Movement response to skin incision: analgesia vs. bispectral index and 95% spectral edge frequency

Abstract

We studied the movement response to skin incision in 68 adult (males/females) ASA I–II patients receiving propofol±fentanyl intravenous anaesthesia using the bispectral index and 95% spectral edge frequency monitoring with an A-1050 EEG monitor. Following Ethics Committee approval, patients were randomly assigned to one of the following four treatments: Group P (n=17): propofol infusion, 1 mg kg ⁻¹ min⁻¹ intravenous for 2 min, followed by propofol infusion, 200 μg kg⁻¹ min⁻¹, until skin incision; Group PF1 (n=17): fentanyl bolus, 1 μg kg⁻¹ intravenous+ propofol infusion as in Group P; Group PF2 (n=17): fentanyl bolus, 2 μg kg⁻¹ intravenous+ propofol infusion as in Group P; and Group PF3 (n=17): fentanyl bolus, 3 μg kg⁻¹ intravenous+ propofol infusion as in Group P. The bispectral index and 95% spectral edge frequency were monitored continuously and recorded prior to induction of anaesthesia (base-line) and at skin incision. Twelve, 10, 4 and 4 patients responded to skin incision in Groups P, PF1, PF2 and PF3, respectively (P and PF1 vs. PF2 or PF3; P=0.0001, and 0.006). The bispectral index and 95% spectral edge frequency were significantly lower at skin incision compared with the base-line values in all the four treatment groups. However, only bispectral index values were significantly lower in the nonmovement as compared with the movement (M) category (32.6±8.9 vs. 37.4±10.3; P=0.04). Though deeper levels of hypnosis to lower bispectral index and 95% spectral edge frequency values may be effective in preventing the movement response to skin incision, provision of adequate analgesia rather than lower bispectral index and 95% spectral edge frequency (clinical maintenance) values may be more reliable for preventing the response to skin incision as bispectral index and 95% spectral edge frequency measure the hypnotic component of the anaesthetic effect. Lower bispectral index values may be more discriminatory as compared with 95% spectral edge frequency values for preventing the movement response to skin-incision.