(B) Emphysema # RESPIRATORY FAILURE may be classified as hypoxic or hypercapnic and may be either acute or chronic.# Hypoxemic respiratory failure (Type I) is characterized by a Pa02of less than 60 mmHg with a normal or low PaCO2.> Most common form of respiratory failure, and it can be associated with virtually all acute diseases of the lung, which generally involve fluid filling or collapse of alveolar units.> Some examples of Type I respiratory failure are cardiogenic or noncardiogenic pulmonary edema, pneumonia, and pulmonary hemorrhage..> Common causes of Type I (hypoxemic) respiratory failure Pneumonia Pulmonary edema Pulmonary fibrosis Asthma Pneumothorax Pulmonary embolism Pulmonary arterial hypertension Pneumoconiosis Granulomatous lung diseases Cyanotic congenital heart disease Bronchiectasis Adult respiratory distress syndrome Fat embolism syndrome Kyphoscoliosis Obesity# Hypercapnic respiratory failure (Type II) is characterized by a PaCO2 of more than 50 mm Hg.> Hypoxemia is common in patients with hypercapnic respiratory failure who are breathing room air.> The pH depends on the level of bicarbonate, which, in turn, is dependent on the duration of hypercapnia.> Common etiologies include drug overdose, neuromuscular disease, chest wall abnormalities, and severe airway disorders < e.g., asthma, chronic obstructive pulmonary disease)# Common causes of Type II (hypercapnic) respiratory failure Chronic bronchitis and emphysema (COPD) Severe asthma Drug overdose Poisonings Myasthenia gravis Polyneuropathy Poliomyelitis Primary muscle disorders Porphyria Cervical cordotomy Head and cervical cord injury Primary alveolar hypoventilation Obesity hypoventilation syndrome Pulmonary edema Adult respiratory distress syndrome Myxedema Tetanus Guillain-Barre syndrome