Abstract： Background Laparoscopic cholecystectomy has been widely used in clinical practice during the recent decades; however,the effects of pneumoperitoneum and the surgery on the coagulation system are largely unknown.This clinical study aimed to observe any possible effects of pneumoperitoneum and the surgery on the coagulation system of patients.Methods This was a prospective observational study.The inclusion criteria included (1) patients with chronic cholecystitis and/or cholecystic polyps and (2) patients in the relief stage of acute cholecystitis.The exclusion criteria included (1) patients in the episodic stage of acute cholecystitis and those complicated with cholangiolithiasis; (2) patients with concomitant hematologic diseases,damages to the liver function,malignant tumors or immune system diseases,or patients complicated with thrombotic or hemorrhagic disorders; and (3) patients who had taken anticoagulant medication within a week before surgery.Fifty patients who were hospitalized into our department for elective laparoscopic cholecystectomy between November 2011 and February 2013 were eligible and enrolled into this study.Of the 50 patients,22 were male and 28 female.The age of the patients ranged from 29 to 78 (mean 56.7±11.5) years.The surgery for each of the 50 patients was performed with the same equipment and conditions.The surgeries for all the patients were performed under general anesthesia with the patients in a 30-degree head-up tilted posture,and the pressure of pneumoperitoneum was maintained at 13 mmHg.Venous blood specimens were taken from each patient before and at the end of pneumoperitoneum (i.e.,0 hour after surgery) and at 8 hours after surgery for determination of prothrombin time (PT),activated partial thromboplastin time (APTT),fibrinogen (Fib),thrombin time (Tr),and D-dimer (DD).The results of the determinations of these parameters were compared.Results (1) All the patients recovered well without any complications.(2) The pre-pneumoperitoneum values of the parameters of coagulation had normalized.(3) The PT values slightly increased (P ＞0.05) at the end of pneumoperitoneum (i.e.,0 hour after surgery) and decreased by 0.5 seconds at 8 hours after surgery as compared to the pre-pneumoperitoneum values (P ＜0.05).(4) APTT at 0 and 8 hours decreased by 1.4 seconds (P ＞0.05) and 3.7 seconds (P ＜0.05) respectively as compared to pre-pneumoperitoneum values,while the difference between the APTT values at 0 and 8 hours after surgery was not statistically significant (P ＞0.05).(5) FIB determined at 0 hour post-operation increased by 0.1 g/L as compared to pre-pneumoperitoneum values (P ＞0.05); however,the FIB values at 8 hours after operation increased by 1.2 g/L as compared to the pre-pneumoperitoneum values (P ＜0.05),and increased by 1.1 g/L as compared to 0 hour post-operation (P ＜0.05).(6) The TT values obtained at 0 and 8 hours post-operation were not significantly different as compared to the pre-pneumoperitoneum values (P ＞0.05).(7) The DD values gradually increased after operation; as compared to pre-pneumoperitoneum values,DD at 0 and 8 hours after operation increased by 210.8 ng/ml and 525.9 ng/ml respectively (P ＜0.05) and DD at 8 hours after operation increased by 315.1 ng/ml as compared to 0 hour post-operation (P ＜0.05).Conclusions The pneumoperitoneum for laparoscopic cholecycstectomy may lead to postoperative hypercoagulation in the patients,and thereby may increase the risks for development of postoperative thrombosis; Patients may have risks for occurrence of thrombosis within 8 hours after the operation,to which attention should be paid in favor of preventing thrombosis.