1. Hypoxia. There are four types: hypoxic hypoxia (decreased Pao2), anemic hypoxia, ischemic hypoxia, and histotoxic hypoxia (tissues cannot use oxygen, secondary to effects of toxins). Although carbon dioxide plays the dominant role in ventilation control, hypoxia from any cause increases ventilatory drive through stimulation of peripheral chemoreceptors found in carotid and aortic bodies. Changes in ventilation occur when arterial Pao2 decreases to < 50 mm Hg. Causes of hypoxia include, but are not limited to, pneumonia, acute respiratory distress syndrome (ARDS), hemothorax, pleural effusion, and pneumothorax.
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