New 'closed-loop' system can provide tightly controlled anesthesia in patients undergoing surgery

A new 'closed-loop' system can precisely adjust levels of anesthetics and analgesic drugs in patients undergoing surgery, reports a study in the March issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).

The system constantly monitors a measure of brain activity, called the bispectral index (BIS), to precisely maintain a target level of anesthesia. "The controller allows the automated delivery of propofol and remifentanil and maintains BIS values in predetermined boundaries during general anesthesia better than manual administration," concludes the new study, led by Dr. Ngai Liu of Hopital Foch, Suresnes, France.

Closed-Loop System Provides Tightly Controlled Anesthesia
The researchers report the evaluation of a "closed-loop controller" to guide intravenous administration of propofol (an anesthetic agent) and remifentanil (a morphine-like opioid drug). In the study, 196 patients undergoing surgery were randomly assigned to receive propofol/remifentanil anesthesia using the closed-loop system or manual drug adjustment.

Based on a global score, the quality and stability of anesthesia were higher in patients assigned to the closed-loop system. They were in the target BIS range 82 percent of the time during surgery, compared to 71 percent in the manual group. "Overshoot" and "undershoot"—anesthesia potentially too deep or not deep enough—were both less frequent in the closed-loop group.

Patients in the closed-loop group received more frequent and smaller dose modifications of both drugs. The overall propofol dose was similar between groups, although patients in the closed-loop group received more remifentanil. There was no difference in responses to painful stimuli—an important indicator of the adequacy of anesthesia. Patients in the closed-loop group had their breathing (tracheal) tube removed an average of one minute earlier.

Although several studies have reported on closed-loop administration of propofol based on BIS measurement, the new report is one of the first to use this approach to controlling remifentanil administration. Especially since it included a wide range of patients undergoing surgery in "real world" conditions, it's an important step forward in the moving this automated anesthesia technology to the operating room. Dr. Liu and colleagues write, "Several improvements of the controller are required before trials on large populations to demonstrate that automated control of anesthetic delivery is a useful tool."

An accompanying editorial by Dr. Anthony R. Absalom of University Medical Center Groningen, the Netherlands, and colleagues praise the study as a "brave and pioneering effort." The computer-controlled system provides more stable control of the BIS than a human anesthesiologist could possibly achieve.

However, Dr. Absalom and co-authors note that the system still has "a lack of theoretical insight" because of limitations in the way it responds to individual variations in sensitivity to anesthetic drugs. "Time, further investigations, and further experience are required to determine how relevant and significant the limitations are," they conclude.