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Review of New Topical Hemostatic Dressings for Combat Casualty Care [Military Medicine]
[May 14, 2014]

Review of New Topical Hemostatic Dressings for Combat Casualty Care [Military Medicine]

(Military Medicine Via Acquire Media NewsEdge) ABSTRACT This review analyzes the new (2008-2013) hemostatic agents and dressings for enhanced efficacy in preclinical studies, and investigates supportive findings among case reports of effectiveness and safety in hospital and prehospital literature. A literature search was conducted using PubMed, National Library of Medicine using key words and phrases. The search revealed a total of 16 articles that fit the criteria established for third-generation hemostatic dressings. There were a total of 9 preclinical, 5 clinical, and 2 prehospital studies evaluated. Evaluation of these third- generation studies reveals that mucoadhesive (chitosan) dressings, particularly Celox Gauze and ChitoGauze, clearly show equal efficacy to Combat Gauze across many dependent variables. Chitosan-based products are ideal prehospital dressings because they are shown to work independently from the physiological clotting mechanisms. Many first-, second-, and third-generation chitosan-based dressings have been in use for years by the United States and other NATO militaries at the point of injury, and during tactical evacuation, in Operation Enduring Freedom and Operation Iraqi Freedom without reported complications or side effects. Based on the reported efficacy and long-term safety of chitosan-based products, increased use of Celox Gauze and ChitoGauze within the Department of Defense and civilian venues merits further consideration and open debate.

INTRODUCTION The most recent (2001-2011) combat mortality analysis revealed that 24% of prehospital deaths (N = 976 of 4,596 cases) were deemed potentially survivable. Of these, 90.9% were attributable to hemorrhage. The three primary sites of lethal hemorrhage are truncal (67%); junctional, i.e., groin, axilla, neck (19%); and extremities (14%).1 Consequently, these three anatomical regions have been the principle focus of hemorrhage research over the past 10 years. Great strides have been made in controlling extremity hemorrhage with tourniquets.2-4 Topical hemostatic agents have also contrib- uted to success in controlling extremity and junctional hemor- rhage. Improving efficacy of these agents in the laboratory (preclinical) setting should continue to translate into improved effectiveness in the real world prehospital and hospital set- tings.5-8 Further research, development, and recommendations should include the next generation of hemorrhage control agents in an effort to decrease the potentially survivable mor- tality rate as successfully demonstrated by the U.S. Army 75th Ranger Regiment.9 Hemostatic agents and dressings can be classified in mul- tiple ways including mechanism of action, the form of the agent, delivery mechanism, the type of wound some have been designed for, and their chronological development and acceptance more recently for combat casualty care.10 For the purposes of this review, they will be considered based on mechanism of action and then the most recently developed hemostatic dressings will be examined for their merit of inclusion within the next set of tactical medicine guidelines. The collective studies on the development of first generation of hemostatic agents for combat casualty care in the Depart- ment of Defense (DoD) started in the 1990s until the first two agents, i.e., HemCon (HC; HemCon Medical Technologies, Portland, Oregon) and QuikClot granules (QC; Z-Medica Wallingford, Connecticut), were reviewed for efficacy and were deemed appropriate for battlefield use in 2003 by the Committee on Tactical Combat Casualty Care (CoTCCC). Subsequently, from 2003 to 2008, a number of newer agents approved by the Food and Drug Administration (FDA), and now called second-generation hemostatic agents/dressings, were tested for improved efficacy at the U.S. Army Institute of Surgical Research and the Naval Medical Research Center. Both DoD laboratories reported that Combat Gauze (CG; Z-Medica, Wallingford, Connecticut), WoundStat (WS; TraumaCure, Bethesda, Maryland), and Celox granules (CE; Medtrade Products, Crew, United Kingdom) were con- sistently more effective than the previously selected first- generation hemostatic agents.11-14 Consequently, the CoTCCC voted to recommend CG as the first-line treatment for life- threatening hemorrhage not amenable to tourniquet place- ment. WS was recommended as the backup agent as combat medical personnel expressed a strong preference for a gauze- type hemostatic dressings because granules were deemed more challenging to apply in field conditions.15 However, based on subsequent animal safety studies, WS was later removed from the TCCC guidelines.16 For the purposes of this review, all subsequent hemostatic dressings approved by FDA for combat casualty care after this decision by the CoTCCC in April 2008 were deemed third-generation dressings.

