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

Nitroglycerin Use in the Emergency Department: Current Perspectives

Nitroglycerin, a fast-acting vasodilator, is commonly used as a first-line agent for angina in the emergency department and to manage chest pain due to acute coronary syndromes. It is also a treatment option for other disease states such as acute heart failure, pulmonary edema, and aortic dissection. Nitroglycerin is converted to nitric oxide, a potent vasodilator, in the body, leading to venodilation at lower dosages and arteriodilation at higher dosages that results in both preload and afterload reduction, respectively. Although nitroglycerin has historically been administered as a sublingual tablet and/or spray, it is often given intravenously in the emergency department as this enables titration to effect with predictable pharmacokinetics. In this review article, we outline the indications, mechanism of action, contraindications, and adverse effects of nitroglycerin as well as review relevant literature and make general recommendations regarding the use of nitroglycerin in the emergency department.

The Effects of Nitroglycerin on the Oxytocin Dose-Response Profile in Oxytocin-Desensitized and Naïve Human Myometrium: An In Vitro Study

BACKGROUND

Nitroglycerin is used for acute reduction in uterine tone. Prolonged oxytocin exposure causes desensitization of oxytocin receptors. It is unknown if nitroglycerin exposure impacts the subsequent action of oxytocin in the setting of oxytocin receptor desensitization. This study investigated the effects of nitroglycerin on oxytocin-desensitized and oxytocin-naïve human myometrium and the subsequent response to oxytocin dose-response testing in vitro.

METHODS

Myometrial samples from 17 elective cesarean deliveries were divided into strips and allocated to 1 of 4 groups: (1) oxytocin desensitized and no nitroglycerin; (2) oxytocin desensitized and nitroglycerin; (3) oxytocin naïve and nitroglycerin; and (4) oxytocin naïve and no nitroglycerin. Final analysis included 28 strips per group. Nitroglycerin groups were exposed to incremental concentrations of nitroglycerin, while no nitroglycerin groups were kept in control (physiological salt) solution. All groups then underwent oxytocin dose-response testing. Primary outcome was motility index (amplitude × frequency; grams × contractions per 10 minutes [g·c/10 min]). Secondary outcomes were amplitude (g), frequency (contractions/10 minutes), and area under the curve (g·s). All outcomes (nitroglycerin and oxytocin dose-response periods) were expressed as a percentage change from baseline. Values were log transformed, compared using regression modeling and reported as the ratio of 2 geometric means (relative difference).

RESULTS

No significant difference was observed in motility index following nitroglycerin administration in oxytocin-desensitized versus oxytocin-naïve groups (relative difference = 19.0%; 95% confidence interval [CI], -32.6 to 109.9; P = .55). On oxytocin dose-response testing, motility index was highest in oxytocin-naïve and no nitroglycerin samples (group 4) (1.356 g·c/10 minutes) followed by oxytocin-naïve and nitroglycerin (group 3) (0.882 g·c/10 minutes), oxytocin-desensitized and no nitroglycerin (group 1) (0.769 g·c/10 minutes), and oxytocin-desensitized and nitroglycerin (group 2) (0.651 g·c/10 minutes) samples. Motility index was significantly reduced in group 1 vs 4 (relative difference = -43.3%; 95% CI, -66.5 to -4.1; P = .034) and group 2 vs 4 (relative difference = -52.0%; 95% CI, -70.9 to -20.8; P = .004). While in groups 3 vs 4, both amplitude (relative difference = -17.8%; 95% CI, -30.9 to -2.2; P = .27) and area under the curve (AUC; relative difference = -17.5%; 95% CI, -30.7 to -1.8; P = .030) were reduced.

CONCLUSIONS

Nitroglycerin-induced relaxation was not different between oxytocin-desensitized and oxytocin-naïve human myometrial strips in vitro. However, oxytocin-induced contractility was attenuated after nitroglycerin exposure in both oxytocin-desensitized and oxytocin-naïve samples, with maximum attenuation observed in desensitized tissues. This finding warrants further clinical studies to explore uterine responsiveness to oxytocin in women with oxytocin-augmented labors after nitroglycerin administration.

