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RESPIRATORY PHYSIOLOGY IN THE DEVELOPING CHILD

Spontaneous ventilation requires adequate function of the central control of breathing, ventilator muscle function, and lung mechanics.

Respiratory failure occurs when the central respiratory drive and/or power are inadequate to overcome the respiratory load. When the cause of this imbalance is irreversible, the condition becomes chronic respiratory failure.

Developmental factors that affect breathing in the infant and young child may include soft thoracic cage, poorly developed intercostal muscles, lack of bucket-handle motion in the rib cage because of the horizontal alignment of the ribs, short diaphragm, fewer type I muscle fibers, smaller airways and increased resistance, and fewer air-exchange units. Less collateral ventilation and decreased stability of the air-exchange units increase likelihood of collapse.

INTRODUCTION

Improvements in the treatment of acute respiratory failure, the development of subspecialties such as pediatric critical care and neonatology, and advancements in invasive (e.g., tracheostomy and positive pressure ventilation) and noninvasive (mask continuous positive airway pressure [CPAP] or bilevel positive airway pressure [BiPAP]) ventilation have led to an increase in the survival of pediatric patients with chronic respiratory failure.

Infants, children, and adolescents with disorders of central control of breathing, disease of the airways, residual lung disease after severe respiratory illness, persistent pulmonary hypertension, and neuromuscular disorders may experience hypercarbic and/or hypoxemic chronic respiratory failure. Although it is generally possible to identify a primary cause for the respiratory failure, many children have multiple causative factors.

Chronic respiratory failure is pulmonary insufficiency for a protracted period, usually 28 days or longer. The goals of long-term mechanical ventilation are to sustain and extend life, to enhance the quality of life, to reduce morbidity, to improve physical and psychological function, and to enhance growth and development. Patients with reversible neuropathies (e.g., Guillain-Barre syndrome, neuropathy of critical illness), bronchopulmonary dysplasia, pulmonary hypertension, airway abnormalities, and congenital heart disease before or after surgical intervention are on long-term ventilation as a bridge for full recovery. Patients are maintained on long-term ventilation until they recover from the initial insult. Patients with conditions such as central hypoventilation, progressive neuromuscular disease, and high quadriplegia may require ventilatory support indefinitely.

The preferred site for a patient's care after initial discharge with a ventilator is within the family home. When social circumstances do not allow this placement, patients may be placed in a highly skilled nursing facility.

Less than 1% of patients admitted to pediatric intensive care units require long-term noninvasive or invasive ventilatory assistance. The polio epidemic in the 1930s through 1950s led to widespread need of respiratory support for children. At that time a negative pressure ventilation device such as the iron lung was used.

The causes for long-term dependency on chronic ventilation or supplemental oxygen may be categorized as follows:

  • Respiratory pump: respiratory muscles, rib cage, ventral abdominal wall (neuromuscular disease, chest ...

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