The effect of different pressures of pneumoperitoneum on the optic nerve sheath diameter (ONSD) - prospective study

Laparoscopic surgery is a unique, minimally invasive technique and a key tool in various therapeutic and diagnostic procedures. In performing this minimal access procedure carbon dioxide (CO2) pneumoperitoneum is created for visualization and to allow surgical manipulation.Increased intra-abdominal pressure (IAP) and CO2 gas during pneumoperitoneum leads to various systemic changes involving cardiovascular, respiratory and cerebral physiology. Though these physiological changes well tolerated by healthy individuals, may have adverse consequences in elderly with borderline organ function and critically ill patients. Conventional method of gas insufflation during laparoscopic surgeries leads to IAP of 12-16 mmHg (standard IAP). It was emphasizedthat with low pressure pneumoperitoneum (IAP <10mmHg) there is less postoperative pain, better hemodynamics, reduced surgical events and also has neuro-protective effect.Several studies documented the effect of raised IAP on intra cranial pressure (ICP). The mechanisms of increase of ICP during laparoscopy may be due to increase IAP impeding drainage of the lumbar venous plexus, impairment of cerebrospinal fluid (CSF) absorption and cerebral vasodilation due to hypercarbia. Raised ICP may cause significant neurological complications. Various methods are used in measuring ICP, which are invasive and time consuming. The optic nerve sheath is in continuity with the dura mater, surrounded by subarachnoid space which is continuous with intracranial subarachnoid space. So any change in ICP is transmitted to optic nerve sheath. Optic nerve sheath diameter (ONSD) measured by ultrasonography a non-invasive imaging technique, is a safe and accurate method in diagnosing increased ICP. In our study we plan to investigate the effect of standard (13-15mmHg) and low (6-8mmHg) pressure pneumoperitoneum on intracranial pressure (ICP) using ultrasound measurements of optic nerve sheath diameter (ONSD).