Effects of fentanyl, alfentanil, remifentanil and sufentanil on loss of consciousness and bispectral index during propofol induction of anaesthesia

The bispectral index (BIS) and a sedation score were used to determine and compare the effect of propofol in the presence of fentanyl, alfentanil, rem ifentanil and sufentanil. Seventy-five non-premedicated patients were assig ned randomly into five groups (15 in each) to receive fentanyl, alfentanil, remifentanil, sufentanil or placebo. Opioids were administered using a tar get-controlled infusion device, to obtain the following predicted effect-si te concentrations: fentanyl, 1.5 ng ml(-1); alfentanil, 100 ng ml(-1); remi fentanil, 6 ng ml(-1); and sufentanil, 0.2 ng ml(-1). After this, a target- controlled infusion of propofol (Diprifusor) was started to increase concen tration gradually, to achieve predicted effect-site concentrations of 1, 2, and 4 mug ml(-1). At baseline and at each successive target effect-site co ncentration of propofol, the BIS, sedation score and haemodynamic variables were recorded. At the moment of loss of consciousness (LOC), the BIS and t he effect-site concentration of propofol were noted. The relationship betwe en propofol effect-site concentration and BIS was preserved with or without opioids. In the presence of an opioid, LOC occurred at a lower effect-site concentration of propofol and at a higher BIS50 (i.e. the BIS value associ ated with 50% probability of LOG), compared with placebo. Although clinical ly the hypnotic effect of propofol is enhanced by analgesic concentrations of mu -agonist opioids, the BIS does not show this increased hypnotic effec t.