Correlation between EEG and heart rate variation in deep enflurane anaesthesia

Relationship between cortical electrical and cardiac autonomic activities in the awake lizard, Gallotia galloti

ECG and EEG signals were simultaneously recorded in lizards, Gallotia galloti, both in control conditions and under autonomic nervous system (ANS) blockade, in order to evaluate possible relationships between the ANS control of heart rate and the integrated central nervous system activity in reptiles. The ANS blockers used were prazosin, propranolol, and atropine. Time-domain summary statistics were derived from the series of consecutive R-R intervals (RRI) of the ECG to measure beat-to-beat heart rate variability (HRV), and spectral analysis techniques were applied to the EEG activity to assess its frequency content. Both prazosin and atropine did not alter the power spectral density (PSD) of the EEG low frequency (LF: 0.5-7.5 Hz) and high frequency (HF: 7.6-30 Hz) bands, whereas propranolol decreased the PSD in these bands. These findings suggest that central beta-adrenergic receptor mechanisms could mediate the reptilian waking EEG activity without taking part any alpha(1)-adrenergic and/or cholinergic receptor systems. In 55% of the lizards in control conditions, and in approximately 43% of the lizards under prazosin and atropine, a negative correlation between the coefficient of variation of the series of RRI value (CV(RRI)) and the mean power frequency (MPF) of the EEG spectra was found, but not under propranolol. Consequently, the lizards' HRV-EEG-activity relationship appears to be independent of alpha(1)-adrenergic and cholinergic receptor systems and mediated by beta-adrenergic receptor mechanisms.

Transient hyperdynamic response associated with controlled hypocapneic hyperventilation during sevoflurane-nitrous oxide mask induction in adults

We assessed hemodynamic variables during sevoflurane face mask anesthetic induction in female ASA physical status I or II patients. Anesthesia was induced with a single-breath inhalation method with 8% sevoflurane in 50% nitrous oxide in oxygen. Thirty patients were randomized either to breathe spontaneously (SB group, n = 15) or to receive controlled ventilation (CV group, n = 15) for 6 min after the loss of consciousness. Noninvasive blood pressure and heart rate (HR) were recorded at 1-min intervals. Mean +/- SD HR increased from 83+/-18 to 112+/-24 bpm at 4 min in the CV group (P < 0.001 between groups and within group compared with baseline). Mean arterial pressure increased from 97+/-9 to 106+/-26 mm Hg at 4 min in the CV group, which was significantly higher than that in the SB group (P < 0.01). In the SB group, mean arterial pressure decreased significantly, from 96+/-8 to 78+/-13 mmHg, at 6 min (P < 0.001), and HR remained unchanged. Therefore, hyperventilation should be avoided during the induction of sevoflurane anesthesia via a mask.

IMPLICATIONS

In this randomized, prospective study, we found that controlled hypocapneic hyperventilation delivered manually during sevoflurane/ N2O/O2 mask induction was associated with a significant transient hyperdynamic response. This kind of hemodynamic arousal can be detrimental to many patients and can be avoided by conducting sevoflurane mask induction with unassisted spontaneous breathing.

The rationale and utility of neurophysiological investigations in clinical monitoring for brain and spinal cord ischaemia during surgery and intensive care

This review concerns the role of neurophysiological monitoring in prevention of damage to the brain or spinal cord from inadequate supply of oxygenated blood during surgery and intensive care. The spontaneous and evoked electrical activity from neurones depends on oxidative metabolism of glucose, the substrate being delivered via the arterial blood supply and not stored locally. In critical situations electrical activity declines as oxygen delivery fails. Since this happens before neuronal death occurs it can provide early warning of risk. Methods for signal processing of EEG for this purpose must include time domain assessment and recognition of burst suppression pattern, as well as frequency domain information, and provide multivariate pattern recognition. Models for monitoring systems require analysis of data sets based on clinical studies where accurate outcome data is available so that valid comparisons between different approaches can be made. Neurophysiological features must be considered in the context of other relevant clinical parameters in the design of effective warning systems for prevention of brain damage due to inadequate oxygen supply.

