La variabilité de la fréquence cardiaque et de la tension artérielle comme indicateurs du bloc sensitif lors de l’analgésie péridurale pour le travail obstétrical

Abstract

Purpose:To evaluate the correlation between the progression of somatosensory blockade and changes in autonomic outflow following the onset of labour epidural analgesia. Methods: Twelve labouring parturients consented to participate in the study. Baseline electrocardiogram, blood pressure (BP) and respiratory rate were recorded for ten minutes. The epidural consisted of 0.125% bupivacaine with 50 µg of fentanyl (total volume 20 mL). Measurements were repeated for ten minutes after initiation of the block. The level of sensory block was measured bilaterally with loss of sensation to ice at twominute intervals. Wavelet transform was used to obtain heart rate (HR) and BP variability every two minutes following the loading dose of epidural medication. High frequency power of HR variability was used to assess changes in parasympathetic activity. The total power of BP variability was used to assess changes in sympathetic activity. A nonparametric repeated measures ANOVA was used for the variability data, and a Spearman rank correlation test was used to evaluate the relationship between the sensory block and HR and BP variability. Results: The sensory block progressed to T9 at ten minutes post-epidural and was the mirror image of the decrease in total power of BP variability. High frequency power of HR variability increased to a plateau at six minutes post-epidural. A significant correlation was found between the increase in sensory block and the observed decrease in BP variability (r = -1.000, P = 0.0028). Conclusion: In this study of labouring parturients, BP variability correlated with the progression of both sympathetic and somatosensory block following epidural anesthesia, while HR variability was shown to be a surrogate marker of increased parasympathetic activity.

Analysis of heart rate variability: a useful tool to evaluate autonomic tone in the anesthetized patient?

“…12 For sympathetic tone, it is analysis of blood pressure variability that has been the most reliable measure. [13][14][15] This signal is obtained from a continuous blood pressure tracing, and the analysis of beat-to-beat variations in blood pressure. Thus in order to "monitor" parasympathetic and sympathetic tone, it is necessary to measure both heart rate and blood pressure variability.…”

“…This has been done successfully in the past, using post-hoc analysis to show changes in both arms of the autonomic nervous system resulting from labour analgesia, using an epidural technique. 13,14 Most cardioactive and vasoactive medications used in anesthesia have specific effects on heart rate and blood pressure variability and thus, the effect of these agents could be followed quite easily in terms of autonomic tone.…”

“…Wavelet transformation is one technique that has been used successfully for this purpose. 13,14,16 Secondly, while changes in parasympathetic and sympathetic tone have been validated using this technique in awake patients, the technique will still have to be validated in anesthetized patients, where autonomic tone is greatly attenuated. Studies are currently underway to validate these measurements.…”

“…12 Pour le tonus sympathique, c'est l'analyse de la variabilité de la pression artérielle qui a constitué la mesure la plus fiable. [13][14][15] Ce signal est obtenu à partir de l'affichage continu de la pression artérielle, et l'analyse des variations de la pression artérielle battement par battement. Ainsi, si l'on veut « monitorer » le tonus parasympathique et sympathique, il faut mesurer la variabilité de la fréquence cardiaque et de la pression artérielle.…”

“…Ceci a été effectué avec succès par le passé, en utilisant une analyse post-hoc afin de montrer les changements survenant dans les deux branches du système nerveux autonome, suite à une péridurale réalisée pour une analgésie pour le travail obstétrical. 13,14 La plupart des médicaments cardiotoniques et vasomoteurs utilisés en anesthésie ont des effets spécifiques sur la variabilité de la fréquence cardiaque et de la pression artérielle et, par conséquent, l'effet de ces agents pourrait facilement être surveillé en termes de tonus autonome.…”