Although there are a number of third-generation dressings now approved by the FDA for combat casualty care to date, only one study examining ChitoGauze (HCG; third generation) vs. CG (second generation) has been presented (August 3, 2010) to the CoTCCC members since April 2008 meeting.17 Consequently, no deliberations among CoTCCC members have occurred from April 2008 to November 2013 with regard to newer third generation hemostatic dressings for the consideration of adding to the TCCC guidelines. It is the intent of this review to present the relevant third-generation hemostatic dressings for efficacy, effectiveness, and safety in preclinical studies, hospital-based and prehospital case reports.

METHODS Electronic literature searches were undertaken using Medline. To capture articles available online before publication, searches were repeated using PubMed. The initial search for English-language articles relating to hemostatic dressings included alternative spellings for combat, battlefield, and hemostatic dressings and agents. Manufacturers of several agents were contacted, where applicable, for technical infor- mation, cost, and licensing. This summary is limited to com- mercially available third generation (April 2008-November 2013) hemostatic dressings in preclinical studies and hospital- based and prehospital case reports, and further limited to stud- ies in which CG is used as the control agent for the preclinical literature. Any study that compared agent efficacy to standard gauze (SG) as the control is excluded from this review because of the clear superiority of the currently recommended dressing (CG). This is in line with the current recommendations for testing hemostatic dressings in the consensus swine model developed by the U.S. Army Institute of Surgical Research.18 Clinical observations were limited to case reports and case series as there are no randomized, controlled trials for hemo- static dressings.

After cross-referencing by hand to ensure criteria were met, the literature search revealed a total of 88 articles. Six- teen articles fit the criteria established for third-generation hemostatic agents. There were 9 preclinical, 5 hospital-based, and 2 prehospital case reports used in this review.

Agent Classifications To date, the article by Granville-Chapman and Midwinter19 is the most detailed presentation on topical hemostatics of the first and second generation. Smith et al and other authors present some of the newer third-generation agents and their mechanism of action.8,20-23 These hemostatic dressings are classified as either factor concentrators, procoagulants, or mucoadhesives. See Table I for a summary description of the relevant characteristics of first-, second-, and third-generation hemostatic dressings pertinent to this review.

Factor Concentrators QuickClot Granules A first-generation agent in TCCC works through rapid absorp- tion of the water content of blood; QuickClot (QC) granules concentrate the cellular and protein components of blood, pro- moting clot formation. QC is a granular preparation of zeolite, an inert volcanic mineral, which rapidly absorbs water in an exothermic reaction-a property which caused safety con- cerns. The original QC comprised granules that were poured into the bleeding wound. A newer generation product, termed QuikClot Advanced Clotting Sponge (Z-Medica, Wallingford, Connecticut), uses zeolite beads enclosed in loose mesh bags, permitting more effective application into wound cavities and easing removal of the product during surgery. QC has been deployed by the U.S. Military since 2003 and the U.K. Ministry of Defense since 2004, and was replaced in the TCCC guide- lines by second-generation dressings in 2008.

Procoagulants Dry Fibrin Sealant Pusateri et al and Kheribadi et al reviewed the historical evolution of the dry fibrin sealant (DFS) dressing, which was developed by a joint collaboration between the American Red Cross and U.S. Army.5,6 It consists of powdered fibrino- gen, thrombin, factor XIII, and calcium on a 4 in. 4 in. polyglactin (Vicryl) backing and is bioabsorbable. This dressing enhances coagulation by providing a high local con- centration of coagulation factors. Despite modern purification technology virtually eliminating the risk of viral transmis- sion, disadvantages of the DFS dressing are its limited pli- ability and that during its application, its flaky consistency results in it sticking to the gloves of responders. The U.S. Military fielded the DFS dressing under an Investigational New Drug Protocol for use in Afghanistan and Iraq on a trial basis in 2003. Shortly thereafter DFS was replaced by the FDA-approved HC and QC products.

