Effects Of CO₂ Insufflation On Cerebrum During Endoscopic Thyroidectomy In A Porcine Model

Part oneEstablishment of animal model for endoscopic thyroidectomyBackgroundThe incidence rate of thyroid disease in female is higher than in male. The postoperative incisional scar, paraesthesia and complaint in the neck (near the wound region) brought some serious psychological problems to female patients who accepted traditional thyroidectomy. The cosmetic requests of the incision in thyroid operations had been proposed by more and more female patients. In recent years the endoscopic surgery developed rapidly and it is the time for this minimally invasive technique used in thyroid surgery. Endoscopic thyroidectomy is the new technique to comply with the cosmetic requests. The targets of this minimally invasive surgery could be summarized by: achievement of the same results as those obtained with traditional surgery, less trauma, better post-operative course, early discharge from hospital and improved cosmetic results.At the beginning of this new technique, conversion to the traditional approach was often occurred due to the bleeding from the vessels or the thyroid dimension. But accompanying with the development of new technique and matched instruments of endoscopy, endoscopic thyroidectomy became more and more consummate. The indication of endoscopic thyroidectomy gradually enlarged. Many reports indicated thyroid carcinoma had been treated by endoscope, although it limited in those small differentiated carcinoma without lymph node involvement.At present the operative cavity during endoscopic thyroidectomy is usually established and maintained by CO₂ insufflation. CO₂ insufflation proved to be a feasible, safe and convenient method for setting up the operative cavity by its rapid absorptive nature. But along with the prolong of the operative time, the pathophysiological changes caused by CO₂ insufflation was apparently observed.The negative influence to cardiopulmonary function and cerebrum caused by CO2 insufflation was gradually noticed. It is very important that lucubrate and decrease these negative effects to the development of endoscopic throid surgery and to the patients who combine with some specific disease.Now the researches revealed CO₂ insufflation during endoscopic thyroidectomy could affect intracranial pressure and those effects were related closely to the insufflation pressure and time. Could those effects lead to cerebral injury according to the different pressure? How to avoid or minimize the cerebral injury? All these problems have to be solved for the advancement of endoscopic thyroid surgery. It is necessary to study the effects of CO2 insufflation to cerebrum during endoscopic thyroidectomy.Then we need a stable animal model which could be repetitive and similar to the mankind for above destinations. The anatomy, physiological and metabolism characteristics of the swine are similar to the mankind. The Chinese experimental minipigs which reared closely by Chinese Agriculture University just possess these advantages such as light weight, perfect antireversion force and stable inheritable character and fit for the research. We choose them to establish the endoscopic thyroidectomy porcine model and study the effects of CO₂ insufflation to cerebrum.Objective1. To establish the animal model for endoscopic thyroidectomy in Chinese experimental minipigs.2. Validating the security, stability and repeatability of this animal model.MethodsNine Chinese minipigs were randomly divided into 3 groups. Group A underwent tracheal intubation general anesthesia without operative procedure and served as the matched controls, Group B underwent traditional thyroidectomy and Group C underwent endoscopic thyroidectomy with CO₂ pressure at 10 mm Hg. Hemodynamics parameters including heart rate (HR), mean arterial blood pressure (MAP), central venous pressure (CVP), arterial partial pressure of CO₂ (PaCO₂), pH and intracranial pressure (ICP) were measured at baseline, 1 h, 2 h, 3 h, 4 h and 30 min after desufflation. Excisional thyroid tissue was weighed and performed pathological examinations. All values are expressed as mean±standard deviation. Independent t-test and ANOVA were used followed by Bonferroni post hoc analysis using SPSS 16.0 analysis software. A probability value <0.05 was regarded as statistically significant.ResultsAll animals tolerated the whole procedure, the traditional thyroidectomy and endoscopic thyroidectomy were successfully performed in all cases with no serious complications. The animal model for endoscopic thyroidectomy was established successfully. But subcutaneous emphysema near operative region appeared in the animals of Group C while the extremity activities diminished within 24 hours postoperatively.All monitored index of the baseline could be served as the normal reference value of mimipigs.Comparison of ICP and the weight of excisional thyroid tissue among different groups were no significant difference (P>0.05). The operative time (P<0.01) and the length of the incisions (P<0.05) between Group B and C were significantly different. The hemodynamics parameters of Group C varied in different time and some of them were statistical significance.Coefficient variation of the baseline monitored values of different index in all animals (n=9) were all lower than 10% except central venous pressure (CV=12.43%). Conclusions1. All animals tolerated the anesthesia and operation, the baseline values of all parameters which could be served as the normal reference value were determinded.2. The endoscopic thyroidectomy porcine model with comparative security, stability and repeatability was established successfully, it could respond the changes of hemodynamics and ICP sensitively during the operative procedure. Part twoEffects of CO₂ insufflation on cerebrum during endoscopic thyroidectomy in a porcine modelBackgroundEndoscopic thyroidectomy is accepted gradually by