A Novel Nonantibiotic Nitroglycerin-Based Catheter Lock Solution for Prevention of Intraluminal Central Venous Catheter Infections in Cancer Patients

For long-term central lines (CL), the lumen is the major source of central line-associated bloodstream infections (CLABSI). The current standard of care for maintaining catheter patency includes flushing the CL with saline or heparin. Neither agent has any antimicrobial activity. Furthermore, heparin may enhance staphylococcal biofilm formation. We evaluated the safety and efficacy of a novel nonantibiotic catheter lock solution for the prevention of CLABSI. Between November 2015 and February 2016, we enrolled 60 patients with hematologic malignancies who had peripherally inserted central catheters (PICC) to receive the study lock solution. The study lock consisted of 15 or 30 μg/ml of nitroglycerin in combination with 4% sodium citrate and 22% ethanol. Each lumen was locked for at least 2 h once daily prior to being flushed. After enrollment of 10 patients at the lower nitroglycerin dose without evidence of toxicity, the dose was escalated to the higher dose (30 μg/ml). There were no serious related adverse events or episodes of hypotension with lock administration. Two patients experienced mild transient adverse events (one headache and one rash) possibly related to the lock and that resolved without residual effect. The CLABSI rate was 0 on lock days versus 1.6/1,000 catheter days (CD) off lock prophylaxis, compared with a rate of 1.9/1,000 CD at the institution in the same patient population. In conclusion, the nitroglycerin-based lock prophylaxis is safe and well tolerated. It may prevent CLABSI when given daily to cancer patients. Large, prospective, randomized clinical trials are needed to validate these findings. (This study has been registered at ClinicalTrials.gov under identifier NCT02577718.).

Techniques for assisting difficult delivery at caesarean section

BACKGROUND

Caesarean section involves making an incision in the woman's abdomen and cutting through the uterine muscle. The baby is then delivered through that incision. Difficult caesarean birth may result in injury for the infant or complications for the mother. Methods to assist with delivery include vacuum or forceps extraction or manual delivery utilising fundal pressure. Medication that relaxes the uterus (tocolytic medication) may facilitate the birth of the baby at caesarean section. Delivery of the impacted head after prolonged obstructed labour can be associated with significant maternal and neonatal complication; to facilitate delivery of the head the surgeon may utilise either reverse breech extraction or head pushing.

OBJECTIVES

To compare the use of tocolysis (routine or selective use) with no use of tocolysis or placebo and to compare different extraction methods at the time of caesarean section for outcomes of infant birth trauma, maternal complications (particularly postpartum haemorrhage requiring blood transfusion), and long-term measures of infant and childhood morbidity.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 September 2015) and reference lists of retrieved studies.

SELECTION CRITERIA

All published, unpublished, and ongoing randomised controlled trials comparing the use of tocolytic agents (routine or selective) at caesarean section versus no use of tocolytic or placebo at caesarean section to facilitate the birth of the baby. Use of instrument versus manual delivery to facilitate birth of the baby. Reverse breech extraction versus head pushing to facilitate delivery of the deeply impacted fetal head.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy.

