Evaluation of pre-emptive intramuscular phenylephrine and ephedrine for reduction of spinal anaesthesia-induced hypotension during Caesarean section

Pre-emptive intramuscular (i.m.) vasopressors were evaluatedin 108 patients undergoing elective Caesarean section underspinal anaesthesia, assigned to four groups in a randomized,double-blind, placebo-controlled study. Group 1 received pre-emptivephenylephrine 4 mg i.m., group 2 received phenylephrine 2 mgi.m., group 3 received ephedrine 45 mg i.m., while controlsreceived an i.m. injection of saline, all given immediatelyafter induction of spinal anaesthesia. Hypotension was definedas a 25% decrease in mean arterial pressure (MAP). Rescue intravenous(i.v.) boluses of ephedrine were given if the patient was hypotensiveor reported nausea, vomiting or dizziness. The incidence ofhypotension was 33% in the phenylephrine 4 mg group comparedwith 70% in the control and phenylephrine 2 mg groups (P=0.03),and 48% in the ephedrine 45 mg group. The phenylephrine 4 mgand ephedrine 45 mg groups had a significantly lower percentagereduction in MAP (–21 (SD 14)% and –22 (14)%) comparedwith controls (–32 (18)%, P=0.04). They also had a lowertotal dose of rescue i.v. ephedrine (15.7 (15.7) mg and 15.8(15.6) mg) compared with controls (28.8 (20.6) mg, P=0.02).We conclude that pre-emptive i.m. phenylephrine 4 mg and ephedrine45 mg reduce the severity of hypotension and the total doseof rescue i.v. ephedrine during spinal anaesthesia for Caesareansection. Br J Anaesth 2001; 86: 372–6