Autoresuscitation of Poloxamer 188 in Pigs With Traumatic Severe Hemorrhage

BACKGROUND

Poloxamer 188 (P188) is a copolymer surfactant with plasma membrane stabilizing action. This study investigated the effects of P188 on blood volume and coagulation in pigs after traumatic hemorrhage and hypotensive resuscitation.

METHODS

Femur fracture was performed in 17 anesthetized pigs, followed by hemorrhage of 55% of estimated blood volume and a 10 min shock period. Afterwards, pigs were randomized to be resuscitated with either normal saline (n = 9, 4 mL/kg, NS group) or P188 (n = 8, 1.33 mL/kg at 150 mg/mL, plus 2.67 mL NS/kg, P188 group). Pigs were monitored for 2 h or until death. Hemodynamics were recorded and blood samples were taken at baseline (BL), after hemorrhage, shock, resuscitation, and at 2 h for blood and coagulation analysis using Rotem®.

RESULTS

All but one pig in each group survived to 2 h. Femur fracture and hemorrhage reduced mean arterial pressure to half of the BL and elevated heart rate to double of the BL (both P < 0.05). Resuscitation with NS or P188 did not return these measurements to BL. Compared to NS, resuscitation with P188 resulted in a smaller reduction of blood volume (76 ± 3% in P188 and 60 ± 2% in NS); higher base excess (3.3 ± 0.9 vs. 0.5 ± 0.9 mM); and lower hematocrit (24 ± 1 vs. 28 ± 1%) and Ca++ (24 ± 1 vs. 28 ± 1 mM). Resuscitation with P188 prolonged aPTT (43 ± 12 vs. 22 ± 3 s, all P < 0.05).

CONCLUSIONS

Following traumatic hemorrhage and hypotensive resuscitation, P188 improved circulation volume and base deficit, but induced slower clotting initiation in pigs. Thus, P188 may have limited benefit as an initial small volume resuscitation adjunct following hemorrhage.

Evaluation of a novel hydrogel intravascular embolization agent in a swine model of fatal uncontrolled solid organ hemorrhage and coagulopathy

Introduction

Current agents for the intravascular embolization of traumatic hemorrhage are used off-label and have been minimally studied with respect to their performance under differing coagulation conditions. We studied the hemorrhage control efficacy of a novel, liquid, polyethylene glycol-based hydrogel delivered as two liquid precursors that polymerize within the target vessel in a unique animal model of severe solid organ injury with and without dilutional coagulopathy.

Methods

Anesthetized swine (n = 36, 45 ± 3 kg) had laparotomy and splenic externalization. Half underwent 50% isovolemic hemodilution with 6% hetastarch and cooling to 33°C-35°C (coagulopathic group). All animals had controlled 20 mL/kg hemorrhage and endovascular proximal splenic artery access with a 4F catheter via a right femoral sheath. Splenic transection and 5-minute free bleeding were followed by treatment (n = 5/group) with 5 mL of gelfoam slurry, three 6-mm coils, up to 6 mL of hydrogel, or no treatment (n = 3, control). Animals received 15 mL/kg plasma and were monitored for 6 hours with continuous blood loss measurement.

Results

Coagulopathy was successfully established, with coagulopathic animals having greater pretreatment blood loss and earlier mean time to death regardless of the treatment group. All control animals died within 100 minutes. Overall survival without coagulopathy was 5/5 for hydrogel, 4/5 for coil, and 3/5 for gelfoam. With coagulopathy, one hydrogel animal survived to the end of the experiment, with 2/4 hydrogel deaths occurring in the final hour of observation. In noncoagulopathic animals, hydrogel demonstrated improved survival time (P < .01) and post-treatment blood loss (1.46 ± 0.8 mL/kg) over controls (18.8 ± 0.7, P = .001), gelfoam (4.7 ± 1.3, P > .05), and coils (4.6 ± 1.5, P > .05). In coagulopathic animals, hydrogel had improved survival time (P = .003) and decreased blood loss (4.2 ± 0.8 mL/kg) compared with control (20.4 ± 4.2, P = .003).

Conclusions

The hydrogel demonstrated equivalent hemorrhage control performance to standard treatments under noncoagulopathic conditions and improved performance in the face of dilutional coagulopathy. This agent should be explored as a potential preferable treatment for the embolization of traumatic solid organ and other injuries. (JVS–Vascular Science 2021;2:43-51.)

Clinical Relevance

In a translational model of severe solid organ injury hemorrhage with and without coagulopathy, a novel hydrogel transarterial embolization agent demonstrated equivalent hemorrhage control performance to standard agents under noncoagulopathic conditions and improved performance in the face of dilutional coagulopathy. This agent represents a promising future treatment for the embolization of traumatic solid organ and other injuries.

Muscle deteriorations become prominent within 24 hours after admission in severely burned adults

BACKGROUND

Severe burn injury results in profound catabolic deterioration. Although burn-related catabolism has been well stated, it is unclear when the catabolic response begins. This study characterized acute changes of muscle protein breakdown at the admission and the day after in severely burned adults.

METHODS

Twelve patients (43 ± 19 years old) with 40% ± 21% total body surface area burns were prospectively enrolled into an observational study approved by institutional review board. Urinary samples were collected on admission day and the day after (day 1). Patient demographic and clinical data of vital signs, blood gas and chemistry, and coagulation status were collected. Catabolic changes of muscle breakdown were quantified by urinary excretion of 3-methylhisitidine, determined by gas chromatography and mass spectrometry analysis.

RESULTS

Compared with admission day, burned patients had elevated mean ± SD arterial pressure (from 90 ± 5 mm Hg to 108 ± 7 mm Hg) and heart rate (from 102 ± 7 beats per minute to 119 ± 4 beats per minute both p < 0.05) after 24 hours. Their 24-hour urinary output was 1,586 ± 813 mL at admission day to 1,911 ± 1,048 mL on day 1. The 24-hour urea excretion was elevated from 172 ± 101 mg/kg per day at admission day to 302 ± 183 mg/kg per day on day 1 (both p < 0.05), with no change in creatinine excretion. Urinary 3-methylhisitidine excretion increased from 0.75 ± 0.74 mg/kg per day at admission to 1.14 ± 0.86 mg/kg per day on day 1 (p < 0.05). The estimated skeletal muscle protein breakdown was increased from 1.1 ± 1.0 g/kg per day at admission day to 1.6 ± 1.2 g/kg per day on day 1 (p < 0.05). There were no changes in prothrombin time, activated partial thromboplastin time, or platelets.

CONCLUSION

In severely burned patients, catabolic muscle protein breakdown is elevated within 24 hours after admission and before changes in coagulation. These findings suggest that early interventions may be needed to effectively attenuate the catabolic responses in burn patients.

LEVEL OF EVIDENCE

Prospective and observational study, level II.

Role of albumin on endothelial basement membrane and hemostasis in a rat model of hemorrhagic shock

BACKGROUND

We sought to determine the extent of loss of endothelial basement membrane (BM), leukocyte recruitment, and changes in coagulation after hemorrhagic shock, followed by limited-volume resuscitation (LVR) with 5% albumin (ALB).

METHODS

Anesthetized rats were bled 40% of blood volume and assigned to treatment groups: untreated (n = 6), LVR with normal saline (NS; n = 8), or LVR with ALB (n = 8). Sham rats (n = 6) underwent all procedures except hemorrhage or resuscitation. Blood samples were assayed for active proteases, such as metalloproteinase 9 (MMP-9) and a disintegrin and metalloproteinase 10 (ADAM-10), BM-type heparan sulfate proteoglycan (perlecan), cell count, and coagulation function. Leukocyte transmigration was used to estimate the net efficiency of leukocyte recruitment in cremaster venules.

