Heart rate and blood pressure variability as markers of sensory blockade with labour epidural analgesia.
OBJECTIVE
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 microg 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 two-minute 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).


CONCLUSIONS
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.
Deschamps
Alain
A
Department of Anesthesiology, Montreal Heart Institute, 5000 Bélanger Street, Montreal, Quebec H1T 1C8, Canada. a.deschamps@umontreal.ca
Kaufman
Ian
I
Geist
Alana
A
Backman
Steven S B
SS
Loo
Karen
K
D000328:Adult; D015360:Analgesia, Epidural; D016362:Analgesia, Obstetrical; D000704:Analysis of Variance; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D016343:Monitoring, Intraoperative; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D011247:Pregnancy; D012119:Respiration / Q000187:drug effects; D015656:Respiratory Mechanics / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D013997:Time Factors