Traumatic Brain Injury and Effects of Altitude - Human Performance ...

Traumatic Brain Injury (TBI) and Effects of Altitude:An Analysis of the Literatureextreme altitude, the three climbers who were most severely impaired also demonstrated EEGabnormalities suggestive of irreversible hypoxic damage in fronto-temporal limbic (hippocampal) brainstructures. Other investigators have reported similar evidence of lasting effects of extreme altitudeexposure on cognitive function (Garrido et al., 1993, 1996; Hornbein et al., 1989).Temporary neuropsychological impairments have also been observed in climbers who have reachedextreme altitudes with the use of supplemental oxygen (Clark et al., 1983; Lowe et al., 2007; Townes etal., 1984), and in volunteers subjected to artificial altitude in the laboratory setting (Ledwith, 1968). Thissuggests that effects of altitude on cognitive performance are probably mediated by hypoxia and thatsupplemental oxygen may play a critical role in preventing permanent damage from sustained orrepeated hypoxic insult to the brain.Military Concerns and Operational ConstraintsMilitary medics, physicians and surgeons must be aware of many direct and indirect environmentalthreats to the survival of injured soldiers. Because the human brain is susceptible and sensitive tophysiological change, medical caregivers need to know what, if anything can be done to avoid ormitigate the potentially harmful effects of time and environment on military casualties in whom TBI isknown or suspected. The Guidelines for the Field Management of Combat-Related Head Trauma (Knuthet al., 2005) emphasized the importance of monitoring and preventing hypoxemia and hypotension,both of which have been identified in different studies as independent predictors of poor outcome inbrain-injured patients (Chestnut et al., 1993; Manley et al., 2001). There is also a need to betterunderstand the possible long-term health and performance implications for warfighters who recoverfrom concussion or TBI and then return to duty in high-altitude settings.TBI can be uniquely difficult to manage effectively in combat settings, which introduce myriad additionalrisks to the survival of injured military personnel and those who provide for their acute medical care andtransport. For example, operational constraints may make it impossible to provide immediate or directtransport from the battlefield to a trauma center with neurosurgical capabilities. Delay itself canincrease the risk of secondary injuries. In addition, the potentially harmful effects of rapid ascent to highaltitude on critically ill and injured patients introduce yet another complex hazard for casualties who areevacuated by aeromedical transport, and for the flight crews who care for them.Military medical flights transporting warfighters from combat zones to medical care centers in Europe orthe U.S. can last for many hours. During this time, patients are exposed to multiple sources ofphysiologic stress, including hypoxia, dehydration and cold temperatures. Even with the benefit oftraining and redundant protective systems in place, fliers of military aircraft do sometimes experiencepotentially deadly hypoxia (Cable, 2003). Although the risks associated with aeromedical transport arenot new to those who practice emergency and military medicine, mitigating and controlling theirpotentially dangerous effects requires knowledgeable preparation and management, adequateresources and careful attention to patient status (Argyros & Cassimatis, 2002; Barnes et al., 2008;Helling & McKinlay, 2005; Johannigman, 2007, 2008; Letarte et al., 1999; Morris, 1992; Reddick, 1977;Turkan et al., 2006).Military personnel who have experienced multiple concussions or are considered to have recoveredfrom TBI are often returned to active duty, where they may fly in non-pressurized aircraft and/or be re-September 14, 2010 12