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Heart rate and blood pressure variability as markers of sensory blockade with labour epidural analgesia

[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]

Alain Deschamps, MD PhD FRCPC^*, Ian Kaufman, MD FRCPC, Alana Geist, BSc, Steven S.B. Backman, MD PhD FRCPC and Karen Loo, MD FRCPC

^* From the Department of Anesthesiology, Montreal Heart Institute, Centre universitaire de santé de l’université de Montréal, Montréal, Québec; the
Department of Anesthesiology, Royal Victoria Hospital, McGill University Health Centre, Montréal, Québec; the
Research Institute of the McGill University Health Centre, Montréal, Québec; and the University of Calgary, Calgary, Alberta, Canada.

Address correspondence to: Dr. Alain Deschamps, Department of Anesthesiology, Montreal Heart Institute, 5000 Bélanger Street, Montreal, Quebec H1T 1C8, Canada. Phone: 514-376-3330, ext: 3732; Fax: 514-376-8784; E-mail: a.deschamps{at}umontreal.ca

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.

This article has been cited by other articles:

				A. Deschamps and A. Denault Analysis of heart rate variability: a useful tool to evaluate autonomic tone in the anesthetized patient?/L'analyse de la variabilite de frequence cardiaque pour evaluer le tonus autonome d'un patient anesthesie : un outil utile ? Can J Anesth, April 1, 2008; 55(4): 208 - 213. [Full Text] [PDF]