Consciousness, cognition and brain networks: New perspectives

Consensus document for multimodal intraoperatory neurophisiological monitoring in neurosurgical procedures. Basic fundamentals

The present work aims to establish a guide to action, agreed by anaesthesiologists and neurophysiologists alike, to perform effective intraoperative neurophysiological monitoring for procedures presenting a risk of functional neurological injury, and neurosurgical procedures. The first section discusses the main techniques currently used for intraoperative neurophysiological monitoring. The second exposes the anaesthetic and non-anaesthetic factors that are likely to affect the electrical records of the nervous system structures. This section is followed by an analysis detailing the adverse effects associated with the most common techniques and their use. Finally, the last section describes a series of guidelines to be followed upon the various intraoperative clinical events.

Predicting unconsciousness after propofol administration: qCON, BIS, and ALPHA band frequency power

During anesthesia induction with propofol the level of arousal progressively decreases until reaching loss of consciousness (LOC). In addition, there is a shift of alpha activity from parieto-occipital to frontal zones, defined as anteriorization. Whilst monitoring LOC and anteriorization would be useful to improve propofol dosage and patient safety, the current devices for anesthetic depth monitoring are unable to detect these events. The aim of this study was to observe LOC and anteriorization during anesthesia induction with propofol by applying electrodes placed in the frontal and parietal areas. Bispectral index (BIS) and quantium consciousness index (qCON) monitors were simultaneously employed. BIS™ and qCON sensors were placed in the frontal and parieto-occipital regions of 10 alopecic patients who underwent anesthesia with propofol, alfentanil, and remifentanil. The initial biophase target of propofol was 2.5 mcg/mL which was gradually increased until reaching LOC. Wilcoxon signed-rank test was used to study differences in alpha power and qCON/BIS indices along the study; and Pk value to evaluate predictive capability of anteriorization of BIS, qCON, and alpha waves. Parietal BIS and qCON values became significantly higher than frontal values 15 min after loss of eye reflex. Anteriorization was observed with both monitors. Pk values for BIS and qCON were strongly predictive of frontal alpha absolute power. During anesthesia induction with propofol it is possible to identify anteriorization with BIS and qCON in the frontal and parieto-occipital regions. Both indices showed different patterns which need to be further studied.

Influence of general anaesthesia on the brainstem

The exact role of the brainstem in the control of body functions is not yet well known and the same applies to the influence of general anaesthesia on brainstem functions. Nevertheless in all general anaesthesia the anaesthesiologist should be aware of the interaction of anaesthetic drugs and brainstem function in relation to whole body homeostasis. As a result of this interaction there will be changes in consciousness, protective reflexes, breathing pattern, heart rate, temperature or arterial blood pressure to name a few. Brainstem function can be explored using three different approaches: clinically, analyzing changes in brain electric activity or using neuroimaging techniques. With the aim of providing the clinician anaesthesiologist with a global view of the interaction between the anaesthetic state and homeostatic changes related to brainstem function, the present review article addresses the influence of anaesthetic drug effects on brainstem function through clinical exploration of cranial nerves and reflexes, analysis of electric signals such as electroencephalographic changes and what it is known about brainstem through the use of imaging techniques, more specifically functional magnetic resonance imaging.