Phenylephrine for blood pressure control in elective cesarean section: therapeutic versus prophylactic doses.

BACKGROUND AND OBJECTIVES Spinal block is commonly used in cesarean sections and, if some prophylactic measures are not taken, the incidence of hypotension is higher than 80%. The objective of this study was to compare the efficacy of the administration of therapeutic or prophylactic doses of phenylephrine to maintain blood pressure in patients undergoing spinal block for elective cesarean section. METHODS One hundred and twenty gravidas undergoing elective cesarean sections under spinal block, randomly divided in three equal groups according to the regimen of phenylephrine administered, were included in this study. In Group 1, continuous infusion of phenylephrine, using an infusion pump at 0.15 microg.kg(-1).min(-1) was administered after the spinal block. In Group 2, a single dose of prophylactic phenylephrine 50 microg was administered after the spinal block, and Group 3 received a single dose of phenylephrine 50 microg in case of hypotension, which was defined as a drop in SBP and/or DBP of up to 20% of baseline levels. The incidence of hypotension, nausea, and vomiting as well as the Apgar score were evaluated. RESULTS The incidence of hypotension was significantly greater in Group 3, affecting 85% of the gravidas. In Groups 1 and 2 hypotension was seen in 17.5% and 32.5% of the cases respectively (p < 0.001). The incidence of nausea was much higher in Group 3 affecting 40% of the patients while in Groups 1 and 2 it was 10% and 15% respectively which was statistically significant. CONCLUSIONS According to the methodology used, this study showed that prophylactic continuous infusion of phenylephrine initiated immediately after the spinal block for cesarean section is more effective in reducing the incidence of hypotension and maternal and fetal side effects.