Noninvasive Neuromonitoring of Hypothermic Circulatory Arrest in Aortic Surgery

Background and Aims: Circulatory arrest carries a high risk of neurological damage, but modern monitoring methods lack reliability, and is susceptible to the generalized effects of both anesthesia and hypothermia. The objective of this prospective, explorative study was to research promising, reliable, and noninvasive methods of neuromonitoring, capable of predicting neurological outcome after hypothermic circulatory arrest. Materials and Methods: Thirty patients undergoing hypothermic circulatory arrest during surgery of the thoracic aorta were recruited in a single center and over the course of 4 years. Neuromonitoring was performed with a four-channel electroencephalogram montage and a near-infrared spectroscopy monitor. All data were tested off-line against primary neurological outcome, which was poor if the patient suffered a significant neurological complication (stroke, operative death). Results: A poor primary neurological outcome seen in 10 (33%) patients. A majority (63%) of the cases were emergency surgery, and thus, no neurological baseline evaluation was possible. The frontal hemispheric asymmetry of electroencephalogram, as measured by the brain symmetry index, predicted primary neurological outcome with a sensitivity of 79 (interquartile range; 62%-88%) and specificity of 71 (interquartile range; 61%-84%) during the first 6 h after end of circulatory arrest. Conclusion: The hemispheric asymmetry of frontal electroencephalogram is inherently resistant to generalized dampening effects and is predictive of primary neurological outcome. The brain symmetry index provides an easy-to-use, noninvasive neuromonitoring method for surgery of the thoracic aorta and postoperative intensive care.Peer reviewe

Real-time algorithm for changes detection in depth of anesthesia signals

This paper presents a real-time algorithm for changes detection in depth of anesthesia signals. A Page-Hinkley test (PHT) with a forgetting mechanism (PHT-FM) was developed. The samples are weighted according to their "age" so that more importance is given to recent samples. This enables the detection of the changes with less time delay than if no forgetting factor was used. The performance of the PHT-FM was evaluated in a two-fold approach. First, the algorithm was run offline in depth of anesthesia (DoA) signals previously collected during general anesthesia, allowing the adjustment of the forgetting mechanism. Second, the PHT-FM was embedded in a real-time software and its performance was validated online in the surgery room. This was performed by asking the clinician to classify in real-time the changes as true positives, false positives or false negatives. The results show that 69 % of the changes were classified as true positives, 26 % as false positives, and 5 % as false negatives. The true positives were also synchronized with changes in the hypnotic or analgesic rates made by the clinician. The contribution of this work has a high impact in the clinical practice since the PHT-FM alerts the clinician for changes in the anesthetic state of the patient, allowing a more prompt action. The results encourage the inclusion of the proposed PHT-FM in a real-time decision support system for routine use in the clinical practice. © 2012 Springer-Verlag

Correlation of EEG spectral entropy with regional cerebral blood flow during sevoflurane and propofol anaesthesia

ENTROPY™ index monitoring, based on spectral entropy of the electroencephalogram, is a promising new method to measure the depth of anaesthesia. We examined the association between spectral entropy and regional cerebral blood flow in healthy subjects anaesthetised with 2%, 3% and 4% end-expiratory concentrations of sevoflurane and 7.6, 12.5 and 19.0 µg.ml-1 plasma drug concentrations of propofol. Spectral entropy from the frequency band 0.8–32 Hz was calculated and cerebral blood flow assessed using positron emission tomography and [15O]-labelled water at baseline and at each anaesthesia level. Both drugs induced significant reductions in spectral entropy and cortical and global cerebral blood flow. Midfrontal-central spectral entropy was associated with individual frontal and whole brain blood flow values across all conditions, suggesting that this novel measure of anaesthetic depth can depict global changes in neuronal activity induced by the drugs. The cortical areas of the most significant associations were remarkably similar for both drugs