Respiratory failure.

Definitions Acute respiratory failure describes any impairment in oxygenation or ventilation in which the arterial oxygen tension falls below 60 mm Hg (acute hypoxemia), the carbon dioxide tension rises above 50 mm Hg (acute hypercarbia, hypercapnia) and the pH drops below 7.35, or both. For patients who have underlying chronic respiratory failure, acute hypercarbia can be diagnosed by an increase in PCO2 by 20 mm Hg from baseline. From a functional standpoint, respiratory failure is defined as the inability of the respiratory system to meet the metabolic needs of the tissues.