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Revista Brasileira de Anestesiologia

Print version ISSN 0034-7094On-line version ISSN 1806-907X

Rev. Bras. Anestesiol. vol.57 no.4 Campinas July/Aug. 2007 



Comparison of the bispectral index in awake patients with cerebral palsy*


Comparación de los valores del índice bispectral en pacientes con parálisis cerebral en estado de vigilia



Verônica Vieira da CostaI; Rafael Villela S. D. Torres, TSAI; Érika Carvalho Pires ArciII; Renato Ângelo Saraiva, TSAIII

IAnestesiologista do Hospital Sarah
IIEstatística do Hospital Sarah
IIICoordenador de Anestesiologia da Rede Sarah de Hospitais

Correspondence to




BACKGROUND AND OBJECTIVES: The EEG-BIS was created after studies in healthy adult subjects, and studies in children were first published in 1998. Cerebral palsy (CP) is secondary to a static lesion of the developing brain. The need to perform exams and surgical procedures to correct deformities, under anesthesia or sedation, is common in these patients. The need for monitoring of the hypnotic state in anesthetized patients has increased; patients with cerebral palsy can be included in this group of patients. The objective of this study was to evaluate the efficacy of the awake EEG-BIS in patients with cerebral palsy (CP) by comparing it with patients without neurological disorders (without CP).
METHODS: Two groups of patients were evaluated: one composed of patients with the diagnosis of cerebral palsy, and the other with subjects without central nervous system (CNS) disorders. The day before the surgery, hospitalized patients were connected to the EEG-BIS monitor and were asked to close their eyes. The values on the monitor were recorded at 10-minute intervals on a standard form, and the mean value for each patient was calculated.
RESULTS: One hundred and eighty-eight patients of both genders, mean age of 10.07 ± 2.9 (CP) and 10.21 ± 3.1 (without CP), were evaluated. The basal EEG-BIS of the PC group was 95.83 ± 5.142 and in the non-CP group was 96.56 ± 1.941, which did not demonstrate a statistically significant difference.
CONCLUSIONS: The signals of the EEG are captured normally and the values of the awake EEG-BIS of CP patients are similar to that of non-CP patients.

Key Words: DISEASES: cerebral palsy; MONITORIZATION: bispectral index


JUSTIFICATIVA Y OBJETIVOS: El EEG-BIS fue creado a través de estudios en pacientes adultos saludables y las primeras publicaciones en niños surgieron a partir de 1998. La parálisis cerebral (PC) es secundaria a la lesión estática del encéfalo en desarrollo. La necesidad de realización de exámenes y procedimientos quirúrgicos para la corrección de deformidades bajo anestesia o sedación es común en esos pacientes. Cada vez más se hace necesaria la monitorización del estado de hipnosis del paciente anestesiado y podemos incluir en ese grupo los pacientes con parálisis cerebral. El objetivo de este estudio fue evaluar la eficiencia del EEG-BIS en los pacientes con parálisis cerebral (PC) en comparación con los pacientes sin enfermedades neurológicas (sin PC), en estado de vigilia.
MÉTODO: Fueron evaluados 2 grupos de pacientes: uno con diagnóstico de parálisis cerebral y otro sin enfermedad del sistema nervioso central (SNC). A la víspera de la intervención, en la enfermería, con los pacientes despiertos era colocado el monitor de EEG-BIS y solicitado que cerrasen los ojos. Los valores que aparecían en la pantalla del monitor, en un intervalo de 10 minutos, eran anotados y registrados en ficha estandarizada, siendo calculado un valor promedio por paciente.
RESULTADOS: Fueron evaluados 188 pacientes, de ambos sexos, con edad promedio de 10, 07 ± 2,9 (PC) y 10,21 ± 3,1 (sin PC) años. El grupo PC presentó EEG-BIS basal de 95,83 ± 5,142 y el grupo sin PC de 96,56 ± 1,941 sin haber una diferencia estadística significativa entre ellos.
CONCLUSIONES: Las señales de EEG se captan normalmente y los valores de EEG-BIS de los pacientes con PC son semejantes a los de los s pacientes sin PC en estado de vigilia.




The bispectral index (EEG-BIS) is a physiologic variable created based on parameters, such as the Fast Fourier Transform, bispectral analysis, and detection of phase-locking, to express numerically the cerebral activity. The data obtained are processed by a monitor known as BIS that generates a numeric value from 0 to 100, where 0 corresponds to the absence of recordable cerebral function and 100 represents awake cerebral activity 1.

The majority of parameters used by the EEG-BIS comes from studies performed in adults, but in 1998 the first studies on pediatric patients were reported 2. More recent studies concluded that the EEG-BIS is adequate to be used in normal children 3-7.

Cerebral palsy is a posture and movement disorder secondary to a static lesion of the developing brain 8. The need to perform complementary exams or surgical interventions to correct deformities, under sedation or anesthesia, is frequent in those patients. The majority of the agents used in anesthesia depress the central nervous system (CNS), and many of those patients have changes in the site of action of these drugs. Therefore, the use of the EEG-BIS can be questionable in patients with cerebral palsy, and its use should be first evaluated in awake patients. This was the objective of this first study.



