Oxytocin augmentation of dysfunctional labor. IV. Oxytocin pharmacokinetics

Stimulation Therapy to Induce Mothers: Protocol for a Multicenter Randomized Controlled Trial

BACKGROUND

More than 1 million women have their labor induced in the United States each year, and synthetic oxytocin infusion is the most common method used. However, compared to spontaneous labor, medical induction is resource intensive, has increased obstetric risks, and is associated with less successful breastfeeding. In contrast to the endogenous oxytocin hormone, which is released in a pulsatile fashion in the brain, synthetic oxytocin is continuously infused intravenously, resulting in important limitations related to efficacy, safety, and cost. Akin to spontaneous labor contractions, infant suckling of the breast nipple is known to stimulate the pulsatile release of endogenous oxytocin from the posterior pituitary gland. Nipple stimulation therapy via an electric breast pump similarly stimulates endogenous oxytocin release and may be a favorable inpatient method for patients undergoing labor induction.

OBJECTIVE

This study aims to examine whether inpatient nipple stimulation therapy is an efficacious labor induction method that increases the likelihood of spontaneous vaginal delivery and sustained breastfeeding and determine whether it is a cost-effective approach.

METHODS

This is a multicenter, pragmatic, open-label, parallel-group randomized controlled trial of nulliparous patients with singleton gestations ≥36 weeks undergoing labor induction. This trial compares inpatient nipple stimulation therapy via an electric breast pump versus immediate synthetic oxytocin infusion without nipple stimulation. This trial including 988 nulliparas will provide adequate statistical power to detect clinically meaningful differences in delivery mode and breast milk as the sole source of nutrition for newborns at hospital discharge or 72 hours after birth.

RESULTS

The project received pilot funding in 2021 and full funding in 2023. Enrollment for this study began in November 2021 at a single site, and as of May 2024, recruitment is underway at 3 study sites. It is anticipated that enrollment will be completed by late 2026.

CONCLUSIONS

Successful completion of this trial will provide rigorous data to determine whether inpatient nipple stimulation therapy with an electric breast pump can improve the way we induce labor and positively impact breastfeeding success and early infant nutrition through lactation.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05079841; https://clinicaltrials.gov/study/NCT05079841.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/63463.

Discontinuation of Oxytocin in the Second Stage of Labor and its Association with Postpartum Hemorrhage

OBJECTIVE

The objective of the study was to evaluate whether patients with oxytocin discontinued during the second stage of labor (≥30 minutes prior to delivery) had a lower rate of postpartum hemorrhage (PPH) compared with those with oxytocin continued until delivery or discontinued <30 minutes prior to delivery.

STUDY DESIGN

Retrospective cohort study was performed from August 1, 2014 to July 31, 2019. Singleton pregnancies of 24 to 42 weeks gestation were included if they reached the second stage of labor and received oxytocin during labor. Patients on anticoagulants were excluded. Patients with oxytocin discontinued ≥30 minutes prior to delivery represented STOPPED and those with oxytocin continued until delivery or discontinued <30 minutes prior to delivery represented CONTINUED. Patient data were abstracted from the electronic medical record. The primary outcome was PPH (≥1,000 mL blood loss). Univariable analyses were performed to compare groups. Multi-variable logistic regression was performed to adjust for prespecified confounders. Planned sub-group analyses by the route of delivery were performed.

RESULTS

Of 10,421 total patients, 1,288 had oxytocin STOPPED and 9,133 had oxytocin CONTINUED. There were no significant differences in age, race, or ethnicity, body mass index, public insurance, gestational diabetes, or pregnancy-induced hypertension between STOPPED and CONTINUED. The PPH rate was 15.2 and 5.7% in STOPPED and CONTINUED, respectively (p < 0.001). After adjusting for confounders, STOPPED remained at higher odds for PPH (adjusted odds ratio 2.859, 95% confidence interval 2.394, 3.414, p < 0.001). Among cesarean deliveries only, there was no significant difference in the rate of PPH between STOPPED and CONTINUED (38.0 vs. 36.4%, respectively, p = 0.730). However, among vaginal deliveries, the rate of PPH was actually lower in STOPPED than CONTINUED (3.4 vs. 5.2%, respectively, p = 0.024).

CONCLUSION

The rate of PPH was higher in patients with oxytocin STOPPED compared with CONTINUED. However, among vaginal deliveries, there was a significantly lower rate of PPH in STOPPED. These disparate findings may be explained by the variable impact of second-stage oxytocin on PPH as a function of delivery type.

KEY POINTS

· It is unclear if oxytocin use in the second stage of labor may independently increase the risk of hemorrhage.. · Patients with oxytocin discontinued during the second stage of labor had a higher rate of PPH.. · PPH was significantly lower among vaginal deliveries in patients with oxytocin discontinued..

Optimal starting dosing regimen of intravenous oxytocin for labor induction based on the population kinetic-pharmacodynamic model of uterine contraction frequency

BACKGROUND

Intravenous oxytocin is commonly used for labor induction. However, a consensus on the initial dosing regimen is lac with conflicting research findings and varying guidelines. This study aimed to develop a population kinetic-pharmacodynamic (K-PD) model for oxytocin-induced uterine contractions considering real-world data and relevant influencing factors to establish an optimal starting dosing regimen for intravenous oxytocin.

METHODS

This retrospective study included pregnant women who underwent labor induction with intravenous oxytocin at Peking University Third Hospital in 2020. A  population K-PD model was developed to depict the time course of uterine contraction frequency (UCF), and covariate screening identified significant factors affecting the pharmacokinetics and pharmacodynamics of oxytocin. Model-based simulations were used to optimize the current starting regimen based on specific guidelines.

RESULTS

Data from 77 pregnant women with 1095 UCF observations were described well by the K-PD model. Parity, cervical dilation, and membrane integrity are significant factors influencing the effectiveness of oxytocin. Based on the model-based simulations, the current regimens showed prolonged onset times and high infusion rates. This study proposed a revised approach, beginning with a rapid infusion followed by a reduced infusion rate, enabling most women to achieve the target UCF within approximately 30 min with the lowest possible infusion rate.

CONCLUSION

The K-PD model of oxytocin effectively described the changes in UCF during labor induction. Furthermore, it revealed that parity, cervical dilation, and membrane integrity are key factors that influence the effectiveness of oxytocin. The optimal starting dosing regimens obtained through model simulations provide valuable clinical references for oxytocin treatment.

Feasibility Study to Compare Oxytocin Function Between Body Mass Index Groups at Term Labor Induction

OBJECTIVE

To determine the feasibility of a protocol to examine the association between oxytocin system function and birth outcomes in women with and without obesity before induction of labor.

