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   Hypercarbic Respiratory Failure

Paco2 is inversely proportional to alveolar ventilation; thus, Paco2 increases when the elimination of carbon dioxide is decreased because of a decrease in minute ventilation. Paco2 also increases if minute ventilation remains constant but carbon dioxide production increases. Primary pulmonary diseases are the most common cause of hypercarbia, although nonpulmonary causes contribute to hypoventilation, increased Paco2, and the need for mechanical ventilatory support.

Minute ventilation can be decreased owing to pulmonary or nonpulmonary factors. Pulmonary causes of impaired minute ventilation include large airway obstruction (e.g., due to the presence of a foreign body or laryngeal spasm), small airway obstruction (e.g., bronchospasm), and destruction of lung parenchyma (e.g., emphysema). Extrapulmonary causes of hypercarbia include neurologic and muscular problems. Neurologic problems include depression of central respiratory drive due to the …