BACKGROUND AND OBJECTIVE: Adequate sensory block for cesarean section under spinal anesthesia is T4-T6 that several factors (local anesthetic dose and baricity, position, rate of injection …) correlate with block height. This study was designed to evaluate the efficacy of intrathecal injection rate of bupivacaine 0.5% on sensory and motor block in cesarean section. 

METHODS: After confirmation of Ethic committee in this double blind clinical trial study, 75 term parturients were evaluated. All of patients underwent spinal anesthesia and allocated randomly to 3 groups (n=25) according to intrathecal injection rate of 10 mg bupivacaine 0.5% and 2.5 μg sufentanil and 0.5 ml normal saline in total volume of 3 ml. Patients received intrathecal local anesthetic by injection rate of 1ml/sec or 3ml/3 sec in Fast group, 0.2 ml/sec or 3ml/15 sec in Moderate group and 0.04 ml/sec or 3ml/75 sec in Slow group. Immediately sensory and motor block level were determined every 1 minute by Pinprick and Bromage score respectively. Blood pressure and heart rate was measured regularly, and nausea, vomiting and ephedrine dose was recorded. (IRCT=IRCT2012122210841N2 )

FINDINGS: Our study demonstrated that sensory level in Fast, Moderate and Slow groups was respectively T4, T5 and T6 that significantly was higher in Fast group. Timing of sensory block in Fast group was 3±0.4 and in Moderate and Slow groups were 4.4±0.7 and 4.2±0.4 minutes respectively (p<0.001). Fast injection of spinal anesthetic significantly increases prevalence of hypotension and reducing time of sensory level to T10 in cesarean delivery (F=114.8±14.4, M=81.6±7 and S=74±18.3 minutes, p<0.001). Incidence of nausea and vomiting in Fast group was 76% and 48% whereas in Moderate was 16% and 8% and in Slow group was 20% and 8% (p<0.001).

CONCLUSION: We concluded that fast intrathecal injection of bupivacaine increases sensory and motor block and hypotension, nausea and vomiting in cesarean section.