Introduction: Resuscitative thoracotomy is an extreme intervention reserved for patients in peri-arrest from suspected thoracic or subdiaphragmatic haemorrhage. Although overall survival is low, selected patients may achieve meaningful recovery when anatomy-driven decision-making and damage control principles are applied. We present a rare case of survival following extreme multi-mechanism trauma requiring clamshell thoracotomy and aortic cross-clamping. Case Presentation: A 40-year-old man sustained severe polytrauma after an alleged shotgun and knife injury to the right chest, and being run over by a vehicle. He rapidly deteriorated during pre-hospital transfer with peri-arrest physiology. Treatment: Code Crimson was activated prior to ED arrival. The patient was intubated without induction agents. Persistent haemodynamic instability prompted immediate clamshell thoracotomy, revealing a large right haemothorax, lung lacerations, and a disrupted right hemidiaphragm with active bleeding from a major liver injury. No pericardial tamponade or left-sided thoracic bleeding was identified. Given ongoing instability from suspected subdiaphragmatic haemorrhage, the descending thoracic aorta was cross-clamped. The liver and diaphragm were packed in ED, allowing transfer to theatre for damage control laparotomy and thoracic exploration. Right lung lacerations were controlled with stapled wedge resections, mammary vessels were ligated, and temporary thoracic and abdominal closure was performed. The patient required prolonged intensive care and staged reconstruction before rehabilitation. Conclusion: This case demonstrates that ED clamshell thoracotomy, guided by physiology and systematic anatomic assessment, can be lifesaving even in extreme multi-mechanism trauma. Aortic cross-clamping functioned as a temporary physiological bridge to definitive haemorrhage control. Survival depended on rapid decision-making and adherence to damage control principles.