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

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Traumatic Brain Injury (TBI) and Effects of Altitude:An Analysis of the LiteratureIntroductionBACKGROUNDTraumatic brain injury (TBI) can occur as the result of external force due to blunt impact (being struck byor striking an object); foreign body penetration of the brain, sudden; brain acceleration or decelerationmovement; or concussive forces from an explosion or blast (see Taber et al., 2006). Depending on theseverity of the underlying injury, TBIs are classified as mild, moderate or severe. Most (75-90%) areclassified as mild TBI (mTBI) or as concussion 1 (Cassidy et al., 2004).TBI is a significant public health concern. An estimated two percent of Americans currently live with TBIrelateddisability and related costs (Rutland-Brown et al., 2006; Thurman et al., 1999). The Centers forDisease Control (CDC) estimates that each year, 1.7 million people in the United States sustain traumaticbrain injuries (TBI). These injuries represent nearly one-third of all injury-related deaths in the U.S.annually, and are the leading cause of death and disability among young adults (CDC, 2006).Importantly, statistics reported by the CDC do not include deployed service member or veteran TBIsfrom federal, military, or Veterans Administration (VA) hospitals which face a variety of uniquechallenges associated with the diagnosis, care and treatment of TBI sustained in recent military conflicts.In cooperation with the Armed Forces Health Surveillance Center, the Defense and Veterans Brain InjuryCenter (DVBIC) tracks and analyzes the incidence of military TBI based on actual medical diagnoses ofTBI within the U.S. armed forces. Their findings show that military TBI incident diagnoses have morethan doubled since 2005.Calendar Year 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009*TBI Incident diagnoses 10, 963 11, 830 12, 469 12, 886 13, 271 12, 025 16, 873 23, 002 28, 557 27, 862* Numbers updated as of 31 December 2009.Information available at DVBIC, http://www.dvbic.org/TBI-Numbers.aspxBroadly recognized as a signature injury of conflicts in Iraq and Afghanistan, TBI is a significant concernfor the U.S. military. Head, face and neck injuries have been reported to account for 22-52% of all battleinjuries sustained by U.S. troops in Iraq and Afghanistan (Okie, 2005; Owens et al., 2008; Wade et al.,2007). In these conflicts, it has been estimated that TBI occurs in approximately 60% of blast casualties(Galarneau et al., 2008). In a recent study of soldiers deployed to Iraq, clinician-confirmed TBI history(primarily mTBI) was identified in more than one of every five (22.8%) soldiers from a Brigade CombatTeam (Terrio et al., 2009). Other studies have found that as many as 28% of military personnel havesustained at least mTBI while deployed to conflicts in Iraq and Afghanistan (Warden, 2006). As theindividual and operational costs of these injuries become increasingly obvious, so does our recognition1 In 1997, the American Academy of Neurology (AAN, 1997) identified its criteria for three grades of concussion severity. Theleast severe of these (Grade 1) is sometimes described as “minor concussion, ” but typically would not meet the diagnosticstandards for mTBI. Therefore, the terms mTBI and concussion overlap, but are not necessarily always interchangeable.Although it is common for the two terms to be used interchangeably, it may not always be appropriate to do so in thediagnostic setting.September 14, 2010 4
Traumatic Brain Injury (TBI) and Effects of Altitude:An Analysis of the Literatureof the need to reduce the vulnerability and improve the survivability of military personnel who face avariety of unique risks in the course of their work.Military TBI patients follow a system of trauma care that begins with triage in the war zone andproceeds to acute care, rehabilitation, and reintegration into their homes and communities (for adescription of TBI clinical care in the Department of Defense, see Jaffe et al., 2009). In 2005, the BrainTrauma Foundation (www.braintrauma.org) published Guidelines for the Field Management of Combat-Related Head Trauma (Knuth et al., 2005) as an evidence-based guide to address the specific needs ofhead injury assessment, treatment and triage/transport decisions in military settings with attention tomilitary operational concerns. However, these guidelines did not specifically address head injury in thecontext of high altitude.Although relatively uncommon in civilian settings, the potentially adverse effects of high (1500-3500meters), very high (3500-5500 meters) or extreme altitude (above 5500 meters) exposure must beweighed in treating head injuries sustained by mountain climbers, aviators, and military personnelinvolved in conflicts at high elevations. The potentially adverse effects of altitude-related factors on TBIoutcome are not fully understood, but have been documented in the published scientific and medicalliterature. Table 1 presents a summary overview of factors and events that are known to threaten thecondition, outcome or survival of TBI patients. Although these events can occur in uncontrolled settingsbefore, during or after TBI, research to date primarily documents the effects of these conditions whenthey occur during the pre-hospital, acute, and/or early post-acute stages of TBI. The informationpresented in Table 1 represents findings published to date, and is not intended to exclude other effects,exposure settings or injury severity levels not yet studied.Table 1. Overview of altitude-related risk factors for adverse TBI outcomeVariableHypoxia(brain pO 2 < 15,PaO 2 < 60, SpO 2< 90%)Hypotension(systolic B/P < 90)Adverse OutcomesReportedMorbidityHosp/ICU length of stayDisabilityMortalityCognitiveFunctionalHosp length of stayDisabilityMortalityCognitiveTBI severitylevels studiedModerateSevereModerateSevereTimes of exposureconsideredPre-hospitalAcutePost-acutePre-hospitalAcutePost-acuteSelected ReferencesAriza et al., 2004 ; Chang et al.,2009 ; Chestnut et al., 1993; Chi etal., 2006 ; Davis et al., 2009 ;Geeraerts et al., 2008; Ghajar,2000; Grissom, 2006; Jiang et al.,2002 ; Kiening, 1996; Mendeloff etal., 1991; Miller, 1978; Schreiberet al., 2002; Stochetti et al., 1996Ariza et al., 2004 ; Chan et al.,1992; Chestnut et al., 1993; Chi etal., 2006 ; Clifton et al., 2002 ;Graham et al., 1989; Letarte et al.,1999;Manley et al., 2001 ; Marionet al., 1991; Marmarou et al.,1991; Morris, 1992; Schreiber etal., 2002 ; Stiver & Manley, 2008September 14, 2010 5
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