Maternal posture influences the extent of sensory block produced by intrathecal dextrose-free bupivacaine with fentanyl for labor analgesia

The cephalad extent of sensory block produced by intrathecal (IT) dextrose-free local anesthetics and opioids has been reported to be quite variable. Most reports describing the effects of IT analgesics do not control for patient posture. Because these medications are hypobaric relative to cerebrospinal fluid (CSF), parturients in a sitting position may develop greater cephalad extents of sensory block than those in a lateral position during IT injection. Parturients in labor were randomized to sitting or lateral position during IT administration of dextrose-free bupivacaine 0.25% with fentanyl 0.005%. Extent of sensory block was evaluated at intervals thereafter. Free flow of CSF was obtained in 20 parturients. Those in a sitting position during IT injection had significantly higher maximal cephalad extent of block than those in a lateral position (mean +/- SD, T-3.1 +/- 2.9 vs T-6.3 +/- 3.4, P = 0.036). Mean cephalad extent of block was greater in the sitting group at 20 and 30 min. When sensory block asymmetry was observed, the extent of block was greater on the nondependent side. Posture during IT injection of this dextrose-free analgesic combination affects extent of sensory block in laboring parturients.