Hemodynamic, respiratory and neorophysiological reactions after high : Velocity behind armor blunt trauma

Abstract: This thesis is addressing Behind Armor Blunt Trauma (BABT), defined as the nonpenetrating injury resulting from a ballistic impact on personal body armor. The protective vest may impede the projectile, but some of the kinetic energy is transferred to the body, causing effects such as pulmonary contusion, apnea, hypotension and occasionally death. Our aims of these studies have been to investigate physiological responses after highvelocity BABT, including EEG (study I). Furthermore, the safety criterion of 44 mm for protective vests (study II), effects of vagotomy (study III), and fluid resuscitation (study IV) has been evaluated. Anaesthetized pigs, wearing body armor on the right side of thorax, were shot with a standard 7.62 mm assault rifle (velocity approx. 800 m/s). We used body armors corresponding to 28 mm impression in clay placed behind the vest (study I and III), 34 mm and 40 mm (study II), and 42 mm (study IV). Several physiological parameters were thereafter monitored during two hours after the shot. Experimental protocol was similar in all studies, except from study III (in which one group received bilateral cervical vagotomy) and study IV, in which 2 groups received Ringer´s acetate (RA) or hypertonic saline with dextrane (HSD). In all studies we observed an immediate drop of blood pressure, desaturation, increased pressure in the lung circulation, suppressed EEG-pattern and pulmonary contusion. In study II and IV, severe hyperkalemia was seen early after the trauma and several animals had serious arrhythmias. Our observed EEG-changes indicate that high-velocity BABT induces brain dysfunction, for at least a couple of minutes. Based on our results, the safety criteria of 44 mm should be considered insufficient when a vest is exposed to highvelocity bullets. Our results show that apnea after BABT is a vagally mediated reflex, that can be inhibited by vagotomy. Fluid resuscitation has limited effects on physiological parameters in our model, although HSD induces less edema formation and a tendency to improved saturation compared to RA.