RESULTS

Hemorrhage significantly lowered red cell count, but white cell and platelet counts did not change (vs. sham). Ionized calcium in plasma was significantly reduced in untreated and remained so after NS. In contrast, ionized calcium was normalized after ALB. Plasma expansion after NS and ALB further reduced leukocyte and platelet counts. Metalloproteinase 9, ADAM-10, and perlecan were significantly higher in untreated rats (vs. sham). Albumin normalized MMP-9, ADAM-10, and perlecan levels, while NS further increased MMP-9, ADAM-10, and perlecan (vs. sham). Transmigrated leukocytes doubled in the untreated group and remained elevated after NS (vs. sham) but normalized after ALB. Albumin reduced every stage of the leukocyte recruitment process to sham levels.

CONCLUSION

Despite similar plasma expansion, NS weakened platelet function contrary to ALB. Plasma expansion with ALB resulted in restoration of BM integrity and attenuation of leukocyte recruitment to tissues, in contrast to NS. Albumin plays a critical role in restoring BM integrity, attenuating leukocyte recruitment to tissues, and optimizing hemostasis by increasing ionized calcium in plasma.

Minimal Effects of Intravenous Administration of Xenogeneic Adipose Derived Stem Cells on Organ Function in a Porcine 40%TBSA Burn Model

Adipose stem cells (ASCs) have shown therapeutic promise for various conditions, including burn injury. While ASCs have immunomodulatory properties, concerns exist over pro-coagulant activity after intravenous (IV) administration. In the present study, we examined IV human ASC delivery in terms of coagulation, organ function, and inflammation in a 40% total body surface area (TBSA) swine burn model. Anesthetized female Yorkshire swine were burned and randomized to receive 15ml/kg Lactated Ringer's containing: no ASCs; a low dose (5x10 5 ASCs/kg), or a high dose (5x10 6 ASCs/kg). For biochemical analysis, blood was collected at baseline (BL), 3, 6, 12, and 24 hours post-burn, while kidney and liver tissue was collected post-euthanasia. A significant, but transient, effect of ASCs was seen on prothrombin times and INR, wherein low doses revealed slight hypercoagulation. Burns increased partial thromboplastin time, fibrinogen, and d-dimer levels, which was unchanged with ASC administration. ASCs tended to exacerbate increases in bilirubin at 3 hours, but this didn't reach statistical significance. A significant effect of ASCs on creatinine and BUN was seen, wherein low doses elevated levels at 24 hours (creatinine, p=0.0012; BUN, p=0.0195). Hepatic and renal TUNEL staining were similar for all groups. A dose-dependent decrease in IL-8 was observed, while low doses significantly increased IL-1RA at 3 (p=0.050), IL-12 at 12 (p=0.021) and IL-6 at 24 hours post-burn (p=0.035). IV administration of xenogeneic ASCs slightly increased coagulation, but effects on burn-induced renal and hepatic dysfunction effects were minimal. Despite some significant immunomodulation, organ dysfunction effects were modest. Collectively, this study provides evidence to be skeptical about xenogeneic ASC administration in regards to burn.

Lessons Learned From the Battlefield and Applicability to Veterinary Medicine-Part 1: Hemorrhage Control

In humans, the leading cause of potentially preventable death on the modern battlefield is undoubtedly exsanguination from massive hemorrhage. The US military and allied nations have devoted enormous effort to combat hemorrhagic shock and massive hemorrhage. This has yielded numerous advances designed to stop bleeding and save lives. The development of extremity, junctional and truncal tourniquets applied by first responders have saved countless lives both on the battlefield and in civilian settings. Additional devices such as resuscitative endovascular balloon occlusion of the aorta (REBOA) and intraperitoneal hemostatic foams show great promise to address control the most difficult forms (non-compressible) of hemorrhage. The development of next generation hemostatic dressings has reduced bleeding both in the prehospital setting as well as in the operating room. Furthermore, the research and fielding of antifibrinolytics such as tranexamic acid have shown incredible promise to ameliorate the effects of acute traumatic coagulopathy which has led to significant morbidity and mortality in service members. Advances from lessons learned on the battlefield have numerous potential parallels in veterinary medicine and these lessons are ripe for translation to veterinary medicine.

Exploring Tourniquet Conversion in Simulation to Develop Concepts and Hypotheses

BACKGROUND

Compared with those of tourniquet application, tourniquet conversion concepts are underdeveloped. The purpose of this project was to develop tourniquet conversion concepts and generate hypotheses.

METHODS

One person performed 100 tests of tourniquet application and conversion. Testing varied by conversion types, materials, and assessments. Conversions were from improvised or Combat Application Tourniquets (C-A-T) to another C-A-T, a new site (with initial C-A-T only), a pneumatic Emergency and Military Tourniquet (EMT), or a pressure dressing (compression bandage or a roll gauze and an elastic wrap). Simulated limbs were created using plastic bottle-based manikins, pool noodle-based manikins, plastic pipes, glass bottles, a rain downspout, and a cardboard poster tube.

RESULTS

Tourniquet application, conversion, and total times averaged 105, 132, and 237 seconds, respectively. Improvised tourniquet time was longer than that of C-A-T (p ≤ .05, all three). By initial tourniquet site, the 2-3 inches site had longer conversion and total time (p ≤ .02, both) compared with highest site. By whether initial tourniquets placed were also used in conversion, total time was shorter if yes (p = .05). Conversion to a pressure dressing was longer in conversion and total time (p ≤ .02, both) compared with conversion to a tourniquet. One wrap was short; we switched to those longer to cover limbs better. Limb types varied for indentation. Conversion communications improved when we used abbreviations and symbols.

CONCLUSIONS

This preliminary project simulated tourniquet conversion to develop clinical concepts and research hypotheses to build a better basis for later research.

Distal organ inflammation and injury after resuscitative endovascular balloon occlusion of the aorta in a porcine model of severe hemorrhagic shock

BACKGROUND AND OBJECTIVE

Resuscitative Endovascular Balloon Occlusion of Aorta (REBOA) has emerged as a potential life-saving maneuver for the management of non-compressible torso hemorrhage in trauma patients. Complete REBOA (cREBOA) is inherently associated with the burden of ischemia reperfusion injury (IRI) and organ dysfunction. However, the distal organ inflammation and its association with organ injury have been little investigated. This study was conducted to assess these adverse effects of cREBOA following massive hemorrhage in swine.

METHODS

Spontaneously breathing and consciously sedated Sinclair pigs were subjected to exponential hemorrhage of 65% total blood volume over 60 minutes. Animals were randomized into 3 groups (n = 7): (1) Positive control (PC) received immediate transfusion of shed blood after hemorrhage, (2) 30min-cREBOA (A30) received Zone 1 cREBOA for 30 minutes, and (3) 60min-cREBOA (A60) given Zone 1 cREBOA for 60 minutes. The A30 and A60 groups were followed by resuscitation with shed blood post-cREBOA and observed for 4h. Metabolic and hemodynamic effects, coagulation parameters, inflammatory and end organ consequences were monitored and assessed.

RESULTS

Compared with 30min-cREBOA, 60min-cREBOA resulted in (1) increased IL-6, TNF-α, and IL-1β in distal organs (kidney, jejunum, and liver) (p < 0.05) and decreased reduced glutathione in kidney and liver (p < 0.05), (2) leukopenia, neutropenia, and coagulopathy (p < 0.05), (3) blood pressure decline (p < 0.05), (4) metabolic acidosis and hyperkalemia (p < 0.05), and (5) histological injury of kidney and jejunum (p < 0.05) as well as higher levels of creatinine, AST, and ALT (p < 0.05).

CONCLUSION

30min-cREBOA seems to be a feasible and effective adjunct in supporting central perfusion during severe hemorrhage. However, prolonged cREBOA (60min) adverse effects such as distal organ inflammation and injury must be taken into serious consideration.

