Obstetric Anesthesia Does the Baricity of Bupivacaine Influence Intrathecal Spread in the Prolonged Sitting Position Before Elective Cesarean Delivery? A Prospective Randomized Controlled Study Christian Loubert,* Stephen Hallworth,† Roshan Ferando,* Malachy Columb,‡ Nisa Patel,* Kavita Saragn,§ and Vinnie Sodhi|| (Anesth Analg, 113:811Y817, 2011) *Department of Anesthetics, University College London Hospital, London; †Department of Anesthetics, Royal London Hospital, London; ‡Department of Anesthesia, University Hospital of South Manchester NHS Foundation Trust, Wythenshawe, Manchester; §Department of Anesthetics, The Lister Hospital, London; and ||Department of Anaesthetics, Queen Charlotte’s and Chelsea Hospital, Imperial College Healthcare NHS trust, London, UK. Copyright * 2012 by Lippincott Williams & Wilkins DOI: 10.1097/SA.0b013e318254da86 W hen difficulties occur during insertion of an epidural catheter for combined spinal-epidural (CSE) anesthesia, the time from the spinal injection of the local anesthetic mixture and the adoption of the supine position with lateral tilt may be delayed. In this situation, undue delay may cause failure of hy- perbaric local anesthetic to spread in a timely fashion and result in inadequate surgical anesthesia. This delay may affect the dis- tribution of local anesthetics of different baricities, with hypo- baric local anesthetic providing a higher level of sensory block. This prospective double-blind randomized controlled trial was performed to determine the effect of gravity on the spread of local anesthetic solutions of 3 different baricities when the CSE tech- nique was used in healthy parturients undergoing elective cesarean section. The 90 parturients, at term with no pregnancy-related com- plications, were randomized to a hyperbaric, isobaric, or hypobaric group. For the hyperbaric solution, 8 mL of 0.5% wt/vol hyper- baric bupivacaine containing glucose 80 mg/mL was added to 1.2 mL (60 Kg) of fentanyl and 0.8 mL of 5% wt/vol glucose. The isobaric solution was prepared by adding 8 mL of plain bupivacaine 0.5% wt/vol to fentanyl 1.2 mL (60 Kg) and 0.8 mL of a solution from a mixture of 8 mL of 5% wt/vol dextrose solution and 2 mL of 0.9% saline. The hypobaric solution was prepared by adding 8 mL of 0.5% wt/vol plain bupivacaine to 1.2 (60 Kg) fentanyl and 0.8 mL of 0.9% saline. Each patient was given an intrathecal injection of 2.5 mL of the stock solution of 10 mg of bupivacaine and 15 Kg of fentanyl. The CSE pro- cedure was performed at the L3-4 interspace using a midline approach with the patient sitting. After the subarachnoid injec- tion, a catheter was placed and fixed 4 cm in the epidural space. The patient was kept in the sitting position for 5 minutes after the end of the spinal injection to simulate the difficulty of in- serting the epidural catheter. She was then moved to the supine position with a 15-degree left lateral tilt. The primary outcome was the level of sensory block to cold during the 25 minutes after the spinal injection. Secondary outcomes were level of sensory block to cold (ethyl chloride spray) at 10, 15, and 20 minutes after the spinal injection and lower limb motor block assessed with a modified Bromage score. Failure of block was defined as a maximal sensory level below T4 at 25 minutes after spinal injec- tion. In these patients, incremental 5-mL boluses of 0.5% wt/vol bupivacaine were given through the epidural catheter. Maternal hypotension and vasopressor requirements (ephedrine 3-mg bolus doses) were also recorded. The 3 groups were similar in age, height, weight, and gestational age. The median sensory levels after spinal injection were T10, T9, and T6 for the hyperbaric, isobaric, and hypobaric groups, respectively. Hypobaric bupivacaine led to block levels that were 2.5 and 3.6 dermatomes higher compared with isobaric and hyperbaric bupivacaine, respectively. At all time points, block heights in the hypobaric group were higher than those in the other groups. All patients in the hypobaric group reached a sensory block at the T4 level at 25 minutes after spinal injection com- pared with 80% of the patients in each of the other groups. Median level of sensory block at 25 minutes after spinal injection reached the cervical dermatomes in 24%, 10%, and 0% of patients in the hypobaric, isobaric, and hyperbaric groups, respectively. No patient required general anesthesia or had breathing discomfort or upper extremity motor block. The groups were similar in the incidences of hypotension, nausea, and vomiting. Compared with the hyperbaric group, median dose requirements for ephedrine increased in the isobaric and hypobaric groups by factors of 1.83 and 3.0, respectively. Infants in the 3 groups had similar Apgar scores. One neonate in the hyperbaric group and 2 in the isobaric group had 1-minute Apgar scores lower than 7, but all recovered and had scores 9 or higher at 5 minutes. The results show a trend toward higher cephalad spread of local anesthetic and a higher rate of successful sensory block with lower baricity. However, use ofhypobaric bupivacaine led to an increased incidence of cervical dermatome blockade and higher consumption of ephedrine, indicating an increased inci- dence of maternal hypotension. These results could have clinical implications in patients in whom placing the epidural catheter is difficult during initiation of CSE anesthesia in the sitting position. COMMENT There is little question that baricity will markedly affect the final sensory and motor levels of local anesthetic placed in the subarachnoid (SA) space. This study showed that gravid patients having subarachnoid block (SAB) in the sitting position, and kept in this position for 5 minutes after SA injection, with 2.5 mL of hypobaric solution containing 10 mg of bupivacaine had faster onset of higher levels of sensory block than those who received the same 10-mg bupivacaine, but in 2.5 mL of a hyper- baric dextrose solution. This is to be expected. The results also show an increased danger of using hypobaric SA solution when the patient is to have SAB performed in the sitting position. Furthermore, I can see no reason to use (and hence the need to mix) a hypobaric solution of bupivacaine when reliable com- mercial hyperbaric solutions of bupivacaine are readily available in the United States as 0.75% bupivacaine in 8.25% dextrose and in Europe as 0.5% bupivacaine in 8% dextrose. When one is Survey of Anesthesiology & Volume 56, Number 3, June 2012 www.surveyanesthesiology.com 123 Copyright © 2012 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.