Neuromonitoring Cuts Stroke Risk Of Carotid Surgery

By Kerri Wachter

ORLANDO -- Targeted neuromonitoring can dramatically reduce stroke complications during and after carotid endarterectomy, according to one expert speaking at the annual meeting of the American Society of Neuroimaging.

"A targeted monitoring strategy--and I stress the word targeted--has virtually eliminated intraoperative stroke and stroke due to postoperative carotid thrombosis in our unit," said A. Ross Naylor, M.D., professor of vascular surgery at the University of Leicester in England.

Carotid endarterectomy (CEA) carries a small but important risk of stroke for both symptomatic and asymptomatic patients. Although neuromonitoring can be an effective way to minimize the risks associated with carotid endarterectomy, there is "more to monitoring than deciding who needs a bit of plastic tubing shoved into their artery. You have to ask the right questions, and then you'll start to get the right answers."

Dr. Naylor reported that his team uses continuous transcranial Doppler (TCD) sonography and completion angioscopy for intraoperative monitoring. "We ask very limited questions of transcranial Doppler," he said. The group tries to maintain a mean middle cerebral artery velocity greater than 15 cm/sec.

Hemodynamic failure is usually not the problem. "I have seen over 1,200-1,500 carotids now in our unit, and I cannot ascribe hemodynamic failure to any patient." Technical errors and thrombosis are the more likely culprits. TCD reveals shunt malfunctions and "is the only method capable of diagnosing on-table thrombosis," he said.

Dr. Naylor and his team use angioscopy to monitor the quality of a procedure. "You can examine the inside of the artery before you restore flow," he said.

The results have been impressive. From 1989 to 1991, they performed 100 CEAs, with an intraoperative stroke rate of 4%. The combined TCD/angioscopy protocol was initiated in 1992. Through 2004, 1,239 patients have undergone CEA with an intraoperative stroke rate of 0.2%.

"What we were most interested to observe, though, was that this protocol had no impact whatsoever on the rate of stroke, due to postoperative carotid thrombosis," said Dr. Naylor.

Luck intervened.

On two occasions, the TCD was left on during the postoperative period. Initially, the patients had no problems but in the very early postoperative period TCD documented 157 emboli in one patient and 348 emboli in the second patient, both resulting in neurologic deficit.

When these patients were reexplored, the team found platelet-rich thrombus, even though other evidence suggested that the quality control monitoring was working.

It's estimated that 50%-60% of patients with sustained high-rate embolization in the early postoperative period progress to thrombotic stroke.

"For the first time ever, you now have the ability to predict and anticipate those small number of patients who are likely to progress on to thrombotic stroke." Dr. Naylor's group now uses 3 hours of TCD postoperative monitoring.

They now intervene in patients with more than 25 emboli in any 10-minute period documented by TCD. Intravenous 10% dextran 40 is started at a rate of 20 mL/hour.

The rate of dextran 40 infusion is titrated, increasing by 5 mL/hour every 10 minutes, to a maximum of 40 mL/hour. If the rate of embolization stabilizes, the dextran 40 therapy is continued for 12 hours.

"Since we instituted this program of selective dextran therapy, it has transformed our practice. We have not had a single stroke due to postoperative carotid thrombosis during that time," Dr. Naylor said.