Application of medical gases in the field of neurobiology

Medical gases, pharmaceutical molecules which offer solutions to a wide array of medical needs, range from traditional gases (oxygen and nitrous oxide) to gases like nitric oxide, carbon monoxide, and hydrogen sulfide--all of which have been recently shown to behave as biological messenger molecules [1]. Some gases, such as helium and xenon, have even been shown to be neuroprotective following various brain injuries such as acute ischemic stroke, perinatal hypoxia-ischemia, traumatic brain injury, and cardiopulmonary bypass-induced neurologic and neurocognitive dysfunctions [2-4]. In this paper, we will briefly introduce and review the history of oxygen, helium, xenon, and hydrogen gas, and discuss the various therapeutic mechanisms that have been proposed in the current literature.Air is composed of 78% nitrogen, 21% oxygen, and less than 1% of other gases. If more oxygen is needed, hyperoxia can be induced to increase the fraction of inhaled oxygen, and therefore the diffusion of oxygen through blood. This can be achieved under normobaric, or hyperbaric conditions. Normobaric hyperoxia (normobaric oxygen, NBO) is applied via a wide variety of masks that allow delivery of inspired oxygen ranging from 24% to 90%. Higher concentrations can be delivered via masks with reservoirs, tightly fitting continuous positive airway pressure-type masks, or through mechanical ventilation. In contrast, under hyperbaric conditions, one can breathe 100% oxygen (small chamber for single occupant), or breathe compressed air and 100% oxygen intermittently through a mask or hood (large multiplace hyperbaric chamber).Hyperoxia is an attractive therapeutic option because it has several properties of an 'ideal' protective agent. Unlike most pharmaceutical drugs, oxygen is simple to administer, easily diffuses to target tissues, is well tolerated, can be delivered in 100% concentrations without significant side effects, and can theoretically be combined with other treatments.To date, the me