Acute pulmonary embolism caused by PMMA: an experimental study in canines

Objective: To establish acute pulmonary embolism model in canines by injecting bone cement (PMMA), via the femoral vein, and to investigate the differences in physiopathological changes of acute pulmonary embolism caused by different volume of PMMA. Methods: A total of 18 adult canis familiars were randomly divided into three groups (A, B and C) with 6 dogs in each group. After the dogs were anaesthetized, thoracic plain CT scanning was performed, which was followed by puncturing of right femoral vein and left femoral artery, placement of vascular sheaths and injection of PMMA via venous sheath. The dose of PMMA used in group A, B and C was 0.5 ml, 1 ml and 2 ml, respectively. Blood gas and mean pulmonary arterial pressure were monitored continuously until 60 minutes after the injection, the results were recorded. The pulmonary angiography was carried out just before and 5 minutes after PMMA injection. One hour after the procedure, thoracic CT scanning, both plain and contrast-enhanced, was performed. The dogs were sacrificed two hours after the operation. The specimens of both lungs were collected and sent for histological examination. Results: Technical success of injecting PMMA through femoral vein was achieved in all eighteen dogs, and the acute pulmonary embolism model was successfully established, which was proved by CT scans and pathological examination. After the injection of PMMA, both the blood partial pressure of oxygen (PO2) and the blood partial pressure of carbon dioxide (PGO2) in all three groups showed no statistically significant changes when compared with those determined before the injection. In group C, the mean pulmonary arterial pressure determined immediately, 30 and 60 minutes after PMMA injection was (24.12±1.74) mmHg, (23.84±1.25) mmHg and (24.17±1.63) mmHg respectively. The pre-injection mean pulmonary arterial pressure was (16.47±0.55) mmHg. The difference in mean pulmonary arterial pressure was statistically pulmonary between pre-injection value and post-injection ones. In group A and B, the post-injection mean pulmonary arterial pressure was not significantly different from the pre-injection value. In all experimental dogs, the post-operative plain CT scans showed that there were high-density shadows on both lungs, especially on lower lung field. In some dogs of group C, the CT scans demonstrated filling-defects in pulmonary arterial branches and signs of atelectasis. Angiography showed no evidence of the obstruction of pulmonary arterial trunk. Pathological examination found the cement emboli within the pulmonary branches, and no secondary thrombosis formation was seen. Conclusion: No significant correlation exists between the severity of acute pulmonary PMMA embolism and the PMMA volume used in procedure if the dose is ≤2 ml. When the patient's cardiopulmonary function is under normal condition, acute pulmonary PMMA embolism caused by 2 ml injection may not lead to an obvious respiratory insufficiency. (authors)