Modeling Principle

The Beagle Hemorrhagic Shock Model is a SCI gold-standard large-animal pathological model of hypovolemic hemorrhagic shock established by indwelling catheter in common carotid artery and gradient controlled uniform blood withdrawal. It accurately recapitulates the complete cascaded pathological process caused by massive traumatic hemorrhage and intraoperative blood loss in clinic, including sharp reduction of effective circulating blood volume, progressive decline of arterial blood pressure, insufficient microcirculatory perfusion of tissues, disorder of hypoxic metabolism in cells, explosive release of systemic inflammatory factors, vascular endothelial injury, apoptotic necrosis of parenchymal visceral cells, and progressive development into multiple organ dysfunction syndrome (MODS) such as acute kidney injury, lung injury and liver injury. It remedies the experimental defects of rodent animals, which have obvious discrepancies with human traumatic hemorrhagic shock in tiny vascular diameter, proportion of circulating blood volume, compensatory regulation ability of blood pressure, intensity of inflammatory storm after shock and temporal evolution law of multiple organ injury.

The systemic vascular anatomical structure, hemorheological properties, compensatory response of sympathetic-adrenal medulla, activation mode of mononuclear macrophage system, tolerance threshold of vascular endothelial barrier, systemic inflammatory response syndrome (SIRS) mediated by TNF-α/IL-1β under shock state, and ischemia-reperfusion injury mechanism of vital organs including liver, kidney and lung of adult Beagle dogs are highly homologous to human circulatory system. Bilateral common carotid arteries are exposed surgically; one side is intubated for continuous controlled blood withdrawal to construct hypovolemic status, and the other side is used for real-time dynamic monitoring of invasive arterial blood pressure and blood sample collection. Blood is withdrawn uniformly step by step according to the percentage of total blood volume to stably maintain mean arterial pressure (MAP) within the target shock range. Insufficient effective circulating blood volume leads to closure of peripheral tissue microcirculation, insufficient oxygen supply to tissue cells resulting in anaerobic metabolism and massive lactic acid accumulation. Sustained hypoperfusion activates innate immune cells to release abundant pro-inflammatory factors, destroying vascular endothelial integrity, and capillary leakage aggravates further loss of effective blood volume. Long-term ischemia followed by ischemia-reperfusion injury induced by fluid resuscitation gradually induces inflammatory infiltration and apoptotic necrosis in heart, liver, kidney and lung, stably forming a complete pathological phenotype of "simple blood loss → hypovolemic hypotension → microcirculatory failure → systemic inflammatory storm → visceral ischemic injury → multiple organ functional damage", which reproduces the classic pathogenic cascade of human traumatic hemorrhagic shock.

Beagle dogs have thick vessels convenient for intubation operation, the blood withdrawal rate and shock blood pressure value can be accurately quantified and controlled, the shock maintenance time is uniform with low discrete degree of individual experimental data, and there is no spontaneous circulatory system lesion. Three pathological stages can be clearly distinguished: early stage of compensatory hypotensive shock, middle stage of microcirculatory failure & inflammatory outbreak shock, and terminal stage of shock with organic multiple organ damage. It serves as a standardized large-animal gold-standard model for translational researches on shock resuscitation fluid formula, anti-shock vasoactive drugs, inflammatory inhibitors, visceral protective preparations and traumatic first-aid regimens.

Modeling Success Criteria

In-vivo Hemodynamics, Blood Gas & Lactic Acid and General Visceral Phenotype

The MAP of Beagle dogs in the sham control group was stably in the normal physiological range, blood lactic acid remained at normal low level, each viscus was ruddy in color, uniform and soft in texture without congestion and edema. The MAP of the model group was stably locked at 35～40 mmHg at 2 h of shock, and blood lactic acid was more than 3 times higher than that of the sham group. Autopsy on Day 6 after resuscitation showed pulmonary congestion & edema, enlarged liver and kidney with interstitial congestion, and myocardial interstitial edema in the heart. The macroscopic phenotype of multiple organ injury induced by shock was obvious with extremely significant statistical difference between groups, which could preliminarily confirm the successful construction of controlled blood withdrawal hemorrhagic shock model.

Quantitative Biochemical Gold-Standard Serum Indexes

The serum levels of TNF-α, IL-1β, IL-6 and HMGB1 in the model group during shock and resuscitation period were extremely significantly higher than those in the sham group; vascular endothelial injury marker vWF increased while NO content decreased; serum ALT, AST, Scr and BUN increased abnormally synchronously indicating substantial liver and kidney damage; blood lactic acid and residual alkali BE values were significantly abnormal, which fully conforms to the biochemical diagnostic characteristics of clinical hemorrhagic shock: lactic acid accumulation caused by hypoperfusion, destruction of endothelial barrier, inflammatory factor storm and impaired liver & kidney function.