Combat Gauze A second-generation hemostatic dressing may be considered the first mineral-based hemostatic gauze. CG is a flexible nonwoven (50-50% rayon/polyester) gauze impregnated with kaolin. Combat Gauze XL (CGX) now offers a new large size gauze option. Kaolin is an aluminum silicate and a known activator of the intrinsic clotting pathway. It is not biodegradable, so it must be removed from the wound before definitive repair is completed. Unlike the adhesive products, this dressing often does not provide immediate hemostasis when applied over wounds, resulting in more blood loss than other agents during application.6,7 Hemostasis is eventually achieved when a hemostatic clot is formed in conjunction with CG on the injury site. Unlike other granular agents, application and removal of CG are easily accomplished and require no special procedures. This agent is reported in use by various U.S. military forces and about a dozen other NATO militaries.

Salmon Thrombin-Fibrinogen Salmon Thrombin-Fibrinogen (STF) dressing contains a pro- prietary mixture of lyophilized salmon thrombin and fibrino- gen, which is layered onto a water-soluble dressing composed of dextran. The action of STF is similar to human thrombin and fibrinogen, but without many of the disadvantages. The STF dressing is applied directly to the injured vessel. The dextran immediately goes into solution upon contact with water (i.e., blood) allowing hydration of the thrombin and fibrinogen molecules, which leads to polymerization into a fibrin clot. Recently, two studies using a femoral wound model confirm the finding from an earlier aortic injury model that the mechanism of action of this dressing is the formation of a large, robust clot that seals over the injury to stop hemor- rhage.22-24 The STF proteins are inexpensive, readily available in large quantities, stable for long periods at ambient tempera- tures, and do not transmit disease.

Mucoadhesive Agents/Dressings Chitosans have widespread applications, have been widely studied in the biomedical field, and are highly biocompati- ble.25 Their chemistry has been previously described.26,27 Chitosan refers to a series of polymers derived from crusta- cean chitin and is a complex carbohydrate that is biodegrad- able. Chitosan breaks down in the body into glucosamine and N-acetyl glucosamine components.28 Extensive safety studies have been conducted on chitosan over many decades. A recent review article summarizes the vast amount of safety studies making it ideal for a range of applications, particu- larly wound healing.29 Chitosan has no intrinsic hemostatic properties and thus works independently of the coagulation system. The hemostatic properties of chitosan appear to be by direct electrostatic interaction between negatively charged cell membranes of the erythrocytes and positively charged chitosan. These agents display strong adherence to tissues and physically seal bleeding wounds.30-32 First-generation chitosan product (HC bandage) relied on a freeze-drying technology to produce a stable and effective format. This was made for a stiff, brittle product that was difficult to apply effectively. Second-generation improve- ments (CE granules) allowed the chitosan to be presented in a granular form that did not rely on freeze-drying, thereby removing the stiff pad limitation. This led to a product that worked consistently on different wound types, equal or supe- rior to HC bandage. However, the granule form was not ideal for application in austere conditions and not favored by many end users within the DoD. For third-generation agents (post April 2008), Celox Gauze (CEG) and HCG addressed this by being able to coat packable gauze with chitosan, to combine the advantages of gauze presentation (as developed by CG) and the chitosan technology for coagulopathic bleeding and reduced blood loss. Chitosan development continued by increasing the mucoadhesion properties (Celox Rapid [CR] Gauze) to reduce application time without manual pressure once inserted.

Even though there are limited published reports on chitosan products (e.g., CE, HC, etc.), they have been used on combat casualties during both Operation Iraq Freedom and Operation Enduring Freedom and are reported to be safe and effective by the United States, United Kingdom, Italian, and other coalitional forces.33-35 Even state emer- gency medical services (EMS) are now making decisions to add third-generation hemostatic dressings for EMS pre- hospital care. After an extensive review of the literature and advice from the EMS Medical Directors Association of California Scope of Practice Committee in April 2013, the California State EMS Authority has approved the use of three mucoadhesive agents, i.e., CEG, CR Gauze, and HC ChitoFlex Pro, to be used along with CG as the current agent (D. Smiley, personal communication).