DESIGN

Prospective descriptive.

SETTING

Academic medical center in the U.S. Midwest.

PARTICIPANTS

Pregnant women scheduled for induction of labor at 40 weeks of gestation or greater (n = 15 normal weight; n = 15 obese).

METHODS

We collected blood samples and abstracted data by chart review. We used percentages to examine adherence to protocol. We used t tests and chi-square tests to describe differences in sample characteristics, oxytocin system function variables, and birth outcomes between the body mass index groups.

RESULTS

The recruitment rate was 85.7%, protocol adherence was 97.1%, and questionnaire completion was 80.0%. Mean plasma oxytocin concentration was higher in the obese group (M = 2774.4 pg/ml, SD = 797.4) than in the normal weight group (M = 2193.5 pg/ml, SD = 469.8). Oxytocin receptor DNA percentage methylation (CpG -934) was higher in the obese group than in the normal weight group.

CONCLUSION

Our protocol was feasible and can serve as a foundation for estimating sample sizes in forthcoming studies investigating the diversity in oxytocin system measurements and childbirth outcomes among pregnant women in different body mass index categories.

The physiology and pharmacology of oxytocin in labor and in the peripartum period

Oxytocin is a reproductive hormone implicated in the process of parturition and widely used during labor. Oxytocin is produced within the supraoptic nucleus and paraventricular nucleus of the hypothalamus and released from the posterior pituitary lobe into the circulation. Oxytocin is released in pulses with increasing frequency and amplitude in the first and second stages of labor, with a few pulses released in the third stage of labor. During labor, the fetus exerts pressure on the cervix of the uterus, which activates a feedforward reflex-the Ferguson reflex-which releases oxytocin. When myometrial contractions activate sympathetic nerves, it decreases oxytocin release. When oxytocin binds to specific myometrial oxytocin receptors, it induces myometrial contractions. High levels of circulating estrogen at term make the receptors more sensitive. In addition, oxytocin stimulates prostaglandin synthesis and release in the decidua and chorioamniotic membranes by activating a specific type of oxytocin receptor. Prostaglandins contribute to cervical ripening and uterine contractility in labor. The oxytocin system in the brain has been implicated in decreasing maternal levels of fear, pain, and stress, and oxytocin release and function during labor are stimulated by a social support. Moreover, studies suggest, but have not yet proven, that labor may be associated with long-term, behavioral and physiological adaptations in the mother and infant, possibly involving epigenetic modulation of oxytocin production and release and the oxytocin receptor. In addition, infusions of synthetic oxytocin are used to induce and augment labor. Oxytocin may be administered according to different dose regimens at increasing rates from 1 to 3 mIU/min to a maximal rate of 36 mIU/min at 15- to 40-minute intervals. The total amount of synthetic oxytocin given during labor can be 5 to 10 IU, but lower and higher amounts of oxytocin may also be given. High-dose infusions of oxytocin may shorten the duration of labor by up to 2 hours compared with no infusion of oxytocin; however, it does not lower the frequency of cesarean delivery. When synthetic oxytocin is administered, the plasma concentration of oxytocin increases in a dose-dependent way: at infusion rates of 20 to 30 mIU/min, plasma oxytocin concentration increases approximately 2- to 3-fold above the basal level. Synthetic oxytocin administered at recommended dose levels is not likely to cross the placenta or maternal blood-brain barrier. Synthetic oxytocin should be administered with caution as high levels may induce tachystole and uterine overstimulation, with potentially negative consequences for the fetus and possibly the mother. Of note, 5 to 10 IU of synthetic oxytocin is often routinely given as an intravenous or intramuscular bolus administration after delivery to induce uterine contractility, which, in turn, induces uterine separation of the placenta and prevents postpartum hemorrhage. Furthermore, it promotes the expulsion of the placenta.

Oxytocin: physiology, pharmacology, and clinical application for labor management

Oxytocin is a peptide hormone that plays a key role in regulating the female reproductive system, including during labor and lactation. It is produced primarily in the hypothalamus and secreted by the posterior pituitary gland. Oxytocin can also be administered as a medication to initiate or augment uterine contractions. To study the effectiveness and safety of oxytocin, previous studies have randomized patients to low- and high-dose oxytocin infusion protocols either alone or as part of an active management of labor strategy along with other interventions. These randomized trials demonstrated that active management of labor and high-dose oxytocin regimens can shorten the length of labor and reduce the incidence of clinical chorioamnionitis. The safety of high-dose oxytocin regimens is also supported by no associated differences in fetal heart rate abnormalities, postpartum hemorrhage, low Apgar scores, neonatal intensive care unit admissions, and umbilical artery acidemia. Most studies reported no differences in the cesarean delivery rates with active management of labor or high-dose oxytocin regimens, thereby further validating its safety. Oxytocin does not have a predictable dose response, thus the pharmacologic effects and the amplitude and frequency of uterine contractions are used as physiological parameters for oxytocin infusion titration to achieve adequate contractions at appropriate intervals. Used in error, oxytocin can cause patient harm, highlighting the importance of precise administration using infusion pumps, institutional safety checklists, and trained nursing staff to closely monitor uterine activity and fetal heart rate changes. In this review, we summarize the physiology, pharmacology, infusion regimens, and associated risks of oxytocin.

A study of the pharmacokinetics and pharmacodynamics of oxytocin at elective caesarean delivery

Oxytocin is widely used to prevent atonic postpartum haemorrhage after caesarean delivery. Initial treatment failure rates are high and inadequate dosing may contribute. Excessive doses, however, are associated with serious adverse effects. The pharmacokinetic data from this context are sparse and there is a lack of data in the immediate postpartum minutes after an initiating bolus. The pharmacodynamic data from this context are exclusively from dose-effect studies, with some suggesting that higher doses of oxytocin are required to provide adequate uterine tone in obese compared with non-obese women. We aimed to perform a pharmacokinetic and pharmacodynamic study that would facilitate more precise weight-based oxytocin dosing. We measured arterial oxytocin concentration, uterine tone and haemodynamic parameters in 25 women in the first 40 min after exogenous oxytocin administration at elective caesarean delivery. Serum oxytocin concentrations varied considerably between individuals. We constructed a one-compartment pharmacokinetic model of exogenous oxytocin deposition, after its administration with an initiating bolus and a maintenance infusion, at elective caesarean delivery. Body weight was evaluated as a potential covariate but was not included in the model due to lack of statistically significant reduction in the objective function. We calculated the volume of distribution and clearance (mean [coefficient of variation]) as 156.1 l [18%] and 83 ml.s-1 [32%] but found no within-individual correlation between serum oxytocin concentration and uterine tone or haemodynamic parameters. In conclusion, we observed a large variation in serum oxytocin concentrations between individuals receiving similar doses of oxytocin and were unable to establish weight-based dosing of exogenous oxytocin at caesarean delivery. Our findings suggest that future studies on oxytocin pharmacokinetics would need large sample sizes. In the absence of such data, oxytocin dosing should continue to be guided by uterine tone assessments and adjusted according to a strategy based on the best evidence from dose-effect studies.

