ReBreathing

Rebreathing refers to the act of inhaling air or gas that has been exhaled previously. In medical and technical contexts it often involves removing carbon dioxide from the exhaled air and sometimes adding oxygen or anesthetic gases to create a closed or semi-closed breathing loop. Rebreathing can occur naturally to a limited extent in normal breathing through anatomical dead space, or deliberately in closed-circuit systems.

In physiology, small amounts of rebreathing occur due to mixing of fresh inspired air with alveolar air in the respiratory tract and dead space. Complete alveolar gas exchange requires adequate ventilation, and excessive rebreathing of CO2 is avoided by the body's normal respiratory drive and regulatory reflexes.

In anesthesia and medical ventilation, rebreathing circuits reuse exhaled gas after CO2 is absorbed by a carbon dioxide absorber and fresh gas is added. This reduces gas waste and can help retain volatile anesthetics. Monitoring of inspired gas composition and end-tidal CO2 is essential to ensure patient safety.

In diving, rebreathers recirculate exhaled gas, removing CO2 and adjusting oxygen content. They include semi-closed and closed-circuit designs. Benefits include extended underwater duration and reduced gas waste; risks involve hypoxia, hypercapnia, oxygen toxicity, scrubber failure, and other faults. Rebreathers require specialized training, precise monitoring, and appropriate bailout options.

Other contexts include spaceflight or other closed-environment scenarios where controlled rebreathing is used to manage resource efficiency. Rebreathing is distinct from open-circuit systems, which vent exhaled gas to the environment.