title: Does the baricity of bupivacaine influence intrathecal spread in the prolonged sitting position before elective cesarean delivery? A prospective randomized controlled study.
abstract: BACKGROUND
  Difficulties in inserting an epidural catheter while performing combined spinal-epidural anesthesia for cesarean delivery may lead to undue delays between the spinal injection of the local anesthetic mixture and the adoption of the supine position with lateral tilt. We hypothesized that this delay may affect the intrathecal distribution of local anesthetic of different baricities such that hypobaric local anesthetic would lead to a higher sensory block level.
  
  
  METHODS
  Healthy parturients with uncomplicated pregnancies undergoing elective cesarean delivery under combined spinal-epidural anesthesia were enrolled in this prospective double-blind randomized controlled trial. The subjects were allocated to receive hyperbaric (hyperbaric group), isobaric (isobaric group), or hypobaric (hypobaric group) spinal bupivacaine 10 mg. After the spinal injection, the subjects remained in the sitting position for 5 minutes (to simulate difficulty in inserting the epidural catheter) before being helped into the supine lateral tilt position. The primary outcome was the sensory block level during the 25 minutes after the spinal injection. Other end points included motor block score, maternal hypotension, and vasopressor requirements.
  
  
  RESULTS
  Data from 89 patients were analyzed. Patient characteristics were similar in all groups. The median [interquartile range] (95% confidence interval) sensory levels after spinal injection were significantly higher with decreasing baricity: hyperbaric T10 [T11-8] (T10-9), isobaric T9 [T10-7] (T9-7), and hypobaric T6 [T8-4] (T8-5) (P < 0.001, Cuzick trend). All patients in the hypobaric group reached a sensory block level of T4 at 25 minutes after spinal injection compared with 80% of the patients in both the isobaric and hyperbaric groups (P = 0.04; difference 20%, 95% confidence interval of difference 4%-33%). Significantly more patients in the hypobaric group had complete lower limb motor block (Bromage score = 4) (hyperbaric 43%, isobaric 63%, and hypobaric 90%; P < 0.001). The incidences of maternal hypotension and nausea and vomiting were similar among groups, although the ephedrine requirements were significantly increased in the isobaric and hypobaric groups by factors of 1.83 and 3.0, respectively, compared with the hyperbaric group (P < 0.001, Cuzick trend).
  
  
  CONCLUSIONS
  We demonstrated that when parturients undergoing cesarean delivery were maintained in the sitting position for 5 minutes after spinal injection of the local anesthetic, hypobaric bupivacaine resulted in sensory block levels that were higher compared with isobaric and hyperbaric bupivacaine, respectively, during the study period.
authors: Department of Anesthetics, University College London Hospital, 235 Euston Rd., London, NW1 2BU, UK.
authors: Christian
authors: C
authors: Loubert
authors: Stephen
authors: S
authors: Hallworth
authors: Roshan
authors: R
authors: Fernando
authors: Malachy
authors: M
authors: Columb
authors: Nisa
authors: N
authors: Patel
authors: Kavita
authors: K
authors: Sarang
authors: Vinnie
authors: V
authors: Sodhi
mesh_terms: D000328:Adult; D000773:Anesthesia, Obstetrical / Q000009:adverse effects; D000775:Anesthesia, Spinal / Q000009:adverse effects; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000009:adverse effects / Q000737:chemistry; D002045:Bupivacaine / Q000008:administration & dosage* / Q000009:adverse effects / Q000737:chemistry; D002585:Cesarean Section; D016009:Chi-Square Distribution; D003720:Densitometry; D004311:Double-Blind Method; D017558:Elective Surgical Procedures; D004809:Ephedrine / Q000627:therapeutic use; D005260:Female; D006112:Gravitation; D006801:Humans; D007022:Hypotension / Q000209:etiology; D007278:Injections, Spinal; D008131:London; D009043:Motor Activity / Q000187:drug effects; D009325:Nausea / Q000139:chemically induced; D056888:Patient Positioning; D011247:Pregnancy; D011446:Prospective Studies; D012677:Sensation / Q000187:drug effects; D013997:Time Factors; D016896:Treatment Outcome; D014662:Vasoconstrictor Agents / Q000627:therapeutic use; D014839:Vomiting / Q000139:chemically induced
chemical_list: D000779:Anesthetics, Local; D014662:Vasoconstrictor Agents; D004809:Ephedrine; D002045:Bupivacaine