Electroencephalographic indices related to hypnosis and amnesia during propofol anaesthesia for cardioversion.

Most previous studies which have assessed the depth of anaesthesia using the Bispectral Index (BIS) have used multi-agent anaesthetics with relatively slow induction and recovery times. Elevation of electroencephalographic (EEG) Beta/Alpha Ratio has been linked to onset of midazolam amnesia. Propofol anaesthesia for cardioversion in 19 patients enabled us to profile the changes in BIS and Beta/Alpha Ratio during a short, single-agent anaesthetic with a relatively rapid induction and recovery period. BIS values did not alter significantly through onset of amnesia and hypnosis as compared with awake values. Cardioversion occurred over a wide range of BIS values (38 to 94), with recovery at a median BIS value of 79. We observed the BIS to lag about 60 s behind the clinical situation (termed BIS60). The BIS60 more closely tracked the clinical level of consciousness, showing statistically significant differences from the uncorrected BIS. (amnesia (median BIS60 = 82, P = 0.02), hypnosis (median BIS60 = 67, P = 0.01), eye opening (median BIS60 = 90, P = 0.001)). An early EEG Beta/Alpha Ratio peak occurred at a mean of 4.6 s (SD = 16.6) after clinical amnesia onset and a late peak at a mean 58 s (SD = 144) after eye opening. There was no significant EEG response to cardioversion. We conclude that: (1) in rapidly changing conditions, the value of the BIS most accurately reflects the level of consciousness of the patient about 60 s in the past, and (2) the onset and offset of propofol-induced amnesia commonly corresponds to a peak in Beta/Alpha Ratio of the EEG.

Possible site of zinc control of hepatoma cell division in Wistar rats.

The effect of zinc on the growth of a transplantable DAB hepatoma in young male Wistar rats was determined. Both a zinc deficiency (less than 0.5 microgram/g feed) as well as high levels of dietary zinc (500 micrograms/g feed) significantly reduced tumor growth. Both high- and low-zinc diets resulted in reduced activity of the salvage pathway of thymidine synthesis as well as reduced 32PO4 incorporation into DNA and diminished DNA polymerase activity. Blockage of the de novo pathway of DNA synthesis by the folate antagonist methotrexate (MTX) resulted in greatly increased flux through the thymidine salvage pathway and increased DNA polymerase activity but decreased 32PO4 incorporation in the transplantable hepatomas in Wistar rats fed normal zinc diets (50 micrograms/g feed). MTX had the effect of reducing all these activities in the groups fed low- and high-zinc diets. These data suggested a site of action of zinc associated with the salvage pathway of thymidine synthesis.