After approval by the Ethics Committee of the hospital, patients with the diagnosis of cerebral palsy, classified according to the criteria set forth by the institution9, ages varying from 6 to 14 years, were included in this study. The control group was composed of patients in the same age range but without CNS disorders.

Every patient was scheduled for surgery and was evaluated by the same anesthesiologist the day before the procedure, after being admitted to the hospital. After patients, parents, or guardians gave their verbal and written consent, the EEG-BIS electrodes were placed according to the international system 10-20 of electrode placement 10, while the patients were awake, at rest, in dorsal decubitus. Patients were asked to close their eyes and, with a signal quality (SQI) of at least 50%, basal EEG-BIS values, which appeared on the screen every 15 seconds, were recorded during 10 minutes. Values obtained during this time were recorded on a standard form, allowing the posterior calculation of the mean value for each patient.

Exclusion criteria for the control group included the presence of CNS disease and/or use of drugs, such as antidepressants and anti-seizure medications, or their refusal to participate in the study.

A descriptive analysis of the data was performed using the non-parametric Mann-Whitney test to compare age, weight, and EEG-BIS value of the CP and non-CP groups. The Chi-square test was used to verify the association of gender and physical status (ASA) between the groups. A significance level of 5% was used.



One hundred and eighty-eight patients of both genders, 75 with CP and 113 without CNS disorders, were evaluated. In the group of patients with CP, every clinical form of the disease was included, regardless of the degree of severity. Absolute basal EEG-BIS values of PC patients showed a great variability, even within the same clinical form of CP (Chart I).

There were no differences regarding age between the study groups. There was a difference in weight between the groups (p < 0.01); the weight of the normal group was greater than the CP group. There was also a difference in physical status (ASA) (p < 0.01); 81% of the patients in the CP group had a physical status ASA II (Table I).



There were no statistically significant differences in mean BIS between both groups (Table II).




The results show that baseline EEG-BIS values of patients with CP are similar to those of patients without cerebral palsy.

The difference in physical status was to be expected, once the majority of patients with cerebral palsy have other associated clinical disorders 11, such as gastroesophageal reflux that can be associated with esophagitis, hindering feeding. It has also been reported that a small number of children with cerebral palsy have difficulty to maintain adequate nutritional status due to problems with mastication or swallowing 11. This could explain the weight difference between the study groups. Regarding the mean EEG-BIS value, it has been reported that it is difficult to obtain a basal EEG-BIS in patients with cerebral palsy due to the increased muscle tonus in some of the clinical forms of this disease 12,13. Since the objective of this study was to evaluate basal EEG-BIS, we decided to do it with hospitalized patients accompanied by their parents or guardians, in an environment the patient felt safe and calm.

The majority of patients had an imaging exam, and the most common change was periventricular leucomalacia, which is a form of hypoxic-ischemic lesion typical of brain immaturity, and it is most commonly seen as a complication of prematurity. Since this lesion was observed in children born at term, it was considered a reflection of the brain lesion that occurred in uterus 14 (Chart I). Despite the existence of cerebral hypoxic-ischemic lesions, there were no differences in mean baseline values of EEG-BIS between CP patients and the control group. Every clinical form of cerebral palsy was included in this study (Chart I), from the mildest forms, in which patients present just a small ambulation deficit, to the most severe forms, in which patients do not walk nor communicate. Maybe this has contributed for the results of this study.

The validation of the EEG-BIS during consciousness and sedation in normal children has already been reported 15,16, and the authors concluded that it is a valid monitoring tool to be used in normal children, awake and under sedation. Monitoring of the level of hypnosis and sedation in children, including those with CP who might potentially have changes at the site of action of most drugs used for sedation or anesthesia, is increasingly necessary and recommended 17,18. There is a report in the literature on the use of EEG-BIS in patients with a diagnosis of CP, but they were under general anesthesia or sedation with oral midazolam 19,20. Considering that there are no reports on the use of this tool in awake CP patients, its use in children with morphological CNS abnormalities, such as periventricular leucomalacia, could lead to questioning of its reliability, since certain areas could present a deficit in blood flow and neuronal mass. The results obtained in the present study demonstrated that the mean EEG-BIS values of CP children, regardless of the type, are similar to those of children with normal neurological development, although there was a considerable discrepancy among some patients, as shown in chart I. Sometimes, children with the same clinical form of CP presented different EEG-BIS values, and in other cases the absolute values are lower than those of children without neurological disease. However, the analysis of the mean values did not show a statistically significant difference. This variability in EEG-BIS values among children with CP has been reported by other authors 15.

One should remember that these children could have associated disorders, such as epilepsy and mental retardation, and that they use drugs, such as anti-seizure medications 21, that associated to the use of anesthetic agents, could interfere or not with the EEG-BIS. Other studies should be done to determine this influence.

It is known that the EEG-BIS can be used in children. One of the groups evaluated in this study was composed of children without cerebral palsy. The mean basal EEG-BIS values in patients with CP were similar to those of patients without CP. This indicates that this tool can also be used in these children.



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Correspondence to:
Dra. Verônica Vieira da Costa
Hospital SARAH – Anestesiologia
SMHS Quadra 501, Conjunto A
70335-901 Brasília, DF

Submitted em 31 de agosto de 2006
Accepted para publicação em 18 de abril de 2007



* Recebido do Hospital SARAH, Brasília-DF

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