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“While previous work suggests that maintaining a lighter plane of anesthesia provides short-term benefits such as faster recovery, better hemodynamic control and reduced respiratory complications, nausea and vomiting and duration of hospitalization, it does not appear to prevent major morbidity,” said lead investigator Basem Abdelmalak, MD, associate professor in the Department of General Anesthesiology and Outcomes Research at the Cleveland Clinic, in Ohio.

The results are part of the DeLiT (Design and Organization of the Dexamethasone, Light Anesthesia and Tight Glucose Control) trial, a randomized, single-center analysis of the effects that dexamethasone, glucose control and, in this case, depth of anesthesia have on perioperative inflammation and complications in surgery patients.

In examining the effects of anesthesia depth, Dr. Abdelmalak and his colleagues compared a composite of more than one dozen serious outcomes—including myocardial infarction, stroke, sepsis and 30-day mortality—in 194 patients given light anesthesia and 187 given deeper anesthesia. Anesthetic depth was evaluated by bispectral index monitoring (BIS, Covidien). Dr. Abdelmalak and his team also compared plasma concentrations of the inflammatory marker high-sensitivity C-reactive protein (hsCRP).

Patients randomized to light and deep anesthesia had median BIS values of 51 (range: 47-54) and 43 (40-48), respectively (P<0.001). Those assigned to lighter anesthesia spent a median of 16% (4%-40%) of their time under sedation with BIS values below 45, compared with 66% (36%-86%) of the time for patients who received deeper anesthesia (P<0.001).

Dr. Abdelmalak’s group found no significant differences in the incidence of morbidity and mortality between the two groups. There also was no correlation between median BIS values, time spent under anesthesia with a BIS value less than 45 and morbidity or mortality. Concentrations of hsCRP were similar in the two groups, according to the researchers.

Dr. Abdelmalak said earlier studies that found an increased incidence of poor outcomes with deeper anesthesia have examined those with other clinical risk factors, including a “triple low” of low BIS, low mean arterial pressure and low mean arterial concentration of volatile anesthesia (Anesthesiology News, November 2009, page 1). However, his group did not look at this combination of possible risk factors.

Kate Leslie, MD, professor of anesthesia and pain management at Royal Melbourne Hospital in Victoria, Australia, led a long-term follow-up study of the B-Aware trial, which also examined the effects of sedation depth in nearly 2,500 surgical patients at high risk for intraoperative awareness (Anesth Analg 2010;110:816-822). Her team found an increased risk for all-cause long-term mortality, myocardial infarction and stroke if patients were sedated at BIS values below 40 for more than five minutes.

Dr. Leslie suggested that one reason Dr. Abdelmalak’s team found no increase in complications and deaths with deeper sedation may have been that differences in sedation depth between the two groups were too narrow.

“Median BIS values were 43 and 51 and the median percentage of time spent at BIS below 45 was only 66% in the deep sedation group,” Dr. Leslie emphasized. “Future investigators should seek greater separation in depth of anesthesia between the two groups. Furthermore, many of the observational studies on the topic have reported excess mortality in the years following surgery, so a long-term follow-up is desirable.”

However, she added, “Dr. Abdelmalak and colleagues have used a very efficient and elegant methodology to address an intriguing and a difficult area to study.”

Daniel Sessler, MD, the Michael Cudahy Professor and Chair of the Department of Outcomes Research at the Cleveland Clinic, and a co-investigator of the current study, said that although the mean BIS difference in the deep and light anesthesia groups was only 8, patients randomized to deep anesthesia spent four times longer with a BIS value less than 45.

“Despite this substantial difference, our primary outcome—a composite of serious complications—did not differ between the groups,” Dr. Sessler said. “While this result appears to contradict the recent report from Leslie et al, that analysis was observational. The underlying B-Aware study was randomized, but the depth-of-anesthesia analysis was not. In contrast, we conducted a randomized trial which provides the strongest protection against bias and confounding.”

The results of the current study may have implications that go beyond important patient safety concerns, said Marc E. Koch, MD, MBA, president and CEO of Somnia, Inc., a national anesthesia management consulting organization in New Rochelle, N.Y.

“With changes in health care before us, tens of millions of new patients—many with surgical needs—will be entering the health care system without the requisite personnel or facility capacity to fully address this new-found volume,” said Dr. Koch, who was not involved in either study. “It is likely that the swath of surgical patients migrating to nonhospital facilities that have more fluidity—and discretion on whom they serve—may offer shorter wait times and lines for surgical bookings and better throughput due to their ability to mitigate the patient congestion many hospitals will see. Because of this, over time, volumes ending up in private ambulatory facilities will be of broader scope and greater acuity.

“Studies have already shown that case duration, in and of itself, is not necessarily associated with higher rates of and major morbidity,” Dr. Koch continued. “This study goes one step further by demonstrating that anesthesia depth does not impact the level of hsCRP or lead to an increase in major morbidity.

“Thus, with longer surgical times, and now deeper planes of anesthesia not necessarily being associated with major morbidity,” he said, “non-hospital facilities may choose to evaluate the sorts of cases they undertake and not necessarily turn away longer cases or those associated with higher planes of anesthesia.”