Intrapartum tocolysis has no effect on fetal lactate concentration

Acute tocolysis

PURPOSE OF REVIEW

Emergency uterine relaxation may decrease the morbidity and mortality of the mother and her fetus. Obstetricians need to be aware of the indications, pharmacological methods, efficacy and complications of acute tocolysis.

RECENT FINDINGS

A variety of pharmacological agents are used to suppress uterine contractions. Newer agents like cyclo-oxygenase-2 inhibitors (Celecoxib) and oxytocin antagonists (atosiban) have been introduced into clinical practice with the hope of reducing the complications of betasympathomimetic drugs. Calcium-channel blockers are used but there are recent case reports of acute pulmonary oedema with the use of these agents. Most of the trials on tocolytics have been for suppression of preterm labour. Nitroglycerin has been used successfully as an acute tocolytic during Caesarean sections and manual removal of placenta. A recent randomized trial has suggested that atosiban may be an option for acute intrapartum tocolysis. This article will review the recent literature on the use of pharmacological agents used to suppress uterine contractions in emergency obstetric situations.

SUMMARY

Acute tocolysis may be indicated in antepartum, intrapartum and postpartum periods for a variety of indications. It may help reduce maternal and fetal morbidity and mortality. The ideal tocolytic is yet to be developed. Research is needed to develop a drug which has a greater uterospecificity with no effect on other organs with a rapid onset and a short duration of action.

Fetal scalp and cord blood lactate

Lactate measurements have been evaluated in intrapartum fetal surveillance for some 30 years. However, it was not until reliable, handheld, microvolume devices were launched during the 1990s that lactate became a clinical option. Retrospective data suggest that lactate determinations in fetal scalp blood are better than pH for predicting severe neonatal morbidity. A randomised controlled trial comparing these two measurements found lactate to be more favourable in clinical practice in terms of less sampling failure and reduced time from the decision to do a fetal scalp blood sample to the clinician receiving the result. At present, a large multicenter randomised control trial is in progress in Sweden to compare lactate and pH measurement for the clinical management of suspected fetal compromise. Main end-points in the study are metabolic acidemia or pH <7.00 in cord arterial blood at delivery. Results are likely to be available in 2-3 years time.

Lactate measurements in scalp and cord arterial blood

Lactate has been measured to evaluate fetal metabolic acidosis for some decades. However, not until the past few years have reliable lactate meters become available for bedside obstetric practice. The new technology, which requires only 5 microl blood, has reduced the sampling failure rate of fetal scalp blood to almost nil. A growing body of evidence has also shown lactate to be good at predicting neonatal outcome.