Development and Validation of a Predictive Model for Hemodynamic Responses to Resuscitation during Uncontrolled Hemorrhage

We investigated whether a statistical model could predict mean arterial pressure (MAP) during uncontrolled hemorrhage; such a model could be used for automated decision support, to help clinicians decide when to provide intravascular volume to achieve MAP goals. This was a secondary analysis of adult swine subjects during uncontrolled splenic bleeding. By protocol, after developing severe hypotension (MAP < 60 mmHg), subjects were resuscitated with either saline (NS) or fresh frozen plasma (FFP), determined randomly. Vital signs were documented at quasi-regular time-step intervals, until either subject death or 300 min. Subjects were randomly separated 50%/50% into training/validation sets, and regression models were developed to predict MAP for each subsequent (i.e., future) time-step. Median time-steps for serially recorded vital signs were +15 min. 5 subjects survived the protocol; 17 died after a median time of 87 min (IQR 78 - 134). The final model consisted of: current MAP; heart rate (HR); prior NS; imminent NS; and imminent FFP. The 95% limits-of-agreement between true subsequent MAP vs. predicted subsequent MAP were +10/-11 mmHg for the 79 time-steps in the training set; and +14/-13 for the 64 time-steps in the validation set. A total of 10 sudden death events (i.e., rapid, fatal MAP decrease within one single time-step) were excluded from analysis. In conclusion, for uncontrolled hemorrhage in a swine model, it was possible to estimate the next documented MAP value on the basis of the subject's current documented MAP; HR; prior NS; and the volume of resuscitation about to be administered. However, the model was unable to predict "sudden death" events. The applicability to populations with wider heterogeneity of hemorrhage patterns and with comorbidities requires further investigation.

Albumin Saturated With Fatty Acids Prevents Decompensation in a Rat Hemorrhagic Shock Trauma Model With Tourniquet and Hypotensive Resuscitation

ABSTRACT

Decompensation is a major prehospital threat to survival from trauma/hemorrhage shock (T/HS) after controlling bleeding. We recently showed higher than expected mortality from a combat-relevant rat model of T/HS (27 mL/kg hemorrhage) with tourniquet (TQ) and permissive hypotensive resuscitation (PHR) with Plasmalyte. Mortality and fluid requirements were reduced by resuscitation with 25% albumin presaturated with oleic acid (OA-sat) compared with fatty-acid -free albumin or Plasmalyte. The objective of this follow-up analysis was to determine the role of decompensation and individual compensatory mechanisms in those outcomes. We observed two forms of decompensation: slow (accelerating fluid volumes needed to maintain blood pressure) and acute (continuous fluid administration unable to prevent pressure drop). Combined incidence of decompensation was 71%. Nearly all deaths (21 of 22) were caused by acute decompensations that began as slow decompensations. The best hemodynamic measure for predicting acute decompensation was diastolic arterial pressure. Decompensation was due to vascular decompensation rather than loss of cardiac performance. Albumin concentration was lower in decompensating groups, suggesting decreased stressed volume, which may explain the association of low albumin on admission with poor outcomes after trauma. Our findings suggest that acute decompensation may be common after trauma and severe hemorrhage treated with TQ and PHR and OA-sat albumin may benefit early survival and reduce transfusion volume by improving venous constriction and preventing decompensation.

Should Albumin be Considered for Prehospital Resuscitation in Austere Environments? A Prospective Randomized Survival Study in Rabbits

BACKGROUND

The new guidelines for prehospital care of combat casualties in shock recommend administration of whole blood or blood components to increase blood pressure to a permissible hypotensive level (i.e., hypotensive resuscitation [HR]). We investigated if 2 h of HR using limited volumes of whole blood, plasma, or albumin would lead to full recovery and long-term survival of rabbits subjected to severe hemorrhagic shock (HS).

METHODS

Following instrumentation, laparotomy was performed on IV-anesthetized spontaneously breathing New Zealand white rabbits (3.0 kg -3.5 kg). Next, ∼40% of rabbits' blood volume was removed producing HS (mean arterial pressure [MAP]∼20 mm Hg). Fifteen minutes later, rabbits were resuscitated with a limited volume (12.5 mL/kg) of rabbit whole blood (fresh whole blood [FWB]), rabbit fresh frozen plasma (FFP), or 5% human albumin (ALB) to a target pressure (MAP) of 60 mm Hg (n=8/grp) and monitored for 2 h. Liver bleeding time was measured at baseline and 10 min after HR. Subsequently, animals were fully resuscitated (blood + lactated Ringer [LR]), surgically repaired, and recovered for 8 days. An untreated group (n = 6) was also included.

RESULTS

Following HS, lactate and base deficit levels were increased to 8.2 ± 1.6 and 12.9 ± 3.1 mM respectively with no difference among groups. A lower volume of FWB volume was required to reach the target MAP (P < 0.05 vs. ALB) but MAP declined during the HR period (P < 0.01 vs. ALB). FWB provided higher hematocrit and platelets but it did not reduce lactate level faster than other fluids. Beside higher fibrinogen, no differences were found in hemostatic or resuscitative effects of FFP versus ALB. Bleeding time was prolonged with ALB and FFP fluids but unchanged with FWB. Untreated rabbits died during shock or shortly after. All treated rabbits except one recovered and lived for 8 days with normal blood tests and similar tissue histology.

CONCLUSIONS

Two hours of HR using a limited volume of FWB, FFP, or ALB led to full recovery and long-term survival of rabbits subjected to HS. Apart from bleeding time, no clinically significant differences were found among the three fluids. Five percent human albumin solutions are isotonic, iso-oncotic, ready-to-use, stable, and compatible with all blood types and should be considered for prehospital resuscitation where blood products are not available or not accepted.

Effect of Intravenous Fluid Volumes on the Adrenal Glucocorticoid Response After Burn Injury in Swine

Severe thermal injury induces metabolic and physiological stress, prompting a disruption in the hypothalamic-pituitary-adrenal axis. The objective of this study was to evaluate potential confounding effects of Lactated Ringer's (LR) resuscitation on adrenal damage and cortisol production following burn. Anesthetized swine were instrumented with jugular catheters and sustained 40% TBSA burns from brass probes heated to 100°C. Animals recovered to consciousness and received IV fluid resuscitation with LR at two different volumes: 15 ml/kg/d (limited volume [LV], n = 6) or 2 ml/kg/%TBSA/d (modified Brooke [MB], n = 6). Nonburned animals (Sham) were both oral and IV fluid restricted (S-FR, n = 4) to induce stress. Computed tomography (CT) angiographies were performed at baseline (BL) and 48 hours postburn, while blood and urine samples were collected at BL, 6, 24, and 48 hours postburn, with euthanasia at 48 hours for adrenal harvesting. Urinary cortisol was elevated following burn/surgery in all animals and returned back to BL in S-FR (404 ± 48 pg/mg creatinine) but not MB (1332 ± 176 pg/mg creatinine; P = .005) or LV (1223 ± 335 pg/mg creatinine; P = .07) by 48 hours. Gene expression of cleavage enzymes (3β-HSD, CYP17, CYP11, and CYP21) along the cortisol synthesis pathway showed minimal changes. Adrenal apoptosis (Terminal deoxynucleotidyl transferase dUTP nick-end labeling [TUNEL] staining) was greatest in the MB group (P ≤ .01) when compared to S-FR, partly due to elevations in c-Jun N-terminal kinase. Adrenal hemorrhaging was also greatest in MB animals, with no differences in tissue volume or wet-to-dry ratio. However, tissue levels of cytokines IL-1β, IL-10, and IL-12 were greatest in LV. Burn injury elevates urinary cortisol and compromises adrenal gland integrity, which is affected by IV fluid volume.

