What condition defines respiratory failure?

Respiratory failure is defined primarily by the inability to move air properly, which can lead to inadequate gas exchange in the lungs. This condition can manifest as either hypoxemia (low oxygen levels) or hypercapnia (elevated carbon dioxide levels) due to various causes such as obstructive diseases, central nervous system problems, or respiratory muscle weaknesses.

When a patient cannot move air effectively, either because of obstruction, insufficient lung mechanics, or other pulmonary issues, the body struggles to maintain adequate oxygenation and clearance of carbon dioxide, leading to respiratory failure. This medical emergency requires prompt evaluation and intervention to restore normal respiratory function.

Other options do not accurately define respiratory failure. Being unable to speak could be related to many factors, not necessarily respiratory failure. A cough is a reflex that can occur in various conditions, and stable oxygen levels indicate effective gas exchange, which contradicts the concept of respiratory failure. Thus, the key characteristic of impaired air movement is what defines respiratory failure.