• Damian J Horstman, Edward T Riley, and Brendan Carvalho.
• Department of Anesthesia, Stanford University School of Medicine, Stanford, California 94305, USA.
• Anesth. Analg. 2009 Jan 1;108(1):240-5.

BackgroundPrevious studies have shown more extensive cephalad sensory blockade in women receiving combined spinal-epidural (CSE) anesthesia compared with single-shot spinal (SSS) anesthesia for elective cesarean delivery. It has been postulated that introduction of the epidural needle during CSE disturbs the negative pressure in the epidural space, resulting in relatively greater cerebrospinal fluid (CSF) pressure and increased spread of intrathecal local anesthetic. We tested the hypothesis that CSE results in more extensive cephalad sensory blockade than SSS anesthesia and that loss-of-resistance during initiation of CSE anesthesia increases CSF pressure compared with SSS.MethodsThirty parturients scheduled for elective cesarean delivery were enrolled in this randomized, double-blind study. Patients received either SSS or CSE anesthesia with equal doses of intrathecal anesthetic (hyperbaric bupivacaine 12 mg, fentanyl 10 microg and morphine 200 microg). Before the intrathecal injection, the CSF pressure was measured with a fiberoptic pressure sensor. Maximum cephalad sensory blockade to pinprick, cold and touch was measured. The total dose of phenylephrine required to maintain baseline arterial blood pressure was also recorded.ResultsThere were no significant differences in the median (interquartile range) pinprick sensory block height [T4 (T4-2) vs T3 (T4-1)] or CSF pressures [6 (4-12) vs 9 (8-12) mm Hg] between the SSS and CSE groups. There were no significant correlations between CSF pressure and block height or total dose of phenylephrine.ConclusionThe SSS and CSE techniques inserted in the lateral decubitus position resulted in similar extent of sensory blockade and CSF pressure. These findings suggest that altering the intrathecal dose is not necessary and that any difference in intrathecal pressure associated with initial placement of an epidural needle in the epidural space during CSE anesthesia is clinically inconsequential.

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