Obstetric Anesthesiology Section Editor: Cynthia A. Wong A Randomized Trial of Maximum Cephalad Sensory Blockade with Single-Shot Spinal Compared with Combined Spinal-Epidural Techniques for Cesarean Delivery Damian J. Horstman, MD, PhD Edward T. Riley, MD Brendan Carvalho, MBBCh, FRCA BACKGROUND: Previous studies have shown more extensive cephalad sensory block- ade 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. METHODS: Thirty 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 g and morphine 200 g). 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. RESULTS: There 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. CONCLUSION: The 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. (Anesth Analg 2009;108:240 –5) Most elective cesarean deliveries are performed under neuraxial anesthesia using either single-shot spinal (SSS), epidural or combined spinal-epidural (CSE) techniques. 1,2 Although many anesthesiologists initiate CSE anesthesia with an intrathecal anesthetic dose similar to what they would use for a SSS tech- nique, previous studies have suggested a smaller dose may be preferable. 3 A study in women undergoing elective cesarean delivery found that despite admin- istration of the same intrathecal local anesthetic dose, a CSE technique resulted in significantly higher (5 dermatomes) sensory blockade compared with a SSS technique. 3 These findings corroborated a similar study in women undergoing minor gynecological procedures that found a 2 dermatome peak sensory blockade difference between SSS and CSE techniques using equivalent intrathecal doses. 4 Both studies con- trolled for patient positioning and did not site an epidural catheter or administer epidural medication during the CSE anesthetic. It has been proposed that the differences in the cephalad extent of sensory blockade between the SSS and CSE techniques may be related to disturbances in the normal subatmospheric epidural pressure or by From the Department of Anesthesia, Stanford University School of Medicine, Stanford, California. Accepted for publication September 4, 2008. This study was conducted at Lucile Packard Children’s Hospital and was funded internally by the Department of Anesthesia, Stanford University School of Medicine, Stanford, California. The authors in- volved in this study received no external financial support. Presented in part as an abstract at the Society for Obstetric Anesthesia and Perinatology Annual Scientific Meeting, April 2007, Banff, Canada. The authors share no relationships with any company or orga- nization with a vested interest in the outcome of this study. Reprints will not be available from the author. Address correspondence to Brendan Carvalho MBBCh, FRCA, Department of Anesthesia, H3580, Stanford University School of Medicine, Stanford, CA 94305. Address e-mail to bcarvalho@ stanford.edu. Copyright © 2008 International Anesthesia Research Society DOI: 10.1213/ane.0b013e31818e0fa6 Vol. 108, No. 1, January 2009 240