Monitoring of ocular perfusion pressure during vitrectomy may prevent visual field defect

Continuous monitoring and management of infusion bottle height and mean ocular perfusion pressure can help maximize safety.

Issue: February 2016

Continuous monitoring of mean ocular perfusion pressure during pars plana vitrectomy may prevent surgically induced visual field defect, a surgeon told colleagues at the FLOREtina meeting in Florence, Italy.

“Unexplained visual field loss after vitrectomy has been reported in up to 14% of patients,” Tommaso Rossi, MD, said.

He cited a study by Taban and colleagues showing that non-arteritic anterior ischemic optic neuropathy (NAION) may develop during vitrectomy and that visual field defects after vitrectomy are common and partly attributable to NAION.

The underlying cause, he explained, is an imbalance between arterial pressure and IOP, resulting in mean ocular perfusion pressure (MOPP) reduction and consequent ischemia.

“During surgery, IOP is significantly higher than in baseline conditions due to the bottle being above 35 mm Hg, while blood pressure tends to be lower because patients are sedated. As a result, the ocular perfusion pressure may remain below safe values for up to 50% of surgery, and optic nerve function may be compromised,” Rossi said.

Continuous monitoring

New software with the Optikon 2000 R-Evolution vitrectomy system processes arterial pressure and IOP data, providing continuous real-time measurement of MOPP during surgery, Rossi said.

Target MOPP values are set preoperatively, and during surgery, the machine signals whether the patient is within or beyond the safety threshold. The surgeon can therefore move the bottle up or down, depending on the arterial pressure of the patient at each moment, he said.

“Glaucoma specialists will tell you, when you go around 50 mm Hg of MOPP it is OK, when you go down below 30 mm Hg of MOPP it is dangerous. The machine tells you what percentage of the surgery is spent in each of the three segments: OK, dangerous, definitely dangerous,” Rossi said. “At end of surgery you get a report telling you the percentage of surgery and the overall number of minutes the patient spent on a certain perfusion pressure, which may help you understand why some patients have visual field loss after surgery.”

Previous study

In a previous study published in Investigative Ophthalmology & Visual Science by Rossi and colleagues, MOPP was calculated intraoperatively in 18 patients undergoing pars plana vitrectomy for a variety of reasons. Sixteen patients (88.9%) had a significant intraoperative MOPP decrease compared with baseline, and 17 (94.4%) dipped at least once during surgery below 30 mm Hg of MOPP. Fifteen patients spent 20% of the overall surgical time below 30 mm Hg of MOPP, and five patients spent more than 50% of the time below that level.

“Most of the 18 patients were beyond the safety threshold for more of the surgery despite bottle height being around 35 mm Hg. We would believe that this bottle height is more or less safe, but if the patient is over 90 over 60 because he or she has been sedated, it is not safe at all,” Rossi said.

The same paper also reported that MOPP “varied significantly during different steps of the same surgery, suggesting that virtually all procedures pose the patient at risk for being exposed to dangerously low perfusion for some time.”

Continuous monitoring and possibly counteracting a decrease in MOPP by modifying bottle height during surgery will make vitrectomy safer, minimizing ischemic complications, Rossi said. – by Michela Cimberle and Matt Hasson

References:
Rossi T, et al. Invest Ophthalmol Vis Sci. 2014;doi:10.1167/iovs.14-14493.
Taban M, et al. Graefes Arch Clin Exp Ophthalmol. 2007;doi:10.1007/s00417-006-0420-5.

For more information:
Tommaso Rossi, MD, is head of the Ophthalmology Department, San Martino University Hospital, Genoa, Italy. He can be reached at Via Benedetto XV, 6 16132, Genoa, Italy; email: tommaso.rossi@usa.net.

Disclosure: Rossi reports no relevant financial disclosures.