Issn Print: 0265-0215

Publication Date: 1996/03/01


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Quantification of autonomic activity during induction of anesthesia by power spectral analysis of heart rate variability: 52.

P. K. Singh

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Excerpt

Power spectral analysis (PSA) of heart rate variability (HRV) may provide important clinical information about the influence of anaesthesia on the autonomic nervous system (ANS). The purpose of this study was to examine the effects of ketamine and midazolam as an anaesthetic induction agent on HRV. Both the drugs are known to have different action on ANS.
Thirty patients of ASA PS 1 were studied. Pre-medication included hydroxizine (0.1 mg kg−1). Fifteen patients were given ketamine (2 mg kg−1) and the remaining 15 patients were given midazolam (0.3 mg kg−1) intravenously to induce anaesthesia. ECG-RR intervals were measured before induction of anaesthesia and thereafter for 10 min during spontaneous breathing. Power spectral density of these data was computed using fast fourier transform. The power of the spectral peaks within each of the measurements was calculated as follows: Low frequency area (LF, 0.04-0.15 Hz), High frequency area (HF, 0.15-0.5 Hz) and total power (0.04-0.5 Hz). Normalized power was derived by dividing power contained in the frequency band by total power as follows: Normalized low frequency (nLF, LF/TOTAL × 100) as an index of sympathetic activity, Normalized high frequency area (nHF, HF/TOTAL × 100) as an index of parasympathetic activity.
Both ketamine and midazolam caused significant reductions in all measurements of HRV power. However, nLF increased along with a decrease in nHF after ketamine and nLF decreased with an increase in nHF after Midazolam. Significant increase in BP and HR after ketamine and decreases in BP with no change in HR were observed after midazolam.
Anaesthesia per se reduces the total HRV variability. The increase and the decrease in nLF after ketamine and midazolam respectively indicates the increase and decrease in sympathetic activity.
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