Hypercoagulation and Hypermetabolism of Fibrinogen in Severely Burned Adults

This study investigated changes in plasma fibrinogen metabolism and changes in coagulation in severely burned adults. Ten patients (27 ± 3 years; 91 ± 6 kg) with 51 ± 3% TBSA were consented and enrolled into an institutional review board-approved prospective study. On the study day, stable isotope infusion of 1-13C-phenylalanine and d5-phenylalanine was performed to quantify fibrinogen production and consumption. During the infusion, vital signs were recorded and blood samples were drawn every hour. Coagulation was measured by thromboelastograph (TEG). Ten normal healthy volunteers (37 ± 7 years; 74 ± 4 kg) were included as the control group. Burned adults had elevated heart rates (120 ± 2 vs 73 ± 5 [control] beats/minute), respiration rates (23 ± 2 vs 15 ± 1 breaths/minute), plasma glucose (127 ± 10 vs 89 ± 2 mg/dl), and fibrinogen levels (613 ± 35 vs 239 ± 17 mg/dl); and decreased albumin (1.3 ± 0.2 vs 3.7 ± 0.1 g/dl) and total protein (4.4 ± 0.2 vs 6.8 ± 0.1 g/dl, all P < .05). Fibrinogen breakdown was elevated in the burn group (2.3 ± 0.4 vs. 1.0 ± 0.3 µmol/kg/minute); and fibrinogen synthesis was further enhanced in the burn group (4.4 ± 0.7 vs 0.7 ± 0.2 µmol/kg/minute, both P < .05). Clotting speed (TEG-alpha) and clot strength (TEG-MA) were increased in the burn group (62 ± 4 vs 50 ± 4°, and 76 ± 2 vs 56 ± 2 mm, respectively, both P < .05). Fibrinolysis of TEG-LY60 was accelerated in the burn group (16 ± 6 vs 3 ± 1) and so was the increase in D-dimer level in the burn group (4.5 ± 0.4 vs 1.9 ± 0.3 mg/l, both P < .05). The hypercoagulable state postburn is in part a result of increased fibrinogen synthesis, over and above increased fibrinogen breakdown.

Increased oxidative phosphorylation in lymphocytes does not atone for decreased cell numbers after burn injury

The acute systemic inflammatory response syndrome (SIRS) and multiorgan dysfunction (MOD) that occur in large burn injuries may be attributed, in part, to immunosuppressive responses such as decreased lymphocytes. However, the mitochondrial bioenergetics of lymphocytes after severe burn injury are poorly understood. The purpose of this study was to examine mitochondrial function of lymphocytes following severe burns in a swine model. Anesthetized Yorkshire swine (n = 17) sustained 40% total body surface area full-thickness contact burns. Blood was collected at pre-injury (Baseline; BL) and at 24 and 48 h after injury for complete blood cell analysis, flow cytometry, cytokine analysis, and ficoll separation of intact lymphocytes for high-resolution mitochondrial respirometry analysis. While neutrophil numbers increased, a concomitant decrease was found in lymphocytes (P < 0.001) after burn injury, which was not specific to CD4⁺ or CD8⁺ lymphocytes. No changes in immune cell population were observed from 24 h to 48 h post-injury. IL 12-23 decreased while a transient increase in IL 4 was found from BL to 24h (P < 0.05). CRP progressively increased from BL to 24h (P < 0.05) and 48h (P < 0.001) post-injury. Routine and maximal mitochondrial respiration progressively increased from BL to 24h (P < 0.05) and 48 h post-injury (P < 0.001). No changes were found in leak respiration or residual oxygen consumption. When considering the reduction in lymphocyte number, the total peripheral lymphocyte bioenergetics per volume of blood significantly decreased from BL to 24h and 48h (P < 0.05). For the first time, we were able to measure mitochondrial activity in intact lymphocyte mitochondria through high-resolution respirometry in a severely burned swine model. Our data showed that the non-specific reduction in peripheral T cells after injury was larger than the increased mitochondrial activity in those cells, which may be a compensatory mechanism for the total reduction in lymphocytes. Additional studies in the metabolic activation of T cell subpopulations may provide diagnostic or therapeutic targets after severe burn injury.

Effects of Donning and Wearing Personal Protective Equipment on Tourniquet Use and Conversion

BACKGROUND

We sought to gather data about the effects of personal protective equipment (PPE) use on tourniquet interventions by preliminarily developing a way to simulate delay effects, particularly on time and blood loss. Such knowledge might aid readiness. Field calls to emergency departments may indicate donning of PPE before patient arrival. The purpose of this study was to investigate (1) delay effects of donning the PPE studied on field-tourniquet control of hemorrhage and (2) delay effects of wearing the PPE on application of a field tourniquet and its conversion to a pneumatic tourniquet.

METHODS

The experiment simulated 30 tests of nonpneumatic field tourniquet use (http://www.combattourniquet.com/wp -content). The research intervention was the use of PPE. Data were grouped. The control group had no PPE (PPE0). PPE1 and PPE2 groups had mostly improvised and off-the-shelf equipment, respectively. PPE1 included donning a coat, goggles, face covering, cap, booties, and gloves. PPE2 had analogous items. The group order was randomized. A test included paired trials: field tourniquet, followed by conversion. An investigator simulated the caregiver. A task trainer simulated a thigh amputation. Donning delays were evaluated as differences in mean times to stop bleeding compared with PPE0. Blood loss results from donning PPE were calculated as the delay multiplied by its bleeding rate, 500mL/min.

RESULTS

PPE0 had no delay: its mean blood loss was 392mL. PPE1 had 805mL more blood loss than PPE0 did. PPE2 exceeded PPE0 by 1004mL. Donning time (blood loss) for PPE1 and PPE2 were 1.4 minutes (712mL) and 1.7 minutes (863mL), respectively. The wearing of PPE did not slow down field tourniquet application or its conversion.

CONCLUSIONS

How long it took to don PPE delayed the time to stop bleeding and increased blood loss, but wearing PPE slowed down neither field tourniquet application nor its conversion.

Conversion: Simulated Method of Exchanging Tourniquet Use for Pressure Dressing Use

BACKGROUND

Given little data to assess guidelines, we sought a way to exchange one type of intervention, field tourniquet use, for another, use of a pressure dressing. The study purpose was to test performance of controlling simulated bleeding with a stepwise procedure of tourniquet conversion.

METHODS

An experiment was designed to assess 15 tests of a caregiver making tourniquet-dressing conversions. Tests were divided into trials: tourniquet use and its conversion. In laboratory conditions, the tourniquet trial was care under gunfire; then, the conversion trial was emergency healthcare. A HapMed Leg Tourniquet Trainer simulated a limb amputation. An investigator provided healthcare.

RESULTS

Mean (± standard deviation [SD]) test time and blood loss were 9 ± 3.6 minutes and 334 ± 353.9mL, respectively. The first test took 17 minutes. By test number, times decreased; the last six took ≤7 minutes. All tourniquet trials controlled bleeding. Mean (±SD) tourniquet pressure and blood loss were 222 ± 18.0mmHg and 146 ± 40.9mL, respectively. Bleeding remained uncontrolled in one conversion. Initial attempts to wrap a dressing were effective in 73% of tries (n = 11 of 15). Four of 15 wrap attempts (27%) were repeated to troubleshoot bleeding recurrence, and the first three tests required a repetition. Mean (±SD) dressing pressures and blood losses were 141 ± 17.6mmHg and 188 ± 327.4mL, respectively. Unsatisfactory conversion trials had a dressing pressure <137mmHg. Dressings and wraps hid the wound to impair assessment of bleeding.

CONCLUSIONS

In testing a method of converting a limb tourniquet to a pressure dressing, the caregiver performed faster with experience accrual. The tourniquet results were uniformly good, but conversion results were worse and more varied. Simulating conversion was disappointing on a manikin and indicated that its redesign might be needed to suit this method. The procedural method constituted a start for further development.

Step Duration Effects on Blood Loss in Simulated Designs of Tourniquet Use Procedure

BACKGROUND

We sought new knowledge by further developing a model of using calculations in the simulation of a first-aid task. The purpose of this study was to develop the model to investigate the performance of tourniquet use in its component steps.

