Sublingual glyceryl trinitrate for uterine relaxation at Caeserean section--a prospective trial

Pre-eclampsia through the eyes of the obstetrician and anesthesiologist

Due to the high risk of morbidity and mortality from unrecognized and untreated pre-eclampsia, clinicians should have a high index of suspicion to evaluate, treat and monitor patients presenting with signs concerning for pre-eclampsia. Early blood pressure management and seizure prophylaxis during labor are critical for maternal safety. Intrapartum, special anesthetic considerations should be employed to ensure the safety of the parturient and fetus. Patients who have pre-eclampsia should be aware that they are at high risk for the future development of cardiovascular disease.

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.

Effects of sublingual nitroglycerin on human uterine contractility during the active phase of labor

Nitroglycerin is administered intravenously in acute obstetric emergencies to relax the uterus. However, complications (eg, hypotension, acute uterine bleeding) are frequent, which prompted a search for alternative routes of administration. We hypothesized that the sublingual administration of nitroglycerin would reduce uterine tone and contractility with few complications. Intrauterine pressure was measured in 12 women who were actively laboring (>4 cm dilatation, regular contractions) with epidural analgesia and who were alert and responsive throughout the study. In a double-blind fashion, subjects were randomized to receive either placebo or sublingual nitroglycerin (3 doses, 800 microg each) 10 minutes apart. The obstetric anesthesiologist continuously monitored maternal blood pressure and fetal heart rate. Cervical dilatation was assessed at the beginning and the end of the protocol. The area under the intrauterine pressure curve (integral) was used to estimate uterine contractility. Intrauterine pressure was analyzed before the randomization code was broken. Nitroglycerin did not alter the intrauterine pressure integral after the first dose (placebo, 3147 mm Hg x s [95% CI, 2206-4088] vs nitroglycerin, 4146 mm Hg x s [95% CI, 2451-5841]; P =.22), second dose (placebo, 3123 mm Hg x s [95% CI, 2447-3799] vs nitroglycerin, 3611 mm Hg x s [95% CI, 2723-4499]; P =.28), or third dose (placebo, 3303 mm Hg x s [95% CI, 2616-3990] vs nitroglycerin, 3810 mm Hg x s [95% CI, 2306-5314]; P =.45). Cervical dilation, basal uterine tone, duration and frequency of uterine contractions, or fetal heart rhythm remained unaffected. Maternal mean arterial pressure decreased significantly after nitroglycerin was administered. All women were delivered vaginally without intervention. Three doses of sublingual nitroglycerin (800 microg per dose) reduce neither uterine activity nor tone, despite lowering maternal blood pressure. If a clinical option, sublingual nitroglycerin will require a higher dose, which would place mother and fetus at risk for complication.

Nitroglycerin as a uterine relaxant: a systematic review

OBJECTIVE

To evaluate the effectiveness of nitroglycerin as a uterine relaxant for preterm labour, fetal extraction at Caesarean section, external version, embryo transfer, cervical dilation for first trimester pregnancy termination, and primary dysmenorrhea.

DESIGN

A systematic review of randomized control trials (RCTs) of nitroglycerin in obstetrics and gynaecology.

METHODS

We searched PubMed (1966-2001), the Cochrane Controlled Trials Register, and the International Journal of Obstetric Anesthesia using text terms quot:nitroglycerin," "glyceryl trinitrate," "uterus," "uterine," and "relaxation." The last search was conducted in January 2001. References from review articles and abstracts from major scientific meetings (1997-2000) were reviewed for relevant publications. RCTs comparing nitroglycerin to either placebo or another therapeutic intervention (ritodrine, magnesium sulphate, and prostaglandin) and whose quality score was equal to or greater than 2 were included (Class I evidence as described in the Report of the Canadian Task Force on the Periodic Health Exam).

RESULTS

Sixty articles were retrieved of which 13 were RCTs. Nitroglycerin was more effective for arresting preterm labour than placebo but not more effective when compared to ritodrine or magnesium. Nitroglycerin was not superior to placebo for uterine relaxation for either fetal extraction at Caesarean section or for external version. There were no differences in ease of embryo transfers when nitroglycerin spray was compared to placebo. In first trimester pregnancy terminations, less force was required to dilate the cervix when nitroglycerin was compared to no treatment. The incidence of preeclampsia was not reduced by nitroglycerin but fewer complications were noted when compared to the placebo group. In patients with primary dysmenorrhea, nitroglycerin significantly decreased pain.

