Local Effect of Ballistic Fragments Embedded Along the Carotid Sheath of a Porcine Animal Model

Abstract

ABSTRACT Introduction Energized ballistic fragments from improvised explosive devices were the most common cause of injury to coalition service personnel during conflicts in Iraq and Afghanistan. Surgical excision of retained fragments is not routinely performed unless there is a concern for injury to vital structures. However, no clear guidelines dictate when or if a fragment should be removed, reflecting a lack of objective evidence of their long-term effects. Using a porcine model, we aimed to evaluate changes to the carotid artery produced by retained fragments over time. Materials and Methods Institutional Animal Care and Use Committee approval for all experiments was obtained before commencement of the study. Eighteen female swine (mean mass 62.0 ± 3.4 kg) were randomized into three study groups corresponding to the time of survival after implantation of ballistic fragments: 1, 6, and 12 weeks. Two animals from each group were randomly assigned to have one of the three different fragments implanted within the right carotid sheath in zones 1-3 of the neck. The left carotid served as the control. The vascular flow rate and arterial diameter were measured at each level before implantation and again after the survival interval. Baseline and interval angiograms were performed to identify gross vascular changes. Results No abnormalities were identified on baseline or interval angiograms. No significant difference was found when the baseline was compared to interval measurements or when compared to the control side for all gross and physiological measures at 1 and 6 weeks (P = .053-.855). After 12 weeks, the flow and diameter changed significantly (P < .001-.03), but this significant change was found in both the control and affected carotid. Conclusions The lack of significant gross anatomical and physiological changes at 6 weeks postimplantation lends evidence toward the current policy that early removal of retained ballistic fragments around cervical vessels is not required. Changes were significant after 12 weeks which suggest that surveillance may be required; however, such changes could be explained by physiological animal growth.