Tyagi Asha, Kakkar Aanchal, Niwal Namrata, Mohta Medha, Sethi Ashok Kumar
Department of Anaesthesiology and Critical Care, University College of Medical Sciences and Guru Teg Bahadur Hospital, New Delhi, India.
Department of Anaesthesiology and Critical Care, RML Hospital and Postgraduate Institute of Medical Education and Research, New Delhi, India.
Saudi J Anaesth. 2017 Oct-Dec;11(4):421-426. doi: 10.4103/sja.SJA_269_17.
Phenylephrine infusion has been shown to decrease rostral spread of plain and hyperbaric local anesthetic (LA) when compared to ephedrine infusion. However, it does not result in higher dose requirement of hyperbaric LA for cesarean section. There is no trial evaluating the effect of phenylephrine infusion on ED50 of a plain intrathecal LA.
Pregnant patients with term uncomplicated singleton pregnancy undergoing elective cesarean section were given combined spinal-epidural anesthesia. They received intrathecal plain levobupivacaine 0.5% in a dose decided by up-and-down sequential allocation method along with 25 μg fentanyl. Intravenous infusion of phenylephrine (100 μg/ml) or normal saline was initiated immediately after intrathecal injection. Systolic arterial pressure ≤0.8 times baseline was treated using rescue boluses of phenylephrine 50 μg.
Demographic, other patient and surgical characteristics were similar in the two groups. ED50 of intrathecal plain levobupivacaine was significantly greater in phenylephrine group (5.5 mg [95% confidence interval (CI): 5.1-5.9 mg]) compared to saline group (4.2 mg [95% CI: 3.4-5.1 mg]) ( = 0.01). Maximum sensory level, time to achieve adequate block, Apgar scores, and umbilical artery pH were similar in both groups. Total phenylephrine dose and patients having significant bradycardia were lesser in the saline group.
Intrathecal dose requirement of plain levobupivacaine is greater using phenylephrine infusion as compared to saline infusion with rescue phenylephrine boluses. When using phenylephrine as a variable dose regimen titrated to maintain blood pressure within 20% of baseline, the ED50 of plain levobupivacaine is 5.5 mg (95% CI: 5.1-5.9 mg).
与麻黄碱输注相比，去氧肾上腺素输注已显示可减少普通和高压局部麻醉药（LA）的头端扩散。然而，它并不会导致剖宫产时高压LA的剂量需求增加。尚无试验评估去氧肾上腺素输注对普通鞘内LA半数有效剂量（ED50）的影响。
择期剖宫产的足月单胎妊娠无并发症孕妇接受腰麻-硬膜外联合麻醉。她们通过上下序贯分配法接受鞘内注射0.5%普通罗哌卡因，剂量由该方法决定，并同时给予25μg芬太尼。鞘内注射后立即开始静脉输注去氧肾上腺素（100μg/ml）或生理盐水。收缩动脉压≤基线值的0.8倍时，使用50μg去氧肾上腺素抢救推注进行治疗。
两组的人口统计学、其他患者和手术特征相似。与生理盐水组（4.2mg[95%置信区间（CI）：3.4 - 5.1mg]）相比，去氧肾上腺素组鞘内普通罗哌卡因的ED50显著更高（5.5mg[95%CI：5.1 - 5.9mg]）（P = 0.01）。两组的最大感觉平面、达到充分阻滞的时间、阿氏评分和脐动脉pH值相似。生理盐水组的去氧肾上腺素总剂量和发生显著心动过缓的患者较少。
与使用去氧肾上腺素抢救推注的生理盐水输注相比，使用去氧肾上腺素输注时普通罗哌卡因的鞘内剂量需求更大。当使用去氧肾上腺素作为可变剂量方案进行滴定以将血压维持在基线值的20%以内时，普通罗哌卡因的ED50为5.5mg（95%CI：5.1 - 5.9mg）。
