Un indice bispectral étrangement élevé

We report a case of a falsely elevated-bispectral index (BIS™) during a general anaesthesia combining remifentanil TCI, desflurane and nitrous oxide for an isolated-limb chemotherapy. During surgery, BIS™ increased and stabilized around 70, with neither residual neuromuscular blockade nor clinical sign of awareness. These high BIS™ values were attributed to high-electromyographic activity and electric artefacts, such as extracorporeal-circulation machine and tourniquet. At the end of the surgery, the BIS™ returned to expected values around 50. The patient did not complain of intraoperative recall. This case reminds us that the BIS™ has some limits as being sensitive to EMG or environment artefacts that should be eliminated before deepening anesthesia. To do so, a decision algorithm is proposed that may be used for all situations of surprising high BIS™, taking into account the level of neuromuscular blockade, clinical response to orders and the presence of devices likely to induce electrical or mechanical artefacts.