Atypical Increases of BIS according to Effect Site Concentration of Propofol in Severely Burn Patients Undergoing Early Escharectomy

Kwok, In Suk; Choi, You Jun; Han, Tae Hyung; Kil, Ho Yeong; Kim, Kwang Min

Abstract

BACKGROUND: This bispectral index, which is used for intravenous anesthetics and inhalation anesthesia, is a scale of sedation and hypnotic effect, which is widely used in clinics. Atypical changes in BIS are expected due to increased cardiac output, decreased blood albumin concentrations and renal function in severe burn patients undergoing early escharectomy. The aim of this study was to compare BIS according to effected site concentrations of propofol during anesthetic induction using propofol TCI in severe burn and nonburn patients.
METHODS
Forty patients were classified as twenty nonburn elective surgical patients (group 1) and twenty burn patients scheduled for escharectomy (group 2). For induction, a propofol TCI device incorporating a prefilled syringe was adjusted to a target concentration of 6mug/ml in flash mode. The bispectral index was checked before induction and at each effect site concentration of propofol (0.5mug/ml interval) until an effect site concentration of 4.5mug/ml. Other suspected contributory factors such as cardiac index, creatinine clearance and albumin were checked simultaneously. The unpaired t-test and repeated measures ANOVA were performed for the statistical analysis.
RESULTS
Below an effect site concentration of propofol of 3mug/ml, no BIS difference was evident between group 1 and group 2. However, at 3.5mug/ml, group 1 was 41.1+/-13.5 and group 2 was 54.7+/-16.6 and at 4mug/ml, group 1 was 40.1+/-2.6 and group 2 was 50.1+/-13.1. Among the suspected contributing factors, cardiac index and albumin showed significant differences between groups 1 and 2 (cardiac index: 3.4+/-0.5 L/min/m2 vs 2.7+/-0.3 L/min/m2, albumin: 4.1+/-0.3 g/dl vs 2.6+/-0.3 g/dl, P<0.05). Creatinine clearance showed no significant difference between the groups.
CONCLUSIONS
Severe burn patients who are expecting early escharectomy had higher BIS values than nonburn patients from an effect site concentration of propofol of 3.5mug/ml. This study suggest that cardiac index should be considered as a factor that influences propofol.