In a small study of 24 women undergoing surgery, giving the peptide Delta Sleep‑Inducing Peptide (DSIP) did not deepen the anesthetic state. Instead, it raised heart rate, lowered heart‑rate variability (a sign of reduced parasympathetic tone), cut the slow‑wave (delta) brain activity, and made the brain‑wave pattern look more like a lighter level of anesthesia.

Delta sleep-inducing peptide (DSIP) is an endogenous peptide that crosses the blood-brain barrier, named after its association with natural sleep and enhanced electroencephalogram (EEG) delta rhythm. The objective of this study was to determine whether DSIP could be used as an adjunct to volatile anaesthesia in humans, our hypothesis being that DSIP is a natural hypnotic that would increase anaesthetic depth. The aims were to assess depth of anaesthesia using bispectral index (BIS), the EEG and heart rate variability (HRV), and to determine whether DSIP altered the symmetry of EEG between the left and right cerebral hemispheres. Twenty-four female ASA I or II patients gave written, informed consent to a protocol approved by our local research ethics committee. Twelve were randomly assigned as controls to receive saline. The other 12 were randomly allocated to receive one of three intravenous bolus doses of DSIP (Clinalfa) at 25, 50 or 100 nmol kg(-1). The first administration of DSIP was while awake and the second after induction of anaesthesia with propofol and maintenance with isoflurane. BIS and EEG parameters were measured continuously using a bilateral electrode montage. DSIP significantly increased heart rate, decreased HRV and, paradoxically, significantly reduced delta rhythm along with reducing burst suppression and increasing BIS at 25 nmol kg(-1) during isoflurane anaesthesia. DSIP also significantly altered bilateral symmetry of EEG. DSIP probably reduced parasympathetic tone and decreased (lightened) the depth of anaesthesia measured using BIS.