Uterine Atony – Causes, Symptoms, Diagnosis, Treatment

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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.

Atony of the uterus also called uterine atony, is a serious condition that can occur after childbirth. It occurs when the uterus fails to contract after the delivery of the baby, and it can lead to a potentially life-threatening condition known as postpartum hemorrhage.
Uterine atony is a loss of tone in the uterine musculature. Normally, contraction of the uterine muscles during labor compresses the blood vessels and reduces flow, thereby increasing the likelihood of coagulation and preventing hemorrhage. A lack of uterine muscle contraction, however, can lead to an acute hemorrhage, as the uterine blood vessels are not sufficiently compressed. Clinically, 75-80% of postpartum hemorrhages are due to uterine atony.

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.

Causes of Uterine Atony

The causes for uterine atony include

  • Prolonged labor and 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.
  • Delayed labor
  • Rapid labor
  • Overdistention of the uterus (enlargement of the uterus) because of the presence of excess amniotic fluid ( a condition called as polyhydramnios) or a large baby
  • Administration of oxytocin, general anesthesia or other drugs during labor
  • Inducing labor using medication
  • Multiple pregnancies or delivering twins or triplets
  • Have had many previous deliveries
  • Fetal macrosomia where the baby is larger than average
  • If delivery was assisted using forceps or vacuum
  • You are over 35 years of age
  • You are medically classified as obese

Many factors can contribute to the loss of uterine muscle tone, including:[rx]

  • overdistention of the uterus
  • multiple gestations
  • polyhydramnios
  • fetal macrosomia
  • prolonged labor
  • grand multiparity (having given birth 5 or more times)
  • precipitous labor (labor lasting less than 3 hours)
  • magnesium sulfate treatment of preeclampsia
  • chorioamnionitis
  • halogenated anesthetics
  • uterine leiomyomata
  • full bladder
  • retained cotyledon, placental fragments
  • placenta previa
  • placental abruption
  • constriction ring
  • incomplete separation of the placenta
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Symptoms of the Uterine Atony

The most common and foremost symptom of uterine atony is that the uterus remains relaxed and without any tension after giving birth. Atony of the uterus is the primary cause of postpartum hemorrhage. Postpartum hemorrhage is excessive bleeding post-delivery and occurs after the placenta is delivered. About 1%-5% of women have a postpartum hemorrhage, and a loss of more than 500 milliliters of blood after delivery of the placenta is defined as postpartum hemorrhage. With most hemorrhages occurring right after delivery (especially in caesarean births), the symptoms include:

  • Uncontrollable and excessive bleeding post-delivery of a baby
  • A drop in blood pressure
  • An increase in the heart rate
  • Pain
  • Back pain
  • Uncontrolled bleeding
  • Decreased blood pressure
  • Increased heart rate
  • The decrease in the red blood cell count
  • Swelling and pain in the vagina and nearby area if bleeding is from a hematoma

Diagnosis of Uterine Atony

History and Physical
  • At prenatal history and risk factor discernment – is key to optimal risk management. Identification of risks allows for the 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 general examination – may reveal hemodynamic instability with tachypnoea, prolonged capillary refill time, tachycardia, and hypotension.
  • Abdominal examination – may show signs of uterine rupture i.e. palpation of fetal parts as it moves into the abdomen from the uterus.
  • Speculum examination – may reveal sites of local trauma causing bleeding.
  • Examine the placenta – to ensure that the placenta is complete (a missing cotyledon or ragged membranes could both cause a PPH).
Laboratory Tests

The appropriate laboratory tests include:

  • Full Blood Count
  • Urea and Electrolytes
  • C-Reactive Protein
  • Coagulation profile
  • Group and Save sample
  • Blood cultures (if the patient is pyrexial)
  • Cross match 4-6 units of blood
  • