Induction and maintenance of general anaesthesia in adult patients can cause important modifications of absolute values of heart Rate (AVHR) and a marked decreased in spontaneous heart rate variability (SHRV). The aim of this work is to present a novel methodology which takes into account a combination of these two factors in order to apply it in paediatric anaesthesia. In term of signal processing, a modification of AVHR is characterised by a slope change into the trend while SHRV is reflected by a spectral modification. This paper is devoted, first, to a precise analysis of these two signals, then to propose a general and unique framework based on abrupt changes detection theory, despite the different behaviour nature of the change. First results demonstrate that heart rate may provide an indicator of recovery period and a useful adjunct in monitoring depth of anaesthesia.