Purpose:
Given the risk of postoperative vision loss secondary to ischemic optic neuropathy and intraocular pressure (IOP) changes with anesthesia and positioning, we hypothesized the combination of Trendelenberg positioning and long case duration of robotic prostatic surgery to produce an increase in IOP and thus a decrease in ocular perfusion pressure (OPP), increasing risk of postoperative vision loss. Our purpose was to examine changes in IOP and associated changes in OPP during robotic prostate surgery, as this has not been well-studied.
Methods:
Six patients undergoing robotic prostate surgery were enrolled in the study. At 6 different time points, systemic blood pressure was recorded and IOP was measured, using a tonopen. The time points were as follows: T1: Awake, upright, prior to administration of any anesthetic; T2: After induction; T3: After Trendelenberg positioning; T4: After pneumoperitoneum; T5: After pneumoperitoneum evacuated; T6: In the recovery room, awake, supine. Mean arterial pressure (MAP) and OPP were then calculated.
Results:
After induction of anesthesia, 2 patients had marked decreases in OPP of more than 25mmHg. In all patients, the OPP further decreased after Trendelenberg. After pneumoperitoneum, change in mean OPP was minimal, but one subject had a large drop in OPP to the low-20s. After evacuation of pneumoperitoneum, 4 patients had further declines in OPP. Table 1 summarizes mean, SD and 95%CI for MAP, IOP, and OPP at each time point.
Conclusions:
This study demonstrated a drop in OPP near to and below a threshold of 50mmHg, suggesting that hemodynamic changes with positioning and abdominal insufflation during robotic prostate surgery may overwhelm autoregulation of blood supply to the optic nerve. This could increase the risk of postoperative ischemic optic neuropathy and vision loss. Further studies are needed to elucidate this risk, as those who are particularly susceptible to optic nerve damage (with glaucoma or have prolonged surgeries) may benefit from interventions to prevent or diminish potential optic nerve damage.
Keywords: intraocular pressure • outflow: trabecular meshwork