Bronchial Surfactant is an enzyme used by humans for use in cryo-chambers. The cryo-inhalant is specifically designed to be accumulated in the throat during sleep, then regurgitated and swallowed upon reawakening. The clear liquid replaces some vital bodily fluids, such as nutrients lost during deep sleep. A person using bronchial surfactant is theoretically able to sleep for extremely long periods of time, thus making it possible that it includes some sort of sedative. However, the exact specifications are not known. People have been observed in cryo-sleep for up to three weeks without using the fluid.

Most people didn't have a problem using the drug, but Jacob Keyes had a profound disgust for it, believing that no matter how the formula is changed, it always tasted like "lime-flavored mucus."[1]


  1. Halo: The Fall of Reach, page 13