Relevant hemostatic agents and dressings of past and current interest (first generation through third generation products) to TCCC are as follows: HemCon The original HC dressing and subsequent modifications are designed for external application, and is one of the first- generation agents developed with some funding by the U.S. Army. It was initially fielded by the Army and was the first agent of choice in the TCCC guidelines beginning in 2003. The dressing is made of freeze-dried chitosan, a partially deacetylated form of chitin (a natural polysaccharide) found abundantly in shellfish. The primary mechanism of HC hemostatic action appears to be strong adherence to wet tis- sues and sealing of the injured vessels. Chitosan also displays some antibacterial properties. HC Medical Technologies has produced a double-sided flexible roll of chitosan, called ChitoFlex Pro. This formulation has been tested in several preclinical studies.36-38 Summary of the preclinical studies5,6 and prehospital (battlefield) studies33 can be found else- where. The most recent third-generation product is called HCG Pro and is approved for external hemorrhage control. Measuring 4 in. 4 ft and Z-folded, this agent is fielded by military forces from the United States, United Kingdom, Israel, and the Netherlands.

Celox CE is a chitosan-based hemostatic agent in granular form containing a proprietary blend of different compounds. Today CE is sold in four configurations: CE Granules, Celox-A (syringe applicator, second-generation agent), CEG, and CR gauze (both third-generation agents). Celox Trauma Gauze (CTG) is no longer available commercially and was replaced by CR gauze. Because chitosan works inde- pendently from the physiological clotting mechanisms, it has also been shown to work in the presence of common antico- agulants.6,8 Although in principle chitosan is a bioabsorbable material, CE hemostatic powder is not considered bioabsorb- able and therefore must be removed from the wound before surgical repair. Because it forms large clumps when wetted with blood, removal of CE from wounds is much easier than other granular/powder agents.

Numerous second-generation preclinical studies report the superior efficacy of Celox products compared to gauze and other agents.11,13,14,36,38-42 Consequently, civilian first responders, and conventional and Special Operations Force military units are carrying various CE products for managing hemorrhage. The third-generation agent CEG is now the hemostatic agent of choice in numerous U.S. military Special Operations Force units as well as city, county, state, and fed- eral law enforcement agencies. Furthermore, the Ministry of Defense, United Kingdom also selected CEG for all military units with two CEG packs in every individual first-aid kit (IFAK).43 Eight other military forces worldwide use CEG now.

Mini Sponge Dressing This device is marketed as XStat (RevMedx, Wilsonville, Oregon). This is the first novel hemostatic agent designed for use in noncompressible junctional areas of the body. Mini sponge dressing (MSD) is applied into a wound cavity using a lightweight applicator. The MSD is composed of multiple cylindrical cellulose-based medical sponges that are com- pressed and coated with chitosan. Each cylinder is 9.8 mm in diameter and compressed to a mean (SD) height of 3.5 (0.5) mm. Upon absorption of blood or other fluid, the cylin- ders expand axially to a mean of 4.8 (0.3) cm in approxi- mately 20 seconds. Handling and dispensing the MSD is facilitated by an applicator, which is composed of a cylindri- cal housing (180.0 30.0 mm), a valve tip, and a plunger mechanism. Each MSD applicator holds 100 mini sponges. Mueller et al report the first study to date comparing MSD to CG for hemostatic effectiveness.44 Preclinical Wound Models Preclinical studies in animal models are conducted initially to determine hemostatic agent efficacy-how well they work in controlled laboratory conditions. Various wound models include venous hemorrhage, arterial hemorrhage, and mixed arterial and venous hemorrhage. The early studies by Holcomb et al used a grade V liver injury in swine resulting in a high-flow, low-pressure venous bleed.45,46 This model is considered lethal with a mortality rate of 50 to 90%. A much greater challenge for hemostatic agents are studies of iso- lated arterial wounding, which creates a high-pressure, high- flow model.47 Alam et al created a high lethal groin wound that is representative of a battlefield wound not amenable to tourniquet use.48 In his model, full transection of the femoral artery and vein created a mixed arteriovenous hemorrhage that was allowed to bleed for 3 to 5 minutes. There is an initial high-flow, high-pressure bleed, but as the mean arterial pressure (MAP) drops venous back-bleeding pre- dominates, which becomes easier to control with hemo- static agents.

