A 49-year-old woman (160 cm tall, weighing 50 kg), with histories of depression and adjustment disorder, was injured in a collision accident with a train, and was rushed to our hospital in a state of cardiopulmonary arrest and with her left leg amputated by the trauma. After arriving at the hospital, she was immediately intubated and ventilated, and resuscitation was continued. She was diagnosed as being in cardiac arrest due to hemorrhagic shock, and emergency thoracotomy and aortic occlusion were performed. Her heartbeat resumed within approximately 20 min, following massive fluid infusion and blood transfusion. Subsequently, the aortic occlusion was converted to percutaneous aortic blockade and the chest was closed, and transection of the right hip and angioembolization of the right superior gluteal artery were performed. She was extubated on the ninth hospitalization day and was given 1 L/min of oxygen by nasal inhalation to maintain SpO2 at above 97%. Blood laboratory test results at this time revealed a prothrombin time-international normalized ratio of 1.09, activated partial thromboplastin time of 25.5 s, fibrinogen level of 238 mg/dL, antithrombin-III (AT-III) of 107.9%, and elevated D-dimer level of 23.59 microg/mL. Thoracoabdominal X-rays showed fractures at Th10, 11, and L3-5, and magnetic resonance imaging showed findings of spinal cord injury at the Th7-11 levels. Along with other treatments, as required, perioperative deep vein thrombosis (DVT) prophylaxis was applied, in the form of withholding of anticoagulation, application of elastic stockings to the lower extremities and intermittent pneumatic compression, without performing lower extremity vascular echocardiography. The patient was scheduled for debridement on the 11th day after right hip dissection surgery, and heparin was to be started thereafter. For debridement, anesthesia was induced with propofol at a target concentration of 2.0 mug/mL, along with remifentanil 0.2 mug/kg/min, followed by rocuronium 50 mg. Anesthesia maintenance was performed with propofol at a target concentration of 1.5-2 microg/mL and remifentanil 0.1-0.2 microg/kg/min, with rocuronium, as needed, for muscle relaxation. Phenylephrine was administered as needed to maintain blood pressure. Intraoperatively, the patient was monitored using standard monitoring techniques, including direct measurement of arterial pressure, electrocardiography, SpO2, and bispectral index. Blood gas analysis showed a partial pressure of arterial oxygen (PaO2) of 121.3 mmHg and a partial pressure of arterial carbon dioxide (PaCO2) of 38.5 mmHg at a fraction of inspiratory oxygen (FiO2) of 0.5 at the start of surgery. Approximately 1 h after the start of surgery, her SpO2 decreased suddenly from 98% to the 60% level, heart rate increased (from 77 to 94 bpm), and blood pressure decreased (from 78/52 to 64/45 mmHg). End-tidal carbon dioxide tension (EtCO2) also decreased (from 33 to 25 mmHg) at the same instant. Although her blood pressure increased with the administration of a vasopressor, poor oxygenation persisted and EtCO2 remained low (19 mmHg). Blood gas analysis performed at this time showed a PaO2 of 53.9 mmHg and PaCO2 of 49.9 mmHg at an FiO2 of 1.0. Based on these findings, we suspected the development of PTE and performed transthoracic echocardiography (TTE). Evaluation revealed pressure overload in the right ventricle. Then, TEE was performed, which revealed a thrombus in the right pulmonary artery (Figure 1). After consulting with a cardiovascular surgeon, venoarterial extracorporeal membrane oxygenation (VA-ECMO) with femoral artery pumping and femoral vein debridement was performed. Following VA-ECMO initiation, her oxygenation improved and hemodynamics stabilized. Since the patient had recently undergone traumatic amputation of her lower leg and there were wounds all over her body, thrombolytic therapy was not administered since it could have increased the risk of bleeding and infection. Contrast-enhanced computed tomography (CT) was performed, which revealed a thrombus in the pulmonary artery (Figure 2). The next day, thrombectomy was performed under an open chest. No anticoagulation was used preoperatively, and the activated clotting time remained between 150 and 180 s while on VA-ECMO. After pulmonary artery thrombectomy, an organic thrombus was also found at the inferior vena cava side of the right atrium, and a dark red to partly white thrombus was observed in the right pulmonary artery (Figure 3). The patient's post-thrombectomy course was uneventful, with the maintenance of hemodynamics and oxygenation. Postoperatively, the patient was admitted to the intensive care unit under sedation and intubation and was extubated on the third postoperative day. Thereafter, she had a good course with no recurrence of PTE. She had no neurological complications.