An Unusual Site for BIS Monitoring

To the Editor: We recently performed an unusual case of BIS monitoring in a patient undergoing surgery in the ventral position. The 52-yr-old patient (ASA physical status: 2) was admitted for burns of second degree (8%) and had to undergo skin graft surgery in the ventral position. The duration of surgery was projected as 90 min and consisted of skin grafting of the back. After induction of anesthesia using fentanyl 5 μg/kg and propofol 2 mg/kg, endotracheal intubation was facilitated using rocuronium 0.6 mg/kg. BIS monitoring (Aspect A-2000 monitoring system, Aspect Medical) was chosen. The patient presented with a completely baldhead. Therefore a BIS reading was attempted via application of the BIS sensor on the occipital region (Fig. 1A). A second BIS sensor was applied at the forehead as standard. Initial readings appeared very similar, with a mean impedance of 2 kg at the occiput and 2.5 kg at the frontal site (Fig. 1B). BIS readings from both sites were recorded every 30 s throughout surgery. Fifty-five minutes after the beginning of BIS monitoring, surgery was finished. Sevoflurane was stopped 6 min after the end of sevoflurane application at a BIS reading of 90, the patient opened his eyes, and was extubated 1 min afterward. The BIS values of the two BIS sensors were compared (Fig. 2). Agreement between the values was calculated at a bias of 1 (BIS occiput: frontal) with limits of agreement of −7 to 9, respectively.Figure 1.: A, shows placement of BIS sensor at the occipital region. B, shows two Aspect 2000 monitors simultaneously recording signals from the occipital region (above) and the frontal region at the beginning of the case.Figure 2.: BIS monitoring via BIS sensors placed frontally and at the occipital region, simultaneously.We present an unusual case of BIS monitoring. Application of the BIS sensor was made possible by the fact that the patient’s head was shaved. Despite the fact that EEG tracing therefore reflected occipital signals, both sites could have been used interchangeably. In this case, occipital monitoring was easier to apply and would have been preferable in order to avoid pressure points. Our case illustrates the possibility to use an alternative monitoring site at the occipital region. Thomas M. Hemmerling, MD, DEAA Stéphane Deschamps, MSc Guillaume Michaud Guillaume Trager, MS, MSc The Neuromuscular Research Group (NRG) Department of Anesthesiology Université de Montréal Montréal, Canada [email protected]

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