Carbon dioxide embolism during salvage transanal total mesorectal excision in “frozen pelvis”: Two case reports

Figure 1 Perioperative hemodynamic and capnographic trends that demonstrate the biphasic signature of carbon dioxide embolism. A: Case 1: The graph depicts the sequence of events surrounding the transient hemodynamic collapse. Phase 1 (“gas lock”) was characterized by the precipitous drop in end-tidal carbon dioxide (ETCO₂, orange solid line) coincident with the significant decline in mean arterial pressure (blue dashed line) and heart rate (pink dash-dot line). Phase 2 (“rebound hypercapnia”) was manifested during resuscitation as a paradoxical surge in ETCO₂ (> 50 mmHg) due to the washout of dissolved carbon dioxide; B: Case 2: The graph illustrates the event that progressed to cardiac arrest, and the subsequent cardiopulmonary resuscitation (CPR). The values shown represent the last recorded measurements immediately prior to CPR initiation. A similar biphasic pattern was observed: An initial drop in ETCO₂ during the gas lock phase, followed by the rebound hypercapnia upon return of spontaneous circulation. CPR: Cardiopulmonary resuscitation; CO₂: Carbon dioxide.

Figure 2 Schematic illustration of the mechanism of carbon dioxide embolism in the “frozen pelvis”. The sagittal cross-section of the male pelvis during salvage transanal total mesorectal excision demonstrates the transanal access platform (gel cap) tightly sealing the anal verge. The laparoscopic instruments were depicted to enter through this single port into the mesorectal plane. The presacral space was encased in dense, white scar tissue (labeled “Frozen Pelvis”) due to prior therapy. The transected presacral vein was held wide open (“Transected, Open Presacral Vein”) by the stiff fibrosis (tethering effect). Blue carbon dioxide bubbles flowed directly from the insufflated rectal cavity into the open venous lumen, driven by the pneumatic pressure gradient.