Preliminary Experience on the Effects of General Anesthesia on Heart Rate Variability during abdominal surgery

The spectral analysis of RR interval variability enables the identification of oscillatory components hidden in it, the sum of which is the total Heart Rate Variability (HRV). This type of analysis allows the bundling of oscillations in heart rate in two main frequency bands: a low frequency band, known as LF (Low Frequency), about 0.10 Hz correlated with the sympathetic nerve activity, and a high frequency, called HF (High Frequency), synchronous with the breath between 0.15 and 0.30 Hz, whose output provides a quantitative estimate of vagal activity. (1-3) The relative importance of these two components, expressed by the ratio between the powers (LF / HF), provides an estimate of the state of sympathetic-vagal balance.

BACKGROUND AND PURPOSE

Previous studies in anesthetized animals and in normal subjects have linked changes in HRV spectral analysis to several mechanisms: alterations in sympathetic and parasympathetic activities, changes in sensitivity of baroreceptors, and interruption of reflex autonomic pathways. (4 -7)
During anesthesia, it was observed that altered HRV correlated to both, the depth of anesthesia and the level of sedation. (7, 8)
Changes in the sensitivity of baroreceptors and / or activity of the autonomic nervous system play a role in the effect of anesthetics on HRV, so that different anesthetics should have different effects on HRV. (9-12)
The aim of this study was to evaluate the effects of deep general anesthesia, done with the simultaneous administration diverse anesthetics, inhaled and injected, on key cardiovascular parameters that explore the heart rate variability, both in time and in frequency domains.

MATERIALS AND METHODS

We studied 15 subjects of both sexes (9 women and 6 men) with a mean age of 53.6 ± 14.3 years with digestive diseases with a prevalence of gallbladder disease. None of the patients used drugs or was suffering from cardiovascular disease or diabetes.
ECG signal recording, lasting 5 minutes each, were made using a hand held digital ECG with dedicated software (Xai-Medica) and then transferred to a PC for subsequent analysis performed by appropriate software.
Protocol
The day of the procedure the basic registration was made in the anesthesia room adjacent to the operating room. The patient was then anesthetized after endotracheal intubation. The recording was performed after anesthesia induction and after 5 minutes after the start of maintenance. The third measurement was performed at 24 hours after surgery.
Anesthesia
All the patients underwent general anesthesia using the following scheme:

Pre-anesthetic - Midazolam 0,04mg/Kg + Fentanil 1,4 g/Kg
Induction - Propofol 1,8-2,5 mg/Kg
Curarization - Cisatracurium 0,2 mg/Kg
Maintenance - Desflurane 4-7% in air and O2 at 50% or Sevoflurane 1-2% in air and O2 at 50%
Fentanyl 0,7g/Kg ogni 30’-45’
Curarization reversal mixture - Prostigmine 35g/Kg+ Atropine 20g/Kg

Analysis of heart rate variability in the time domain

The following measures in the time domain were taken into consideration:

1. SDNN (mean of all normal RR intervals expressed in ms and its standard deviation expressed in ms);
2. rMSSD (square root of average squared differences between each successive RR interval in ms);
3. pNN50% (percentage of successive RR intervals differing by more than 50 ms compared to the total RR intervals).

Analysis of heart rate variability in the frequency domain

The HRV analysis was performed on the recordings of RR intervals by the application of the Fourier transform method, as well as by the auto regressive method.
The data are expressed in standard units.

Statistics: All variables were tested to verify the normality of their distribution through the test of Kolmogorov-Smirnof. When data exceeded the test, ANOVA statistical analysis for repeated measures was applied.
Values are presented as mean ± SD. Changes that had a P