METHODS

We aimed to design an experiment on a desktop computer by mathematically manipulating simulated data in tourniquet use. A time factor of tourniquet use was ranged widely through time challenges in five degrees from ideal to worst performances. Redesigning the task was assessed by time costs and blood losses.

RESULTS

The step of tourniquet application took 17% of the trial time and securing the tourniquet after bleeding control took the longest amount of the trial time, 31%. A minority of the time (48% [17% + 31%] to apply tourniquet plus secure it) was spent after the tourniquet touched the patient, whereas most of the time (52%) was spent before the tourniquet touched the patient. The step of tourniquet application lost 14% of the total blood lost, whereas no blood was lost during securing the tourniquet, because that was the moment of bleeding control despite securing the tourniquet taking much time (31%). Most (86%) of blood lost occurred before the tourniquet touched the patient. But blood losses differed 10-fold, with a maximum of 2,434mL, which, when added to a pretask indication blood loss of 177mL, summed to 2,611mL. Before redesigning the task, costs of donning gloves and calling 9-1-1 included uncontrolled bleeding, but gloving mitigated risk of spreading pathogens among people. By step and person, redesigns of the task altered the risk-benefit profile.

CONCLUSIONS

The model was useful because it simulated where most of the bleeding occurred before the tourniquet touched the patient. Modeling simulated redesigns of the task, which showed changes in the task's risk-benefit profile by step and among persons. The model generated hypotheses for future research, including the capability to screen candidate ideas among task designs.

Differing Resuscitation With Aortic Occlusion in a Swine Junctional Hemorrhage Polytrauma Model

BACKGROUND

Resuscitative endovascular balloon occlusion of the aorta (REBOA) and Abdominal Aortic and Junctional Tourniquet (AAJT) have received much attention in recent as methods for temporary control of junctional hemorrhage. Previous studies typically used the animal's shed blood for resuscitation. With current interest in moving REBOA to prehospital environment, this study aimed to evaluate the hemodynamic and metabolic responses to different resuscitation fluids used with these devices.

METHODS

In swine (Sus scrofa), shock was induced using a controlled hemorrhage, femur fracture, and uncontrolled hemorrhage from the femoral artery. Infrarenal REBOA or AAJT was deployed for 60 min during which the arterial injury was repaired. Animals were resuscitated with 15 mL/kg of shed whole blood (SWB) or fresh frozen plasma (FFP) or 30 mL/kg of a balanced crystalloid (PlasmaLyte).

RESULTS

Animals in the AAJT and REBOA groups did not show any measurable differences in hemodynamics, metabolic responses, or survival with AAJT or REBOA treatment; hence, the data are pooled and analyzed among the three resuscitative fluids. SWB, FFP, and PlasmaLyte groups did not have a difference in survival time or overall survival. The animals in the SWB and FFP groups maintained higher blood pressure after resuscitation, (P < 0.001) and required significantly less norepinephrine to maintain blood pressure than those in the PlasmaLyte group (P < 0.001). The PlasmaLyte resuscitation prolonged prothrombin time and decreased thromboelastography maximum amplitude.

CONCLUSIONS

After 60 min, infrarenal REBOA or AAJT aortic occlusion SWB and FFP resuscitation provided better blood pressure support with half of the resuscitative volume of PlasmaLyte. Swine resuscitated with SWB and FFP also had a more favorable coagulation profile. These data suggest that whole blood or component therapy should be used for resuscitation in conjunction with REBOA or AAJT, and administration of these fluids should be considered if prehospital device use is pursued.

Impact of oral resuscitation on circulating and splenic leukocytes after burns

BACKGROUND

Hemodynamic aberrations after severe burns are treated with aggressive intravenous (IV) fluid resuscitation however, oral resuscitation has been proposed in resource poor scenarios. Previously we have shown that animals receiving oral fluid following burns were able to recover kidney function. However, immune function such as circulating and splenic immune cell populations after oral or intravenous fluid administration was not examined. Herein, we perform a follow up analysis of splenic tissue and plasma from the previous animal study to examine the splenic response following these resuscitation strategies after burn injury.

METHODS

Eighteen anesthetized Yorkshire swine receiving 40%TBSA contact burns were randomized to receive either: (1) no fluids (Fluid Restricted; negative control), (2) 70 mL/kg/d Oral Rehydration Salt solution (Oral), or (3) 2 mL/kg/%TBSA/d of lactated Ringer's solution IV. Blood was drawn for blood cell analysis, and CT scans were performed before and 48 h post-burn, at which point spleens were harvested for histological, Western blot, and RT-PCR analyses.

RESULTS

Splenic artery diameter decreased by -0.97 ± 0.14 mm in fluid-restricted animals, while IV led to an increase of 0.68 ± 0.30 mm. No significant differences were detected in white and red pulp. IV fluids reduced the population of splenic monocytes (CD163; P = 0.001) and neutrophils (MPO protein; P = 0.13), as well as cytokines IL-8 (P = 0.003), IFN-γ (P = 0.11) and TNFα (P = 0.05). Additionally, withholding IV fluids consistently decreased the expression of FoxP3, CCR6, and IL17β in spleen, suggesting a shift in T-cell phenotype with IV resuscitation.

CONCLUSIONS

The route of fluid administration has a minor influence on the changes in circulating and splenic leukocytes post-burn in the acute phase. Further research is needed to help guide resuscitation approaches using immunologic markers of splenic function following burns.

Cremaster muscle perfusion, oxygenation, and heterogeneity revealed by a new automated acquisition system in a rodent model of prolonged hemorrhagic shock

Local blood flow/oxygen partial pressure (Po₂) distributions and flow-Po₂ relationships are physiologically relevant. They affect the pathophysiology and treatment of conditions like hemorrhagic shock (HS), but direct noninvasive measures of flow, Po₂, and their heterogeneity during prolonged HS are infrequently presented. To fill this void, we report the first quantitative evaluation of flow-Po₂ relationships and heterogeneities in normovolemia and during several hours of HS using noninvasive, unbiased, automated acquisition. Anesthetized rats were subjected to tracheostomy, arterial/venous catheterizations, cremaster muscle exteriorization, hemorrhage (40% total blood volume), and laparotomy. Control animals equally instrumented were not subjected to hemorrhage/laparotomy. Every 0.5 h for 4.5 h, noninvasive laser speckle contrast imaging and phosphorescence quenching were employed for nearly 7,000 flow/Po₂ measurements in muscles from eight animals, using an automated system. Precise alignment of 16 muscle areas allowed overlapping between flow and oxygenation measurements to evaluate spatial heterogeneity, and repeated measurements were used to estimate temporal heterogeneity. Systemic physiological parameters and blood chemistry were simultaneously assessed by blood samplings replaced with crystalloids. Hemodilution was associated with local hypoxia, but increased flow prevented major oxygen delivery decline. Adding laparotomy and prolonged HS resulted in hypoxia, ischemia, decreased tissue oxygen delivery, and logarithmic flow/Po₂ relationships in most regions. Flow and Po₂ spatial heterogeneities were higher than their respective temporal heterogeneities, although this did not change significantly over the studied period. This quantitative framework establishes a basis for evaluating therapies aimed at restoring muscle homeostasis, positively impacting outcomes of civilian and military trauma/HS victims.NEW & NOTEWORTHY This is the first study on flow-Po₂ relationships during normovolemia, hemodilution, and prolonged hemorrhagic shock using noninvasive methods in multiple skeletal muscle areas of monitored animals. Automated flow/Po₂ measurements revealed temporal/spatial heterogeneities, hypoxia, ischemia, and decreased tissue oxygen delivery after trauma/severe hemorrhage. Hemodilution was associated with local hypoxia, but hyperemia prevented a major decline in oxygen delivery. This framework provides a quantitative basis for testing therapeutics that positively impacts muscle homeostasis and outcomes of trauma/hemorrhagic shock victims.