Changes in heart rate variability during induction of anesthesia with fentanyl and midazolam

OBJECTIVE

The study was designed to evaluate changes in autonomic nervous system function during induction of anesthesia with fentanyl, midazolam, and pancuronium and to answer the question of dose-dependency of these effects.

DESIGN

Prospective, randomized.

SETTING

A university hospital.

PARTICIPANTS

Forty consecutive cardiac surgical patients.

INTERVENTIONS

Anesthesia was induced with fentanyl, midazolam, and pancuronium. The patients were assigned to four groups differing in dosages of fentanyl plus midazolam and speed of injection. Fentanyl, 7.5 micrograms/kg (group A), 12.5 micrograms/kg (group B), and 20.0 micrograms/kg (group C) plus midazolam, 0.075 mg/kg (group A), 0.125 mg/kg (group B), and 0.200 mg/kg (group C) were administered over 10 minutes; in group D, fentanyl, 7.5 micrograms/kg, and midazolam, 0.075 mg/kg, were administered within 1 minute.

MEASUREMENTS AND MAIN RESULTS

Heart rate variability (HRV) was measured using parameters in the time domain and the frequency domain. The comparison of preinduction HRV with the intra-anesthetic epochs did not show significant differences with respect to heart rate, coefficient of variation, and root mean squared successive differences. Spectral analysis showed significant reductions of power in the vasomotor band (0.01 to 0.05 Hz) and the low-frequency band (0.05 to 0.15 Hz) in all groups. Power in the high-frequency band (0.15 to 0.50 Hz) decreased slightly, but this did not reach the significance level. A dose dependency of these changes was found in the low-frequency band only.

CONCLUSIONS

Parameters of HRV suggest that induction with fentanyl, midazolam, and pancuronium decreases sympathetic but not parasympathetic autonomic system activity. The anesthetic induction technique's modulation of autonomic nervous system balance is better represented by means of spectral analysis than by analysis in the time domain. This modulation was largely independent of the doses administered and independent of the speed of injection.

Light-induced arousal affects simultaneously EEG and heart rate variability in the rat

In awaken rats, ECG and EEG were simultaneously analysed in order to quantify the cortical EEG and beat-to-beat heart rate variability (HRV) in response to light onset. The HRV bands LF (40-200 mHz), MF (200-600 mHz) and HF (600-2500 mHz) and the EEG bands delta (1-4 Hz), theta (4-8 Hz), alpha (8-13 Hz) and beta (13-32 Hz) were assessed. Light onset induced a significant arousal reaction in the EEG, manifested by a global decrease in total spectral power and a shift towards theta and beta bands, while total HRV spectral power increased, with a shift to the sympathetic-related MF band. This simultaneous changes in HRV and EEG induced by light onset could be triggered by the same common factor that controls both oscillatory responses.

Atropine abolishes electroencephalogram-associated heart rate changes without an effect on respiratory sinus arrhythmia during anaesthesia in humans

Heart rate fluctuates with the electroencephalogram burst suppression pattern during anaesthesia: increasing at burst onset and decreasing at suppression. Heart rate also oscillates with positive pressure ventilation. The effects of atropine on these heart rate changes were studied in 12 patients during isoflurane anaesthesia and positive pressure ventilation at a frequency of 6 cycles min-1. Four additional patients served as controls. A bolus dose of atropine (20 micrograms kg-1 intravenously) abolished the electroencephalogram-correlated heart rate changes; however, the amplitude of respiratory sinus arrhythmia was not changed after atropine. The control mechanism of the burst suppression pattern in electroencephalogram also affects parasympathetic heart rate control. The control mechanisms of respiratory sinus arrhythmia during anaesthesia with positive pressure ventilation differ from those during spontaneous breathing awake.

