What is “absorption atelectasis”?

  • Absorption atelectasis refers to the tendency for airways to collapse if proximally obstructed. Alveolar gases are reabsorbed; this process is accelerated by nitrogen washout techniques.

Oxygen shares alveolar space with other gases, principally Nitrogen. Nitrogen is poorly soluble in plasma, and thus remains in high concentration in alveolar gas. If the proximal airways are obstructed, for example by mucus plugs, the gases in the alveoli gradually empty into the blood along the concentration gradient, and are not replenished: the alveoli collapse, a process known as atelectasis. This is limited by the sluggish diffusion of Nitrogen. If nitrogen is replaced by another gas, that is if it is actively “washed out” of the lung by either breathing high concentrations of oxygen, or combining oxygen with more soluble nitrous oxide in anesthesia, the process of absorption atelectasis is accelerated. It is important to realize that alveoli in dependent regions, with low V/Q ratios, are particularly vulnerable to collapse.


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