Clearly, there are ongoing challenges interpreting agent efficacy given the various wound models used to test the agents. Additionally, one of the continuing assumptions of current animal wound models is that the outcome of efficacy studies is transferable to humans with complex and varying wound geometry and with application by first responders who may have little experience with application compared to an investigator in the lab. Other than observational data and limited survey data33,49,50 agent effectiveness in the hands of the prehospital provider has yet to be well documented. Devlin et al stated that an ideal wound model does not exist. Standardizing hemorrhage wound models is challeng- ing because of the multiple variables involved, i.e., wound preparation, wound mechanism, free bleed duration, agent packing technique, manual pressure duration, frequency of manual pressure with rebleeding, fluid resuscitation vari- ables, and the duration of the observation period.50 Recently, a DoD consensus group accepted a standardized swine hem- orrhage wound model (6-mm femoral arteriotomy) for topi- cal hemostatic agents in an effort to decrease the limitations and variability of outcomes across these studies.18 Hemostatic agent studies are ideally done in several phases. Studies using the United States Army Institute of Surgical Research model serve as a first step in demonstrating efficacy in the face of a significant bleeding challenge. Follow- ing this are common injury subtypes such as blast51 or pene- trating.41,52 Finally, clinical studies as well as prehospital battlefield studies should be performed in an effort to deter- mine consistency of effectiveness and safety for a given hemostatic agent.

Key Preclinical Third-Generation Studies A DoD-sponsored study by the Naval Medical Research Unit, San Antonio, evaluated the largest number of hemo- static agents since the end of the second-generation phase (2008).53 This study used the DoD standardized hemorrhage model for topical hemostatic dressings. These investigators examined four third-generation hemostatic dressings in com- parison to CG (control). Each gauze group consisted of ten randomized animals. For each swine, one of five hemostatic gauzes (CG, CGX, CTG, CEG, or HCG) was packed into the wound site. Direct pressure (3 minutes) was then applied, and the animals were rapidly resuscitated to achieve and maintain a MAP of 60 mmHg for 150 minutes or until death. Animal survival, hemostasis, and blood loss were assessed as primary endpoints.

The results showed that higher rates of survival were found with CGX, CEG, and HCG when compared to CG, although these results did not reach statistical significance. CGX was superior to CG in initial hemostasis ( p = 0.02). In initial blood loss, both CGX ( p = 0.026) and CEG ( p = 0.046) were found to be superior to CG. Although clinically relevant, there were no significant differences amongst groups in post-treatment blood loss. This is mostly likely because of low statistical power to discriminate significant differences based on small sample size in each group. All animals were subject to histologic analysis regardless of outcome. The analysis revealed no significant damage to the tissues examined.

These authors state that FDA-approved hemostatic dress- ings performed at least as well as the current standard of care (CG) with no agent superiority based on hemostasis, survival, and blood loss.53 Of particular note, one factor that differen- tiated CGX and CEG was their mass (nearly twice the mass of other test agents). These authors state that because CGX exhibited a higher degree of efficacy (immediate hemostasis and 10-minute blood loss) than the traditional and smaller CG, it may be inferred that the performance differences observed are not necessarily attributable to the kaolin content of the gauze, but rather the total mass of test gauze applied. This concept reinforces the fundamentals of traditional wound packing and pressure dressing application for manag- ing severe bleeding. Furthermore, they state that the current standard for point-of-injury hemorrhage control may need to be re-evaluated or alternatively the standard of care expanded to include CEG, CTG, HCG, and CGX.53 Another third-generation agent study by Schwartz et al reported that HCG is as efficacious as CG in a swine hem- orrhage model.21 HCG had faster time to hemostasis, and less total blood loss and fluid resuscitation requirements although not statistically different from CG for the same lack of statistical power as stated above, but still is very clinically relevant. Anecdotally, because of these results, Medical College of Georgia changed their hemostatic dress- ing of choice to HCG in the emergency department.17 Xie et al also reported similar findings with overall efficacy when HCG was compared to CG.54 They reported signifi- cantly faster 2-minute hemostasis (63% vs. 25 %; p = 0.04), favorable trends for less total blood loss, average time to achieve hemostasis, and 3-hour survival time in a preclinical hemorrhagic wound model.

