Hemorrhagic shock is the leading cause of early death in war casualties. The co-effects of a hyperthermic environment and hemorrhagic shock exacerbate the pathophysiological process, however, standardized animal models for this combined injury are still lacking. This study aims to establish a stable and reliable animal model of fatal hemorrhagic shock under hyperthermic conditions, providing a tool for elucidating the mechanisms of combined injury and screening treatment strategies.

① SPF-grade SD rats (weighing 200 to 220 g) were randomly divided into 25℃ group, 32℃ group, 35℃ group, and 38℃ group (n=12). After 12 h of ambient exposure, core temperature and survival were monitored to determine an optimal hyperthermia modeling temperature. After 35 ℃ was identified as determined as the optimal hyperthermic condition, the rats were randomly assigned to groups with graded blood loss (20%, 30%, 40%, 50% and 60%, n=32) to establish a hyperthermic hemorrhagic shock model. A lethal blood loss volume was defined based on a 6 h spontaneous mortality rate >70%. Subsequently, 3 groups (n=8) were set up: Sham group, lethal hyperthermic hemorrhagic shock model, and lactated Ringer’s (LR) solution resuscitation group. LR solution was infused at twice the shed blood volume. The 6 h survival rate, core temperature, respiratory rate, hemodynamic parameters, arterial blood gas, electrolytes, plasma osmotic pressure, as well as cardiac, liver and renal function indicators were detected. ② To verify model stability, cross-species validation was further performed using Bama miniature pigs (weighing 15 to 20 kg). A total of 18 minipigs were randomly and equally divided into Sham group, lethal hyperthermic hemorrhagic shock group and LR resuscitation group. The same protocols (35 ℃ hyperthermic preconditioning for 12 h, 50% total blood volume loss and resuscitation with LR solution) were applied. Hemodynamics, organ function and short-term survival were observed to validate the reliability of the model and the resuscitation efficacy of LR solution.

① Exposure to 35 ℃ induced a stable high core temperature ranging from 38.9 ℃ to 39.1 ℃ in rats, with no significant difference in 12 h survival duration compared with the normothermic group, indicating that 35 ℃ was suitable for hyperthermia model establishment. The rats subjected to 50% blood loss under 35 ℃ hyperthermic conditions presented a 6 h spontaneous mortality rate >70%, meeting the standard of a lethal hemorrhagic shock model. Meanwhile, the survival rate recovered to 53.125% after resuscitation with LR solution, which could effectively distinguish the intervention efficacy of resuscitation. The rat intervention experiments demonstrated that, compared with the Sham group, the rats in the 50% lethal hyperthermic hemorrhagic shock group exhibited significantly elevated core temperature, accompanied by marked declines in mean arterial pressure (MAP), left ventricular systolic pressure (LVSP) and maximal change rate of left intraventricular pressur (±dp/dt_max), suggesting severe circulatory dysfunction (P<0.05). In addition, significant reductions in pH value, base excess (BE), partial pressure of oxygen (PO₂) and oxygen saturation (SO₂) as well as remarkable elevations in lactic acid (Lac), serum Na⁺ and plasma osmotic pressure were observed, indicating severe acid-base imbalance, electrolyte disturbance and abnormal cardiac, liver and renal functions (P<0.05). Compared with the lethal hyperthermic hemorrhagic shock group, resuscitation with LR solution significantly reduced core temperature, serum Na⁺, blood urea nitrogen (BUN) and serum creatinine (Scr) levels, and restored MAP, LVSP ±dp/dt_max, pH value and SO₂, thereby alleviating hemodynamic disturbance, internal environment imbalance and renal dysfunction (P<0.05). However, LR solution exerted no obvious improvement in Lac, aspartate aminotransferase (AST) or alanine aminotransferase (ALT) levels. ② Cross-species validation results in Bama miniature pigs were consistent with the rat model. Lethal hyperthermic hemorrhagic shock induced severe circulatory failure, multiple organ dysfunction and a low 6 h survival rate of 16.7% in large animals. Resuscitation with LR solution significantly ameliorated hemodynamic parameters, decreased organ injury biomarkers, and raised the 6 h survival rate to 50% (P<0.05)., confirming the cross-species stability of the established model and the protective effect of LR solution.

A stable and reproducible animal model of lethal hemorrhagic shock combined with 35 ℃ hyperthermia is successfully established, which remedies the deficiencies of existing single-hit hemorrhagic shock models. Resuscitation with LR solution can effectively relieve hyperthermia, hemodynamic disorders and electrolyte disturbances, mitigate cardiac and renal injury, and improve short-term survival. This study provides experimental evidence for mechanistic research and clinical treatment strategies of hemorrhagic shock under hyperthermic conditions.