical and mechanical sensors throughout the circulatory and respiratory systems). All three components are tightly integrated, and dysfunction of one can lead to respiratory distress or failure.

Respiratory function is tightly controlled by a complex network of central and peripheral chemoreceptors and mechanoreceptors responding to information from the body about the status of the respiratory system. This network modulates the neural output to the respiratory muscles, affecting the timing and force of respiratory effort. Central chemoreceptors in the ventral reticular nuclei of the medulla are sensitive to changes in pH and partial pressure of carbon dioxide (PCO₂) of cerebrospinal fluid. The intrinsic brain-stem function of the dorsal and ventral respiratory centers of the medulla controls inspiration and expiration, respectively. The apneustic center in the pons increases the depth and duration of inspiration, whereas the pneumotaxic center decreases depth and duration. The cerebellum, hypothalamus, motor cerebral cortex, and limbic system also play a role in mediating respiration. Carotid and aortic bodies are peripheral chemoreceptors sensitive to the partial pressure of oxygen (PO₂), PCO₂, and pH in arterial blood. Mechanoreceptors (stretch, juxtacapillary, and irritant reflex) distributed along the airways, lung parenchyma, and chest wall respond to lung volume, changes in pulmonary microvasculature, chest wall muscle activity, and environmental irritants.

Information from central and peripheral receptors is integrated in the brainstem, and efferent impulses are transmitted to alter respiratory function and maintain homeostasis. Even slight alterations in arterial pH, PO₂, or PCO₂ stimulate the respiratory centers to modify the respiratory pattern. Increased arterial PCO₂ and decreased arterial PO₂ lead ...