Kheirabadi et al state that there is a need for a new gener- ation dressing that can consistently demonstrate efficacy and safety in preclinical studies, and effectiveness in the hospital and prehospital setting independent of the coagulation sta- tus.6 Hemostatic products are generally tested in efficacy studies when swine are in a normal acid-base status with a normally functioning coagulation system. This does not reflect combat casualties that present with hypothermia, aci- dosis, and coagulopathy. Indeed, the prevalence of early coagulopathy in combat casualties may be as high as 38% on admission to the field hospital and is a marker of injury severity and increased mortality.55,56 Because the hemostatic function of CG depends primarily on the blood-clotting activ- ity of hosts, this dressing may be found to be less effective in coagulopathic patients.23 However, recent studies report good success with hemostasis in a coagulopathic model (hypothermia and hemodilution).57,58 Because of the heterogenous nature of combat wounds, and the likelihood of coagulopathy in severe combat trauma, combat medics might consider carrying two hemostatic dress- ings with different mechanisms of action. If the initial hemo- static dressing is ineffective as a result of either the type wound pattern or the presence of coagulopathy, then another type of agent can be applied. Thus, it is a logical strategy to add a third-generation mucoadhesive dressing to the medic aid bag for managing severe bleeding. Consequently, it is essential that investigators evaluate hemostatic dressings in both normal and coagulopathic models to determine their efficacy.

Two recent preclinical studies examined the efficacy of STF dressings in normal and coagulopathic swine.22,23 STF combines a soluble dextran dressing with lyophilized salmon thrombin and fibrinogen. STF was tested against CG in a standard swine femoral artery hemorrhage.22 Survival, blood loss, and time to hemostasis were similar between the groups. Based on angiography, it was noted that three CG-treated animals formed a clot within the wound, but the clot did not adhere to the femoral artery injury. All ten of the STF-treated animals formed a clot in the wound that adhered and sealed the arterial injury site. None of the STF-treated animals bled following manual lower extremity repeat movement as a simulated walking maneuver. Three of five STF-treated ani- mals re-established blood flow distal to the injury as dem- onstrated by angiography. These authors report that STF dressing is as efficacious as CG in treating hemorrhage in noncoagulopathic swine. It is important to note that these authors state CG achieved hemostasis by occlusive compres- sion of the artery.

The same wound model was used to test the hypothesis that the STF dressing would be better able to control hemor- rhage and prolong survival in coagulopathic swine compared to CG.23 The survival rate (50% CG, 90% STF) was not statistically significant before a simulated walking maneuver, but after limb manipulation this became significant ( p = 0.005). This led to a significant difference in overall survival time. As reported in their first study, clots formed over the arterial injury in 100% of STF-treated animals compared to 0% in CG-treated animals. STF-treated animals consumed less host coagulation factors overall with a significant differ- ence found in platelet count ( p = 0.03). Angiographic obser- vation of distal blood flow was seen twice as often with the STF dressing as with CG. They conclude that STF dressing allows a higher survival rate after limb manipulation, greater survival time ( p = 0.05), and a more stable dressing than CG in coagulopathic swine. It is important to note that STF is not FDA approved at this time.

Since the first-generation DFS, fibrin dressings have evolved to overcome the early concerns of disease transmis- sion.5,20 When they become commercially available, they should be considered for use in hospitals, tactical evacuation and casualty evacuation platforms, and possibly by medics. Even though the cost of these fibrin dressings is lower than when first developed, they still may be cost prohibitive for every IFAK kit.

Mueller et al investigated the effectiveness of MSD as compared to CG control (N = 8) using a subclavian artery and vein transection wound model.44 Each animal had a 3-second free bleed followed by randomly assigning either MSD or CG for insertion. After the MSD was inserted and filled the wound space with mini sponges, no external pres- sure was applied. Only one CG was initially inserted with one SG placed on top followed by 3 minutes of external pressure. One reapplication was allowed for CG. Fluid resus- citation was provided to maintain pretreatment MAP during a 60-minute observation period. The results showed that MSD was highly efficacious in achieving hemostasis when compared to CG (total blood loss and survival). No signifi- cant difference was found for hemostasis at 4 minutes. There were significant differences in favor of MSD with respect to hemostasis at 60 minutes ( p = 0.007), survival to 60 minutes (p = 0.026), and total blood loss ( p = 0.021). These authors state that this agent and delivery device fulfill an unmet urgent need for junctional hemorrhage.

