Uterine Atony

Etiology

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.[2]

Epidemiology

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.[3]

Pathophysiology

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.

History and Physical

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.

Evaluation

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.

Treatment / Management

Prenatal Readiness

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.

Intrapartum Prevention

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:

1. Oxytocin (Pitocin) can be given IV 10 to 40 units per 1000 ml or 10 units intramuscularly (IM). The rapid undiluted infusion may cause hypotension.
2. Methylergonovine (Methergine) given IM 0.2 mg. Given every 2 to 4 hours. Should be avoided in patients with hypertension.
3. 15-methyl-PGF2-alpha (Hemabate) given IM 0.25 mg. Given every 15 to 90 minutes for a maximum of 8 doses. Should be avoided in asthmatics. May cause diarrhea, fevers, or tachycardia. It is expensive.
4. Misoprostol (Cytotec): 800 to 1000 mg placed rectally. May cause a low-grade fever. It has a delayed action.
5. Dinoprostone (Prostin E2) 20 mg vaginal or rectal suppository may be given every 2 hours.

Surgical Treatment

Should the medications fail with persisting excess bleeding, then surgical management is engaged.[4]

Tamponade Techniques

1. Uterine packing with gauze (with vaginal packing to ensure its retention, thus a uterovaginal packing) with Foley catheter insertion to allow bladder drainage. The uterine packing should be tight and uniform, and it is a quickly and efficiently achieved with rolled gauze ribbons.
2. Bakri balloon (with vaginal packing to ensure its retention) with Foley catheter insertion to facilitate bladder drainage.

Surgical Management Techniques

1. Uterine curettage for retained products
2. Uterine artery ligation (O' Leary), with an option to for extending arterial ligation to tubo-ovarian vessels.
3. Compression sutures such as the B-Lynch are typically reserved for clinical scenarios where bimanual compression of the uterus leads to arrest in bleeding.
4. Hypogastric artery ligation (performed by Gyn/Onc)
5. Hysterectomy

Differential Diagnosis

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.

Prognosis

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.