patients due to its advantages including minimal invasion, fewer bleeding, better post-operative recovery course, early discharge from hospital and improved cosmetic results. Unlike the abdominal and thoracic cavity, there is no natural cavity in the neck. A man-made operative cavity in the neck must be established before endoscopic thyroidectomy. At present the operative cavity during endoscopic thyroidectomy is usually maintained by CO₂ insufflation after its establishment. CO₂ insufflation proved to be a feasible, safe and convenient method for maintaining the operative cavity by its rapid absorptive nature.Accompanying with the development of endoscopic thyroidectomy. the operative time extends with the increasing difficulty and types of this operation. Long time CO₂ insufflation causes apparent pathophysiological changes of the organism. These changes led by CO₂ absorption in the tissue and its direct pressure are noticed by scholars.The negative influence to cardiopulmonary function and cerebrum caused by CO₂ insufflation is the obstacle to the development of endoscopic thyroidectomy. It is very important that lucubrate and decrease these negative effects as far as possible to the development of endoscopic thyroid surgery and to the patients who combine with any other specific disease.Some studies showed that the incidence rate of headache and vomiting after laparoscopic abdominal operations was higher than that after traditional abdominal operations and believed that it was related with the increase of the intracranial pressure. The clinical observations and animal experiments revealed the increase of ICP would happen whatever in the abdominal or cervical endoscopic operations when the operative cavity was maintained by CO₂ insufflation. The increase of ICP was correlated with the pressure and time of CO₂ insufflation. This showed CO₂ insufflation influenced the cerebrum to some degree. But at present the researches about these effects to cerebrum limited in the intracranial pressure and seldomly to the cerebral injury and its pathological and electronic microscopic changes. It is necessary for the development of endoscopic throid surgery to study the effects of CO2 insufflation to cerebrum during endoscopic thyroidectomy.In view of the current status of the fundamental research on endoscopic thyroid surgery, we plan to explore the effects to cerebrum caused by CO2 insufflation during endoscopic thyroidectomy through the porcine model.Objective1. To observe the effects on the hemodynamics and intracranial pressure causing by different CO₂ insufflation pressure during endoscopic thyroidectomy using the animal model.2. To observe the pathological and electronic microscopic findings of the cerebral tissue and explore the cerebral injury caused by CO2 insufflation.3. To validating the suitable pressure for CO2 insufflation during endoscopic thyroidectomy.MethodsTwelve Chinese minipigs were randomly divided into 4 groups. Group A underwent traditional thyroidectomy and served as the matched controls. Group B, C and D underwent endoscopic thyroidectomy and respectively with CO₂ pressure at 5 mm Hg, 10 mm Hg and 15 mm Hg. HR, CVP, MAP, Arterial partial pressure of CO₂ (PaCO₂), pH and Intracranial pressure (ICP) were measured respectively at baseline, 1 h, 2 h, 3 h, 4 h and 30 min after desufflation. Three trocars' inserted technique and suprasternal fossa approach was used during endoscopic thyroidectomy. After exposing the thyroid glands, left thyroid lobe and the fatty tissue and lymph nodes near right cervical vaginae vasorum was removed completely.Removed the whole cerebrum from the skull under intravenous anesthesia after a week postoperatively. The brain tissue was observed by pathological and electronic microscopic examinations respectively. All values are expressed as Mean±Std.. Independent t-test and ANOVA was used followed by Bonferroni post hoc analysis using SPSS 16.0 analysis software. A probability value <0.05 was regarded as statistically significant.ResultsEndoscopic thyroidectomy was successfully performed in all cases with no serious complications such as bleedings, gas embolism and postoperative death. But the incidence of subcutaneous emphysema near operative region (neck and upper thorax) in the animals of Group D were higher than those of Group B and C. In addition, extremity activities obviously diminished with lower reaction and food ingested in the animals of Group D within 48-72 hours postoperatively.In Group C, mild hypercarbia and acidosis, light increase of the arterial blood pressure and central venous pressure were observed; In Group D, obvious hypercarbia and acidosis, increase of the arterial blood pressure and central venous pressure were observed.All measured values in Group A and B were no significant difference (P>0.05); In Group C the increase of PaCO₂ and the decrease of pH value in different time were significantly different while the mild increase ICP without statistical significance (P>0.05). In Group D the increase of PaCO₂ and ICP, decrease of PH value were significantly different.Compared with Group A, mild cerebral edema was found in Group B while obvious cerebral edema in Group C and D. Comprison of the count of glial cells between Group A and B was not significantly different (P>0.05); Comparisons between other each group have significantly changes (P<0.01). Obvious increased apoptosis neurons and glial cells were observed in Group C and D under electron microscopy. Conclusions1. Long time CO₂ insufflation at high pressure (15 mm Hg) during endoscopic thyroidectomy could cause hypercarbia, acidosis and increase of ICP.2. CO₂ insufflation during endoscopic thyroidectomy could cause cerebral edema and the increase of the neuron and glial cells apoptosis.3. We suggest the pressure of CO₂ insufflation should be lower than 10 mm Hg, 5 mm Hg is the relatively safe and recommended pressure to minimize the negative effects of the cerebrum.