MedWire News: An automatic system that monitors patients' needs for anesthesia and analgesia during surgery outperforms manual control of anesthesia on some indices, research shows.
"The current study demonstrated the interest of automated technology for monotonous and repetitive tasks," say Marc Fischler (Hôpital Foch, Suresnes, France) and colleagues. But they add: "The human brain is more efficient in making complex decisions."
The team used the M-Entropy monitor (GE Healthcare, Helsinki, Finland), which analyzes two electroencephalogram parameters: state entropy (SE) and response entropy (RE). The system used SE to assess need for an anesthetic (propofol) and RE to gauge the need for an analgesic (remifentanil).
Sixty-one patients undergoing elective surgery were randomly assigned to undergo anesthesia induction and maintenance controlled by the M-Entropy monitor or by an experienced anesthesiologist.
The automatic system made a median of 28 remifentanil and 21 propofol dose adjustments per hour during the maintenance phase, compared with 10 and eight adjustments, respectively, by the anesthesiologists.
The primary outcome was a global score of SE, which included maintenance of SE between 40 and 60. The average score was significantly lower in the M-Entropy group than in the manual control group, at 25 versus 44, indicating tighter control of anesthesia by the automatic system.
Automatic control maintained SE within the 40-60 range 80% of the time versus 60% of the time with manual control.
"We make the assumption that tight control of SE or RE is preferable to greater variability," say Fischler et al in Anesthesiology. "However, there is currently no evidence that tight control actually improves patient outcomes."
Indeed, measures such as blood loss, somatic events, neuromuscular block boluses, median normalized morphine dose, and time to extubation did not differ between the groups.
Editorialists Gregory Crosby and Deborah Culley (Brigham and Women's Hospital, Boston, Massachusetts, USA) stress that the study was not a direct test of electroencephalogram-guided drug delivery. "Rather it was about who or what did a better job using the information."
In this respect, computer control was as good as or slightly better than the anesthesiologists, yet "the current processed electroencephalogram monitors are no panacea for anesthetic depth monitoring and likely will never be able to handle all eventualities, patients, and drug combinations," say Crosby and Culley.
They also note that the trial was underpowered to detect differences in intraoperative awareness, making a larger study essential.
"Indeed, because of wide interindividual variation in the bispectral index or spectral entropy during administration of commonly used anesthetic agents, others have questioned the ability of these indices to differentiate reliably consciousness from unconsciousness," they say.
MedWire (http://www.medwire-news.md/) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012
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