[SNAP-index and bispectral index during induction of anaesthesia with propofol and remifentanil]

Measurement of "depth of anesthesia" is of enormous interest to the anesthesiologist. New monitor systems, based on the electroencephalogram (EEG) were developed. The aim of the present study was to compare the SNAP index and the Bispectral index during induction of anesthesia with propofol and remifentanil.

After IRB approval and written informed consent we investigated 19 female patients during minor gynecologic surgery. Target controlled infusion (TCI) of propofol was increased in a step-by-step mode (0.5 micro g/kg) every 1 min until the patients lost response to the modified Observer's Assessment of Alertness/Sedation scale (MOAAS). 5 min after the patient lost response remifentanil 0.4 micro g/kg/min was started. Every 20 s SNAP index, BIS, spectral edge frequency, mean arterial blood pressure, heart rate and MOASS were recorded. Prediction probability ( P(K)) was used to analyze the relationship of MOAAS, TCI propofol, and all investigated parameters. Changes after start of remifentanil were analyzed with Friedman and Wilcoxon test.

SNAP index ( P(K) = 0.91) and BIS ( P(K) = 1.0) were able to distinguish reliably between MOAAS = 5 and MOAAS = 0. Start of remifentanil infusion resulted in statistically significant changes for all parameters except the SNAP index (p > 0,05).

SNAP index and BIS were reliable parameters to distinguish different levels of sedation, but SNAP index was not able to reflect the analgesic potency of remifentanil during propofol infusion.