The Impact Of Pneumoperitoneum And Posture On Respiratory Function During Laparoscopy In Morbidly Obese Patients

Objective: Surgery and anesthesia on morbidly obese patients carry an appreciable risk,especially laparoscopic surgery.The effect of maneuvers accompanying laparoscopy,such as pneumoperitoneum,Trendelenburg and reverse Trendelenburg position,on respiratory system mechanics and oxy- genation in morbidly obese patients is significant, and this effect is inco- mpletely characterized. By comparing the indicators of respiratory mecha- nics and blood gas analysis results of obese patients and those with normal body weight before and after pneumoperitoneum in different positions, we can understand the characteristics of respiratory system in morbidly obese patients, analyse the various possible factors affecting the respiratory function , probe the differences between fat persons and standard weight persons.Methods: we studied 20 female patients undergoing laparoscopic gynecologic operation and laparoscopic cholecystectomy.All patients were ASA physical statusⅠorⅡ,non-smokers,and free of cardiac, pulmonary, renal or neuromuscular disease.And then each group was fractionated to the morbidly obese group and the normal weight group according to BMI(body mass index).All patients received premedication with IM Atropine(0.5mg) and Luminal(0.1g) 30 minutes before anesthesia. After preoxygenation, an- esthesia was induced by intravenous injection with midazolam,fentanyl, etomidate.Treacheal intubation(7.0~7.5mm inside diameter endoreacheal t- ube) was facilitated with atracurium. Total IV anesthesia was maintained with propofol,atracurium and fentanyl. The lungs were ventilated with oxygen(fraction of inspired oxygen [FiO2=1]) with intermittent positive- pressure ventilation (IPPV), and the ventilator setting was set at a frequency of 10 breaths/min and a tidal volume of 8ml/kg .The machine applying pne- umoperitoneum pours a gas to abdominal cavity inner first with 1L/min speed,the 6L/min speed continues aerating,to make abdominal cavity inner pressure maintain in 12~15mmHg.The Peak was recorded by using the ane- sthesia apparatus. A continuous blood gas monitor was used to monitor PaCO2 and PaO2. These datas were recorded in supine, Trendelenburg (30°head-down), and reverse Trendelenburg (30°head-up) body positions before and after insufflation of the abdomen with CO2. Pulmonary oxyg- enation was assessed by the alveolar-to-arterial oxygen tension difference according to PaCO2 and PaO2.Data are means±sD.Effects of body position, weight and abdominal insufflation were analyzed by repeated measures analysis of variance. And then we can described polyline maps.Results: Peak was higher in morbidly obese compared with normal- weight patients before or during pneumoperitoneum, either undergoing laparoscopic cholecystectomy or laparoscopic gynecologic operation(P<0.05). Whereas body posture (head down and head up) did not induce addi- tional large alteration . Pneumoperitoneum caused a significant increase in Peak (P<0.05,P<0.01), these changes was larger in morbidly obese pat- ients compared with normal-weight patients(P<0.05). Only body weight, and not the body position or pneumoperitoneum, was a significant factor in determining the alveolar-to-arterial oxygen tension difference. And the dif- ference was higher in morbidly obese patients than the normal-weight pat- ients all the time(P<0.01).Conclusion: Morbidly obesity and pneumoperitoneum have significant effects on respiratory mechanics, whereas PaO2 was adversely affected only by increased body weight.Repositioning the patient from the supine position into the Trendelenburg or reverse Trendelenburg position had no effect on oxygenation either before or after abdominal insufflation.