The outcome from all nine studies is that seven third- generation agents are at least efficacious or in some studies superior to CG to control severe bleeding. See Table II for summaries of these nine preclinical studies.21-23,44,53,54,59-61 Key Third-Generation Clinical Reports There are limited clinical data to support the use of topical hemostatic agents for use in civilian or military medical treatment facilities. Observational and retrospective reports have inherent bias and cannot establish causality. Random- ized clinical trials in trauma populations are extraordinarily difficult and nearly impossible in the combat environment. Therefore, military physicians accumulate observational experience and share these lessons learned. A summary of published data that report the successful clinical use of hemostatics are limited to QC,49,62 HC,32,63 CG,64 and Celox products (CE and CEG).34,65,66 The outcome of these five surgical case reports is that these third-generation agents (CEG and Modified Rapid Deployable Hemostat [mRDH]) were effective to control severe in a total of 27 patients and in some cases more effective to create hemostasis when com- pared to other standard therapies, including CG. See Table III for the summary of these five third-generation clinical case reports.64,66-69 Key Third-Generation Prehospital Reports With the significant challenges to conduct prospective studies in theater, there are currently few published reports in the prehospital setting with hemostatic agents, particularly any third-generation agents. The latest review by Smith et al covers first generation through some of the current third- generation agents.8 Numerous observational reports exist and are being collected in DoD Lessons Learned Centers. Any series published regarding civilian EMS are limited to first-generation agents. To date only two third-generation agent reports from the United States and United Kingdom have been published. An additional report describes the application of CEG by the U.K. Medical Emergency Response Teams during tactical aeroevacuation platform.70 They described the technique used to successfully apply this agent in a difficult junctional area. Because the U.K. Ministry of Defense uses CEG exclusively, it is anticipated that further reports on the use of this agent are forthcoming. There are successful reports on the effectiveness of CEG in combat casualty care. There was a positive outcome to create hemo- stasis with the use of CEG in a total of seven patients based on blunt and penetrating trauma as reported in these two prehospital case reports. See Table IV for a summary of the case reports.35,71 Summary of Hemostatic Agent/Dressing Safety Studies Hemostatic agents are viewed by the FDA as Class II medical devices and have received marketing clearance by proving that the new products are equivalent to similar agents already approved for external temporary use to control bleeding. The intent of FDA standard safety testing is to evaluate for an adverse effect of chemicals that may be eluted or extracted from a medical device. Consequently, these tests do not eval- uate any agent for biocompatibility and whether they are safe for applying over an external wound with access to the sys- temic circulation. These standard safety tests required by the FDA for medical devices appear to be inadequate for hemo- static agents that are particularly prothrombotic and/or gran- ular in nature.

Consequently, Kheirabadi et al suspected that granular agents such as WS (smectite) might cause thrombogenic activity in direct contact with injured vessels.16 These inves- tigators assessed the safety of CG and WS agents. Computed tomography angiography and direct observation showed that the majority of vessels treated with WS were occluded with large thrombi, whereas no abnormality was seen in SG- or CG-treated vessels.

WS granules and thrombus were also found in the lung of one subject. Histological examination revealed significant endothelial and transmural damages in the WS-treated ves- sels. The histological changes from gauze and CG treatment were similar and mild. These findings regarding WS were validated in another laboratory.72 To date no studies have reported using the same in vivo or in vitro safety evaluations as reported by Kheirabadi for any other first-, second-, or third-generation agents. The possible reason for a lack of studies using these methods could be as a result of the lack of an accepted consensus agreement among DoD and academic laboratories for standardized safety testing.

Preclinical studies have evaluated other safety assessment methods to those of Kheirabadi et al16,73,74 with hemostatic agents in both short-term (2-3 hours) use and 14-day use. Watters et al reported that when SG, CG, and CEG dressings were used in their femoral wound model, all agents had similar findings of mild intimal and medial edema in the histological examinations. No inflammation, necrosis, or deposition of dressing particles in vessel walls was observed. No histologic or ultrastructural differences were found between the study dressings.60 Floyd et al examined the safety of STF dressing as com- pared to CG in a femoral artery hemorrhage model.22 After treatment, they used fluoroscopy angiography to determine that 3 of 5 CG animals formed a thrombus within the wound. They noted further that the clots did not adhere to the femoral artery injury, whereas 4 STF-treated animals formed a clot in the wound that adhered and sealed the arterial injury site. This most likely explains why none of the STF-treated animals bled following the simulated walk- ing maneuver.