Burn-induced reductions in mitochondrial abundance and efficiency are more pronounced with small volumes of colloids in swine

Severe burn injury results in systemic disruption of metabolic regulations and impaired cardiac function. Restoration of hemodynamic homeostasis utilizing intravenous (IV) fluids is critical for acute care of the burn victim. However, the effects of burns and resuscitation on cardiomyocyte mitochondria are currently unknown. The purpose of this study is to determine cardiac mitochondrial function in a swine burn model with subsequent resuscitation using either crystalloids or colloids. Anesthetized Yorkshire swine (n = 23) sustained 40% total body surface area burns and received IV crystalloids (n = 11) or colloids (n = 12) after recovery from anesthesia. Non-burned swine served as controls (n = 9). After euthanasia at 48 h, heart tissues were harvested, permeabilized, and analyzed by high-resolution respirometry. Citrate synthase (CS) activity was measured, and Western blots were performed to quantify proteins associated with mitochondrial fusion (OPA1), fission (FIS1), and mitophagy (PINK1). There were no differences in state 2 respiration or maximal oxidative phosphorylation. Coupled complex 1 respiration decreased, while uncoupled state 4_O and complex II increased significantly due to burn injury, particularly in animals receiving colloids (P < 0.05). CS activity and electron transfer coupling efficiency were significantly lower in burned animals, particularly with colloid treatment (P < 0.05). Protein analysis revealed increased FIS1 but no differences in mitophagy in cardiac tissue from colloid-treated compared with crystalloid-treated swine. Taken together, severe burns alter mitochondrial respiration in heart tissue, which may be exacerbated by early IV resuscitation with colloids. Early IV burn resuscitation with colloids may require close hemodynamic observation. Mitochondrial stabilizing agents incorporated into resuscitation fluids may help the hemodynamic response to burn injury.

Automated noninvasive evaluation of blood flow and oxygenation in rats integrated with systemic physiological monitoring

BACKGROUND

Many studies evaluating blood flow and oxygen partial pressure (PO2) do not directly measure both parameters, are confined to few locations/microvessels, and depend on investigator's selection of measuring sites. Moreover, clinically/physiologically relevant systemic parameters are not simultaneously recorded. We implemented an automated system for prolonged blood flow/PO2 acquisition in large areas while collecting relevant systemic information.

METHODS

In anesthetized animals, cardiorespiratory parameters were continuously recorded. Other data were collected at baseline and hourly after 4 hours of hemorrhagic shock. A cremaster muscle was spread over a pedestal fixed to a motorized stage. One 2-dimensional tissue scan allowed 16 noninvasive PO2 measurements using oxygen-dependent phosphorescence quenching and fiber optics. Blood flow was estimated using laser speckle contrast imaging in the same areas used for PO2 measurements. At each timepoint, blood was sampled for extensive biochemistry/coagulation profile.

RESULTS

The system was used successfully by different operators. A set of flow/PO2 measurements was completed in less than 90 seconds. Muscle flow and PO2 correlated with some but not several systemic parameters, emphasizing the importance of performing both local and systemic evaluations.

CONCLUSION

System advantages include integration between local and over 40 systemic parameters, unbiased data collection/analysis, improved performance/sampled area, easy expansion, implementation and maintenance, no customized programming, and simplified training. Combining this system with trauma/prolonged HS models will enhance our ability to investigate tissue stability and select better resuscitation strategies to improve outcomes and survival.

LEVEL OF EVIDENCE

Diagnostic test, level V.

Interoperable Readiness to Use Tourniquets by One's Familiarity With Different Models

BACKGROUND

We investigated interoperability for a first aid provider to perform simulated use of three tourniquet models of maximal, moderate, and minimal familiarity.

METHODS

The experiment was focused on the tourniquets used by an expert who rendered aid on a manikin by using three models of tourniquet with different extents of familiarity: The familiarity with Combat Application Tourniquet (C-A-T) was maximal; that for Special Operations Forces Tactical Tourniquet (SOFTT) was moderate, and that for Military Emergency Tourniquet (MET) was minimal. Each model had a band-and-rod design. Interoperability changes as intermodel differences were beneficial or costly in that performances were improved or impaired in units of time, ease, blood, and pressure. Each model had 10 tests, and test order was randomized by model. The HapMed Leg Tourniquet Trainer simulated a limb amputation.

RESULTS

In comparison of interoperability burdens, sums of 10 test durations by model for C-A-T, SOFTT, and MET were 38, 77, and 64 minutes, respectively; C-A-T was fastest (p ≤ .002, both). The sums of times to stop bleeding for C-A-T, SOFTT, and MET were 334, 953, and 826 seconds, respectively; C-A-T was fastest (p ≤ .0013, both). The sums of blood losses for C-A-T, SOFTT, and MET were 2105, 3287, and 4256mL, respectively; that for C-A-T was least (p ≤ .0005, both). The mean ease of use differed, with C-A-T being easiest (p ≤ .0046, both). The mean pressure differed, with C-A-T being higher than SOFTT (p = .0073).

CONCLUSIONS

Timesaving strongly favored the model with which the user had maximal familiarity. In theory and simulation, interoperability bears costs in successfully attaining it, in maintaining it, and in failing either. The user's familiarity with tourniquet model was associated with improved interoperability as seen by improved performances. If multiple models are fielded, then organizations may plan on extra spending, supplying, training, and managing.

Operational Advantages of Enteral Resuscitation Following Burn Injury in Resource-Poor Environments: Palatability of Commercially Available Solutions

BACKGROUND

In recent combat operations, 5% to 15% of casualties sustained thermal injuries, which require resource-intensive therapies. During prolonged field care or when caring for patients in a multidomain battlefield, delayed transport will complicate the challenges that already exist in the burn population. A lack of resources and/or vascular access in the future operating environment may benefit from alternative resuscitation strategies. The objectives of the current report are 1) to briefly review actual and potential advantages/caveats of resuscitation with enteral fluids and 2) to present new data on palatability of oral rehydration solutions.

METHODS

A review of the literature and published guidelines are reported. In addition, enlisted US military active duty Servicemembers (N = 40) were asked to taste/rank five different oral rehydration solutions on several parameters.

RESULTS AND CONCLUSIONS

There are several operational advantages of using enteral fluids including ease of administration, no specialized equipment needed, and the use of lightweight sachets that are easily reconstituted/ administered. Limited clinical data along with slightly more extensive preclinical studies have prompted published guidelines for austere conditions to indicate consideration of enteral resuscitation for burns. Gatorade® and Drip-Drop® were the overall preferred rehydration solutions based on palatability, with the latter potentially more appropriate for resuscitation. Taken together, enteral resuscitation may confer several advantages over intravenous fluids for burn resuscitation under resource-poor scenarios. Future research needs to identify what solutions and volumes are optimal for use in thermally injured casualties.

Ease of Use of Emergency Tourniquets on Simulated Limbs of Infants: Deliberate Practice

BACKGROUND

To investigate questions about application of emergency tourniquets in very young children, we investigated practices of Combat Application Tourniquet (C-A-T) use on a simulated infant-sized limb to develop ways to improve readiness for caregiving.

METHODS

This study was conducted as investigations of C-A-Ts used by two individuals in deliberate practice. The practice setup simulating a limb of infants aged 3-5 months included a handrail (circumference, 5.25 in.). This setup needed a specific modification to the instructions for use to adhere the band between the clips. Each user performed 100 practices.

RESULTS

With accrual of experience, application time was shorter for each user, on average in a power law of practice, and more ease was associated when less time was taken to apply the tourniquet. The ease of use was associated with accrued experience through deliberate practice of a tourniquet user while under coached learning. A check of tourniquet fit on a 4.25-in. limb also entailed the modification used in the 5.25-in. limb. However, an additional modification of wrapping the band in a figure-8 pattern around the rod was needed because the rod and clip could not meet. The fit on a 3.25-in. limb was impracticable for a workaround. Tourniquet use was harder for smaller limbs (i.e., 4.25 in. and 3.25 in.). A map of tourniquet fit was sketched of which sized limbs were too big, too small, within the fit zone, or at its borders.

