European Society of Anaesthesiologists; 8th Annual Meeting with the Austrian International Congress; Vienna, Austria, 1-4 April 2000
Background and goal of study: Heart Rate Variability (HRV) monitors the fluctuations of autonomic nervous system (ANS) outflow to the heart as well as the balance between its components (sympathetic and parasympathetic). It is known that the HRV characteristic changes differently under different methods of anaesthesia. However, it is unclear how HRV is influenced during halathane induction in children. In this study, an advanced time-frequency spectral analysis was used to examine the dynamic changes of spectral components during halothane induction in pediatric patients.
Materials and methods: Thirty ASA 1 patients (3-6 years), scheduled for elective surgery, were randomly allocated into three groups. The anaesthesia was induced with 3% halothane in 6 L of O2/N2O (2:3) and endotracheal intubation was performed. The effect of 10, 15 and 20 minutes (three groups) halothane induction on spectra power was examined at the following periods: (1) baseline, immediately after induction (2) preintubation (3) postintubation and (4) maintenance phases. Multiple spectra were generated to demonstrate the time-related spectral components of HRV by MATLAB (MathWrks Inc., MA, USA). One-way ANOVA was used for the statistic analysis.
Results and discussion: The time-frequency analysis method can generate multiple spectra continuously, we can observe the change in HRV during different time segments in the induction phase. In our study, marked reductions in the power of HRV spectra (low frequency 0.04-0.15 Hz, high frequency 0.15-0.4 Hz, and total power) were found after halothane induction. A significant increase in LF/HF ratio after intubation in 10-min group suggests that sympathetic nervous system activation is not blocked totally by halothane. The fluctuations in the power of LF and HF after intubation in the 20-min group were significantly lower than the other two groups. It indicates a better anaesthetic depth for endotracheal intubation.
Conclusion: Time-frequency spectral analysis of HRV is a useful tool for continuously assessing the dynamic changes of the ANS. Twenty minutes halothane inhalation may attenuate the sympathetic response of endotracheal intubation in pediatric patients.
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