These findings indicate an association between gestational week (Weeks 31-39) and a reduction in both CSF volume and dural sac surface area. These reductions may, at least in part, explain the facilitation of the spread of intrathecal anesthesia in pregnant women.

Limited dural sac coating and decreased leakage from the foramina of saline injected into the epidural space may account for the facilitation of longitudinal spread of epidural analgesia in pregnant women. The epidural volume effect is greater in pregnant than in nonpregnant women.

No abstract

S olution injected into the epidural space spreads freely, but not necessarily uniformly. In pregnant women, the dural sac is narrowed, and this narrowing may facilitate the spread of neuraxial block. The distribution of injected epidural solution may differ in pregnant and nonpregnant women. This study investigated the distribution of epidural saline injection and the extent of cerebrospinal fluid (CSF) reduction in pregnant women.Eight healthy women with a full-term singleton pregnancy and 8 nonpregnant nulliparous volunteers were studied. A day before exogenous oxytocin administration to augment labor, an epidural puncture was done at the L3-L4 level using loss-ofresistance technique with saline, without injecting more than 1 mL saline. An epidural catheter was advanced 3 to 5 cm into the epidural space. Low thoracic and lumbosacral axial magnetic resonance (MR) imaging was performed to measure CSF volume after catheter insertion. Sagittal MR images of the lower thoracic lumbosacral column were obtained to determine the level of the disk between T11 and 12 vertebrae. Low thoracic, lumbar, and spinal axial MR images caudal from this site were obtained at 8-mm increments. After the images were obtained, 10 mL saline was injected into the epidural space, and immediately thereafter, MR images were obtained in the same order as before the epidural saline injection. Cerebrospinal fluid volumes before and after epidural saline injection were compared. Dural sac coating was based on the observation of epidural saline in the anterior epidural space after injection in axial MR images at the pedicle levels from T12 to L5. Saline leakage from the foramina was determined using the same procedure at 6 disk levels from T11YT12 to L4YL5. Leakage of saline from the foramina was determined by counting the foramina that had saline on either side of the criteria line, defined as a straight line passing through the center of the intervertebral joint and the point of contact with the vertebral body at the disk level.Compared with nonpregnant women, the anterior and lateral epidural venous plexuses in the pregnant women were enlarged in association with dural sac narrowing, with the result that CSF volume before saline injection in the pregnant women was notably less than that in the nonpregnant women (42.0 T 4.2 and 33.6 T 6.5 mL, respectively; P G 0.05). In nonpregnant women, saline spread freely through the epidural space and coated the cylindrical dural sac with partial leaking through the foramina with no pattern. In pregnant women, saline did not leak through the intervertebral foramina, and the enlarged epidural venous plexus interfered with the dural sac coating, leading to only posterior accumulation of saline at the level of the pedicles of the vertebral bodies. Dural sac coating was not seen in any of the images from the pregnant women and in 3 of those from nonpregnant women. Saline leakage from the foramina was seen in images from 6 nonpregnant women and in none of the pregnant women. Mean CSF volume decreased in both g...

concerned following oxytocin-augmented or induced labor. The apparent conclusion is that there is no justification for the use of the ''more risky'' internal IT uterine contraction monitoring when the ''less risky'' ET monitoring appears just as effective. However, I would argue to the contrary in view of the findings that there were no greater complications from IT compared to ET monitoring. The authors point out their numbers (IT = 734, ET 722) did not have the power to confirm this from the standpoint of maternal comfort following catheter insertion, and for the subgroup analysis of obese women (mean pregravid BMI in these Dutch mothers was but 25.4 kg/m 2 ). The IT method often has much to recommend it over ET. Furthermore, 138 (19.1%) of the ET group did have uterine catheters inserted during labor; 51 for amniotic saline infusion for meconium and the others for problems of interpretation of ET. Hence, while ET will frequently suffice for interpretation of uterine contractions for the majority of patients and may be preferred in cases of infection and maternal HIV, the lack of an increased risk associated with intrauterine catheter insertion in this large study would support IT if there is a question of ET interpretation.Lastly, I am disheartened by the fact that only 801 of 1456 (55%) mothers were afforded epidural analgesia, which in this clinician's opinion is indicated for oxytocin augmentation or induction of labor. These medical interventions are usually associated with considerably more maternal pain and stress than that associated with spontaneous labor. In addition, effective labor epidural analgesia might well be associated with better interpretation of ET as the comfortable mother would tolerate the prolonged placement of the tocodynamometry strapped to her abdomen and would be far more likely to remain quiet during contractions, thus rendering a far better evaluation of her uterine contractions. Comment by Brett B. Gutsche, MDT he spread of local anesthetic in the spinal and epidural space during pregnancy may be influenced by the compression of the dural sac by the engorged epidural venous plexus. However, the extent of the reductions in the cerebrospinal fluid (CSF) volume and dural sac surface area induced by dural sac compression are not clear. The authors used magnetic resonance imaging (MRI) to examine the pregnancy-induced changes in the lumbosacral CSF volume and dural sac surface area in 18 healthy women.Eighteen women who had no spinal abnormalities agreed to participate in this study. MRI scans were obtained twice for each patient while they were in a supine position (4 women were studied before pregnancy and 14 women were scanned 3 to 7 mo after parturition) and each patient was also studied at 31 to 39 weeks gestation. Low thoracic and lumbosacral axial MRI scans for the measurement of CSF volume and dural sac surface area were obtained. Axial scans were obtained at 8-mm increments (3 mm thick, 5-mm interval) with a fast-spin echo sequence. The center level of the disk between T11 an...