Extremity trauma exacerbates acute kidney injury following prolonged hemorrhagic hypotension

Comparing the effects of various fluid resuscitative strategies on Glycocalyx damage in a canine hemorrhage model

Hemorrhagic shock and subsequent resuscitation can cause significant dysregulation of critical systems, including the vascular endothelium. Following hemorrhage, the endothelial lining (glycocalyx) can shed, causing release of glycocalyx components, endothelial activation, and systemic inflammation. A canine model of hemorrhagic shock was used to evaluate five resuscitation fluids, including Lactated Ringers+Hetastarch, Whole Blood (WB), Fresh Frozen Plasma+packed Red Blood Cells (FFP+pRBC), and two hemoglobin-based oxygen carrier (HBOC) fluids, for their impact on glycocalyx shedding. Under anesthesia, purpose-bred adult canines were instrumented and subjected to a controlled hemorrhage with blood being drawn until a mean arterial pressure of <50 mmHg was reached or 40 % of the estimated blood volume was removed. Canines were left in shock for 45 mins before being resuscitated with one of the resuscitation fluids over 30 mins. Following resuscitation, the dogs were monitored up to 2 weeks. Following an additional 3-4 weeks for washout, the canines repeated the protocol, undergoing each resuscitation fluid individually. Blood samples were collected during each round at various timepoints for serum isolation, which was used for detection of glycocalyx biomarker. Comparison of baseline and post-hemorrhage alone showed a significant reduction in serum protein (p<0.0001), heparan sulfate (p<0.001), and syndecan-1 (p<0.0001) concentrations, and a significant increase in hyaluronan (p<0.0001) concentration. Intercomparisons of resuscitation fluids indicated minimal differences in glycocalyx markers over time. Comparisons within each fluid showed dynamic responses in glycocalyx biomarkers over time. Relative to individual baselines, syndecan-1 was significantly reduced after resuscitation in most cases (p<0.0001), excluding WB and FFP+pRBC. In all cases, VE-cadherin was significantly elevated at 24 hr compared to baseline (p<0.001). Hyaluronan was significantly elevated by 3 hr in all cases (p<0.01), except for HBOC fluids. Total glycosaminoglycans were significantly reduced only at 3 hr (p<0.001) for non-HBOC fluids. Similarly, heparan sulfate was significantly reduced with all fluids between resuscitation and 24 hr (p<0.01), except WB. The temporal changes in canine glycocalyx biomarkers were atypical of hemorrhage response in other species. This suggests that the hemorrhage lacked severity and/or typical glycocalyx biomarkers do not reflect the canine endothelium compared to other species. Further research is needed to characterize the canine endothelium and the response to resuscitation fluids.

Multicompartmental Trauma Induces Persistent Inflammation and Organ Injury

INTRODUCTION

Previous preclinical models of multicompartmental injury have investigated its effects for durations of less than 72 h and the long-term effects have not been defined. We hypothesized that a model of multicompartmental injury would result in systemic inflammation and multiorgan dysfunction that persists at 1 wk.

METHODS

Male and proestrus female Sprague-Dawley rats (n = 16/group) underwent polytrauma (PT) (unilateral right lung contusion, hemorrhagic shock, cecectomy, bifemoral pseudofractures) and were compared to naive controls. Weight, hemoglobin, plasma neutrophil gelatinase-associated lipocalin, and plasma toll-like receptor 4 were evaluated on days two and seven. Bilateral lungs were sectioned, stained and assessed for injury at day seven. Comparisons were performed in Graphpad with significance defined as ∗P <0.05.

RESULTS

Rats who underwent PT had significant weight loss and anemia at day 2 (P = 0.001) compared to naïve rats which persisted at day 7 (P = 0.001). PT rats had elevated plasma neutrophil gelatinase-associated lipocalin at day 2 compared to naïve (P <0.0001) which remained elevated at day 7 (P <0.0001). Plasma toll-like receptor 4 was elevated in PT compared to naïve at day 2 (P = 0.03) and day 7 (P = 0.01). Bilateral lungs showed significant injury in PT cohorts at day 7 compared to naïve (P <0.0004). PT males had worse renal function at day seven compared to females (P = 0.02).

CONCLUSIONS

Multicompartmental trauma induces systemic inflammation and multiorgan dysfunction without recovery by day seven. However, females demonstrate improved renal recovery compared to males. Long-term assessment of preclinical PT models are crucial to better understand and evaluate future therapeutic immunomodulatory and anti-inflammatory treatments.

A clinically-relevant mouse model that displays hemorrhage exacerbates tourniquet-induced acute kidney injury

Hemorrhage is a leading cause of death in trauma. Tourniquets are effective at controlling extremity hemorrhage and have saved lives. However, tourniquets can cause ischemia reperfusion injury of limbs, leading to systemic inflammation and other adverse effects, which results in secondary damage to the kidney, lung, and liver. A clinically relevant animal model is critical to understanding the pathophysiology of this process and developing therapeutic interventions. Despite the importance of animal models, tourniquet-induced lower limb ischemia/reperfusion (TILLIR) models to date lack a hemorrhage component. We sought to develop a new TILLIR model that included hemorrhage and analyze the subsequent impact on kidney, lung and liver injuries. Four groups of mice were examined: group 1) control, group 2) hemorrhage, group 3) tourniquet application, and group 4) hemorrhage and tourniquet application. The hemorrhagic injury consisted of the removal of 15% of blood volume through the submandibular vein. The tourniquet injury consisted of orthodontic rubber bands applied to the inguinal area bilaterally for 80 min. Mice were then placed in metabolic cages individually for 22 h to collect urine. Hemorrhage alone did not significantly affect transcutaneous glomerular filtration rate (tGFR), blood urea nitrogen (BUN) or urinary kidney injury molecule-1 (KIM-1) levels. Without hemorrhage, TILLIR decreased tGFR by 46%, increased BUN by 162%, and increased KIM-1 by 27% (p < 0.05 for all). With hemorrhage, TILLIR decreased the tGFR by 72%, increased BUN by 395%, and increased urinary KIM-1 by 37% (p < 0.05 for all). These differences were statistically significant (p < 0.05). While hemorrhage had no significant effect on TILLIR-induced renal tubular degeneration and necrosis, it significantly increased TILLIR-induced lung total injury scores and congestion, and fatty liver. In conclusion, hemorrhage exacerbates TILLIR-induced acute kidney injury and structural damage in the lung and liver.

