Uterine atony refers to the corpus uteri myometrial cells inadequate contraction in response to endogenous oxytocin that is released in the course of delivery. It leads to postpartum hemorrhage as delivery of the placenta leaves disrupted spiral arteries which are uniquely void of musculature and dependent on contractions to mechanically squeeze them into a hemostatic state. Uterine atony is a principal cause of postpartum hemorrhage, an obstetric emergency. Globally, this is one of the top 5 causes of maternal mortality.
Risk factors for uterine atony include prolonged labor, precipitous labor, uterine distension (multi-fetal gestation, polyhydramnios, fetal macrosomia), fibroid uterus, chorioamnionitis, indicated magnesium sulfate infusions, and prolonged use of oxytocin. Ineffective uterine contraction, either focally or diffusely, is additionally associated with a diverse range of etiologies including retained placental tissue, placental disorders (such as morbidly adherent placenta, placenta previa, and abruption placentae), coagulopathy (increased fibrin degradation products) and uterine inversion. Body mass index (BMI) above 40 (class III obesity) is also a recognized risk factor for postpartum uterine atony.
The absence of effective contraction of the uterus after delivery complicates 1 in 40 births in the United States and is responsible for at least 75% of cases of postpartum hemorrhage.
Contraction of the myometrium that mechanically compresses the blood vessels supplying the placental bed provides the principal mechanism uterine hemostasis after delivery of the fetus, and the placenta is concluded. The process is complemented by local decidual hemostatic factors such as tissue factor type-1 plasminogen activator inhibitor as well as by systemic coagulation factors such as platelets, circulating clotting factors.
At prenatal history and examination, risk factor discernment is key to optimal risk management. Identification of risks allows for planning and availability of resources that might be needed including personnel, medication, equipment, adequate intravenous access, and blood products. The American College of Obstetricians recommends that women be identified prenatally as high risk for postpartum hemorrhage based on the presence of placenta accreta spectrum, pre-pregnancy BMI greater than 50, clinically significant bleeding disorder, or other surgical-medical high-risk factors. Part of the planning should be to develop a plan that allows delivery at a facility with an appropriate level of care for these patients' needs.
The diagnosis is made during the physical exam immediately upon conclusion of an obstetric vaginal or cesarean delivery. Direct palpation at cesarean delivery (typically after the closure of the uterine incision) or indirect examination at bimanual examination after a vaginal delivery reveals a boggy, soft, and an unusually enlarged uterus, typically with co-existent bleeding from the cervical os (harder to appreciate at cesarean deliveries). An expeditious exclusion of retained gestational products or obstetric lacerations quickly excludes additional co-concomitant etiologies. The possibility of coagulopathies is considered and pursued if clinically indicated. The physical examination suggested above may involve obstetric ultrasound imaging.
Diagnosis of diffuse uterine atony is prompted typically by finding of more than usual blood loss during examination demonstrating a flaccid and enlarged uterus, which may contain a significant amount of blood. With focal localized atony, the fundal region may be well contracted while the lower uterine segment is dilated and atonic, which may difficult to appreciate on abdominal examination, but may be detected on vaginal examination. A digital exploration of the uterine cavity (if adequate anesthesia is available), or bedside obstetric ultrasound imaging to reveal an echogenic endometrial stripe is an essential examination, as is a timely examination with adequate lighting to exclude an obstetric laceration.
If the woman is at a medium risk for intrapartum, blood should include be typed and screened. Women with a medium risk factor for uterine atony-related postpartum hemorrhage include prior uterine surgery, multiple gestation, grand multiparity, prior PPH, large fibroids, macrosomia, body mass index greater than 40, anemia, chorioamnionitis, prolonged second stage, oxytocin longer than 24 hours, and magnesium sulfate administration. Those assessed to be high risk should be typed and cross-matched for those at high risk of PPH. High-risk criteria include placental previa or accreta, bleeding diathesis, 2 or more medium risk factors for uterine atony. Use of a cell saver (blood salvage) should be considered for women at increased risk of postpartum hemorrhage, but this is not cost-effective to be routine.
This includes optimal management of the third stage of labor. Active management of the third stage includes uterine massage with concomitant sustained low-level traction on the umbilical cord. Simultaneous oxytocin infusion is helpful, although it is reasonable to defer it to after delivery of the placenta.
Initial Medical Treatment
If uterine atony occurs, healthcare providers should be ready for initial medical management which is directed to the use of medications to improve tone and induce uterine contractions. Massaging the uterus is also effective, as is ensuring an empty cavity. Maternal support with intravenous (IV) fluids is commenced through preferably an u8-gauge, intravenous catheter. A team approach is initiated with the summoning of the needed personnel through a standardized built-in alert system. Medications used for postpartum hemorrhage secondary to Uterine atony include the following:
Should the medications fail with persisting excess bleeding, then surgical management is engaged.
Surgical Management Techniques
The typical physical findings elude detection in the presence of uterine eversion when the endometrial surface everts into the vagina and allowed by uterine atony. This typically occurs after a vaginal delivery, and the usual findings of an enlarged boggy uterus are unavailable and replaced by findings of an intra-vaginal mass that is cherry colored (endometrium) and should be immediately replaced back into the uterine cavity, after which restoration of uterine tone prevents its recurrence.
Women with a prior PPH have as much as a 15% risk of recurrence in a subsequent pregnancy. The risk of recurrence depends, in part, on the underlying cause and associations such as class 3 obesity may have a higher recurrence risk.
Postpartum anemia is common after an episode of uterine atony and postpartum hemorrhage. Severe anemia due to PPH may require red cell transfusions, depending on the severity of anemia and the degree of symptomatology attributable to anemia. A common practice is to offer a transfusion to symptomatic women with a hemoglobin value less than 7 g/dL. In most cases of uterine atony-related postpartum hemorrhage, the amount of iron lost is not fully replaced by the transfused blood. Oral iron should thus be also considered. Parenteral iron therapy is an option as it accelerated recovery. Most women with mild to moderate anemia, however, resolve the anemia sufficiently rapidly with oral iron alone and do not need parenteral iron.
In recognition that the majority of the cases of postpartum hemorrhage are due to uterine atony, implementation of a systemic approach in birthing units is advocated by all leading professional bodies.
The Joint Commission recommends that obstetrical staff undergo interprofessional team training to teach staff to work together and communicate more effectively when postpartum hemorrhage (most due to uterine atony) occurs. The Commission is in favor of clinical drills to help staff prepare for the clinical event, as well as conducting debriefings after such events to evaluate team performance and identify areas for improvement. Simulation team training can help to identify areas that need strengthening, and regular, unannounced, simulated, postpartum hemorrhage scenarios in real-life settings, such as the labor and delivery units or post-anesthesia care units, may also increase comfort with the protocols and teamwork required in such emergencies. Such a systemic approach creates a positive trajectory toward improved obstetric outcomes and is also endorsed by the Association of Women's Health, Obstetric and Neonatal Nurses (AWHONN). An interprofessional team approach will provide the best patient outcomes. [Level V]
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