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02-09-2010 | Anaesthesiology | Article

Closed-loop system maintains tight hypnosis control


Free abstract

MedWire News: A rule-based adaptive closed-loop system for propofol administration maintains superior control of anesthesia compared with manual administration, report Canadian researchers.

But editorialist Peter Glass (Stony Brook University Medical Center, New York, USA) contended that closed-loop anesthesia systems still have a long way to go to prove themselves better than manual control.

In the current study, control of hypnosis, defined as being within 10% of the bispectral index (BIS) target of 45, was achieved for 55% of the time in the 20 patients randomly assigned to the closed-loop group.

This was significantly higher than the 33% rate achieved in 20 patients assigned to manual propofol administration, report Thomas Hemmerling (Montreal General Hospital) and team in the Canadian Journal of Anesthesia.

Poor control of hypnosis (>30% from BIS target) occurred for 7% versus 19% of the time in patients assigned to closed-loop or manual administration, respectively.

Also, patients assigned to closed-loop administration emerged from hypnosis significantly faster than those assigned to manual administration, at 9 versus 12 minutes.

The team's closed-loop system is controlled from a computer, which determines the propofol dose based on an algorithm. The user only has to enter the age and weight of the patient and the target BIS, and the system thereafter controls the rate of propofol infusion. The target BIS can be adjusted during surgery if needed.

In his editorial, Glass agreed that closed-loop hypnosis systems have proven successful, and do make sense if analgesia is given with a regional anesthetic, so that only hypnosis is required during surgery.

But he stressed that "the interaction of noxious stimulation, analgesia, hypnosis, and anesthesia is complex."

For example, he said that "if opiates are provided for analgesia during times of intense noxious stimuli, a closed-loop system would respond by increasing the hypnotic to maintain the pre-set BIS value, whereas the more appropriate response may be to provide a brief period of increased analgesia."

He said: "No closed-loop system is able, as yet, to make such subtle decisions."

Glass also noted that the BIS of 45 in the current study minimizes the complicating effects of noxious stimuli and analgesia and said that closed-loop systems must be tested under more challenging conditions.

"We should compare the best anesthetic each anesthesia provider can administer," he said.

"Only then can we determine if automated control of anesthesia is a futuristic novelty or a present day reality. I remain optimistic that closed-loop control of anesthesia ultimately will prove to be superior and will become routine in providing anesthesia."

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Eleanor McDermid