CONCLUSION

C-A-Ts mechanically fit the simulated limbs of infants aged 3-5 months, and C-A-T use was practicably easy enough to allow experienced users to fit tourniquets to limbs well using a specific modification of the routine technique. The findings and knowledge generated in this study are available to inform researches and developments in best preparation practices for instructing first aid.

Deliberate Practice in Combat Application Tourniquet Placement by Loop Passage

BACKGROUND

We sought opportunities to develop learning practices of individual first aid providers. In this study, we simulated deliberate practice in placing limb tourniquets.

METHODS

This study comprised tourniquet uses by two experienced persons. Their practice sessions focused on developing a motor skill with periodic coaching. The Combat Application Tourniquet is 1.5-inches wide and was used in a technique of loop passage around the end of the limb to place it 2-3 inches above the wound. The simulated limb was a Z-Medica Hemorrhage Control Trainer. Both users applied the tourniquet six times over 5 days to accrue 30 uses individually (N = 60 tourniquet applications for the study).

RESULTS

When represented as summary parameters, differences were small. For example, average ease of use was the same for both users, but such parameters only took a snapshot of performance, yielding a general assessment. However, for a learning curve by use number, a surrogate of experience accrual, application time revealed spiral learning. The amount that users compressed a limb averaged -15% compared with its unsqueezed state. Placement accuracy was classified relative to gap widths between the tourniquet and the wound, and of 60 performances, 55 were satisfactory and five were unsatisfactory (i.e., placement was <2 inches from the wound). When a tourniquet only overlaid the 2-inch edge of the placement zone (i.e., tourniquet was 2-3.5 inches away from the wound), no error was made, but errors were made in crossing that 2-inch edge. These gauging errors led us to create a template for learners to see and to demonstrate what the meaning of 2-3 inches is.

CONCLUSION

Each metric had value in assessing first aid, but turning attention to gauging wound-tourniquet gaps revealed placement errors. Analysis of such errors uncovered what 2-3 inches meant in operation. Spiral learning may inform the development of best readiness practices such as coaching deliberate-practice sessions.

Limb Tourniquet Configuration: Preliminary Investigation of Problems and Principles

BACKGROUND

A tourniquet's readiness during emergencies depends on how it is configured. We investigated configuration so ways of improving readiness can be developed.

METHODS

This study was conducted at the Institute of Surgical Research in 2018 as sequential investigations by one user of Combat Application Tourniquets (C-A-Ts) in a band-and-rod design.

RESULTS

Each tourniquet comes packaged with paper instructions for use, which include directions on how to configure it in preparation for caregiving. The paper and video instructions for use omit tensioning of the tourniquet in configuration, and the video misconfigured a time strap over the rod. In first-aid classrooms, we saw unwitting learners troubleshoot that misconfiguration. Problems with configuration were also seen in caregiving and with tourniquets stowed in kits. In deliberate practice, we self-applied a tourniquet to a thigh. In configuration after each of 100 uses, tourniquet elongation due to tensioning averaged 2.4 in was important for restoring the tourniquet to its full length. During configuration, if the C-A-T's stabilization plate slid along the band, out of position, the user slid the plate back into position. In various ways of testing other C-A-Ts, elongations averaged from 0.4 in to 0.9 in, depending on whether the tourniquet was self-applied or applied to a firm manikin. Elongation increments accrued as the tourniquet's band flattened. Configuration time averaged 22 seconds, and accrued experience improved the compactness of configuration.

CONCLUSION

People are too often unreliable at putting C-A-Ts into the optimal configuration for use. That ready-to-use configuration includes the tourniquet being at its full length, having the stabilization plate positioned correctly along the band, and having the strap fastened to its clip of origin. When used, tourniquets had normal, small elongations in part due to band flattening. This tourniquet study showed the importance of optimal configuration to first-aid readiness practices.

Large Animal Models of Proximal Aortic Balloon Occlusion in Traumatic Hemorrhage: Review and Identification of Knowledge Gaps Relevant to Expanded Use

BACKGROUND

The aim of this study was to review and summarize the large animal data on resuscitative endovascular balloon occlusion of the aorta (REBOA) for traumatic hemorrhage and identify knowledge gaps pertinent to the proposed broader use of the technique in prehospital situations.

METHODS

A review of published large animal models of traumatic hemorrhage incorporating REBOA with a primary outcome of the effect of aortic occlusion was performed. Data were collected on experimental protocols, hemodynamic effects, resuscitation requirements, mortality, metabolic and tissue consequences of induced ischemia-reperfusion, and effects on hemorrhage volume and other injuries.

RESULTS

A limited number of REBOA studies exist, and there is variability in the species and size of animals used. Various controlled and uncontrolled hemorrhage protocols have been studied, and a number of balloon devices used. Hemodynamic effects of occlusion were consistent as were basic systemic physiological effects. Minimal study of the effects of partial aortic occlusion and hemodynamic and metabolic physiology distal to the balloon has been performed, and partial or complete occlusion times >90 min have not been studied.

CONCLUSIONS

Significant knowledge gaps exist, which are potentially relevant to the expanded use of REBOA. Investigation into the physiology of partial occlusion and the metabolic effects and potential mitigation strategies for large-scale ischemia and reperfusion are particularly needed.

Isolation and Characterization of Multipotent CD24+ Cells From the Renal Papilla of Swine

Over 100,000 patients in the United States are currently waiting for a kidney transplant. With just over 10,000 cadaveric kidneys transplanted annually, it is of the utmost importance to optimize kidney viability upon transplantation. One exciting avenue may be xenotransplantation, which has rejuvenated interest after advanced gene editing techniques have been successfully used in swine. Simultaneously, acute kidney injury (AKI) is associated with high morbidity and mortality and currently lacks effective treatment. Animal models have been used extensively to address both of these issues, with recent emphasis on renal progenitor cells (RPCs). Due to anatomical similarities to humans we aimed to examine progenitor cells from the renal papillae of swine kidneys. To do this, RPCs were dissected from the renal papillae of healthy swine. Cell surface marker expression, proliferation, and differentiation of the RPCs were tested in vitro. Additionally, a mixed lymphocyte reaction was performed to examine immunomodulatory properties. RPCs displayed spindle shaped morphology with limited self-renewing capacity. Isolated RPCs were positive for CD24 and CD133 at early passages, but lost expression with subsequent passaging. Similarly, RPCs displayed myogenic, osteogenic, and adipogenic differentiation capacities at passage 2, but largely lost this by passage 6. Lastly, direct contact of RPCs with human lymphocytes increased release of IL6 and IL8. Taken together, RPCs from the papilla of porcine kidneys display transient stem cell properties that are lost with passaging, and either represent multiple types of progenitor cells, or a multipotent progenitor population. In instances of ischemic insult, augmentation of/with RPCs may potentiate regenerative properties of the kidney. While the use of swine for transplantation and ischemia studies confers obvious advantages, the populations of different progenitor cell populations within pig kidneys warrants further investigation. Ultimately, while gene editing techniques enhance the potential for xenotransplantation of organs or cells, the ultimate success of this strategy may be determined by the (dis)similarities of RPCs from different species.

