Respiratory failure.

Abstract

1. Dennis C. Stokes, MD* 1. 2. *Associate Professor of Pediatrics, Clinical Director, Pediatric Pulmonary Medicine, Vanderbilt Children’s Hospital, Vanderbilt University School of Medicine, Nashville, TN. Dr. Stokes is an Advisory Board Consultant for the Genentech, Inc-sponsored Epidemiologic Study of Cystic Fibrosis. Respiratory failure represents the failure of compensatory mechanisms that attempt to preserve gas exchange in the face of lung disease, chest wall disease, or respiratory muscle weakness. Respiratory failure is not strictly defined by a specific set of blood gas values, but usually represents the final stage of these compensatory mechanisms that presents as increasing respiratory distress. Respiratory failure may occur primarily because of inability to provide either adequate oxygenation, as in adult respiratory distress syndrome (ARDS) or pneumonia, or because of the inability to ventilate adequately, as in neuromuscular weakness or upper airway obstruction. The adequacy of ventilation is determined by minute ventilation, which is a product of tidal volume and respiratory rate. Reduction in either tidal volume (eg, chest wall disease) or respiratory rate (eg, central nervous system disease) can lead to respiratory failure. In addition, overall ventilation is reduced by the ventilation of poorly perfused lung units (“deadspace” ventilation) seen in diffuse lung disease. In most situations of severe hypoxemia, the predominant mechanism of hypoxemia is mismatching between ventilation and perfusion, resulting in severe intrapulmonary shunting. Infants and young children are particularly prone to respiratory failure because of smaller airways, mechanical instability of the chest wall, and rapid fatigue of respiratory muscles and diaphragm. A child who is in respiratory distress but has good air movement, color, and tone is “compensated” and usually can be watched carefully while supplemental oxygen is begun and attention is turned to assessment and diagnostic studies. The overall goal is to preserve gas exchange and prevent sudden and catastrophic development of cardio-pulmonary arrest while treating the underlying condition. Three cases illustrate the spectrum of respiratory failure. The first is a 6-month-old who has croup and presented with acute respiratory symptoms and dramatic inspiratory stridor. Despite loud stridor, he was feeding well and …