Vibration stimulus induced EEG bursts in isoflurane anaesthesia

The EEG and heart rate reactions to vibration stimulus were studied in 14 patients during moderately deep surgical isoflurane anaesthesia, at a level when EEG showed a burst suppression pattern. Vibration applied to the palm of the hand induced bursts in EEG in 12 patients, usually with a latency of about 0.5 sec from the onset, or from the end of the 3 sec stimulus. Increases in heart rate were seen at bursts related to both vibration onset and offset, as well as at spontaneous bursts. With spontaneous bursts, an initial positive wave was frequently seen. In 6 patients the vibration induced bursts were different in shape from the spontaneous bursts; no initial positive wave was seen before the negative DC shift in Cz-Fz recording. We conclude that EEG bursts can be evoked by a non-noxious stimulus such as vibration in patients during isoflurane anaesthesia.

Slow potentials of EEG burst suppression pattern during anaesthesia

EEG burst suppression pattern was recorded during propofol and isoflurane anaesthesia. Using a long time constant, i.e. a high-pass filter with low cut-off frequency, revealed slow potentials, DC shifts, during bursts. These have been extensively studied in conjunction with cognitive-evoked potentials and epileptic discharges, but not previously in burst suppression EEG.

Effects of fentanyl-diazepam-pancuronium anesthesia on heart rate variability: a spectral analysis

The effects of induction of anesthesia with fentanyl, 62.1 +/- 7.9 micrograms/kg, diazepam, 0.21 +/- 0.08 mg/kg, and pancuronium on beat-to-beat heart rate variations were studied in seven patients undergoing cardiac surgery. Spectral analysis was used to determine the intensity of the variations in each of the two main frequency bands in which variations are known to occur: (1) high-frequency band, mediated by the parasympathetic nervous system, at the frequency band of respiration, and (2) the low-frequency band, mediated by both sympathetic and parasympathetic nervous systems, at 0.04-0.12 Hz. Both the mean low- and high-frequency band areas were significantly decreased after induction of anesthesia. The ratio of high-to-low frequency band areas increased significantly after induction of anesthesia, from 45% to 62% (P less than 0.05). These results suggest that fentanyl-diazepam-pancuronium anesthesia decreases total autonomic nervous system activity and alters the balance between parasympathetic and sympathetic activities. Thus, spectral analysis of heart rate variations during anesthesia may provide a quantitative measure of assessing the activity of the autonomic nervous system.

Respiratory sinus arrhythmia is reversed during positive pressure ventilation

In order to study the relationship between heart rate and depth of anaesthesia, respiratory sinus arrhythmia (RSA) was investigated during enflurane and isoflurane anaesthesia in 28 patients (15-39 years). Positive pressure ventilation (six breaths min-1) was used. Respiratory sinus arrhythmia was evaluated during light anaesthesia, deep anaesthesia (burst suppression in EEG) and light anaesthesia again by using signal averaging technique. In most patients, decrease of the heart rate was seen during inspiration (positive tracheal pressure), and increase during expiration. Respiratory sinus arrhythmia did not disappear in deep anaesthesia. Inter-individual variation in the magnitude and phase relationship of respiratory sinus arrhythmia was considerable, and was not associated to the level of anaesthesia.

Correlation of instantaneous heart rate and EEG suppression during enflurane anaesthesia: synchronous inhibition of heart rate and cortical electrical activity?

EEG burst suppression and instantaneous heart rate were studied during enflurane anaesthesia in 15 patients. Heart rate increased at EEG burst onset and decreased at suppression onset. Short epileptic discharges accompanied by an increase in heart rate were seen in 2 patients. We suggest that suppressions in EEG may be caused by active inhibition, with synchronous decrease of heart rate.

EEG burst-suppression pattern correlates with the instantaneous heart rate under isoflurane anaesthesia

The correlation between electroencephalogram (EEG) and instantaneous heart rate was studied in deep isoflurane anaesthesia when the EEG showed a burst-suppression pattern in 15 patients aged 19-39 years. At the onset of EEG burst, the heart rate started to accelerate, and at the onset of suppression it started to decelerate. These changes in heart rate are similar to those we have previously described with enflurane, despite several differences in the effects of these two anaesthetics on EEG and on the cardiovascular system. We hypothesise that the heart-rate changes are due to central inhibition mediated by the vagus nerve during EEG suppression.