Preoperative cerebral oxygen saturation could be a risk marker for adverse cardiac surgery outcome

A study published in the January 2011 issue of Anesthesiology is one of the first to show that low preoperative cerebral oxygen saturation (ScO2) could be an important physiological risk marker for adverse outcome in cardiac surgery patients.

Lead study author Matthias Heringlake, M.D., and his colleagues from Universitaet zu Luebeck, Germany, observed ScO2 levels in 1,178 cardiac surgery patients by using noninvasive near-infrared spectroscopy (NIRS), a quick and simple method of monitoring, among other things, the adequacy of a patient's brain oxygen supply.

"Preoperative ScO2 levels are reflective of the severity of patients' cardiopulmonary dysfunction, they are associated with short-term and long-term postsurgical complications, and they might be an important risk predictor in patients undergoing cardiac surgery," said Dr. Heringlake.

Previous studies have indicated that avoiding a decrease in ScO2 below levels that were measured before surgery improves the outcomes of cardiac surgical patients. The majority of these studies included patients who had acceptable ScO2 levels before surgery.

Dr. Heringlake's study is perhaps the first to concentrate on those patients who come into surgery with already low ScO2 levels. He said his study shows that a preoperative ScO2 level of less than 50 percent was an independent indicator of mortality in the patients he observed.

"Our data clearly show that preoperative ScO2 levels reflect cardiopulmonary function. Consequently, maintaining patients with low preoperative ScO2 on this level may not be appropriate," said Dr. Heringlake. "Further research is needed to determine the optimal perioperative ScO2 target for these patients."

In an accompanying editorial, John M. Murkin, M.D., F.R.C.P.C., of the Schulich School of Medicine at the University of Western Ontario, praised the work of Dr. Heringlake for opening up new research questions in this important area of study.

"Could presurgical ScO2 levels act as a preemptive marker for patients requiring more intensive monitoring and expectant care in the postoperative period, thus enabling earlier planning and mobilization of necessary resources?" asked Dr. Murkin. "And perhaps most intriguingly… would early preoperative treatment of low ScO2 enhance postoperative recovery and decrease perioperative morbidity? While such speculations are currently beyond the evidence presented here, the report by Dr. Heringlake and colleagues is a provocative step in that direction."

Dr. Heringlake said that his findings could have relevant implications for other clinical fields in which cerebral NIRS monitoring is utilized, such as in high-risk patients undergoing noncardiac surgery and in patients experiencing medical emergencies.

"Preoperative ScO2 levels are related to a person's overall cardiopulmonary function, and they may thus serve as a noninvasive estimate of not just cerebral oxygen levels, but the overall oxygen demands of the patient," said Dr. Heringlake.