Lumbosacral cerebrospinal fluid volume in humans using three-dimensional magnetic resonance imaging.

BACKGROUND: The clinical response to spinal anesthesia is influenced by lumbosacral cerebrospinal fluid (CSF) volume, which is highly variable among patients. METHODS: Lumbosacral magnetic resonance images were obtained in 71 patients using a long echo time (TE = 198 msec), fast spin echo sequence with fat suppression. Three-dimensional images were created and lumbosacral CSF volume was estimated using a threshold-based region growing algorithm. RESULTS: A validation experiment using a water bath and cadaveric spinal cord demonstrated that the technique was accurate (1.4 +/- 0.4% difference between estimated and measured). The coefficient of variance was 0.42% among the three estimated CSF values per subject. The mean calculated volume was 35.8 +/- 10.9 mL with a range of 10.6-61.3 mL. Lumbosacral CSF volume was widely variable among patients and was inversely proportional to body mass index (r = -.276, P = 0.02). Mean calculated lumbosacral CSF volumes were smaller in the group of subjects that had radiographic diagnoses of spinal stenosis when compared with subjects with no diagnosis (mean difference -8.4 mL, 95% CI of the difference, -16.1 to -0.8 mL, P = 0.03) and were not different when compared with those with herniated disk disease (mean difference -6.4 mL, 95% CI of the difference -14.7 to 1.9 mL, P = 0.19). CONCLUSIONS: Application of this technique to clinical investigations may further enhance our understanding of spinal anesthesia.

The risk of cesarean delivery with neuraxial analgesia given early versus late in labor.

BACKGROUND: Epidural analgesia initiated early in labor (when the cervix is less than 4.0 cm dilated) has been associated with an increased risk of cesarean delivery. It is unclear, however, whether this increase in risk is due to the analgesia or is attributable to other factors. METHODS: We conducted a randomized trial of 750 nulliparous women at term who were in spontaneous labor or had spontaneous rupture of the membranes and who had a cervical dilatation of less than 4.0 cm. Women were randomly assigned to receive intrathecal fentanyl or systemic hydromorphone at the first request for analgesia. Epidural analgesia was initiated in the intrathecal group at the second request for analgesia and in the systemic group at a cervical dilatation of 4.0 cm or greater or at the third request for analgesia. The primary outcome was the rate of cesarean delivery. RESULTS: The rate of cesarean delivery was not significantly different between the groups (17.8 percent after intrathecal analgesia vs. 20.7 percent after systemic analgesia; 95 percent confidence interval for the difference, -9.0 to 3.0 percentage points; P=0.31). The median time from the initiation of analgesia to complete dilatation was significantly shorter after intrathecal analgesia than after systemic analgesia (295 minutes vs. 385 minutes, P<0.001), as was the time to vaginal delivery (398 minutes vs. 479 minutes, P<0.001). Pain scores after the first intervention were significantly lower after intrathecal analgesia than after systemic analgesia (2 vs. 6 on a 0-to-10 scale, P<0.001). The incidence of one-minute Apgar scores below 7 was significantly higher after systemic analgesia (24.0 percent vs. 16.7 percent, P=0.01). CONCLUSIONS: Neuraxial analgesia in early labor did not increase the rate of cesarean delivery, and it provided better analgesia and resulted in a shorter duration of labor than systemic analgesia.