Respiratory acidosis
LIFE-THREATENING DISORDERAn acid-base disturbance characterized by reduced alveolar ventilation and manifested by hypercapnia (partial pressure of arterial carbon dioxide [PaCO2] greater than 45 mm Hg), respiratory acidosis can be acute (from a sudden failure in ventilation) or chronic (as in long-term pulmonary disease). The prognosis depends on the severity of the underlying disturbance and on the patient’s general condition.
Causes
Respiratory acidosis can result from airway obstruction or parenchymal lung disease, which interferes with alveolar ventilation, or from chronic obstructive pulmonary disease (COPD), asthma, severe adult respiratory distress syndrome, chronic bronchitis, large pneumothorax, extensive pneumonia, or pulmonary edema.
Hypoventilation compromises excretion of carbon dioxide produced through metabolism. The retained carbon dioxide then combines with water to form an excess of carbonic acid, decreasing the blood pH. As a result, the concentration of hydrogen ions in body fluids, which directly reflects acidity, increases.
In addition, several factors predispose the patient to respiratory acidosis:
Drugs: Narcotics, anesthetics, hypnotics, and sedatives decrease the sensitivity of the respiratory center.
Central nervous system (CNS) trauma: Medullary injury may impair ventilatory drive.
Chronic metabolic alkalosis: Respiratory compensatory mechanisms attempt to normalize pH by decreasing alveolar ventilation.
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