Automated control of anesthesia ten years later: futuristic novelty or present day reality

The specialty of anesthesia evolved following the discovery that drugs were able to create a reversible state of unconsciousness enabling surgical interventions to be performed. The need for human control over such powerful and potentially dangerous compounds was implicit in developing the specialty. The notion of anesthesia as an art practiced by professionals versed in human physiology and pharmacology has not been challenged until recently. In essence, we have known very little about the fundamental nature of anesthesia, and, without a doubt, we have not had means to measure it. John Snow, one of the earliest and most pre-eminent anesthesiologist of his time, stated early on in his career that the greatest challenge is knowing when the ether had been carried far enough, i.e., that the practice of anesthesia was an art rather than a precise science. What has changed to make us believe that we can hand over the control of the anesthetic state to a robot or, more precisely, to a computer-controlled algorithm? The manuscript by Hemmerling et al. in this issue of the Journal certainly forces us to consider whether relinquishing control would be a viable option for providing anesthesia. Our understanding of the nature of anesthesia and our ability to measure at least a component of the anesthetic state have evolved over the past 15 years. Seminal work by Rampil and Antognini has contributed enormously to our knowledge of the anesthesia paradigm. Rampil demonstrated that the ablation of a movement response to a noxious stimulus is due to the action of a volatile anesthetic on a spinal process rather than on a process of the brain. Antognini demonstrated that a significantly higher minimum alveolar concentration was required to prevent movement when anesthetizing a goat’s brain independently of the spinal cord than was required when exposing both the brain and the spinal cord to the volatile anesthetic. These two pieces of information clearly indicated that a critical suppression of the spinal cord is required to achieve anesthesia, yet the spinal cord is not responsible for loss of consciousness, an essential element of general anesthesia. Soon after this work, it was shown that opiates could reduce the minimum alveolar concentration (MAC) of a volatile anesthetic to a value equal to their MAC awake concentration. That is to say, as sufficient opiate is added during the administration of a volatile anesthetic to provide general anesthesia, the concentration of volatile anesthetic is reduced to that which is just needed to render an individual unresponsive to a verbal stimulus. This is not too dissimilar to using a combination of spinal/epidural analgesia and adding just enough volatile anesthetic to render the patient unconscious. Based on this information, I would propose that anesthesia involves initially rendering the patient unconscious by a mechanism within a consciousness centre in the brain and, secondly, preventing a noxious stimulus from reaching this consciousness centre. This knowledge also makes us appreciate that we must be able to measure the effects of the anesthetic on both brain function and spinal cord function if we are to create an automated system to control anesthesia— a challenge. In the late 1940 s and early 1950 s, Bickford began to evaluate the electroencephalogram (EEG) as a measure of anesthetic drug effect and its correlation to loss of consciousness. At this early stage, an automated system of drug delivery to provide anesthesia started to develop. The EEG is a very complex wave pattern that several investigators have tried to reduce to a single derived value P. S. A. Glass, MD (&) Department of Anesthesiology, Stony Brook University Medical Center, HSC Level 4-060, Stony Brook, NY 11794-8480, USA e-mail: pglass@notes.cc.sunysb.edu