The Cutaneous Microbiome and Wounds: New Molecular Targets to Promote Wound Healing

The ecological community of microorganisms in/on humans, termed the microbiome, is vital for sustaining homeostasis. While culture-independent techniques have revealed the role of the gut microbiome in human health and disease, the role of the cutaneous microbiome in wound healing is less defined. Skin commensals are essential in the maintenance of the epithelial barrier function, regulation of the host immune system, and protection from invading pathogenic microorganisms. In this review, we summarize the literature derived from pre-clinical and clinical studies on how changes in the microbiome of various acute and chronic skin wounds impact wound healing tissue regeneration. Furthermore, we review the mechanistic insights garnered from model wound healing systems. Finally, in the face of growing concern about antibiotic-resistance, we will discuss alternative strategies for the treatment of infected wounds to improve wound healing and outcomes. Taken together, it has become apparent that commensals, symbionts, and pathogens on human skin have an intimate role in the inflammatory response that highlights several potential strategies to treat infected, non-healing wounds. Despite these promising results, there are some contradictory and controversial findings from existing studies and more research is needed to define the role of the human skin microbiome in acute and chronic wound healing.

Complement inhibition ameliorates blast-induced acute lung injury in rats: Potential role of complement in intracellular HMGB1-mediated inflammation

BACKGROUND AND OBJECTIVE

Complement activation as an early and important inflammatory process contributes to multiple organ dysfunction after trauma. We have recently shown that complement inhibition by decay-accelerating factor (DAF) protects brain from blast-overpressure (BOP)-induced damage. This study was conducted to determine the effect of DAF on acute lung injury induced by BOP exposure and to elucidate its possible mechanisms of action.

METHODS

Anesthetized adult male Sprague-Daley rats were exposed to BOP (120 kPa) from a compressed air-driven shock tube. Rats were randomly assigned to three experimental groups: 1) Control (no BOP and no DAF treatment), 2) BOP (120 kPa BOP exposure), and 3) BOP followed by treatment with rhDAF (500μg/kg, i.v) at 30 minutes after blast. After a recovery period of 3, 24, or 48 hours, animals were euthanized followed by the collection of blood and tissues at each time point. Samples were subjected to the assessment of cytokines and histopathology as well as for the interaction of high-mobility-group box 1 (HMGB1) protein, NF-κB, receptor for advanced glycation end products (RAGE), C3a, and C3aR.

RESULTS

BOP exposure significantly increased in the production of systemic pro- and anti-inflammatory cytokines, and obvious pathological changes as characterized by pulmonary edema, inflammation, endothelial damage and hemorrhage in the lungs. These alterations were ameliorated by early administration of rhDAF. The rhDAF treatment not only significantly reduced the expression levels of HMGB1, RAGE, NF-κB, C3a, and C3aR, but also reversed the interaction of C3a-C3aR and nuclear translocation of HMGB1 in the lungs.

CONCLUSIONS

Our findings indicate that early administration of DAF efficiently inhibits systemic and local inflammation, and mitigates blast-induced lung injury. The underlying mechanism might be attributed to its potential modulation of C3a-C3aR-HMGB1-transcriptional factor axis. Therefore, complement and/or HMGB1 may be potential therapeutic targets in amelioration of acute lung injury after blast injury.

Enteral resuscitation with oral rehydration solution to reduce acute kidney injury in burn victims: Evidence from a porcine model

Intravenous (IV) resuscitation of burn patients has greatly improved outcomes and become a cornerstone of modern burn care. However, the heavy fluids and vascular access required may not be feasible in austere environments, mass casualty, or delayed transport scenarios. Enteral resuscitation has been proposed for these situations; we sought to examine the effectiveness of this strategy on improving burn-induced kidney injury. Anesthetized Yorkshire swine sustaining 40% TBSA full-thickness contact burns were randomized to three groups (n = 6/group): fluid deprivation, ad libitum water access, or 70 mL/kg/d Oral Rehydration Salt solution (ORS). Urine and blood were collected at baseline (BL), 6, 12, 24, 32, and 48h post-burn, at which point tissue was harvested and CT angiography performed. Although fluid consumption by ad libitum and ORS groups were matched (132±54mL/kg versus 120±24mL/kg, respectively), ORS intake increased urine output compared with water and no water (47.3±9.0 mL/kg versus 16.1±2.5 mL/kg, and 24.5±1.7 mL/kg respectively). Plasma creatinine peaked 6h following burn (1.67±0.07mg/dL) in all animals, but at 48h was comparable to BL in animals receiving water (1.23±0.06mg/dL) and ORS (1.30±0.09mg/dL), but not fluid deprived animals (1.56±0.05mg/dL) (P<0.05). Circulating levels of blood urea nitrogen steadily increased, but also decreased by 48h in animals receiving enteral fluids (P<0.05). Water deprivation reduced renal artery diameter (-1.4±0.17mm), whereas resuscitation with water (-0.44±0.14 mm) or ORS maintained it (-0.63±0.20 mm;P< 0.02). Circulating cytokines IL-1β, IL-6, IFNγ, and GM-CSF were moderately elevated in the fluid-deprived group. Taken together, the data suggest that enteral resuscitation with ORS rescues kidney function following burn injury. Incorporating enteral fluids may improve outcomes in resource-poor environments and possibly reduce IV fluid requirements to prevent co-morbidities associated with over-resuscitation. Studies into different volumes/types of enteral fluids are warranted. While ORS has saved many lives in cholera-associated dehydration, it should be investigated further for use in burn patients.

Bleeding Control With Limb Tourniquet Use in the Wilderness Setting: Review of Science

The purpose of this review is to summarize tourniquet science for possible translation to wilderness settings. Much combat casualty data has been studied since 2005, and use of tourniquets in the military has changed from a last resort to first aid. The US Government has made use of tourniquets a health policy aimed to improve public access to bleeding control items. International authorities believe that education in first aid should be universal, as all can and should learn first aid. The safety record of tourniquet use is mixed, but users are reliably safe if trained well. Well-designed tourniquets can reliably attain bleeding control, may mitigate risk of shock progression, and may improve survival rates, but conclusive proof of a survival benefit remains unclear in civilian settings. Even a war setting has a bias toward survivorship by sampling mostly survivors in hospitals. Improvised tourniquets are less reliable than well-designed tourniquets but may be better than none. The tourniquet model used most often in 2016 by the US military is the Combat Application Tourniquet (C-A-T), and civilians use an array of various models, including C-A-T. Evidence on tourniquet use to date indicates that most uses are safe and effective in civilian settings. Future directions for study relevant to the wilderness setting include consideration of research priorities, study of the burdens of injury or capability gaps in caregiving for various wilderness settings, determination of the skill needs of outdoor enthusiasts and wilderness caregivers, and survey of wilderness medicine stewards regarding bleeding control.

Use Your Noodle to Simulate Tourniquet Use on a Limb With and Without Bone

BACKGROUND

The purpose of this study was to simulate first aid by mechanical use of a limb tourniquet on a thigh with and without bone to better understand best caregiving practices.

METHODS

Two investigators studied simulated first aid on a new pool "noodle," a plastic cylinder with a central air tunnel into which we inserted a wood dowel to simulate bone. Data were gathered by group (study and control, n = 12 each). The control group comprised data collected from simulated tourniquet use on the model with bone present. The study group comprised data from simulated tourniquet use on the model without bone.

RESULTS

Comparing compression with and without bone, the mean volumes of compressed soft tissues alone were 303mL and 306mL, respectively. When bone was present, the volume of soft tissues was squeezed more, yielding a smaller size by 3mL (1%). The bone had a volume of 41mL and pressed statically outward with an equal force oppositely directed to the inward compression of the overlying soft tissues. With bone removed and compression applied, the mean residual void was 16mL, because 25mL (i.e., 41mL minus 16mL) of soft tissues had collapsed inward. The volume of the limb under the tourniquet with and without bone was 344mL and 322mL, respectively. The collapse volume, 25mL, was 3mL more than the difference of the mean volume of the limb under the tourniquet. More limb squeeze (22mL) looked like better compression, but it was actually worse-an illusion created by collapse of the hidden void.

CONCLUSION

In simulated first aid, mechanical modeling demonstrated how tourniquet compression applied to a limb squeezed the soft tissues better when underlying bone was present. Bone loss altered the compression profile and may complicate control of bleeding in care. This knowledge, its depiction, and its demonstration may inform first-aid instructors.