Maternal and newborn plasma oxytocin levels in response to maternal synthetic oxytocin administration during labour, birth and postpartum - a systematic review with implications for the function of the oxytocinergic system

BACKGROUND

The reproductive hormone oxytocin facilitates labour, birth and postpartum adaptations for women and newborns. Synthetic oxytocin is commonly given to induce or augment labour and to decrease postpartum bleeding.

AIM

To systematically review studies measuring plasma oxytocin levels in women and newborns following maternal administration of synthetic oxytocin during labour, birth and/or postpartum and to consider possible impacts on endogenous oxytocin and related systems.

METHODS

Systematic searches of PubMed, CINAHL, PsycInfo and Scopus databases followed PRISMA guidelines, including all peer-reviewed studies in languages understood by the authors. Thirty-five publications met inclusion criteria, including 1373 women and 148 newborns. Studies varied substantially in design and methodology, so classical meta-analysis was not possible. Therefore, results were categorized, analysed and summarised in text and tables.

RESULTS

Infusions of synthetic oxytocin increased maternal plasma oxytocin levels dose-dependently; doubling the infusion rate approximately doubled oxytocin levels. Infusions below 10 milliunits per minute (mU/min) did not raise maternal oxytocin above the range observed in physiological labour. At high intrapartum infusion rates (up to 32 mU/min) maternal plasma oxytocin reached 2-3 times physiological levels. Postpartum synthetic oxytocin regimens used comparatively higher doses with shorter duration compared to labour, giving greater but transient maternal oxytocin elevations. Total postpartum dose was comparable to total intrapartum dose following vaginal birth, but post-caesarean dosages were higher. Newborn oxytocin levels were higher in the umbilical artery vs. umbilical vein, and both were higher than maternal plasma levels, implying substantial fetal oxytocin production in labour. Newborn oxytocin levels were not further elevated following maternal intrapartum synthetic oxytocin, suggesting that synthetic oxytocin at clinical doses does not cross from mother to fetus.

CONCLUSIONS

Synthetic oxytocin infusion during labour increased maternal plasma oxytocin levels 2-3-fold at the highest doses and was not associated with neonatal plasma oxytocin elevations. Therefore, direct effects from synthetic oxytocin transfer to maternal brain or fetus are unlikely. However, infusions of synthetic oxytocin in labour change uterine contraction patterns. This may influence uterine blood flow and maternal autonomic nervous system activity, potentially harming the fetus and increasing maternal pain and stress.

European Guidelines on Perinatal Care - Oxytocin for induction and augmentation of labor[Formula: see text]

OF RECOMMENDATIONS1. Oxytocin for induction or augmentation of labor should not be started when there is a previous scar on the body of the uterus (such as previous classical cesarean section, uterine perforation or myomectomy when uterine cavity is reached) or in any other condition where labor or vaginal delivery are contraindicated. (Moderate quality evidence +++-; Strong recommendation).2. Oxytocin should not be started before at least 1 h has elapsed since amniotomy, 6 h since the use of dinoprostone (30 min if vaginal insert) and 4 h since the use of misoprostol (Low quality evidence ++- -; Moderate recommendation).3. Cardiotocography (CTG) should be performed and a normal pattern without tachysystole should be documented for at least 30 min before oxytocin is used. Continuous CTG, with adequate monitoring of both fetal heart rate and uterine contractions, should be maintained for as long as oxytocin is used, and thereafter until delivery (Low ++- - to moderate +++- quality evidence; Strong recommendation).4. For labor induction, at least 1-h should be allowed after amniotomy before oxytocin infusion is started, to evaluate whether adequate uterine contractility has meanwhile ensued. For augmentation of labor, if the membranes are intact and there are conditions for a safe amniotomy, the latter should be considered before oxytocin is started (Very low quality evidence +- --; Weak recommendation).5. Oxytocin should be administered intravenously using the following regimen: 5 IU oxytocin diluted in 500 mL of 0.9% normal saline (NaCl) (each mL contains 10 mIU of oxytocin), in an infusion pump at increasing rates, as shown in Table 1, until a frequency of 3-4 contractions per 10 min is reached, a non-reassuring CTG pattern ensues, or maximum rates are reached (Low quality evidence ++ - -; Strong recommendation). If the frequency of contractions exceeds 5 in 10 min, the infusion rate should be reduced, even if a normal CTG pattern is present. With a non-reassuring CTG pattern, urgent clinical assessment by an obstetrician is indicated, and strong consideration should be given to reducing or stopping the oxytocin infusion. The minimal effective dose of oxytocin should always be used. (Low ++- - to Moderate +++- - quality evidence; Strong recommendation).[Table: see text]6. Use of oxytocin for induction and augmentation of labor should be regularly audited (Low quality evidence ++--; Strong recommendation).

Intrapartum transfer of oxytocin across the human placenta: An ex vivo perfusion experiment

INTRODUCTION

Investigation of the maternal to fetal transfer of oxytocin across the dually perfused term human placenta.

METHODS

Human placentae obtained from term singleton pregnancies were utilized in a dual recirculating model of ex vivo placental perfusion. Six placentae from women delivering by elective cesarean at term were perfused, one blank and five with the test substance synthetic oxytocin (0.8 ng/mL) (OX) added to the maternal perfusate for 180 min. Antipyrine was used as positive control to validate overlap of the maternal and fetal circuits. The concentration of OX was determined by radioimmunoassay.

RESULTS

A fall in maternal concentration of OX was seen throughout the experiment. At 90 min of perfusion a state of equilibrium was reached between maternal and fetal concentrations; however after 180 min the fetal concentration of OX was higher than that of the maternal. 31 % of the test substance was accounted for at the end of the experiment - suggesting OX protein binding and a high degree of oxytocinase activity.

DISCUSSION

The ex vivo perfusion experiments revealed low transfer of OX to the fetal circuit below physiologically relevant concentrations.

