Effects of thiopental on bispectral index and heart rate variability.
OBJECTIVE
Thiopental has been reported to reduce sympathetic tone, however, it is not clear whether change in heart rate variability is associated with depth of anaesthesia. The purpose of the present study was to evaluate changes in heart rate variability at different depths of hypnosis during induction of anaesthesia with thiopental.


METHODS
We studied 17 ASA I patients scheduled for minor surgery. The depth of hypnosis was monitored by the BIS. Spectral analysis of heart rate variability using a maximum entropy method resulted in a characteristic power spectrum with two main regions, a high frequency and a low frequency. Haemodynamics, entropy, low frequency, high frequency and low frequency/high frequency were monitored in an awake state and after the induction of anaesthesia.


RESULTS
Heart rate increased in a BIS-dependent manner, whereas blood pressure showed no significant changes during the study period. High frequency, entropy and low frequency decreased with a reduction in the BIS value. Low frequency/high frequency showed no significant change during the study period.


CONCLUSIONS
Induction of anaesthesia with thiopental increased heart rate and decreased high frequency, entropy and low frequency in a BIS-dependent manner, indicating that thiopental reduces cardiac parasympathetic tone depending on the depth of hypnosis.
Tsuchiya
S
S
Department of Anesthesiology, School of Medicine, Sapporo Medical University, Sapporo, Japan.
Kanaya
N
N
Hirata
N
N
Kurosawa
S
S
Kamada
N
N
Edanaga
M
M
Nakayama
M
M
Omote
K
K
Namiki
A
A
D000328:Adult; D000704:Analysis of Variance; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D017558:Elective Surgical Procedures; D004569:Electroencephalography / Q000187:drug effects*; D019277:Entropy; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D008875:Middle Aged; D019647:Oral Surgical Procedures; D013874:Thiopental / Q000494:pharmacology*
D018686:Anesthetics, Intravenous; D013874:Thiopental