The Dose-dependent Effects of Phenylephrine for Elective Cesarean Delivery Under Spinal Anesthesia

Abstract

A lthough use of a prophylactic phenylephrine infusion concurrently with a fluid coload can virtually eliminate hypotension associated with spinal anesthesia, maternal reactive hypertension and bradycardia are concerns. The ideal dosing regimen for a phenylephrine infusion to prevent hypotension is unknown. This double-blind, placebo-controlled study investigated the dose of phenylephrine, when given as a prophylactic fixed-rate infusion, that is associated with the fewest interventions needed to maintain maternal systolic blood pressure (SBP) within 20% of baseline.The patients who participated were >36 weeks' gestational age and scheduled for an elective cesarean delivery under spinal anesthesia. The baseline SBP was calculated using a mean of the first 3 consecutive measurements taken 5 minutes apart. A physician blinded to the infusion group intervened when SBP was ± 20% outside of baseline. Patients were randomly allocated to a placebo (control) group (PE 0) or 1 of 4 fixed-rate phenylephrine infusion regimens: 25, 50, 75, or 100 mg/min (PE 25, PE 50, PE 75, PE 100, respectively). Standard noninvasive monitoring was used, and spinal anesthesia was performed at the L3-4 or L4-5 interspace with 15 mg fentanyl, 150 mg preservative-free morphine, and 1.6 mL 0.75% hyperbaric bupivacaine. After injection of the intrathecal medication, the study drug was administered at 60 mL/h combined with the fluid coload. BP readings were obtained every minute for the first 10 minutes after spinal injection and then every 2.5 minutes thereafter. Oxytocin (5 U) was given intravenously as a bolus after delivery, followed by an infusion over the next 2 hours. The study drug was infused until 10 minutes after delivery, after which management was at the discretion of the anesthesiologist. The primary end point was the number of physician interventions required to maintain maternal SBP within 20% of baseline and to treat bradycardia. Other parameters recorded included hemodynamic changes, incidence of intraoperative nausea and vomiting, and umbilical cord blood gas values.The groups (n = 20, 20, 20, 19, and 22 for groups PE 0, 25, 50, 75, 100, respectively) did not differ in patient demographic characteristics, maximum height of sensory block, time from skin incision to delivery, time from uterine incision to delivery, volume of lactated Ringer solution infused, or estimated blood loss. The phenylephrine doses of 25 and 50 mg/min were associated with significantly fewer interventions (0.5 and 1.5, respectively) to maintain target BP compared with 5 interventions in the 100-mg/min group (P = 0.004 and P = 0.02, compared to the PE 50 and PE 25 intervention groups, respectively). However, no differences were found in the number of interventions needed to keep SBP within the target range in the control group compared with those receiving phenylephrine infusions. The incidence of predelivery hypotension was significantly lower in groups PE 50 (0, range 0À2), PE 75 (0, range 0À0), and PE 100 (0, range 0À 1) compared with the PE 0 group (2,...

Effect of Acute Administration of an Herbal Preparation on Blood Pressure and Heart Rate in Humans

“…m -Synephrine (hydroxyl group in the meta position) is not a constituent of bitter orange nor is it present in standardized C. aurantium reference materials 22 . The m -synephrine (phenylephrine) is readily available as an over-the-counter nasal decongestant, is also used as an ophthalmic product for mydriasis, and is known for its cardiovascular effects 23 .…”

The Influence Of The Infusion Of Ephedrine And Phenylephrine On The Hemodynamic Stability After Subarachnoid Anesthesia In Senior Adults - A Controlled Randomized Study

“…Kamenik and Eržen [34] showed that CO decreases after SA in the group of middle-aged patients not receiving crystalloids as well as in the group of patients who received crystalloids before SA, while CO increases in the group of patients receiving lactated Ringer's solution at the time of spinal block. Later on, Zorko and Kamenik [35] have shown that the infusion of 1000 mL of lactated Ringer after spinal block prevented the decrease of CO after SA, CO was actually increasing while the infusion was running. In our study, we used a slightly modified hydration strategy.…”

Eficacia de fenilefrina en la prevención de hipotensión en cesárea bajo anestesia subaracnoidea

“…La hipotensión bajo anestesia subaracnoidea en cesárea es uno de los principales eventos adversos relacionados directamente con el acto anestésico 4,5 , asociándose a importantes complicaciones tanto maternas como fetales. El objetivo de los estudios actuales está enfocado en la búsqueda del vasopresor ideal, que evite la aparición de hipotensión, considerándose el uso de la efedrina 14,15 , fenilefrina [16][17][18][19][20][21][22][23] , etilefrina. En la actualidad fenilefrina es el más usado 17 , pero no se ha podido establecer la forma ideal de administración, la dosis requerida y su presentar, pueden ser menores respecto de las dosis usadas en pacientes que no reciben profilaxis.…”

“…Se han diseñado múltiples estrategias encaminadas a reducir de forma significativa la frecuencia de presentación de hipotensión, el colocar a la gestante en decúbito lateral izquierdo para disminuir la compresión aortocava 9 , el empleo de bolos de líquidos intravenosos [10][11][12] ; la reducción de la dosis de anestésico 13 , la elevación o compresión de los miembros inferiores 9 y la administración de vasopresores [14][15][16] , son ejemplos de ello, con resultados contradictorios en su eficacia 17 . En los últimos años, ha surgido un interés particular por la administración de fenilefrina profiláctica, dado su principal efecto α adrenérgico [18][19][20] , sin embargo, los estudios realizados 21-,23 no han determinado la dosis o la forma de administración que resulte eficaz en la prevención de este evento adverso.…”