These post-treatment examinations help to partially explain the mechanism of action for these two agents. CG appeared to control hemorrhage by direct compression and occlusion of the injured vessel, either by the dressing itself, or in conjunction with a clot in the wound. None of the three clots found in ten animals adhered to the arterial injury but rather seemed to contribute to vessel compression. It was noted that the STF dressing controlled hemorrhage by for- mation of a clot that adhered to, and partially or completely sealed over, the arterial injury site. The sealant property allowed re-establishment of blood flow into the distal limb based on fluoroscopy. This was verified by direct observa- tion and palpation of the artery after dressing removal. Also, gross examination of femoral arteries demonstrated no distal thrombi.

Recently, Inaba et al examined long-term efficacy and safety of kaolin- and chitosan-based hemostatic agents for hemorrhage control in a 14-day survival, damage-control swine model of grade IV liver injury.73 Animals were ran- domized to four groups: CG, CE, CEG, or SG as the control. After long-term evaluations of efficacy and safety at 48 hours and 14 days, they noted that there was no histologic differ- ence between treatment groups in the depth of necrosis of the liver or small bowel in direct contact with the hemostatic agents. However, for both the CE and CEG groups, all ani- mals had macroscopic evidence of adhesions. These adhe- sions led to several deaths attributed to bowel obstruction. This was most pronounced in the animals treated with CE because the powdered agent became dispersed throughout the peritoneal cavity during the 14 days. No distal emboli were found with either CG or CEG, but 1 animal in the CE group had material in the coronary vessels. However, no embolic complications or negative outcomes occurred. A chitosan review article and wound management studies present an overview of safety studies indicating nontoxicity.29,75 Depending on the form, chitosan left in place may have slow absorption and lead to inflammation, but wound-healing stud- ies show it is biocompatible and safe.

After many years of clinical use the first study demon- strating the safety of a chitosan bandage in shellfish allergic subjects was conducted.76 Nine of ten (90%) subjects reported a shrimp allergy history and five (50%) reported multiple shellfish allergies. All participants completing the study had positive skin prick test and serum immunoglobulin E testing to at least one shellfish; eight (80%) had shrimp positive skin prick test and ten (100%) demonstrated shrimp- specific immunoglobulin E. All participants tolerated the HC bandage without reaction. No other studies using chitosan bandages in studies have reported any allergic response to agents.

In summary, no definitive safety testing similar to the Kheirabadi model has occurred on the more recently developed hemostatic agents. Although decades of use of chitosan in the clinical setting as well as multiple case reports of its use as a hemostatic agent exist, the evidence for the safety of chitosan dressings is encouraging but not conclusive.

CONCLUSION The outcome of all nine preclinical studies reveals that these new hemostatic dressings are at least as efficacious or superior to the current standard of care (CG) to control severe bleeding, particularly in the most important primary endpoint-survival. Observational prehospital and hospital case reports give evidence to support these preclinical find- ings. Although the safety of chitosan dressings is not defini- tively resolved, the cumulative experience from decades of chitosan science, and the past decade of DoD preclinical studies and clinical reports is promising. These newer dress- ings show improved efficacy, particularly CEG and HCG. These two chitosan-based products are ideal prehospital dressings because they work independently from the coagu- lation cascade and are currently FDA approved. The current widespread use of CEG and HCG within NATO militaries, and selected use within DoD and civilian EMS venues cer- tainly merits further consideration and open debate on the efficacy and safety of these agents. Although other third- generation agents (i.e., MSD and STF) also show great promise of effectiveness, it is essential to remain vigilant to the FDA approval and further validation of agent efficacy, mechanism of action, and safety.

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CAPT Brad L.Bennett, MSC USN (Ret.)*; CDR Lanny Littlejohn, MC USN[dagger] *Military and Emergency Medicine Department, F. Hébert School of Medicine, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814.

[dagger]Department of Emergency Medicine, Naval Medical Center Portsmouth, 620 John Paul Jones Circle, Portsmouth, VA 23708.

I am a military service member. This work was prepared as part of my official duties. Title 17 U.S.C. 105 provides that "Copyright protection under this title is not available for any work of the United States Government." Title 17 U.S.C. 101 defines a U.S. Government work as a work prepared by a military service member or employee of the U.S. Government as part of that person's official duties.

The views expressed in this article are those of the author(s) and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the U.S. Government.

doi: 10.7205/MILMED-D-13-00199 (c) 2014 Association of Military Surgeons of the United States

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