Review of Evidence-Based Methods for Successful Labor Induction

Induction of labor is increasingly a common component of the intrapartum care. Knowledge of the current evidence on methods of labor induction is an essential component of shared decision-making to determine which induction method meets an individual's health needs and personal preferences. This article provides a review of the current research evidence on labor induction methods, including cervical ripening techniques, and contraction stimulation techniques. Current evidence about expected duration of labor following induction, use of the Bishop score to guide induction, and guidance on the use of combination methods for labor induction are reviewed.

Cervical Ripening and Labor Induction and Augmentation, 5th Edition

Cervical ripening and induction and augmentation of labor are common procedures in labor and birth units. The potential risks and benefits for the procedure should be explained to women so that they can make informed decisions. Clinicians should be knowledgeable about the methods and medications used and be skilled in maternal-fetal assessment. Adequate nurse staffing is required to monitor the mother and fetus to promote the best possible outcomes. This practice monograph includes information on mechanical and pharmacologic methods for cervical ripening; labor induction and augmentation with oxytocin, a high alert drug; and nurse staffing levels and skills needed to provide safe and effective care during cervical ripening and labor induction and augmentation.

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.

Cervical Ripening and Labor Induction and Augmentation, 5th Edition

Cervical ripening and induction and augmentation of labor are common procedures in labor and birth units. The potential risks and benefits for the procedure should be explained to women so that they can make informed decisions. Clinicians should be knowledgeable about the methods and medications used and be skilled in maternal-fetal assessment. Adequate nurse staffing is required to monitor the mother and fetus to promote the best possible outcomes. This practice monograph includes information on mechanical and pharmacologic methods for cervical ripening; labor induction and augmentation with oxytocin, a high alert drug; and nurse staffing levels and skills needed to provide safe and effective care during cervical ripening and labor induction and augmentation.

Oxytocin Guidelines Associated with Compliance to National Standards

OBJECTIVE

Develop a multidisciplinary, consensus-driven, evidence-based approach to oxytocin use, while adhering to national guidelines.

DESIGN

This was a quality improvement project that used the Plan Do Study Act method to create cycles of change over several years. To initiate discussion, a survey was administered at a social event for providers from divergent community practices that addressed the controversial aspects of oxytocin use. Graphic feedback was provided showing divergences between answers and the evidence. The perinatal team directed design and implementation of this project with specific involvement of a nurse quality improvement coordinator and nurse educator.

MEASURES

Process, outcome, and balancing measures were used to evaluate the program. Process measure: use of a standardized order-set.

OUTCOME MEASURE

rate of adherence to the resultant protocol. Balancing measures: 1) maximum oxytocin dose, 2) time from oxytocin initiation to birth, 3) cesarean birth rates, and 4) Apgar scores.

RESULTS

An initial increase in adherence to the protocol decreased with the loss of the "paper" order-set. Adherence improved when computerized physician order entry was adjusted: 2006: 73%, 2007: 95%; 2011: 57%, 2013: 100% (p = 0.007, 2006 vs. 2007) (p < 0.001, 2006 vs. 2013). Compliance with the protocol was associated with a decrease in maximum oxytocin dose and in time between oxytocin initiation and birth (p < 0.001).

CONCLUSION

Consistency and safety in patient care can be accomplished using literature-based evidence and active consensus building among members of the perinatal team. A standardization process must be integrated into the electronic medical record to become a sustained part of a practice culture.

Inter-institutional variations in oxytocin augmentation during labour in German university hospitals: a national survey

BACKGROUND

There are several international guidelines on oxytocin regimens for induction and augmentation of labour, but no agreement on a standardised regimen in Germany. This study collated and reviewed the oxytocin regimens used for labour augmentation in university hospitals, with the long-term aim of contributing to the development of a national clinical guideline.

METHODS

Germany has 34 university hospital compounds, representing 39 maternity units. In this observational study we asked units to provide standard operational procedures on oxytocin augmentation during labour or provide the details in a structured survey. Data were collected on the dosage of oxytocin, type and volume of solutions used, indications and contraindications for use and discontinuation, case-specific administration, and on who developed the procedures. Findings were analysed descriptively.

RESULTS

A total of 35 (90%) units participated in this study. Standard operating procedures were available in 24 units (69%), seven units (20%) did not have procedures and information was missing from four units (11%). Midwives participated in the development of standard operating procedures in 15 units (43%). Infusions were most commonly prepared using six units of oxytocin in 500 ml 0.9% normal saline solution (12 mU/ml). The infusions were started at 120 mU/hour and increased by 120 mU/hour at 20-min intervals up to a maximum dosage of 1200 mU/hour. The most common indication for use was delayed progress in labour. Infusions were stopped when uterine contractions became hypertonic and/or the fetal heart rate showed signs of distress. Most of the practices described aligned with international guidance. All units used reduced oxytocin dosages for women with a history of previous caesareans section, as recommended in the international guidelines, and restrictive use was advised in multiparous women. The main difference between units related to combined use of amniotomy and oxytocin, recommended by three guidelines but used in only four maternity units (11%).

CONCLUSIONS

While there was considerable variation in the oxytocin augmentation procedures, most but not all practices used in these 35 German maternity units were comparable. Establishing a national guideline on the criteria for and administration of oxytocin for augmentation of labour would eliminate the observed differences and minimise risk of administration and medication error.

Prosocial effects of an oxytocin metabolite, but not synthetic oxytocin receptor agonists, in a mouse model of autism

Currently, there are no established pharmaceutical strategies that effectively treat social deficits in autism spectrum disorder (ASD). Oxytocin, a neurohormone that plays a role in multiple types of social behaviors, has been proposed as a possible therapeutic against social impairment and other symptoms in ASD. However, from the standpoint of pharmacotherapy, oxytocin has several liabilities as a standard clinical treatment, including rapid metabolism, low brain penetrance, and activity at the vasopressin (antidiuretic hormone) receptors. The present studies describe findings from a preclinical screening program to evaluate oxytocin receptor (OXTR) agonists and oxytocin metabolites for potential clinical use as more optimal treatments. We first investigated two synthetic oxytocin analogs, TC-OT-39 and carbetocin, using in vitro cell-based assays for pharmacological characterization and behavioral tests in the BALB/cByJ mouse model of ASD-like social deficits. Although both TC-OT-39 and carbetocin selectively activate the OXTR, neither synthetic agonist had prosocial efficacy in the BALB/cByJ model. We next evaluated two oxytocin metabolites: OT(4-9) and OT(5-9). While OT(5-9) failed to affect social deficits, the metabolite OT(4-9) led to significant social preference in the BALB/cByJ model, in a dose-dependent manner. The increased sociability was observed at both 24 h and 12 days following the end of a subchronic regimen with OT(4-9) (2.0 mg/kg). Overall, these results suggest that the prosocial effects of oxytocin could be mediated by downstream activity of oxytocin metabolites, raising the possibility of new pathways to target for drug discovery relevant to ASD.