CONCLUSION

Although nitroglycerin is widely used, its superiority over currently used tocolytic agents is unproven. (Class C recommendation) Nitroglycerin has been demonstrated to decrease pain associated with dysmenorrhea. (Class A recommendation)

New developments in the management of preterm labor

Current management of preterm labor has not changed the incidence of preterm delivery; therefore, significant research effort has been concentrated on the search for new methods of management. New tocolytics like inhibitors of cyclooxygenase 2 and nitric oxide donors have been tested in animal models and in preliminary clinical trials with promising results. Inhibition of cervical ripening may be one alternative to tocolysis. This new approach has a potential to be a valuable method of management of preterm labor if human studies confirm the promising results reported in animals. Growing evidence suggests that premature delivery may be associated with infection or fetal growth abnormalities, with dire consequences to the fetus. If these associations are to be included in risk and benefit assessment, then inhibition of preterm labor may prove to be detrimental to the fetus.

Glyceryl trinitrate and acute uterine relaxation: a literature review

The use of nitro-vasodilators for achieving rapid uterine relaxation in the resolution of obstetric emergencies has been documented for nearly 120 years. Glyceryltrinitrate (GTN) is the most commonly used nitro-vasodilator for this purpose, with the presumed mechanism of action being via nitric oxide and cyclic guanosine monophosphate (cGMP) mediated processes. GTN is known to release nitric oxide to effect smooth muscle relaxation and some dose response data is available for its vasodilator activity. Human myometrium is known to synthesize and respond to nitric oxide, with changes in the production of and sensitivity to nitric oxide being subject to the cyclical and gestational state of the uterus. Experimental data on the efficacy of GTN in reliably producing uterine relaxation is conflicting and inconsistent. A total of 32 studies and case reports on the use of GTN in achieving rapid uterine relaxation have appeared in the English language literature. Case reports are subject to reporting bias and prospective randomized controlled trials are not without design flaws. Indications for the use of GTN in achieving rapid uterine relaxation cover the antepartum, intrapartum and postpartum periods. The safety of GTN during obstetric emergencies appears high, with no adverse maternal or neonatal outcomes. To establish the efficacy of GTN in reliably achieving uterine relaxation, well designed randomized controlled trials in labouring women are required.

Nitroglycerin application during cesarean delivery: plasma levels, fetal/maternal ratio of nitroglycerin, and effects in newborns

OBJECTIVE

We sought to investigate maternal and fetal nitroglycerin metabolization and to assess the clinical condition of neonates after intravenous nitroglycerin application during cesarean delivery.

STUDY DESIGN

At the time of the uterine puncture incision, either 0. 25 mg or 0.5 mg nitroglycerin or a physiologic sodium chloride solution was administered as an intravenous bolus. Plasma concentrations of nitroglycerin and its metabolites were measured in maternal venous blood and in umbilical blood samples taken immediately after cord clamping. Arterial blood pressure, pulse rates, and Apgar scores were recorded for the neonates 1, 5, and 10 minutes after birth.

RESULTS

Sixty-two patients were included in the pharmacokinetic study. Median maternal plasma levels 1 and 5 minutes after injection of 0.5 mg nitroglycerin were 80 and 3.2 ng/mL, respectively; median maternal plasma levels 1 and 5 minutes after injection of 0.25 mg nitroglycerin were 38 and 1.2 ng/mL, respectively. In the umbilical vein 1 minute after application of 0. 5 mg or 0.25 mg nitroglycerin, the plasma levels were 0.41 and 0.09 ng/mL, respectively, and in the umbilical artery they were 0.03 and 0.008 ng/mL, respectively. Circulatory parameters and Apgar scores in the neonates did not differ significantly from those found in the placebo group.

CONCLUSION

The level of nitroglycerin in umbilical plasma was two to three orders of magnitude lower than that found in maternal plasma and clearly in a subtherapeutic range. There was no indication that prenatal application of nitroglycerin to facilitate obstetric management is hazardous for neonates.