BACKGROUND: This double-blind randomized study was undertaken to assess 
agitation, Bispectral Index (BIS) and EEG changes during induction of 
anaesthesia with sevoflurane in children premedicated with midazolam or 
clonidine.
METHODS: Children were allocated randomly to receive rectal midazolam 0.4 mg 
kg(-1) (n=20) or oral clonidine 4 microg kg(-1) (n=20) as premedication. Rapid 
induction of anaesthesia was achieved with inhalation of sevoflurane 8% in 
nitrous oxide 50%-oxygen 50%. After tracheal intubation, the children's lungs 
were mechanically ventilated and the inspired sevoflurane concentration was 
adjusted to achieve an end-tidal fraction of 2.5%. The EEG and BIS were recorded 
during induction until 10 min after tracheal intubation. The EEG was analysed 
using spectral analysis at five points: baseline, loss of eyelash reflex, 15 s 
before the nadir of the BIS (BIS(nadir)), when both pupils returned to the 
central position (immediately before intubation), and 10 min after intubation.
RESULTS: Agitation was observed in 12 midazolam-treated and five 
clonidine-treated patients (P=0.05). At baseline, EEG rhythms were slower in the 
clonidine group. Induction of anaesthesia was associated with similar EEG 
changes in the two groups, with an increase in total spectral power and a shift 
towards low frequencies; these changes were maximal around the end of the second 
minute of induction (BIS(nadir)). When the pupils had returned to the central 
position, fast EEG rhythms increased and BIS was higher than BIS(nadir) 
(P<0.05). In both groups, agitation was associated with an increase in slow EEG 
rhythms at BIS(nadir).
CONCLUSIONS: Compared with midazolam, clonidine premedication reduced agitation 
during sevoflurane induction. During induction with sevoflurane 8% (oxygen 
50%-nitrous oxide 50%), the nadir of the BIS occurred at the end of the second 
minute of inhalation. Agitation was associated with a more pronounced slowing of 
the EEG rhythms at BIS(nadir) compared with inductions in which no agitation was 
observed. The BIS may not follow the depth of anaesthesia during sevoflurane 
induction in children.