Editorial Comment on: Effect of Mannitol on Ultrasonographically Measured Optic Nerve Sheath Diameter as a Surrogate for Intracranial Pressure During Robot-Assisted Laparoscopic Prostatectomy with Pneumoperitoneum and the Trendelenburg Position by Jun et al.

Regarding the concept that ultrasonographic measurement of the optic nerve sheath diameter may serve as a practical and reliable technique to noninvasively evaluate the intracranial pressure of patients undergoing robot-assisted laparoscopic prostatectomy in the steep Trendelenberg position with carbon dioxide pneumoperitoneum with the intent to administer mannitol if indicated to decrease optic nerve sheath diameter as a surrogate to intracranial pressure: Concern for intracranial pressure elevation and undesirable sequelae (postoperative neurologic deterioration) during robot-assisted laparoscopic prostatectomy and other robot-assisted laparoscopic operations in the pelvis (most significantly, gynecologic oncology and colorectal operations) is real, as is concern for intraocular pressure elevation causing postoperative visual loss, especially in patients with glaucoma. ¹ To date, measurement and evaluation of intracranial pressure and intraocular pressure have not been practical, although this study suggests measurement itself may not be clinically necessary before administration of mannitol.

Use of point-of-care ultrasonography has become pervasive in the practice of anesthesiology: performance of nerve blocks (preoperatively, intraoperatively, and postoperatively), placement of intravascular catheters, and, for diagnosis, including but not limited to evaluation of placement of endotracheal tube and immediate detection of pneumothorax after central line placement, or identification of postoperative hematoma in postanesthesia care unit without waiting for a radiograph or computed tomography scan.

Ultrasonography equipment is thus now readily available as are anesthesiologists trained to use it. Equipment ranges from large and sophisticated equipment placed in vascular surgery suites to a hand-held device not much larger than a glucometer or other point-of-care laboratory instrument that transmits an image to a personal cell phone.

Anesthesiologists trained in the use of ultrasound appear always to be interested in mastering new techniques, and optic nerve sheath diameter appears to be quite adoptable as a technique. Thus use of mannitol could be limited to those at risk based on optic nerve sheath diameter.

However, mannitol is administered with low risk during other laparoscopic operations, most notably during laparoscopic partial nephrectomy (for renal protection, prior to renal artery cross-clamping), with no significant untoward sequelae, and could, even without the use of ultrasound to identify those at risk of elevated intracranial pressure or intraocular pressure, be administered empirically. Patients could then be effectively rehydrated once they are returned to a supine position, at the end of the case and in the postanesthesia care unit.