Ephedrine is a sympathomimetic drug that binds to X-and 0-receptors but also indirectly enhances norepinephrine release. It raises blood pressure by raising heart rate and cardiac output and by variably elevating peripheral vascular resistance. In early animal studies, ephedrine preserved uteroplacental blood flow during pregnancy compared with ai-receptor agonists. Accordingly, it had been the preferred vasopressor for obstetrical use. Phenylephrine is a pure a-agonist and elevates blood pressure solely through vasoconstriction. A metaanalysis of seven randomized trials by Lee (2002a) suggests that the safety profiles of ephedrine and phenylephrine are comparable. Following their systematic review of 14 reports, Lee (2002b) questioned whether routine prophylactic ephedrine is needed for elective cesarean delivery. Although fetal acidemia has been reported with prophylactic ephedrine use, this was not observed with prophylactic phenylephrine use (Ngan Kee, 2004).
High or Total Spinal Blockade. Most often, high or total spinal blockade follows administration of an excessive dose of local anesthetic or inadvertent injection into the subdural or subarachnoid space. Subdral injection manifests as a high but patchy block even with a small dose of local anesthetic agent, whereas subarachnoid injection typically leads to complete spinal blockade with hypotension and apnea. hese conditions must be immediately treated to prevent cardiac arrest. In the undelivered woman: (1) the uterus is immediately displaced laterally to minimize aortocaval compression; (2) efective ventilation is established, preferably with tracheal intubation; and (3) intravenous fluids and vasopressors are given to correct hypotension. If chest compressions are to be performed, the woman is placed in the left-lateral position to allow left uterine displacement.
Postdural Puncture Headache. Leakage of cerebrospinal fluid (CSF) from the dura mater puncture site can lead to postdural puncture or "spinal headache." Presumably, when the woman sits or stands, the diminished CSF volume creates traction on pain-sensitive central nervous system structures. Another mechanism may be the compensatory cerebral vasodilation in response to the loss of CSF-the Monro-Kellie doctrine (Mokri, 2001).
Rates of this complication can be reduced by using a small-gauge spinal needle and avoiding multiple punctures. In a prospective, randomized study of ive diferent spinal needles, Vallejo and associates (2000) concluded that Sprotte and Whitacre needles had the lowest risks of postdural puncture headaches. Sprigge and Harper (2008) reported that the incidence of postdural puncture headache was 1 percent in more than 5000 women undergoing spinal analgesia. Postdural puncture headaches are much less frequent with epidural blockade because the dura mater is not intentionally punctured. he incidence of inadvertent dural puncture with epidural analgesia approximates 0.2 percent (Introna, 2012; Katircioglu, 2008). here is no good evidence that placing a woman absolutely lat on her back for several hours is efective in preventing this headache.
Once headache develops, it is managed aggressively, as expectant management increases hospital-stay lengths and subsequent emergency-room visits (Angle, 2005). Conservative management, such as luid administration and bed rest, is largely inefective. If not efectively treated, postdural puncture headache can persist as a chronic headache (Webb, 2012).