Labor Induction Techniques: Which Is the Best?

Induction of labor is a common procedure undertaken whenever the benefits of prompt delivery outweigh the risks of expectant management. Cervical assessment is essential to determine the optimal approach. Indication for induction, clinical presentation and history, safety, cost, and patient preference may factor into the selection of methods. For the unfavorable cervix, several pharmacologic and mechanical methods are available, each with associated advantages and disadvantages. In women with a favorable cervix, combined use of amniotomy and intravenous oxytocin is generally the most effective approach. The goal of labor induction is to ensure the best possible outcome for mother and newborn.

Oxytocin Use in Labor: Legal Implications

Oxytocin is one of the most commonly used medications in obstetrics and has been associated with claims of negligence in cases of adverse outcomes. Errors involving intravenous oxytocin administration for induction or augmentation of labor are most commonly dose related and include failure to avoid or treat tachysystole or failure to asses or treat a fetal heart rate pattern indicative of disruption in oxygenation. Clinicians should be knowledgeable regarding pharmacokinetics of oxytocin and the effect of uterine contractions on fetal oxygenation as well as safe titration of oxytocin to achieve the desired effect while minimizing harm.

The Oxytocin Product Correlates with Total Oxytocin Received during Labor: A Research Methods Study

OBJECTIVE

Total dose of oxytocin received during labor is an important variable in studies of human labor but is difficult to calculate. We sought to identify a surrogate measure for total dose of oxytocin received.

STUDY DESIGN

For each subject receiving oxytocin during labor, the oxytocin total dose received in labor was calculated as the area under the curve. Maximal oxytocin infusion rate, total duration of oxytocin infusion, and the product of both, defined as the oxytocin product, were then each correlated with the total dose of oxytocin received using the Pearson's correlation coefficient.

RESULTS

Oxytocin dosing data were available from 402 women at Duke and 6,907 women from Pithagore6. The two variables alone, or combined as the oxytocin product, demonstrated a high correlation with the oxytocin total dose (r > 0.7), with the oxytocin product demonstrating the highest (r > 0.9). This was true whether labor was induced or augmented and whether delivery was vaginal or cesarean.

CONCLUSION

The oxytocin product, composed of two easily obtained variables, demonstrated a very high correlation with total oxytocin dose received in labor and represents a simple and accurate surrogate for total dose of oxytocin received during labor. The oxytocin product can be used in clinical studies in which oxytocin dose is an important variable.

The association of single-nucleotide polymorphisms in the oxytocin receptor and G protein-coupled receptor kinase 6 (GRK6) genes with oxytocin dosing requirements and labor outcomes

BACKGROUND

Oxytocin is a potent uterotonic agent that is widely used for induction and augmentation of labor. Oxytocin has a narrow therapeutic index and the optimal dosing for any individual woman varies widely.

OBJECTIVE

The objective of this study was to determine whether genetic variation in the oxytocin receptor (OXTR) or in the gene encoding G protein-coupled receptor kinase 6 (GRK6), which regulates desensitization of the oxytocin receptor, could explain variation in oxytocin dosing and labor outcomes among women being induced near term.

STUDY DESIGN

Pregnant women with a singleton gestation residing in Durham County, NC, were prospectively enrolled as part of the Healthy Pregnancy, Healthy Baby cohort study. Those women undergoing an induction of labor at 36 weeks or greater were genotyped for 18 haplotype-tagging single-nucleotide polymorphisms in OXTR and 7 haplotype-tagging single-nucleotide polymorphisms in GRK6 using TaqMan assays. Linear regression was used to examine the relationship between maternal genotype and maximal oxytocin infusion rate, total oxytocin dose received, and duration of labor. Logistic regression was used to test for the association of maternal genotype with mode of delivery. For each outcome, backward selection techniques were utilized to control for important confounding variables and additive genetic models were used. Race/ethnicity was included in all models because of differences in allele frequencies across populations, and Bonferroni correction for multiple testing was used.

RESULTS

DNA was available from 482 women undergoing induction of labor at 36 weeks or greater. Eighteen haplotype-tagging single-nucleotide polymorphisms within OXTR and 7 haplotype-tagging single-nucleotide polymorphisms within GRK6 were examined. Five single-nucleotide polymorphisms in OXTR showed nominal significance with maximal infusion rate of oxytocin, and two single-nucleotide polymorphisms in OXTR were associated with total oxytocin dose received. One single-nucleotide polymorphism in OXTR and two single-nucleotide polymorphisms in GRK6 were associated with duration of labor, one of which met the multiple testing threshold (P = .0014, rs2731664 [GRK6], mean duration of labor, 17.7 hours vs 20.2 hours vs 23.5 hours for AA, AC, and CC genotypes, respectively). Three single-nucleotide polymorphisms, two in OXTR and one in GRK6, showed nominal significance with mode of delivery.

CONCLUSION

Genetic variation in OXTR and GRK6 is associated with the amount of oxytocin required as well as the duration of labor and risk for cesarean delivery among women undergoing induction of labor near term. With further research, pharmacogenomic approaches may potentially be utilized to develop personalized treatment to improve safety and efficacy outcomes among women undergoing induction of labor.

Uterotonic Medications: Oxytocin, Methylergonovine, Carboprost, Misoprostol

Uterine atony is a common cause of primary postpartum hemorrhage, which remains a major cause of pregnancy-related mortality for women worldwide. Oxytocin, methylergonovine, carboprost, and misoprostol are commonly used to restore uterine tone. Oxytocin is the first-line agent. Methylergonovine and carboprost are both highly effective second-line agents with severe potential side effects. Recent studies have called into question the effectiveness of misoprostol as an adjunct to other uterotonic agents, but it remains a useful therapeutic in resource-limited practice environments. We review the current role these medications play in the prevention and treatment of uterine atony.

Titration of Intravenous Oxytocin Infusion for Postdates Induction of Labor Across Body Mass Index Groups

OBJECTIVE

To evaluate whether oxytocin titration for postdates labor induction differs among women who are normal weight, overweight, and obese and whether length of labor and birth method differ by oxytocin titration and body mass index (BMI).

DESIGN

Retrospective cohort study.

SETTING

U.S. university-affiliated hospital.

PARTICIPANTS

Of 280 eligible women, 21 were normal weight, 134 were overweight, and 125 were obese at labor admission.

METHODS

Data on women who received oxytocin for postdates induction between January 1, 2013 and June 30, 2013 were extracted from medical records. Oxytocin administration and labor outcomes were compared across BMI groups, controlling for potential confounders. Data were analyzed using χ², analysis of variance, analysis of covariance, and multiple linear and logistic regression models.