MAIN RESULTS

Seven randomised controlled trials, involving 582 women undergoing caesarean section were included in this review. The risk of bias of included trials was variable, with some trials not adequately describing allocation or randomisation.Three comparisons were included. 1. Tocolysis versus no tocolysisA single randomised trial involving 97 women was identified and included in the review. Birth trauma was not reported. There were no cases of any maternal side-effect reported in either the nitroglycerin or the placebo group. No other maternal and infant health outcomes were reported. 2. Reverse breech extraction versus head push for the deeply impacted head at full dilation at caesarean section Four randomised trials involving 357 women were identified and included in the review. The primary outcome of birth trauma was reported by three trials and there was no difference between reverse breech extraction and head push for this rare outcome (three studies, 239 women, risk ratio (RR) 1.55, 95% confidence interval (CI) 0.42 to 5.73). Secondary outcomes including endometritis rate (three studies, 285 women, average RR 0.52, 95% CI 0.26 to 1.05, Tau I² = 0.22, I² = 56%), extension of uterine incision (four studies, 357 women, average RR 0.23, 95% CI 0.13 to 0.40), mean blood loss (three studies, 298 women, mean difference (MD) -294.92, 95% CI -493.25 to -96.59; I² = 98%) and neonatal intensive care unit (NICU)/special care nursery (SCN) admission (two studies, 226 babies, average RR 0.53, 95% CI 0.23 to 1.22, Tau I² = 0.27, I² = 74%) were decreased with reverse breech extraction. No differences were observed between groups for many of the other secondary outcomes reported (blood loss > 500 mL; blood transfusion; wound infection; mean hospital stay; average Apgar score).There was significant heterogeneity between the trials for the outcomes mean blood loss, operative time and mean hospital stay, making comparison difficult. However the operation duration was significantly shorter for reverse breech extraction, which may correspond with ease of delivery and therefore, the amount of tissue trauma and therefore, significantly less blood loss. Given the heterogeneity, we cannot define the amount of difference in blood loss, operative time or hospital stay however. 3. Instrument (vacuum or forceps) versus manual extraction at elective caesarean section Two randomised trials involving 128 women were identified and included in the review. Only one trial reported maternal and infant health outcomes as prespecified in this review. This trial reported birth trauma as an outcome but there were no instances of birth trauma in either comparison group. There were no differences found in mean fall in haemoglobin (Hb) between groups (one study, 44 women, MD 0.03, 95% CI -0.53 to 0.59), or in uterine incision extension (one study, 44 women, RR 0.70, 95% CI 0.13 to 3.73).

AUTHORS' CONCLUSIONS

There is currently insufficient information available from randomised trials to support or refute the routine or selective use of tocolytic agents or instrument to facilitate infant birth at the time of difficult caesarean section. There is limited evidence that reverse breech extraction may improve maternal and fetal outcomes, though there was no difference in primary outcome of infant birth trauma. Further randomised controlled trials are needed to answer these questions.

Ischemic heart disease in pregnancy

While ischemic heart disease in reproductive-age women is rare, cardiac disease is a leading cause of maternal mortality. In turn, coronary artery disease is one of the most common causes of maternal cardiac death. The incidence of coronary artery disease in pregnancy may be rising due to the increasing prevalence of comorbid risk factors. Diagnosis and clinical management of ischemic cardiac disease is largely similar in the pregnant and non-pregnant patient, and the majority of medications and diagnostic and interventional procedures are compatible with pregnancy with a few important exceptions. Care for ischemic cardiac disease in pregnancy may be suboptimal because: (1) diagnosis is delayed because many symptoms of ischemic cardiac disease are common in pregnancy, (2) a diagnostic workup is insufficiently thorough, and/or (3) consultants may be hesitant to perform diagnostic and interventional procedures in obstetric patients. Obstetric providers should be aware of the possibility of ischemic cardiac disease in pregnancy, particularly in patients with comorbid risk factors. If ischemic cardiac disease is suspected, a thorough workup should be performed.

Tocolysis for assisting delivery at caesarean section

BACKGROUND

Caesarean section involves making an incision in the woman's abdomen and cutting through the uterine muscle. The baby is then delivered through that incision. Difficult caesarean birth may result in injury for the infant. Medication that relaxes the uterus (tocolytic medication) may facilitate the birth of the baby at caesarean section.

OBJECTIVES

To compare the use of tocolysis (routine or selective use) with no use of tocolysis or placebo at the time of caesarean section for outcomes of infant birth trauma, maternal complications (particularly postpartum haemorrhage requiring blood transfusion), and long-term measures of infant and childhood morbidity.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (January 2006), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2006, Issue 1) and PubMed (1966 to January 2006).

SELECTION CRITERIA

Use of tocolytic agents (routine or selective) at caesarean section versus no use of tocolytic or placebo at caesarean section to facilitate the birth of the baby.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data.

MAIN RESULTS

A single randomised trial involving 97 women was identified and included in the review. Maternal and infant health outcomes were not reported.

AUTHORS' CONCLUSIONS

There is currently insufficient information available from randomised trials to support or refute the routine or selective use of tocolytic agents to facilitate infant birth at the time of caesarean section.

