Evaluation of the effect of different peep applications on optic nerve diameter in obese patients undergoing laparoscopic surgeries

Evaluation of the effect of different PEEP applications on optic nerve diameter in obese patients undergoing laparoscopic surgeries Background and purpose Positive end-expiratory pressure (PEEP) application, which is used to improve oxygenation by keeping the alveoli open, may cause an additional increase in intracranial pressure (ICP) by compressing cerebrospinal flow outflow and cerebral venous drainage during pneumoperitoneum in obese patients who undergo laparoscopic surgery. Measurement of noninvasive optic nerve sheath diameter (ONSD) via ultrasonography is used to determine increasing ICP. In this study, we aimed to evaluate the effect of different PEEP applications on optic nerve diameter in obese patients undergoing laparoscopic surgery. Materials and Methods In our study, 26 patients with a Body Mass Index (BMI) of 30 and above and with ), American Society of Anesthesiologists Physical Status Classifications (ASA ) I-II status undergoing laparoscopic surgery in the reverse Trendelenburg position were included. After anesthesia induction, the patients were divided into PEEP 5 group and PEEP 8 group by the closed envelope method. Patients' gender, age, weight, BMI, ASA status, operations performed, hemodynamic data during the case (systolic-diastolic-mean arterial pressures, pulse, saturation) and ONSD were recorded intraoperatively at regular intervals. After anesthesia induction, ONSD measurement of patients were performed with linear ultrasound probe over the closed eyes eyelid horizontally at 5th minute (T1), 5th minute (T2) and 30th minute (T3) of the pneumoperitoneum and at the end of surgery (T4), and averaged. Optic nerve sheath diameter over 5.5 mm was considered significant. IBM SPSS Statistics 20 version was used for statistical analysis, p <0.05 values were considered statistically significant. Results: 12 patients in PEEP 5 groups and 10 patients in PEEP 8 groups completed the study. In total, 17 women (77.3%) and 5 men (22.7) participated and it was statistically significant between the two groups (p = 0.020). There was no difference in demographic (age, BMI, comorbidity, ASA) and hemodynamic data between the groups. No difference was observed in the patients of ONSD at all times measured between the two groups intraoperatively. When we compared the ONSDs within the groups, there was no difference within the group of PEEP 5 , wheras the measurements at 5 minutes (T2)and 30 minutes (T3) after pneumoperitoneum , and at the end of surgery (T3) in the PEEP 8 group were significantly higher than the T1 measurements acceptedas basal measurement. When we evaluated ONSD by dividing the patients into 3 groups according to their BMI indexes (BMI between 30-30.4, BMI between 35-39.9, BMI≥ 40), no statistically significant difference was observed between the groups, while the increase in T2, T3 and T4 measurements according to the basal measurements were higher in BMI of 40 and above than other groups . Discussion and Conclusion Obesity is associated with multipl life threatening conditions. Although there are studies in laparoscopic obesity surgery investigating the relationship between obesity and ICP in the literature, there are a limited number of studies comparing PEEP. In our study, we believe that the effect of 8 PEEP application on the optic nerve diameter in obese patients who underwent laparoscopic surgery is similar to the group in which PEEP 5 was applied, therefore PEEP 8 can be used in obese patients who underwent lung protective ventilation. As the PEEP increments may increase ONSD becouse of the duration of pneumoperitoneum and BMI risings, we thoght that PEEP increasings would be safer by measuring ONSD with US. Key words: obesity, laparoscopy, ONSD, PEEP