ABSTRACT
INTRODUCTION Respiratory failure is a condition in which the respiratory system fails in one or both of its gas-exchanging functions, i.e. oxygenation of mixed venous blood and/or elimination of carbon dioxide from it. Respiratory failure is conventionally defined as the condition in which the arterial PO2 (PaO2) is less than 60 mm Hg, the arterial PCO2 (PaCO2) is higher than 45 mm Hg or both. Therefore, the diagnosis of respiratory failure is a laboratory one but it is important to emphasize that these cut-off values are not rigid; they simply serve as a general guide in combination with the history and clinical assessment of the patient. Respiratory failure may be acute, chronic, or acute on chronic. The clinical presentation of patients with acute and chronic respiratory failure is usually quite different. While acute respiratory failure is characterized by life-threatening derangements in arterial blood gases and acid-base status, the manifestations of chronic respiratory failure are more indolent and may be clinically inapparent. Although the causes of respiratory failure are diverse, common underlying pathophysiologic mechanisms exist.1
