Uterine Tachysystole

Uterine tachysystole is more than 5 contractions in 10 minutes, averaged over 30 minutes, with or without fetal heart rate changes. It is caused mainly by oxytocin, misoprostol or dinoprostone, and sometimes by abruption or spontaneous labour. It matters because frequent contractions reduce the time for placental blood flow between contractions, so the fetus can become hypoxic and acidotic.

• Risk factors: oxytocin infusion at high rate, misoprostol or dinoprostone use, previous uterine scar, abruption, cocaine use, parity.
• A contraction lasting more than 2 minutes is hypertonus.
• Most cases settle within 10 to 15 minutes after stopping the drug.

Women have very frequent painful contractions with little rest between them. The fetal heart rate may show late or variable decelerations, tachycardia or reduced variability.

• Contractions every 1 to 2 minutes.
• Maternal distress and urge to push before full dilatation.
• Differential diagnosis: normal strong labour, hypertonic dysfunction, placental abruption, uterine rupture, hyperstimulation with fetal heart changes, drug effect.
• Complications: fetal hypoxia and acidosis, hyperstimulation, abruption, cervical or perineal tears, precipitate labour, uterine rupture, caesarean section.

The diagnosis is by counting contractions with tocography.

• Cardiotocography with tocography: count contractions over 30 minutes (more than 5 in 10 minutes on average).
• Fetal heart rate baseline, variability, accelerations and decelerations.
• Drug history (oxytocin rate, misoprostol or dinoprostone time and dose); abdominal palpation for tone between contractions.
• Maternal pulse, blood pressure; examination for bleeding or scar tenderness.

The principle is to stop the cause, resuscitate the fetus and relax the uterus if the heart rate is abnormal.

• Supportive: stop or reduce oxytocin; remove the dinoprostone insert, and wipe misoprostol remnants from the vagina; left lateral position; oxygen 10 L/minute by mask while preparing for delivery; empty the bladder; continuous cardiotocography; reassess in 10 to 15 minutes.
• Pharmacological: Ringer's lactate 500 to 1000 mL IV over 15 to 30 minutes; terbutaline 0.25 mg subcutaneous once if tachysystole persists with an abnormal fetal heart rate; ephedrine 5 to 10 mg IV for hypotension after epidural; restart oxytocin at half the earlier rate after 30 minutes if the tracing is normal and contractions are 5 or fewer in 10 minutes; oxytocin 10 IU IM after birth.
• Procedures: caesarean section if the tracing stays pathological after 30 minutes of treatment, and at once for bradycardia, abruption or scar pain; assisted vaginal delivery if fully dilated.
• Special groups: a uterine scar needs immediate review for scar rupture and a lower threshold for caesarean section; women with heart disease or hypertension avoid terbutaline and use glyceryl trinitrate 400 micrograms sublingual.
• Red flags: fetal heart rate below 110 or above 160 beats per minute, late decelerations, bradycardia, scar pain, bleeding, maternal tachycardia.
• Follow-up: umbilical cord blood gas at birth; newborn Apgar score and examination; observe for 24 hours if depressed; review at 6 weeks.