RESULTS

Women who were obese received more oxytocin than women who were overweight in the unadjusted analysis of variance (7.50 units compared with 5.92 units, p = .031). Women who were overweight had more minutes between rate changes from initiation to maximum than women who were obese (98.19 minutes compared with 83.39 minutes, p = .038). Length of labor increased with BMI (p = .018), with a mean length of labor for the normal weight group of 13.96 hours (standard deviation = 8.10); for the overweight group, 16.00 hours (standard deviation = 7.54); and for the obese group, 18.30 hours (standard deviation = 8.65). Cesarean rate increased with BMI (p = .001), with 4.8% of normal weight, 33.6% of overweight, and 42.4% of obese women having cesarean births.

CONCLUSION

Women who were obese and experienced postdates labor induction received more oxytocin than women who were non-obese and had longer length of labor and greater cesarean rates.

Oxytocin for preventing postpartum haemorrhage (PPH) in non-facility birth settings

BACKGROUND

Postpartum haemorrhage (PPH) is the single leading cause of maternal mortality worldwide. Most of the deaths associated with PPH occur in resource-poor settings where effective methods of prevention and treatment - such as oxytocin - are not accessible because many births still occur at home, or in community settings, far from a health facility. Likewise, most of the evidence supporting oxytocin effectiveness comes from hospital settings in high-income countries, mainly because of the need of well-organised care for its administration and monitoring. Easier methods for oxytocin administration have been developed for use in resource-poor settings, but as far as we know, its effectiveness has not been assessed in a systematic review.

OBJECTIVES

To assess the effectiveness and safety of oxytocin provided in non-facility birth settings by any way in the third stage of labour to prevent PPH.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register, the WHO International Clinical Trials Registry Platform (ICTRP), ClinicalTrials.gov (12 November 2015), and reference lists of retrieved reports.

SELECTION CRITERIA

All published, unpublished or ongoing randomised or quasi-randomised controlled trials comparing the administration of oxytocin with no intervention, or usual/standard care for the management of the third stage of labour in non-facility birth settings were considered for inclusion.Quasi-randomised controlled trials and randomised controlled trials published in abstract form only were eligible for inclusion but none were identified. Cross-over trials were not eligible for inclusion in this review.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility, assessed risk of bias and extracted the data using an agreed data extraction form. Data were checked for accuracy.

MAIN RESULTS

We included one cluster-randomised trial conducted in four rural districts in Ghana that randomised 28 community health officers (CHOs) (serving 2404 potentially eligible pregnant women) to the intervention group and 26 CHOs (serving 3515 potentially eligible pregnant women) to the control group. Overall, the trial had a high risk of bias. CHOs delivered the intervention in the experimental group (injection of 10 IU (international units) of oxytocin in the thigh one minute following birth using a prefilled, auto-disposable syringe). In the control group, CHOs did not provide this prophylactic injection to the women they observed. CHOs had no midwifery skills and did not in any way manage the birth. All other CHO activities (outcome measurement, data collection, and early treatment and referral when necessary) were identical across the control and oxytocin CHOs.Although only one of the nine cases of severe PPH (blood loss greater or equal to 1000 mL) occurred in the oxytocin group, the effect estimate for this outcome was very imprecise and it is uncertain whether the intervention prevents severe PPH (risk ratio (RR) 0.16, 95% confidence interval (CI) 0.02 to 1.30; 1570 women (very low-quality evidence)). Similarly, because of the lack of cases of severe maternal morbidity (e.g. uterine rupture) and maternal deaths, it was not possible to obtain effect estimates for those outcomes (both very low-quality evidence).Oxytocin compared with the control group decreased the incidence of PPH (> 500 mL) in both our unadjusted (RR 0.48, 95% CI 0.28 to 0.81; 1569 women) and adjusted (RR 0.49, 95% CI 0.27 to 0.90; 1174 women (both low-quality evidence)) analyses. There was little or no difference between the oxytocin and control groups on the rates of transfer or referral of the mother to a healthcare facility (RR 0.72, 95% CI 0.34 to 1.56; 1586 women (low-quality evidence)), stillbirths (RR 1.27, 95% CI 0.67 to 2.40; 2006 infants (low-quality evidence)); andearly infant deaths (0 to three days) (RR 1.03, 95% CI 0.35 to 3.07; 1969 infants (low-quality evidence)). There were no cases of needle-stick injury or any other maternal major or minor adverse event or unanticipated harmful event. There were no cases of oxytocin use during labour.There were no data reported for some of this review's secondary outcomes: manual removal of placenta, maternal anaemia, neonatal death within 28 days, neonatal transfer to health facility for advanced care, breastfeeding rates. Similarly, the women's or the provider's satisfaction with the intervention was not reported.

AUTHORS' CONCLUSIONS

It is uncertain if oxytocin administered by CHO in non-facility settings compared with a control group reduces the incidence of severe PPH (>1000 mL), severe maternal morbidity or maternal deaths. However, the intervention probably decreases the incidence of PPH (> 500 mL).The quality of the one trial included in this review was limited because of the risk of attrition and recruitment biases related to limitations in the follow-up of pregnant women in both arms of the trials and some baseline imbalance on the size of babies at birth. Additionally, there was serious imprecision of the effect estimates for most of the primary outcomes mainly because of the size of the trial, very few or no events and CIs around both relative and absolute estimates of effect that include both appreciable benefit and appreciable harm.Although the trial presented data both for primary and secondary outcomes, it seemed to be underpowered to detect differences in the primary outcomes that are the ones more relevant for making judgments about the potential applicability of the intervention in other settings (especially severe PPH).Therefore, taking into account the extreme setting where the intervention was implemented, the limited role of the CHO in the trial and the lack of power for detecting effects on primary (relevant) outcomes, the applicability of the evidence found seems to be rather limited.Further well-executed and adequately-powered randomised controlled trials assessing the effects of using oxytocin in pre-filled injection devices or other new delivery systems (spray-dried ultrafine formulation of oxytocin) on severe PPH are urgently needed. Likewise, other important outcomes like possible adverse events and acceptability of the intervention by mothers and other community stakeholders should also be assessed.

In Vitro Comparative Effect of Carbetocin and Oxytocin in Pregnant Human Myometrium with and without Oxytocin Pretreatment

Background

The purpose of this study was to compare in vitro contractile effects of oxytocin and carbetocin on human term pregnant myometrium with and without oxytocin pretreatment.

