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Response to letter by Dr Hegarty
- Stephen R Froom (29 June 2008)
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Relevance of Bispectral Index in Paediatric Intensive care
- Dominic Hegarty (16 June 2008)
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Stephen R Froom, Consultant Paediatric Anaesthetist
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We would like to thank Dr Hegarty for his interest and response to our study. It is known that the Bispectral index (BIS) monitor is less reliable in sedated infants the under one year of age . Of the 28 sets of data in our study, five were between six months and one year of age (four of these five were from the same infant). Malviya et al. showed that the mean BIS and the cutoff values on the receiver-operating-characteristic curve for mild, moderate, and deep sedation were significantly lower in infants six months compared with older children at each sedation level 1. Ganesh and colleagues titrated anaesthetic agents to specific BIS values under general anaesthesia in the paediatric age group2. He found that the utility of BIS monitoring in infants, particularly those less than six months old, is questionable, as there is little correlation between BIS values and other measures of the depth of anaesthesia in this subset of patients. Bannister et al designed a study to evaluate the effect of BIS monitoring on anesthetic use and recovery characteristics in paediatric patients against standard practice (SP) 3. She showed that in the children six months to three years of age, there were no significant differences between the SP and BIS groups in anaesthetic use or recovery measures. In infants less than six months of age less volatile agent was used in the BIS group. I agree with Dr Hegarty that age should be taken into account when analyzing data derived from BIS monitoring. All sedation scoring systems for measuring sedation levels in critically ill sedated children in ICU suffer from the same problem of poorly distinguishing between deep and moderate sedation. This includes the University of Michigan sedation scale (UMSS). Motas et al. warned that the UMSS may underestimate the number of patients in deep sedative stages, since the actual measurement requires physical stimulation of the patient 4. Thus, application of the stimulus will tend to shift subjects from a deeper level of sedation to a lighter level (they wake up in response to stimulation). This will then skew the cut-off number used to distinguish deep from light sedation. The COMFORT score is validated to measure level of sedation and psychological distress in sedated children. This distress may be due to intentional stimulation, such as physiotherapy or tracheal suctioning, or non- intentional such as awareness or anxiety. The benefit of the COMFORT score being non-invasive is that the confounding factor of stimulation is not added. The major benefit of the UMSS when comparing BIS to a sedation scale is that it is practically very quick to perform and therefore more accurately reflects the BIS value at that very point in time. The BIS is known to fluctuate considerably especially during stimulation. I encourage a study that would validate BIS and the UMSS in sedated ill children during a period of stimulation. References: 1. Malviya S, Voepel-Lewis T, Tait AR. Anesth Analg 2005; 102 :389-94. 2. Ganesh, Arjunan; Watcha, Mehernoor F. Current Opinion in Anaesthesiology. June 2004; 17(3) :229-234. 3. C.F. Bannister, .K. Brosius, J. C. Sigl, B. J. Meyer, P. S. Sebel. Anesth Analg 2001;92:877-881. 4. Motas D ,McDermott NB ,VanSickle T ,Friesen RH. Pediatr Anesth 2004; 14 (3) : 256–260. Conflict of Interest:None declared |
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Dominic Hegarty, SpR Anaesthesia & Intensive Care Medicine Our Lady's Hospital fo Sick Children, Crumlin, Dublin, Ireland
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Dear Sir, Bispectral index (BIS) offers a “probability of state” measurement derived by empirically estimating the electroencephalogram (EEG) parameters in an adult volunteer database (1). In general, the electrical activity of the brain changes during growth and development, warranting age-specific considerations and cautious interpretation for EEG’s and BIS data (2). Indeed in children younger than 1 year of age the limited discriminative value of the BIS has been reported (3). Fromm et al. (4) identified a discrepancy between the left and right side of the brain BIS in children, however, there is a wide range of age reported within the nineteen patients examined. If adequately powered, age-specific data supported the discrepancy between the left and right BIS this would make the results truly clinically relevant. Secondly, to circumvent part of the problem surrounding stimulation in sedation studies, it is generally recommended that BIS should be measured immediately before stimulation to be contemporaneous with the University of Michigan sedation scale (UMSS). This scale depends on stimulation and it has been shown to indicate good correlation with BIS (- 0.73) (3). While the use of the COMFORT scale may be “the most practical scoring system in the PICU” it may not be the most appropriate assessment tool to use in conjunction with BIS, and it is not validated as a measure of psychological stress following physiotherapy / tracheal stimulation. Perhaps the UMSS should be considered in future studies in this area. Yours, Dr. Dominic Hegarty, SpR Anaesthesia & Intensive Care Medicine, Our Lady’s Hospital for Sick Children, Dublin, Ireland. References: 1. Crick F, Koch A. Nat Neurosci 2003; 6:119-26 2. Kerssens C, Sebel PS. Anesth Analg 2006; 102:380-2 3. Malviyan S, Voepel-Lewis T, Tait AR. Anesth Analg 2005; 102 :389-94 4.Fromm SR, Malan CA, Mecklenburgh JS, Price M et al. Br J Anaesth 2008; 100:690-6 Conflict of Interest:None declared |
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