Signs of myocardial ischaemia after injection of oxytocin: a randomized double-blind comparison of oxytocin and methylergometrine during Caesarean section.
BACKGROUND
ECG changes, similar to those seen during myocardial ischaemia, together with symptoms of chest pain, are common during Caesarean section (CS). We hypothesized that oxytocin administration has cardiovascular effects leading to these symptoms and ECG changes.


METHODS
Forty women undergoing elective CS under spinal anaesthesia were given an i.v. bolus of either 10 IU of oxytocin (Group OXY-CS, n=20) or 0.2 mg of methylergometrine (Group MET-CS, n=20), in a double-blind, randomized fashion after delivery. Ten healthy, non-pregnant, non-anaesthetized women were used as normal controls (Group OXY-NC, n=10) and were given 10 IU of oxytocin i.v. Twelve-lead ECG, on-line, computerized vectorcardiography (VCG), and invasive arterial pressure were recorded.


RESULTS
Oxytocin produced a significant increase in heart rate, +28 (SD 4) and +52 (3) beats min(-1) [mean (SEM); P<0.001], decreases in mean arterial pressure, -33 (2) and -30 (3) mm Hg (P<0.001), and increases in the spatial ST-change vector magnitude (STC-VM), +77 (12) and +114 (8) microV (P<0.001), in CS patients and controls, respectively. Symptoms of chest pain and subjective discomfort were simultaneously present. Methylergometrine produced mild hypertension and no significant ECG changes.


CONCLUSIONS
Oxytocin administered as an i.v. bolus of 10 IU induces chest pain, transient profound tachycardia, hypotension, and concomitant signs of myocardial ischaemia according to marked ECG and STC-VM changes. The effects are related to oxytocin administration and not to pregnancy, surgical procedure, delivery, or sympathetic block from spinal anaesthesia.
Svanström
M C
MC
Department of Thoracic Anaesthesiology, Umeå University Hospital, SE-901 85 Umeå, Sweden.
Biber
B
B
Hanes
M
M
Johansson
G
G
Näslund
U
U
Bålfors
E M
EM
D000328:Adult; D000773:Anesthesia, Obstetrical / Q000379:methods; D000775:Anesthesia, Spinal; D001794:Blood Pressure / Q000187:drug effects; D002585:Cesarean Section; D004311:Double-Blind Method; D004562:Electrocardiography / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007430:Intraoperative Care / Q000009:adverse effects; D007431:Intraoperative Complications; D008755:Methylergonovine / Q000009:adverse effects*; D017202:Myocardial Ischemia / Q000139:chemically induced* / Q000175:diagnosis; D010120:Oxytocics / Q000009:adverse effects*; D010121:Oxytocin / Q000009:adverse effects*; D011247:Pregnancy
D010120:Oxytocics; D010121:Oxytocin; D008755:Methylergonovine