Xenon System Protects the Brain in Critically ill Newborns

A newly developed closed circuit xenon (Xe) breathing system may make xenon safe and cost-efficient for use in protecting the brains of critically ill infants, according to a new study.

Developed by researchers at the University of Wales (Swansea, United Kingdom) and the University of Bristol (United Kingdom), the closed circuit Xe delivery system is fitted to a conventional newborn ventilator, and essentially recaptures the exhaled xenon so that the infant can rebreathe it. The system also replenishes precise amounts of oxygen and other gases as needed. Functionally, the neonatal ventilator provided breaths of oxygen to a lower chamber, compressing a hanging bag within it; this bag communicated with the upper closed part of the breathing system that contains soda lime, unidirectional valves, Xe-oxygen analyzers, and a tracheal tube connection. At each end-inspiration, this bag emptied fully and a bolus of oxygen (the driving gas) crosses over from the lower to upper chamber via an additional valve. This mechanically substitutes the gas uptake from the circle during the previous breath cycle (i.e., oxygen + small volume of Xe) with an equivalent volume of oxygen, creating a slow-rising inspired oxygen concentration. This is offset by manual injection of Xe boluses, infrequently at steady state, due to the low-Xe uptake of the patient.

The system takes advantage of the fact that uptake of xenon by the lung is very low: when a given amount of xenon is inhaled, most of it is then exhaled out again. The Xe delivery method was tested successfully in newborn pigs for up to 16 hours, and the researchers found that they could precisely control the depth of anesthesia, while delivering exactly the right amount of oxygen. The piglets had stable vital signs and recovered without any complications. Using the closed circuit system, the researchers estimate that xenon could be used for surgery in critically ill newborns for as little as U.S. $2 per hour, and the system itself could be developed as a single use device, with or without cooling of body temperature (hypothermia), previously the only technique known to protect the brain in infants with low-oxygen injury. The study was published in the August 2009 issue of Anesthesia & Analgesia.

"We believe that the simple design and operational cost of the system should make the delivery of xenon—once considered prohibitively expensive for routine medical use—safe and inexpensive for newborns requiring surgery and anesthesia for life-threatening birth defects,” concluded lead author John Dingley, M.D., of the University of Wales, and colleagues.

Xenon is a colorless, heavy, odorless noble gas, present in the Earth's atmosphere in trace amounts. Xenon has profound biological effects; in high concentrations, it can induce unconsciousness. For several years, researchers have known that xenon provides protection against some forms of low-oxygen injury to the brain. However, because xenon is very expensive, its use is currently limited to a few experimental centers.

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University of Wales
University of Bristol