Effects of CO2 insufflation on cerebrum during endoscopic thyroidectomy in a porcine model

The operative cavity during endoscopic thyroidectomy is maintained mainly by CO(2) insufflation. We designed this study to explore the effects of CO(2) insufflation on the cerebrum during endoscopic thyroidectomy in a porcine model. Twelve Chinese minipigs were randomly divided into four groups. Group A underwent traditional thyroidectomy and served as the control group. Groups B, C, and D underwent endoscopic thyroidectomy at CO(2) pressures of 5, 10, and 15 mmHg, respectively. Arterial partial pressure of CO(2) (PaCO(2)), pH, and intracranial pressure (ICP) were measured at five time points. Cerebral tissue was removed and evaluated pathologically and by transmission electron microscopy (TEM). There were no statistical differences between group A and group B in all measured values. PaCO(2) increased and pH decreased gradually, while ICP did not change significantly in Group C. In Group D, PaCO(2) increased and pH decreased gradually, while ICP increased significantly. In Groups C and D, cerebral edema appeared obviously and the quantity of glial cells increased significantly compared with that in Groups A and B. The ultrastructures of neurons and glial cells changed apparently, accompanied by increasing apoptosis in Groups C and D as seen by TEM. Lengthy CO(2) insufflation at high pressure (15 mmHg) caused an increase in ICP and cerebral edema during endoscopic thyroidectomy. It even caused cerebral edema at 10 mmHg in spite of no increase in ICP. Therefore, we suggest that the pressure of CO(2) insufflation should be lower than 10 mmHg, and that 5 mmHg is the relatively safe and recommended pressure.