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INTRODUCTION

Critical care medicine is the discipline of caring for patients with acute life-threatening conditions or conditions likely to cause serious harm if not rapidly addressed. This work requires a detailed understanding of human physiology, the pathophysiology of severe illness and injury, the intricate interactions between organ systems and therapies, as well as an understanding of and experience with the rapidly changing technologies available in a modern pediatric intensive care unit (PICU). The science of caring for the critically ill patient continues to advance rapidly as the molecular mediators of illness have become better defined and new therapies are brought into clinical use. Critical care, then, is a highly complex, multidisciplinary field in which optimal patient outcomes require a team-oriented approach, including critical care physicians and nurses; respiratory therapists; pharmacists; consulting specialists; physical, occupational and recreational therapists; and social services specialists.

RESPIRATORY CRITICAL CARE

ACUTE RESPIRATORY FAILURE

ESSENTIALS OF DIAGNOSIS & TYPICAL FEATURES

  • Inability to deliver oxygen or remove carbon dioxide.

  • PaO2 is low while PaCO2 is normal in hypoxemic respiratory failure (ventilation/perfusion [V/Q] mismatch, diffusion defects, and intrapulmonary shunt).

  • PaO2 is low and PaCO2 is high in hypercapnic respiratory failure (alveolar hypoventilation seen in central nervous system [CNS] dysfunction, oversedation, neuromuscular disorders).

  • Noninvasive mechanical ventilation can be an effective treatment for hypercapnic respiratory failure and selected patients with hypoxemic respiratory failure.

  • Conventional mechanical ventilation should be accomplished within a strategy of “lung-protective” ventilation.

  • Extracorporeal membrane oxygenation (ECMO) is a viable option for patients failing conventional mechanical ventilation.

Pathogenesis

Acute respiratory failure, defined as the inability of the respiratory system to adequately deliver oxygen or remove carbon dioxide, is a major cause of morbidity and mortality in infants and children. Anatomic and developmental differences place infants and young children at higher risk than older children or adults for respiratory failure. An infant’s thoracic cage is more compliant, allowing a greater tendency toward alveolar collapse. The intercostal muscles are poorly developed and unable to achieve the “bucket-handle” motion characteristic of adult breathing, and the diaphragm is shorter and relatively flat with fewer type I muscle fibers, making it less effective and more easily fatigued. The infant’s airways are also smaller in caliber resulting in greater resistance to airflow and greater susceptibility to occlusion by mucus plugging and mucosal edema, particularly in the setting of respiratory infections. Alveoli in children are smaller and have less collateral ventilation than adults, again resulting in a greater tendency to collapse and develop atelectasis. Finally, young infants may have a more reactive pulmonary vascular bed, impaired immune system, or residual effects from prematurity, all of which increase the risk of respiratory failure.

Respiratory failure can be due to inadequate oxygenation (hypoxemic respiratory failure) or inadequate ventilation (hypercapnic respiratory failure) or both. Hypoxemic respiratory failure occurs in three situations: (1) Ventilation-perfusion ...

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