Methods

This laboratory investigation was conducted on myometrial samples from women undergoing elective cesarean deliveries. The samples were dissected into four strips and suspended in individual organ bath chambers containing physiologic salt solution. After equilibration, they were pretreated with oxytocin 10−5 M (experimental group) or physiologic salt solution (control group) for 2 h and then subjected to dose–response testing with increasing concentrations of oxytocin or carbetocin (10−10 to 10−5 M). The amplitude, frequency, motility index (amplitude × frequency), and area under the curve of contractions were recorded and analyzed during the equilibration and dose–response periods. Comparisons were made between oxytocin-induced and carbetocin-induced contractions in control and oxytocin-pretreated groups. Motility index was the primary outcome measure.

Results

Sixty-three experiments were performed (carbetocin, n = 31; oxytocin, n = 32) on samples from 18 women. The motility index of contractions (√g.contractions/10 min) produced by oxytocin was significantly higher than carbetocin in both control (regression-estimated difference, 0.857; 95% CI, 0.290 to 1.425; P = 0.003) and oxytocin-pretreated (0.813; 0.328 to 1.299; P = 0.001) groups. The motility index was significantly lower in oxytocin-pretreated groups than their respective controls for both oxytocin (−1.040; −1.998 to −0.082; P = 0.03) and carbetocin (−0.996; −1.392 to −0.560; P &lt; 0.001).

Conclusions

In vitro contractions produced by oxytocin are superior to carbetocin in human myometrium with or without oxytocin pretreatment. Oxytocin pretreatment results in attenuation of contractions induced by both oxytocin and carbetocin.

Induction of labour

OBJECTIVE

To review the most current literature in order to provide evidence-based recommendations to obstetrical care providers on induction of labour.

OPTIONS

Intervention in a pregnancy with induction of labour.

OUTCOMES

Appropriate timing and method of induction, appropriate mode of delivery, and optimal maternal and perinatal outcomes.

EVIDENCE

Published literature was retrieved through searches of PubMed, CINAHL, and The Cochrane Library in 2010 using appropriate controlled vocabulary (e.g., labour, induced, labour induction, cervical ripening) and key words (e.g., induce, induction, augmentation). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies. There were no date or language restrictions. Searches were updated on a regular basis and incorporated in the guideline to the end of 2010. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.

VALUES

The evidence in this document was rated using criteria described in the Report of the Canadian Task Force on Preventative Health Care (Table 1). SUMMARY STATEMENTS: 1. Prostaglandins E(2) (cervical and vaginal) are effective agents of cervical ripening and induction of labour for an unfavourable cervix. (I) 2. Intravaginal prostaglandins E(2) are preferred to intracervical prostaglandins E(2) because they results in more timely vaginal deliveries. (I).

Oxytocin Pretreatment Attenuates Oxytocin-induced Contractions in Human Myometrium In Vitro

Background:

Oxytocin receptor desensitization has been shown to occur in humans at biomolecular level and in isolated rat myometrium; however, its effect on human myometrial contractility has not been demonstrated. The objective of this in vitro study was to investigate the contractile response of human pregnant myometrium to oxytocin after pretreatment with different concentrations of oxytocin for variable durations.

Methods:

Myometrial samples were obtained from 62 women undergoing elective cesarean deliveries under regional anesthesia. The strips were pretreated with oxytocin 10−10, 10−8, 10−5M, or physiological salt solution (control) for 2, 4, 6, or 12 h, followed by a dose–response testing with oxytocin 10−10 to 10−5M. Amplitude and frequency of contractions, motility index, and area under the curve during the dose–response period were recorded, analyzed with linear regression models, and compared among groups.

Results:

Pretreatment with oxytocin 10−5 and 10−8M significantly reduced motility index (estimate [standard error]: −0.771 [0.270] square root units, P = 0.005 and −0.697 [0.293], P = 0.02, respectively) and area under the curve (−3.947 [1.909], P = 0.04 and −4.241 [2.189], P = 0.05, respectively) compared with control group, whereas pretreatment with oxytocin 10−10M did not significantly attenuate contractions. Increase in duration of oxytocin pretreatment from 2 to 12 h significantly decreased amplitude (type 3 generalized estimating equation analysis: chi-square = 14.0; df = 3; P = 0.003), motility index (chi-square = 9.3; df = 3; P = 0.03), and area under the curve (chi-square = 10.5; df = 3; P = 0.02), but not the frequency of oxytocin-induced contractions.

Conclusion:

Pretreatment with oxytocin decreases oxytocin-induced myometrial contractions in a concentration and time-dependent manner, likely as a function of the oxytocin receptor desensitization phenomenon.

Current pharmacotherapy options for labor induction

INTRODUCTION

Labor induction is now reported to occur in up to 30 - 40% of obstetrical patients. There are a number of pharmacological options available to facilitate labor induction, including oxytocin and analogues of prostaglandins E1 and E2, which have particular utility when labor induction necessitates cervical ripening, as when labor induction occurs in the context of an unfavorable cervix.

AREAS COVERED

This paper reviews acceptable pharmacological options for labor induction, especially when cervical ripening is required. These options include oxytocin and a number of prostaglandin formulations using dinoprostone and misoprostol. It also covers several analyses of published clinical trials (Phase-III) describing evidence of effectiveness.

EXPERT OPINION

Oxytocin is best used when labor needs to be induced in the context of a favorable cervix. When the cervix is not favorable, cervical ripening using prostaglandins should precede labor induction. Either dinoprostone or misoprostol are superior to oxytocin alone for cervical ripening. However, judicious, careful considerations need to be made at the outset of labor induction so as to balance maternal and fetal risks, and these should be guided by institutional policies that reflect the evidence-base.

A model for educational simulation of the effect of oxytocin on uterine contractions

Fetal oxygenation is sometimes compromised due to hyperstimulation of uterine contractions (UC) following labor augmentation with oxytocin. We present a model for educational simulation that incorporates the pharmacokinetic-pharmacodynamic properties of oxytocin, reproducing the effect of this drug on UC features. Six UC tracings were generated, reflecting different relevant situations. Three independent experts identified correctly the simulated situations in all tracings and attributed an average realism score of 9.4 (0-10). The model presented for simulation of the effect of oxytocin on UC provides sufficiently realistic results to be used in healthcare education and can easily be adapted to different patients and educational scenarios.