Effects of extremity trauma on physiological responses to hemorrhage in conscious rats

Although physiological responses to hemorrhage are well-studied, hemorrhage is often accompanied by trauma, and it remains unclear how injury affects these responses. This study examined effects of extremity trauma on cardiorespiratory responses and survival to moderate (37%; H-37) or severe (50%; H-50) hemorrhage in rats. Transmitter and carotid catheter implantation and extremity trauma (fibular fracture and muscle injury) were conducted 2 wk, 24 h, and 90 min, respectively, before conscious hemorrhage. Mean arterial pressure (MAP) and heart rate (HR; via telemetry), and respiration rate (RR), minute volume (MV), and tidal volume (TV; via plethysmography) were measured throughout the 25 min hemorrhage and remainder of the 4 h observation period. There were four groups: 1) H-37, no trauma (NT; n = 17); 2) H-37, extremity trauma (T, n = 18); 3) H-50, NT (n = 20); and 4) H-50, T (n = 20). For H-37, during and after hemorrhage, T increased HR (P ≤ 0.031) and MV (P ≤ 0.048) compared with NT rats. During H-50, T increased HR (0.041) and MV (P = 0.043). After hemorrhage, T increased MV (P = 0.008) but decreased HR (P = 0.007) and MAP (P = 0.039). All cardiorespiratory differences between T and NT groups were intermittent. Importantly, both survival time (159.8 ± 78.2 min vs. 211.9 ± 60.3 min; P = 0.022; mean ± SD) and percent survival (45% vs. 80%; P = 0.048) were less in T versus NT rats after H-50. Trauma interacts with physiological systems in a complex manner and no single cardiorespiratory measure was sufficiently altered to indicate that it alone could account for increased mortality after H-50.NEW & NOTEWORTHY In both civilian and military settings, severe hemorrhage rarely occurs in the absence of tissue trauma, yet many animal models for the study of hemorrhage do not include significant tissue trauma. This study using conscious unrestrained rats clearly demonstrates that extremity trauma worsens the probability of survival after a severe hemorrhage. Although no single cardiorespiratory factor accounted for the increased mortality, multiple modest time-related cardiorespiratory responses to the trauma were observed suggesting that their combined dysfunction may have contributed to the reduced survival.

A novel animal model to study delayed resuscitation following traumatic hemorrhage

A focus of combat casualty care research is to develop treatments for when full resuscitation after hemorrhage is delayed. However, few animal models exist to investigate such treatments. Given the kidney's susceptibility to ischemia, we determined how delayed resuscitation affects renal function in a model of traumatic shock. Rats were randomized into three groups: resuscitation after 1 h (ETH-1) or 2 h (ETH-2) of extremity trauma and hemorrhagic shock, and sham control. ETH was induced in anesthetized rats with muscle injury and fibula fracture, followed by pressure-controlled hemorrhage [mean arterial pressure (MAP) = 55 mmHg] for 1 or 2 h. Rats were then resuscitated with whole blood until MAP stabilized between 90 and 100 mmHg for 30 min. MAP, glomerular filtration rate (GFR), creatinine, blood gases, and fractional excretion of sodium (nFENa+) were measured for 3 days. Compared with control, ETH-1 and ETH-2 exhibited decreases in GFR and nFENa+, and increases in circulating lactate, creatinine, and blood urea nitrogen (BUN) before and within 30 min after resuscitation. The increases in creatinine, BUN, and potassium were greater in ETH-2 than in ETH-1, whereas lactate levels were similar between ETH-1 and ETH-2 before and after resuscitation. All measurements were normalized in ETH-1 within 2 days after resuscitation, with 22% mortality. However, ETH-2 exhibited a prolonged impairment of GFR, increased nFENa+, and a 66% mortality. Resuscitation 1 h after injury therefore preserves renal function, whereas further delay of resuscitation irreversibly impairs renal function and increases mortality. This animal model can be used to explore treatments for prolonged prehospital care following traumatic hemorrhage.NEW & NOTEWORTHY A focus of combat casualty care research is to develop treatment where full resuscitation after hemorrhage is delayed. However, animal models of combat-related hemorrhagic shock in which to determine physiological outcomes of such delays and explore potential treatment for golden hour extension are lacking. In this study, we filled this knowledge gap by establishing a traumatic shock model with reproducible development of AKI and shock-related complications determined by the time of resuscitation.

Pathophysiology of Hemorrhage as It Relates to the Warfighter

Saving lives of wounded military Warfighters often depends on the ability to resolve or mitigate the pathophysiology of hemorrhage, specifically diminished oxygen delivery to vital organs that leads to multi-organ failure and death. However, caring for hemorrhaging patients on the battlefield presents unique challenges that extend beyond applying a tourniquet and giving a blood transfusion, especially when battlefield care must be provided for a prolonged period. This review will describe these challenges and potential strategies for treating hemorrhage on the battlefield in a prolonged casualty care situation.