Isomer Predicts Poor Outcome After TAA Repair

BY BETSY BATES

SAN DIEGO -- Elevated levels of an isomer in cerebrospinal fluid can predict adverse neurologic outcomes following thoracic aortic aneurysm repair, researchers reported in a poster presentation at the annual meeting of the American Neurological Association.

Dr. Michael L. McGarvey of the University of Pennsylvania in Philadelphia, and Dr. Sindhu Ramchandren of the University of Michigan in Ann Arbor, found a correlation between changes over baseline in isoprostane levels and poor neurologic outcomes in a prospective study of 40 patients.

Isoprostanes have proved to be sensitive and specific markers of lipid peroxidation and oxidative damage in vivo.

During the study, isoprostanes were measured in cerebrospinal fluid (CSF) for 24 hours, beginning preoperatively. A change in CSF isoprostanes of at least 0.15 ng/mL over baseline had an 89% probability of predicting a bad neurologic outcome following surgery.

Isoprostanes measurement was performed in the University of Pennsylvania's general laboratory, and could be replicated in a tertiary hospital laboratory at a cost of about $50 per patient, said Dr. Ramchandren.

Intraoperative somatosensory evoked potentials (SSEPs) were also measured and had a 76% probability of predicting a bad outcome. SSEPs are electrical signals generated by the nervous system in response to stimuli, and might be a "useful adjunctive measure" in identifying thoracic aortic aneurysm patients at risk, the investigators noted.

Thoracic aortic aneurysms are associated with high morbidity and mortality. Approximately half rupture, a generally fatal complication.

Surgical repair is a precarious procedure; mortality of 50% has been reported in emergent cases and 3%-15% in scheduled cases. The incidence of paraplegia after surgery is 5%-15%, they noted.

At the university, an aggressive approach that involved measuring intraoperative SSEPs, initiating CSF drainage at the onset of surgery and throughout 24 hours, and conducting perioperative neurologic examinations, nonetheless showed an 11% rate of transient paraplegia and a 3% rate of permanent paraplegia between 2000 and 2001.

The investigators undertook a study of CSF isoprostanes, CSF lactate, and SSEPs in an attempt to identify which patients might be at highest risk of a poor neurologic outcome so that targeted, aggressive clinical management might be applied.

Of the three measurements, only CSF lactate proved of little benefit in achieving that goal in 40 patients, 35 of whose surgeries were scheduled and 5, emergent.

The authors recommended confirmation of their study in a larger multicenter trial.

"Dr. McGarvey and his group have shown that intensive monitoring and aggressive blood pressure management, among other factors, can reduce the incidence of delayed paraplegia post- [thoracic aortic aneurysm] repair," Dr. Ramchandren said in an interview.

"Unfortunately, we do not currently know how long to continue this level of care for all patients, and costwise, it would be impractical [to use it for everyone]. Having a 24-hour sample that identifies patients at risk would help identify those patients whom we can target for more intensive care," Dr. Ramchandren added.

The lead surgeon on the study was Dr. Joseph E. Bavaria. Financial support was provided by a grant from the Hospital of the University of Pennsylvania.

When asked to comment upon this story, Dr. Ali F. AbuRahma, professor of surgery and chief of vascular surgery at the Robert C. Byrd Health Sciences Center, West Virginia University, Charleston Area Medical Center stated: "This is a nice study on a very challenging clinical problem, which carries a relatively high morbidity and mortality.

"Several authorities have advocated various methods to monitor patients and, perhaps, minimize the development of paraplegia after thoracic aortic aneurysm repair. These include, but are not limited to intraoperative SSEPs and CSF drainage, and now this study advocates monitoring the level of isoprostanes in the CSF.

"The conclusions of this study are somewhat limited by the sample size and, as suggested by the authors, a larger multicenter study would be helpful. The clinical implications of this study on the new endovascular treatment for thoracic aortic aneurysms need to be investigated also," according to Dr. AbuRahma.