Pitfalls and challenges when assessing the depth of hypnosis during general anaesthesia by clinical signs and electronic indices

Abstract

The objective of this article was to review the present methods used for validating the depth of hypnosis. We introduce three concepts, the real depth of hypnosis (DHreal), the observed depth of hypnosis (DHobs), and the electronic indices of depth of hypnosis (DHel-ind). The DHreal is the real state of hypnosis that the patient has in a given moment during the general anaesthesia. The DHobs is the subjective assessment of the anaesthesiologist based on clinical signs. The DHel-ind is any estimation of the depth of hypnosis given by an electronic device. The three entities DHreal, DHobs and DHel-ind should in the ideal situation be identical. However, this is rarely the case. The correlation between the DHobs and the DHel-ind can be affected by a number of factors such as the stimuli used for the assessment of the level of consciousness or the administration of analgesic agents or neuro muscular blocking agents. Opioids, for example, can block the response to tactile and noxious stimuli, and even the response to verbal command could vanish, hence deeming the patient in a lower depth of hypnosis than the real patient state. The DHel-ind can be disturbed by the presence of facial muscular activity. In conclusion, although several monitors and clinical scoring scales are available to assess the depth of hypnosis during general anaesthesia, care should be taken when interpreting their results.

Performance of Anesthetic Depth Indexes in Rabbits under Propofol Anesthesia

“…The cortical depression reflected in the electroencephalogram would be expected to have better prediction probability with propofol clinical effects. 21 We point out some possible explanations for the ability of the electromyographic activity to predict clinical signs: First, there are some important limitations related to the use of clinical scales of anesthetic depth. 22 Although applied in the daily clinical practice, their correlation with real cerebral hypnotic drug effect is not well established because surrogate observations, such as reflex responses and eyeball position, result from independent neurologic pathways and are not directly involved in the neurologic process of consciousness.…”

Cerebral State Index during Propofol Anesthesia

“…To investigate this, we selected the OAA/S score because it provides a good correlation with a clinical reflection of the hypnotic component of anesthesia and has been tested prospectively, 27 although it has its limitations, as we pointed out in a previous article. 28 Burst suppression represents a benign pattern frequently seen in a healthy brain at deep levels of the hypnotic component of anesthesia. It can be identified in the raw electroencephalogram and is composed of episodes of electrical quiescence (the "suppression") alternated with high-frequency, high-amplitude electrical activity (the "bursts").…”

Automation of anaesthesia: a review on multivariable control

“…However, clinical signs alone are not reliable for measuring anaesthetic adequacy [19,89]. They are subjective, discontinuous [45] and vary considerably depending on patient, disease, drug and surgical technique [89]. Continuous quantitative measurement can not only improve the quality of assessment, but is also essential as a controlled variable in a closed-loop control system.…”