BACKGROUND During caesarean delivery under spinal anaesthesia hypotension may be managed by norepinephrine in preference to phenylephrine due a perception of less bradycardia and fewer reductions in cardiac output. OBJECTIVE As the optimum prophylactic dose of norepinephrine is unclear, we aimed to investigate its dose–response for preventing postspinal hypotension in caesarean delivery. DESIGN A randomised, double-blinded, dose-finding study. SETTING Jiaxing University affiliated Women and Children Hospital, Jiaxing, China. PATIENTS Ninety-nine patients undergoing elective caesarean delivery from 1 February to 5 August: excluding patients with ASA III or above, preeclampsia or hypertension, pre-existing or gestational diabetes, BMI more than 35 kg m−2, height less than 150 cm or with more than 175 cm, or with contraindications to local anaesthesia. INTERVENTIONS Patients received 0, 0.04, 0.05, 0.06 or 0.07 μg kg−1 min−1 preventive norepinephrine infusions immediately after intrathecal injection of 10 mg bupivacaine with 5 μg sufentanil. MAIN OUTCOME MEASURES The norepinephrine (Median effective dose) or (95% effective dose) ED50 and ED95, which were estimated using Probit analysis to compare haemodynamic changes associated with the different doses. RESULTS The incidence of hypotension was 70, 47.4, 40, 20 and 15% in the 0, 0.04, 0.05, 0.06 and 0.07 μg kg−1 min−1 groups, respectively. The ED50, ED80 and ED95 values were 0.029 (95% CI 0.008 to 0.042 μg kg−1 min−1), 0.068 (95% CI 0.055 to 0.099 μg kg−1 min−1) and 0.105 μg kg−1 min−1 (95% CI 0.082 to 0.172 μg kg−1 min−1), respectively. Apgar scores or umbilical arterial pH were similar among groups. CONCLUSION The ED50, ED80 and ED95 were 0.029, 0.068 and 0.105 μg kg−1 min−1 respectively. A 0.07 μg kg−1 min−1 norepinephrine infusion may be optimum for preventing postspinal hypotension after intrathecal injection of 10 mg bupivacaine combined with 5 μg sufentanil. TRIAL REGISTRATION Chinese Clinical Trial Registry (identifier: ChiCTR-TRC-1800014614).

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BACKGROUND: Ondansetron has been shown to reduce the incidence of hypotension and vasopressor requirement during spinal anesthesia for obstetric and nonobstetric surgery. However, the magnitude of this effect has not been fully quantified. In this parallel-group, randomized, double-blinded study, we determined the effective dose in 50% of subjects (ED50) of a prophylactic phenylephrine infusion for preventing hypotension in patients who received a single dose of intravenous ondansetron 4 mg or saline control before combined spinal–epidural anesthesia for elective cesarean delivery. ED50 values obtained were compared to estimate the effect of ondansetron versus placebo on vasopressor requirement. METHODS: Sixty parturients were randomly assigned to receive ondansetron (group O) or saline control (group C) 10 minutes before positioning for induction of spinal anesthesia. A prophylactic phenylephrine infusion was used to prevent hypotension. The first patient in each group received a phenylephrine infusion at the rate of 0.5 µg/kg/min. The infusion rate for each subsequent patient was varied with increments or decrements of 0.05 µg/kg/min based on the response of the previous patient, and the effective dose of the phenylephrine infusion for preventing hypotension in 50% of patients (ED50) was calculated for each group and compared using up-down sequential analysis. Probit regression was applied as a backup and sensitivity analysis was used to compare ED50 values for phenylephrine between groups by comparing calculated relative mean potency. RESULTS: The ED50 (mean [95% confidence interval (CI)]) of the rate of phenylephrine infusion was lower in group O (0.24 µg/kg/min [0.10–0.38 µg/kg/min]) compared with group C (0.32 µg/kg/min [0.14–0.47 µg/kg/min]) (P < .001). The total consumption of phenylephrine (mean ± standard deviation [SD]) until delivery was lower in group O (316.5 ± 25.9 µg) than in group C (387.7 ± 14.7 µg, P = .02). The estimate of relative median potency for phenylephrine for group O versus group C was 0.74 (95% CI, 0.37–0.95). CONCLUSIONS: Under the conditions of this study, intravenous ondansetron 4 mg reduced the ED50 of a prophylactic phenylephrine infusion by approximately 26% in patients undergoing cesarean delivery under combined spinal–epidural anesthesia.

BackgroundStudies have shown that abdominal girth and vertebral column length have high predictive value for spinal spread after administering a dose of plain bupivacaine. we designed a study to identify the specific correlations between abdominal girth, vertebral column length and a 0.5 % dosage of plain bupivacaine, which should provide a minimum upper block level (T12) and a suitable upper block level (T10) for lower limb surgeries.MethodsA suitable dose of 0.5 % plain bupivacaine was administered intrathecally between the L3 and L4 vertebrae for lower limb surgeries. If the upper cephalad spread of the patient by loss of pinprick discrimination was T12 or T10, the patient was enrolled in this study. Five patient variables and intrathecal plain bupivacaine dose were recorded. Linear regression and multiple regression analyses were performed.ResultsTotals of 111 patients and 121 patients who lost pinprick discrimination at T12 and T10, respectively, were analyzed in this study. Linear regression analysis showed that only abdominal girth and plain bupivacaine dose were strongly correlated (r =−0.827 for T12, r = −0.806 for T10; both p < 0.0001). Multiple linear regression analysis showed that both abdominal girth and vertebral column length were the key determinants of plain bupivacaine dose (both p < 0.0001). R2 was 0.874 and 0.860 for the loss of pinprick discrimination at T12 and T10, respectively.ConclusionsOur data indicated that vertebral column length and abdominal girth were strongly correlated with the dosage of intrathecal plain bupivacaine for the loss of pinprick discrimination at T12 and T10. The two regression equations were YT12 = 3.547 + 0.045X1-0.044X2 and YT10 = 3.848 + 0.047X1- 0.046X2 (Y, 0.5 % plain bupivacaine volume; X1, vertebral column length;and X 2, abdominal girth), which can accurately predict the minimum and suitable intrathecal bupivacaine dose for lower limb surgery to a great extent, separately.