Variable Rate Phenylephrine Infusion for Prevention of Spinal-induced Hypotension for Cesarean Delivery

Variable Rate Phenylephrine Infusion for Prevention of Spinal-induced Hypotension for Cesarean Delivery

Crystalloid Coload Combined With Variable Rate Phenylephrine Infusion for Prevention of Hypotension During Spinal Anesthesia for Elective Cesarean Delivery vs Crystalloid Coload Alone

Rapid administration of crystalloid immediately after induction of spinal anesthesia (coload) to be more effective in terms of managing hypotension as compared to administering crystalloid before spinal anesthesia (preload). Phenylehrine infusion is a safe and effective way to reduce incidence and frequency of hypotension during SA for cesarean delivery. Hypotension was virtually eliminated by use of high-dose prophylactic phenylephrine infusion at a rate of 100 µg/min and rapid crystalloid coload up to two liters (administration at the time of SA). However, incidence of reactive hypertension was frequent up to 47% with decrease in maternal heart rate (HR). This may raise concern in patients in whom increase of blood pressure may be detrimental, like chronic hypertension and in the presence of a compromised uteroplacental blood flow. A recent study found that infusing phenylephrine at a fixed rate of 75 and 100 ug/min is associated with more episodes of hypertension than placebo or the lower infusion rates of 25 and 50 ug/min respectively. However, there was no reduction in the number of physician interventions (phenylephrine boluses and stopping the infusion) needed to maintain maternal systolic blood pressure within 20% of baseline among all groups. Prophylactic fixed rate infusions may have limited application in clinical practice, and a variable rate (i.e. modifying the rate according to hemodynamics) has been advocated. The bolus administration of phenylephrine to treat hypotension is still commonly used, but requests multiple interventions from the anesthesiologists and is time consuming. Eighty patients scheduled for cesarean delivery under spinal anesthesia will be assigned to one of two groups. Immediately after spinal injection, rapid crystalloid colaod of lactated Ringer of 15 mL/kg over a period of 10-15 min will be initiated. Patients in Group I will receive infusion of normal saline (placebo) and patients in group II variable infusion rate of phenylephrine started at 0.75 ug/kg (close to the dose of 50 ug/min recommended for fixed infusion rate). The number of interventions needed to maintain maternal systolic blood pressure within 20% of baseline, hemodynamic performance, intraoperative nausea and vomiting, and umbilical cord blood gases will be compared between the two groups. We will define a reliable and safe method to ensure maternal hemodynamic stability during spinal anesthesia for cesarean delivery with the least physician interference.

PHenylephrine infusion started at 0.75 microgram per kg per mL started at spinal injection till delivery

Prophylactic variable rate of saline infusion where we adjusted the pump at a starting rate of 0.75 µg/kg/min, equivalent to 0.0075 mL/kg/min of saline

Prophylactic variable rate of saline infusion where we adjusted the pump at a starting rate of 0.75 µg/kg/min, equivalent to 0.0075 mL/kg/min of saline

Number of Physician Interventions Needed to Maintain Maternal Blood Pressure After Spinal Anesthesia Within 20% of Baseline and to Treat Bradycardia During Cesarean Delivery.

Physician interventions are triggered by hemodynamic changes more than 20% of baseline. The intervention can be one or more of the following: stopping the phenylephrine infusion changing the rate of phenylephrine infusion rescue intravenous bolus of phenylephrine (100 µg) for hypotension rescue intravenous bolus of atropine (0.4 mg) for bradycardia

Inclusion Criteria: Parturients beyond 37 weeks gestation ASA І or ІІ Exclusion Criteria: pregnancy-induced hypertension chronic hypertension multiple pregnancy fetal compromise diabetes mellitus polyhydramnios body weight >100 kg major systemic disease anemia (hemoglobin concentration<10 g/dl) clotting diathesis