The Effect of Posture and Baricity on the Spread of Intrathecal Bupivacaine for Elective Cesarean Delivery

Abstract

Posture and baricity during induction of spinal anesthesia with intrathecal drugs are believed to be important in determining spread within the cerebrospinal fluid. In this double-blind prospective study, 150 patients undergoing elective cesarean delivery were randomized to receive a hyperbaric, isobaric, or hypobaric intrathecal solution of 10 mg bupivacaine during spinal anesthesia induced in either the sitting or right lateral position. After an intrathecal injection using a combined-spinal technique patients were placed in the supine wedged position. We determined the densities of the three intrathecal solutions from a previously validated formula and measured using a DMA-450 density meter. Data collection included sensory level, motor block, episodes of hypotension, and ephedrine use. Statistical analysis included analysis of variance and Cuzick's trend. In the lateral position, baricity had no effect on the spread of sensory levels for bupivacaine compared to the sitting position, where there was a statistically significant difference in spread with the hypobaric solution producing higher levels of analgesia than the hyperbaric solution (P = 0.002). However, the overall differences in maximal spread only differed by one dermatome, with the hyperbaric solution achieving a median maximum sensory level to T3 compared with T2 for the isobaric and hypobaric solutions. Motor block was significantly (P = 0.029) reduced with increasing baricity and this trend was significant (P = 0.033) for the lateral position only. Hypotension incidence and ephedrine use increased with decreasing baricity (P = 0.003 and 0.004 respectively), with the hypobaric sitting group having the most frequent incidence of hypotension (76%) as well as cervical blocks (24%; P = 0.032).

Comparison of Maternal and Neonatal Effects of Combined Spinal Epidural Anesthesia in the Sitting or Lateral Position During Elective Cesarean Section

“…In studies, in which hemodynamic effects of maternal position was compared, independent from the severity of hypotension, 1-and 5-minutes Apgar scores are similar in lateral and sitting positions (11,18,19,21,23). Similarly, in our study, besides no difference was found between the groups, none of the newborns had a 1-and 5-minutes Apgar score <7.…”

“…Spinal anaesthesia using the same local anaesthetic agent in the same dose and volume can lead to different levels of sensory block according to the changes in the baricity of the local anaesthetic agent. Hallworth and colleagues (21) in their study evaluating the effects of 10 mg hyperbaric, isobaric and hypobaric bupivacaine forms on the mother's position and hemodynamic characteristics, found the mean maximum sensory block level in sitting and lateral positions as T3 in the hyperbaric groups, and T2 in the isobaric and hypobaric groups. In the hyperbaric group, there were 3 patients (12%) with cervical dermatome involvement in the lateral position; however, none of the patients in sitting position had cervical dermatome involvement.…”

Effects of sitting up for five minutes versus immediately lying down after spinal anesthesia for Cesarean delivery on fluid and ephedrine requirement; a randomized trial

“…The reduction in SBP could be explained in part by the rapid cephalad spread of the local anesthetic and the accompanying sympathectomy 12,15 and in part by aortocaval compression caused by the gravid uterus despite the 15°left tilt that was used in all patients. A study by Rees et al 16 supports these findings; they showed that even a true 15°left table tilt is associated with some aortic compression.…”

“…There were no differences in systolic blood pressure (P = 0.127) or heart rate (P = 0.831) over time between groups. Time to a modified Bromage score of 2 was longer in Group S than in Group L [101 (15) min vs 88 (14) min, respectively; P \ 0.001]. Conclusions Sitting the patient up for five minutes rather than laying the patient down immediately after spinal anesthesia for Cesarean delivery decreased intraoperative sensory block height, ephedrine and fluid requirements, and intraoperative nausea, vomiting, and shortness of breath without affecting systolic blood pressure or the success of the anesthetic.…”

Optimizing bupivacaine dosing for Cesarean delivery — I

“…In a study examining the effects of posture and baricity on spinal anesthesia, Hallworth et al added 1.6 mL normal saline and 0.4 mL D5W to 8 mL of 0.5% bupivacaine to make an isobaric solution as measured by a density meter. 4 A more easily obtained local anesthetic solution isobaric to CSF in pregnancy is 1% tetracaine in water. 5,6 It is prepared by adding 2 mL sterile water to a 20 mg ampoule of lyophilized tetracaine.…”