Prophylactic Phenylephrine Administration between 50 and 100 Micrograms Intravenous Slow Injection on Hypotension and Bradycardia after Spinal Anesthesia in Patients Undergoing Cesarean Section: A Randomized, Single-Blind Study

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Ratikorn Anusorntanawat


Introduction: According to the international recommendation, phenylephrine should be used routinely and preferably prophylactically via single-dilution technique, and/or prefilled syringes with or without a smart pump for management of hypotension after spinal anesthesia during cesarean section. However, there are several limitations of the use of phenylephrine, equipment and routine administration of this drug is not popular in Thailand. Objectives: To compare the incidence of hypotension, bradycardia and the other side effects after prophylactic phenylephrine administration between 50 and 100 micrograms (mcg) intra- venous slow injection after spinal anesthesia in patients undergoing cesarean section. Methods: Sixty-two patients undergoing elective cesarean section during October to December 2021. Coloading with 0.9% NaCl intravenous during performing spinal anesthesia with 0.5% hyperbaric bupivacaine 2.2 ml. plus preservative-free morphine 0.2 mg. After finishing spinal anesthesia, the patients were randomized into two groups. P50 (n=31) and P100 (n=31) groups which were prophylactic administered by IV slow injection of phenylephrine 50 and 100 mcg in 10 ml within 30 seconds with opening three ways of 3-way stopcock to imitate the function of a smart pump, respectively. Hypotension (SBP <10% of baseline) was rescued with phenylephrine 100 mcg and bradycardia was treated with atropine 0.6 mg. The other side effects were recorded. Results: The incidence of hypotension in P100 group was significantly lower than in P50 group (P=0.04). There were no statistically significant differences in bradycardia, arrhythmia, total dose of phenylephrine, reactive hypertension (SBP >10% of baseline), maternal nausea and vomiting score as well as Apgar score between the two groups. Conclusions: Prophylactic phenylephrine administration 100 mcg. IV slow injection within 30 seconds with opening three ways of 3-way stopcock to imitate the function of a smart pump is effective to lower the incidence of hypotension than 50 mcg and severe side effects were not found after spinal anesthesia for cesarean section.

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Ohpasanon P, Chinachoti T, Sriswasdi P, Srichu S. Prospective study of hypotension after spinal anesthesia for cesarean section at Siriraj Hospital: incidence and risk factors, Part 2. J Med Assoc Thai. 2008;91:675-80.

Somboonviboon W, Kyokong O, Charuluxananan S, Narasethakamol A. Incidence and risk factors of hypotension and bradycardia after spinal anesthesia for cesarean section. J Med Assoc Thai. 2008;91:181-7.

Russell IF. Spinal anaesthesia for caesarean section. The use of 0.5% bupivacaine. Br J Anaesth. 1983;55:309-14.

Saravanan S, Kocarev M, Wilson RC, Watkins E, Columb MO, Lyons G. Equivalent dose of ephedrine and phenylephrine in the prevention of post-spinal hypotension in Caesarean section. Br J Anaesth. 2006;96:95-9.

Anusorntanawat R. Incidence and risk factors associated with spinal anesthesia induced predelivery hypotension for cesarean section. Region 4-5 Med J. 2015;34:267-79.

Tan HS, Habib AS. The optimum management of nausea and vomiting during and after cesarean delivery. Best Pract Res Clin Anaesthesiol. 2020;34:735-47.

Kinsella SM, Carvalho B, Dyer RA, et al. International consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia. Anaesthesia. 2018;73:71-92.

นวัตกรรมวิสัญญี. [cited 27 สิงหาคม 2562]. Available from:

Uerpairojkit K, Anusorntanawat R, Sirisabya A, Chaichalothorn M, Charuluxananan S. Neonatal effects after vasopressor during spinal anesthesia for cesarean section: a multicenter, randomized controlled trial. Int J Obstet Anesth. 2017;32:41-7.

Fitzgerald JP, Fedoruk KA, Jadin SM, Carvalho B, Halpern SH. Prevention of hypotension after spinal anaesthesia for caesarean section: a systematic review and network meta-analysis of randomised controlled trials. Anaesthesia. 2020;75:109-21.

Anusorntanawat R. A comparison of phenylephrine administration between intravenous bolus and slow injection in treatment of spinal anesthesia-induced hypotension on bradycardia and other side effects in patients undergoing cesarean section: a randomized, single-blind study. Thai J Anesthesiol. 2020;46:80-7.

Anusorntanawat R, Uerpairojkit K, Thongthaweeporn N, Charuluxananan S. Safety of phenylephrine in antihypotensive treatment during spinal anesthesia for cesarean section. J Med Assoc Thai. 2016;99:188-96.

Sharwood-Smith G, Drummond GB. Hypotension in obstetric spinal anaesthesia: a lesson from pre-eclampsia. Br J Anaesth. 2009;102:291-4.

Langesaeter E, Rosseland LA, Stubhaug A. Continuous invasive blood pressure and cardiac output monitoring during cesarean delivery: a randomized, double-blind comparison of low-dose versus high-dose spinal anesthesia with intravenous phenylephrine or placebo infusion. Anesthesiology. 2008;109:856-63.

Lee JE, George RB, Habib AS. Spinal-induced hypotension: incidence, mechanisms, prophylaxis, and management: summarizing 20 years of research. Best Pract Res Clin Anaesthesiol. 2017;31:57-68.

Farkas A, Dempster J, Coker SJ. Importance of vagally mediated bradycardia for the induction of torsade de pointes in an in vivo model. Br J Pharmacol. 2008;154:958-70.

นวัตกรรมวิสัญญี Left uterine displacement for cesarean section [Internet] [Cited 29 December 2021]. Available from:

Lirk P, Haller I, Wong CA. Management of spinal anaesthesia-induced hypotension for caesarean delivery: a European survey. Eur J Anaesthesiol. 2012;29:452-3.