Nitroglycerin for Relaxation to Establish a Fetal Airway (EXIT Procedure)

BACKGROUND

The ex utero intrapartum treatment (EXIT) procedure is a technique designed to establish an airway at the time of delivery in fetuses at risk of airway obstruction and requires maintenance of uterine relaxation to continue placental perfusion and prevent placental separation. We describe the use of intravenous nitroglycerin to maintain uterine relaxation during the EXIT procedure.

CASE

A 17-year-old primigravida with a fetus known to have an anterior neck mass was admitted for a scheduled operative delivery at 38 weeks of gestation using a modified EXIT procedure. Anesthesia was administered with a combined spinal-epidural technique. Intravenous nitroglycerin was administered as a bolus and then as a continuous infusion to maintain uterine relaxation until evaluation of the neonatal airway was completed.

CONCLUSION

Intravenous nitroglycerin is an effective agent for maintenance of uterine relaxation and placental perfusion during the EXIT procedure.

Therapeutic interventions targeting the nitric oxide system: current and potential uses in obstetrics, bone disease and erectile dysfunction

Nitric oxide is involved in a countless number of physiological processes and is known to have cytoprotective as well as cytotoxic effects. Increased knowledge about the multifaceted role of nitric oxide in a variety of disease states has led to the design of multiple treatment strategies involving the nitric oxide system. The current review focuses on recent research advances in the fields of obstetrics, bone disease and erectile dysfunction that have led to current or potential future therapies involving nitric oxide.

Steady-state maternal and fetal plasma concentrations of glyceryl trinitrate (GTN) in the preterm sheep

The administration of glyceryl trinitrate (GTN; nitroglycerin) is increasing during preterm pregnancies, yet its disposition and, importantly, the extent of fetal exposure remain to be elucidated. When used as a tocolytic (pharmacological agent that stops uterine contractions), it is administered transdermally (24–48 h). Here, we quantified the maternal and fetal steady-state plasma concentrations of maternal intravenous GTN in preterm sheep and continuously monitored maternal and fetal vascular parameters to observe possible dose-dependant vascular effects. Preterm (120 days gestation) pregnant sheep (n = 6) were instrumented with maternal femoral arterial (MA) and venous (MV) and fetal femoral arterial (FA) and umbilical venous (UV) polyethylene blood-sampling catheters. During maternal GTN infusion (3.0 µg·kg–1·min–1, 60-min duration) the steady-state GTN concentrations ([GTN]) were as follows: MA, 98.6 ± 9.0 nM; UV, 17.4 ± 7.6 nM; and FA, <5 nM. There were no changes in maternal and fetal mean arterial pressure and heart rate or in uterine activity. Overall, the steady-state [GTN] was established by 5 min, and the UV/MA ratio of [GTN] was 0.18. The FA [GTN] (<5 nM) indicates that the fetus cleared essentially all GTN in the UV, and the maternal and fetal heart rate and mean arterial pressure appear to be independent of maternal GTN infusion.Key words: nitroglycerin, pharmacokinetics, maternal-fetal exchange, pregnancy, cardiovascular.

Medical and obstetric problems complicating pregnancy

The present review addresses several medical and obstetric factors/problems, and their interactions during pregnancy. These include the following: maternal age; morbidity and mortality during pregnancy; thromboembolism; gestational diabetes; haemolysis, elevated liver enzymes, low platelets syndrome; human immunodeficiency virus; hepatitis C; preterm labour; antenatal administration of corticosteroids; intrapartum surveillance; breech delivery; and caesarean section.

Anaesthetic management of a caesarean section in a patient with Marfan's syndrome and aortic dissection

This report describes a case of a Stanford Type B aortic dissection (originating distal to the left subclavian artery and extending to the aortic bifurcation and proximal left iliac artery) in a 31-year-old primigravid woman who was at 39 weeks gestation and had Marfan's syndrome. The dissection was managed conservatively. Caesarean section was performed under epidural anaesthesia with aggressive control of hypertension. Postoperatively, there was no extension of the dissection and no aneurysm formation. She was discharged from hospital two weeks after delivery and remained asymptomatic at six months. There are no plans for surgical intervention.