Histopathological Characteristics of Heart, Lung, Liver and Kidney

Sequential pathological injury changes of hemorrhagic shock can be observed via combined staining of various visceral tissues with HE, Masson and TUNEL:

1. Peak shock stage at 2 h: mild congestion and edema in pulmonary interstitium, a small amount of hydropic degeneration in liver and kidney cells, slight infiltration of inflammatory cells in tissues and mild increase of apoptotic cells;
2. Progressive stage on Day 3 after resuscitation: destruction of alveolar structure, massive inflammatory infiltration in pulmonary interstitium, swelling and degeneration of hepatocytes and renal tubular epithelial cells, obvious increase of visceral apoptotic number;
3. Terminal stage on Day 6 after resuscitation: thickened alveolar wall, extensive pulmonary congestion and edema, necrosis and shedding of renal tubules, large-area inflammatory infiltration in liver tissue, myocardial cell edema accompanied by interstitial inflammatory exudate, and massive increase of TUNEL-positive apoptotic cells, which perfectly recapitulates the progressive pathological evolution law from transient hypoperfusion to substantial multiple organ damage caused by hemorrhagic shock in human beings.

Gold-Standard Indexes of Inflammation and Endothelial Injury Pathways

Hypovolemic status of the model group induced tissue hypoperfusion, continuous activation of NF-κB signaling pathway drove the release of abundant pro-inflammatory factors to form systemic inflammatory response. Inflammatory mediators attacked vascular endothelium resulting in damaged endothelial barrier and capillary leakage. Ischemia combined with resuscitation reperfusion injury up-regulated the activity of visceral cell apoptotic pathway, gradually causing organic damage of heart, liver, kidney and lung. It accurately conforms to the complete pathological mechanism of controlled blood withdrawal: decreased effective blood volume – tissue hypoperfusion – inflammatory outbreak – endothelial injury & leakage – ischemia-reperfusion injury – multiple organ dysfunction, serving as the core academic basis for verifying effective model formation.

Model Advantages

This model is a well-recognized large-animal gold-standard model for hemorrhagic shock constructed by controlled blood withdrawal in the field of emergency and critical care SCI. The 6-day standardized modeling process can stably recapitulate complete pathological phenotypes highly homologous to humans, including hypovolemic shock, systemic inflammatory response, ischemia-reperfusion injury and functional & organic multiple organ injury. The vascular anatomy, blood rheology, intensity of systemic inflammatory response and visceral ischemia tolerance of Beagle dogs are highly consistent with human beings. The depth of shock blood pressure is controllable with mild experimental process and low intra-group data dispersion, and the experimental repeatability is obviously superior to small animals such as rodents and rabbits. The modeling method adopts physical quantitative blood withdrawal to induce hypovolemia, which highly conforms to the pathogenesis essence of clinical traumatic hemorrhagic shock without mixed toxic interference caused by chemical drug induction. Blood can be collected for many times during the experiment and hemodynamics can be monitored in real time with sufficient multi-viscera samples, which is suitable for preclinical efficacy and safety evaluation of various shock resuscitation fluids, anti-shock vasoactive drugs, inflammatory antagonists, visceral protective drugs and traumatic first-aid regimens. Experimental data are widely accepted by high-impact SCI journals of emergency medicine, critical care medicine and pharmacology, which is applicable for National Natural Science Foundation projects, master & doctoral proposal writing, emergency & critical care graduation theses and translational medical researches on visceral protection in shock.

Research Applications

The Beagle Hemorrhagic Shock Model is mainly applied to analyze basic pathological mechanisms including insufficient effective circulating blood volume caused by controlled blood loss, hypoperfusion hypoxic injury of tissues, inflammatory factor storm induced by NF-κB pathway activation, damage and leakage of vascular endothelial barrier, superimposed injury of ischemia-reperfusion, and MODS triggered by inflammatory infiltration and apoptosis of multiple viscera. It is specially used for screening and verifying crystal/colloid resuscitation fluid formulas, small-molecule anti-shock drugs, natural anti-inflammatory active components, visceral protective biological preparations and on-site traumatic first-aid intervention schemes with functions of stably maintaining circulatory perfusion, inhibiting systemic inflammatory storm, protecting vascular endothelial integrity, alleviating ischemic apoptotic injury of viscera, improving visceral function after resuscitation and reducing long-term multiple organ damage after shock. It is widely adopted for excavation of pathogenic molecular targets of visceral injury in shock, elucidation of interactive regulatory network among perfusion, inflammation and endothelial injury, as well as preclinical in-vivo efficacy verification of various shock treatment drugs and fluid supplementation systems in large animals. It acts as an essential and scarce standardized large-animal gold-standard model in the fields of critical emergency pharmacology, shock pathophysiology and traumatic treatment.

beagle hemorrhagic shock model, controlled blood withdrawal, hypovolemic shock, microcirculation disturbance, insufficient tissue perfusion, multiple organ injury, shock resuscitation drug & fluid formulation preclinical evaluation