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General Anesthesia: S. Mérat, J.-P. Lévecque, Y. Le Gulluche, Y. Diraison, L. Brinquin, and J.-J. Hoffmann Intérêt potentiel du BIS pour détecter une souffrance cérébrale importante : [BIS monitoring may allow the detection of severe cerebral ischemia] Can J Anesth 2001; 48: 1066-1069 [Abstract] [Full text] [PDF]

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BIS monitoring for detection of cerebral ischaemia

Simon D Whyte   (1 February 2002)

BIS monitoring for detection of cerebral ischaemia 1 February 2002
Simon D Whyte, Clinical Lecturer in Paediatric Anaesthesia Royal Liverpool Children's Hospital Send letter to journal: Re: BIS monitoring for detection of cerebral ischaemia sdwhyte{at}liv.ac.uk Simon D Whyte	Sir, I read with interest the reports of Mérat & colleagues (Can J Anesth 2001; 48: 1066-1069) & would like to report a similar observation in a 3 year old child, who was recently anesthetised in our institution. A 3 yr old boy presented for routine day case surgery. Induction with propofol 3.5mg/kg, laryngeal mask airway (LMA) insertion & maintenance of anesthesia with isoflurane in O2/N2O were entirely uneventful. As part of an ongoing evaluation, bispectral index monitoring was instituted after induction, using a BisSensor electrode & a Bispectral Index monitor version 3.3 (Aspect Medical Systems, Newton, MA). BIS readings remained stable in the range 40-50 intraoperatively. At the end of the procedure, anesthesia was discontinued & the child transferred to the recovery area with both LMA & BIS monitoring in situ, & breathing high flow oxygen through a Jackon Rees circuit. In recovery, pulse oximetry was recommenced & the child allowed to wake up in his own time. BIS readings gradually increased through the range 60-70. At a BIS value of 78, the child began to cough & make purposeful movements & the laryngeal mask was removed by the recovery nurse. The child then developed laryngospasm, as evidenced by paradoxical chest wall movement, tracheal tugging & quiet stridor. Apnea rapidly supervened & airway control was taken over by the anesthesiologist, who attempted to provide positive pressure ventilation via the Jackson Rees circuit, with little success. As the oxygen saturation fell into the low 80s, the BIS readings began to decrease. By the time the oxygen saturation reached its lowest value of 76%, the BIS had fallen to 52. The laryngospasm broke whilst suxamethonium was being drawn up & the child became easy to hand ventilate. Oxygen saturation was rapidly restored to >95%, but the BIS values remained in the range 50-60 for two to three minutes, before slowly recovering to the pre-LMA removal value over approximately the next five minutes. Subsequently, BIS rose into the low 80s, at which point the child awoke & began to cry, rendering further BIS monitoring impossible. A postoperative visit 2 hours later revealed no apparent adverse sequelae to the episoade of laryngospasm & the child was later discharged home as planned. The bispectral index is a variable derived from the frontotemporal cortical EEG. The reduction in cortical electrical activity during cerebral hypoxemia has been detected by cerebral function monitoring & it is not surprising that BIS would also be affected. The reduction in higher frequency EEG activity & EEG amplitude that occurs during hypoxemia would account for the fall in the BIS value. I agree with Mérat & colleagues that the application of BIS monitoring to detect cerebral ischemia warrants further investigation.