Clinicians' guide to the use of oxytocin for labor induction and augmentation

Oxytocin is commonly used in obstetrics for labor induction and augmentation. Careful assessment of the individual clinical situation based on indications and contraindications is essential to enhancing safe and effective use. Counseling the woman and her partner regarding potential risks and benefits before use is necessary to promote informed consent. At least 39 weeks of gestation is required for elective labor induction. Recent research has shown that deferring elective induction until cervical readiness has been achieved without the use of pharmacologic agents can be beneficial in reducing the risk of cesarean birth associated with elective induction. A conservative physiologic oxytocin protocol for labor induction and augmentation is recommended to minimize the risk of side effects. Although treatment of excessive uterine activity related to oxytocin has not been studied prospectively, several interventions such as maternal repositioning, an intravenous fluid bolus, and discontinuation of the oxytocin infusion are beneficial in returning uterine activity to normal, based on retrospective review of oxytocin-induced tachysystole. Perinatal quality measures from the National Quality Forum and the Joint Commission can be useful in monitoring care related to induction of labor. These include elective births before 39 weeks of pregnancy and cesarean births for low-risk, first-birth mothers.

Oxytocin exposure during labor among women with postpartum hemorrhage secondary to uterine atony

OBJECTIVE

We sought to determine if women with severe postpartum hemorrhage (PPH) secondary to uterine atony received greater amounts of oxytocin during labor compared to women without PPH.

STUDY DESIGN

Subjects with severe PPH secondary to uterine atony, who received a blood transfusion, were compared to matched controls. Total oxytocin exposure was calculated as the area under the concentration curve (mU/min*min). Variables were compared using paired t test, χ², and logistic regression.

RESULTS

Women with severe PPH had a mean oxytocin area under the curve of 10,054 mU compared to 3762 mU in controls (P < .001). After controlling for race, body mass index, admission hematocrit, induction status, magnesium therapy, and chorioamnionitis using logistic regression, oxytocin area under the curve continued to predict severe PPH.

CONCLUSION

Women with severe PPH secondary to uterine atony were exposed to significantly more oxytocin during labor compared to matched controls.

Oxytocin pretreatment decreases oxytocin-induced myometrial contractions in pregnant rats in a concentration-dependent but not time-dependent manner

Recent biomolecular studies have shown that continuous exposure of human myometrial cells to oxytocin results in a significant loss of responsiveness to subsequent oxytocin stimulation, perhaps because of desensitization of the oxytocin receptors. However, it is unclear whether this phenomenon results in a reduction of the contractile activity of the uterine muscle in humans or animals. The objective of our study was to investigate the in vitro response of the uterine muscle of pregnant rats to oxytocin, following preexposure to varying concentrations of oxytocin, for varying durations. Longitudinal myometrial strips were isolated from 16 pregnant Wistar rats at 19 to 21 days of gestation and preexposed to oxytocin 10(-10) or 10(-8) mol/L (experimental groups) or physiological salt solution (control groups) for 1- or 4-hour period. All muscle strips were then subjected to a dose-response study with oxytocin 10(-10) to 10(-5) mol/L. The area under the curve, frequency, and amplitude of contractions were recorded and compared between the groups. The area under the curve, frequency, and amplitude of the oxytocin-induced contractions were all significantly suppressed in the groups preexposed to oxytocin 10(-8) mol/L compared to either the control groups (P < .0001) or the groups preexposed to oxytocin 10(-10) mol/L (P < .0001). There was no difference in the oxytocin-induced myometrial contractions between the groups preexposed to oxytocin for either the 1- or 4-hour periods. The inhibition of the oxytocin-induced contractile response of pregnant rat myometrium is observed as early as 1 hour of preexposure to oxytocin and is dependent on the preexposed oxytocin concentration and not on the duration of its exposure.

Oxytocin: new perspectives on an old drug

Oxytocin is the drug most commonly associated with preventable adverse perinatal outcomes and was recently added by the Institute for Safe Medication Practices to a small list of medications "bearing a heightened risk of harm," which may "require special safeguards to reduce the risk of error." Current recommendations for the administration of this drug are vague with respect to indications, timing, dosage, and monitoring of maternal and fetal effects. A review of available clinical and pharmacologic data suggests that specific, evidence-based guidelines for the intrapartum administration of oxytocin may be derived from available data. If implemented, such practices may reduce the likelihood of patient harm. These suggested guidelines focus on limited elective administration of oxytocin, consideration of strategies that have been shown to decrease the need for indicated oxytocin use, reliance on low-dose oxytocin regimens, adherence to specific semiquantitative definitions of adequate and inadequate labor, and an acceptance that once adequate uterine activity has been achieved, more time rather than more oxytocin is generally preferable. The use of conservative, specific protocols for monitoring the effects of oxytocin on mother and fetus is likely not only to improve outcomes but also reduce conflict between members of the obstetric team. Implementation of these guidelines would seem appropriate in a culture increasingly focused on patient safety.

Improving patient safety and uniformity of care by a standardized regimen for the use of oxytocin

Oxytocin is 1 of the most commonly used drugs in labor and has been associated with adverse maternal and fetal outcomes. In an attempt to improve patient safety, we constructed a standardized protocol for labor induction with oxytocin. We reviewed the numerous publications regarding oxytocin use for either induction or augmentation of labor in order to determine if there was a protocol available that would maximize success of delivery and minimize the adverse maternal and fetal effects of the drug. Using the literature review and the specific pharmacokinetics of oxytocin, we developed a standardized approach for the dilution and administration of oxytocin in order to improve patient safety, develop uniformity of the drug use, maximize its benefits, and minimize its side effects. We suggest that a standardized approach to oxytocin use be adopted that uses an oxytocin dilution of 10 mU/mL, initial dose of 2 mU/min (12 mL/hr), incremental increase of 2 mU (12 mL) every 45 minutes until adequate labor with the maximum dose being 16 mU/min (96 mL/hr).

Oxytocin for induction of labor

Oxytocin is the most common pharmacologic agent used for the induction and augmentation of labor. Oxytocin protocols can be divided into high-dose and low-dose protocols depending on the initial dose and the amount and rate of sequential increase in dose. Despite the frequency with which oxytocin in used in clinical practice, there is little consensus regarding which protocol is most appropriate. The purpose of this chapter is to review the most current data concerning recommendations for the use of oxytocin in the induction of labor, including cases of intrauterine fetal demise and vaginal birth after cesarean.

Induction of labor

The rate of labor induction continues to rise significantly in the United States because of a growing use of labor induction for postterm pregnancies and elective induction of labor. Although different types and doses of prostaglandins used for cervical ripening often initiate uterine activity, the principal role of these agents is to soften the unripe cervix independent of uterine activity. Several systematic reviews with meta-analyses have shown that prostaglandins are superior to placebo and oxytocin alone in ripening of the cervix. Numerous studies and meta-analyses have assessed misoprostol's efficacy and safety as a labor induction agent. The most appropriate dose and route of administration has not yet been confirmed.