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Blast Injury

Blast Injury. Surg Cdr Jane Risdall Royal Navy Consultant Neuroanaesthetist/Intensivist Senior Lecturer, Academic Dept Military Anaesthesia and Critical Care Visiting Research Fellow, University of Cambridge Cambridge Trauma Conference 24 April 2014. The Problem.

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Blast Injury

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  1. Blast Injury Surg Cdr Jane Risdall Royal Navy ConsultantNeuroanaesthetist/Intensivist Senior Lecturer, Academic Dept Military Anaesthesia and Critical Care Visiting Research Fellow, University of Cambridge Cambridge Trauma Conference 24 April 2014

  2. The Problem • Blast injuries are a current and increasing problem (Champion HR J Trauma 2009, Nelson TJ J Am Coll Surg 2006) • 46% casualties treated by US Forward Surgical Teams suffered injuries from blast (Rush RM Am J Surg 2005) • More blast casualties are likely if enhanced blast weapons are used (Dearden P JRAMC 2001)

  3. What is meant by blast?

  4. Shock front Edge of explosive products Detonation of bare explosive • Blast wave • Shock wave • Dynamic overpressure • Heat from explosive products • Radiant • Convective

  5. Blast Injuries • Primary • Rapid acceleration of body wall by blast wave : generation of pressure wave eg. lung damage (blast lung) • Secondary • Fragments and debris : penetrating injuries eg. damage to major blood vessels, haemorrhage • Tertiary • Gross body displacement : limb avulsions eg. blunt injuries including musculo-skeletal

  6. Blast (explosive) Injuries • Primary (shock wave) • Rapid displacement of body wall by shock wave • Generation of pressure wave: damage to gas filled organs & at fluid gas interfaces • BLAST LUNG

  7. Blast (explosive) Injuries 2 • Secondary (fragments and debris) • Penetrating injuries • Soft tissue injuries • Contamination • TISSUE VIABILITY and HAEMORRHAGE

  8. Blast (explosive) Injuries 3 • Tertiary (translational, blast wind) • Gross body displacement • Limb avulsions • TRAUMATIC AMPUTATIONS and BLUNT TRAUMA

  9. Blast: multiple mechanisms of injury • Pressure (shock wave) • Energised fragments and debris • Blast winds • Throwing things against the body • Throwing the body against things • Heat • Convection • Radiation

  10. Unique features of blast exposure • Blast wave • Shock wave • Dynamic overpressure • Confounder • Location of explosion

  11. Blast overpressure/time profiles Idealised blast wavein free space Blast in a room/tunnel/enclosed vehicle

  12. Primary Blast Injury • Effects of shock wave: • Rapid displacement of body wall • Coupling of shock wave to generate pressure wave which damages gas filled organs in particular

  13. Primary blast injury to the thorax • Pulmonary contusion and oedema Hunter Proc Royal Soc Med 1941, Zuckerman Lancet 1940 • Reduced gas transfer Damon et al Aerospace Med 1993 • Vagal driven cardiorespiratory response • Bradycardia • Hypotension • Apnoea/rapid shallow breathing • Rapid onset (2-5 secs) Krohn et al Lancet 1942, Guy et al J Trauma 1998, Ohnishi et al Exp Physiol 2001

  14. Primary blast lung • Acute pulmonary oedema • Alveolar haemorrhage with consolidation • Pneumothorax/haemopneumothorax • Thrombo-embolic phenomena • Release of pulmonary inflammatory mediators • Systemic Inflammatory Response Syndrome (SIRS)

  15. Clinically • Oxygenation is likely to be very difficult, may require ECMO • ARDS picture is universal • However, this is compounded by the effects on other systems…

  16. Acute cardiovascular response to thoracic blast Kirkman et al Philos Trans R Soc LondBiolSci 2011

  17. Sham blast 500 Blast 400 HR (b.min-1) 300 200 120 80 MBP (mmHg) 40 0 0 5 10 15 20 25 30 35 40 Vol Haemorrhage (%BV) Effects of blast on the response to haemorrhage Sawdon et al Exp Physiol2002

  18. Mild Blast Brain Injury • Circumstantial evidence of neuropsychological problems after blast exposure • Okie NEJM 2005 • Belanger et al J Rehabil Res Dev 2005 • Lew J Rehabil Res Dev 2005 • Evidence of neuronal injury but mechanism unclear • Cernak et al Brain Inj 2001 • Cernak et al J Trauma 2001 • Moochhala et al J Trauma 2004 • Unknown: whether neuropsychological symptoms caused by blast

  19. Thoracic protection attenuates neuronal injury • Anaesthetised rats exposed to 126-147 kPa overpressure (whole body) • ± thoracic protection (Kevlar® vest) • Vest attenuated • Cardiovascular response to blast • Neuronal injury Long et al J Neurotrauma 2009

  20. Significant Blast Brain Injury • Blast-exposed casualties show increased incidence and severity of brain oedema Armonda et al Neurosurgery 2006 • Can be serious and life-threatening • May require hemicraniectomy to decompress • Mechanism and specific treatment unknown Bauman et al J Neurotrauma 2009

  21. Mechanisms • Physical • Shear forces within the brain • Vascular stretch • Bulk acceleration of the head • Molecular • Unknown • Evidence for inflammatory mediators • Local • Systemic

  22. Cardiovascular effects of isolated blast exposure to the head

  23. Although these animals received a significant cranial blast exposure (that would have been fatal if directed at the thorax) there was no evidence of histological damage (haemorrhage, oedema, leucocyte infiltration) in brain sections taken eight hours post exposure.

  24. Elevation in endogenous Epo and pro-inflammatory cytokines MIP1α, IL6, IL1α and IL1β were also detectable but at levels below those permitting quantification. The trend was suggestive of an increase in the blast exposed group.

  25. Elevation in endothelial integrins

  26. qRT-PCR array of inflammatory genes • 87 genes involved in inflammation analysed (qRT-PCR array) • Data presented as fold change (Blast vs control) • Biologically relevant changes in genes if: • >2 fold change and • p-value <0.05

  27. Up-regulated inflammatory genes

  28. Summary • Blast injuries are multimodal • Pressure wave • Penetrating trauma • Blunt trauma • Each injury should be managed initially in accordance with standard algorithms • Multiple systems will be affected • Inflammation will play a significant role in the subsequent clinical course

  29. Questions?

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