Steep Trendelenburg positioning is required for optimal surgical exposure for certain procedures, including robotic assisted laparoscopic urologic and gynecologic procedures. The position is associated with increased intracranial pressure (ICP) and its complications such as post-operative vision loss (POVL) and post-op delirium [Lee 2013]. Therefore, it is essential to measure ICP intra-operatively in order to implement real time management. The gold standard for ICP measurement is an external ventricular drain (EVD). However, it is invasive and not practical for the majority of non-neurosurgical procedures. Trans-ocular ultrasound measurement of Optic nerve sheath diameter (ONSD) is a non-invasive alternative for ICP measurement [Tayal et al 2007; Nash et al 2016]. Compared to EVD it is non-invasive, less expensive and efficient. It has been validated as a screening tool for identification of patients with elevated ICP who required treatment in several larger studies [Nash et al 2016; Blecha et al 2017]. During these procedures prior pre-cautions to prevent increased ICP focused on fluid restriction/selection. Ultrasound measurement of ONSD has not been routinely employed. Furthermore, consideration has rarely been given to the benefits of total intravenous anesthesia (TIVA) rather than volatile anesthetics for anesthesia maintenance during these procedures. Considering the complications of increased ICP, sonographic measurement could prove to be a practical method to efficiently monitor the ICP surrogate [Riaz et al 2016; Nash et al 2016; Banerjee et al 2017]. This study will perform intra-operative sonographic ONSD measurements in order to compare the change in ONSD during transition from inhalational maintenance anesthesia (using sevoflurane) to total intravenous anesthesia (TIVA) using propofol.~While other studies have demonstrated that the use of pneumoperitoneum and steep Trendelenburg positioning can lead to an increase in ICP as determined by use of ONSD (Robba et al. 2016), this study describes the added role of ONSD measurement for guiding the choice of anesthesia maintenance (TIVA vs sevoflurane) during surgery in the steep-Trendelenburg position.
We will prospectively compare change in ONSD during anesthesia with sevoflurane-only versus anesthesia with propofol-only in two groups of patients undergoing urologic and gynecologic surgery in the steep Trendelenburg position. We hypothesize that there will be a significant decrease in the size of ONSD during transition from sevoflurane-only anesthesia to propofol-only anesthesia.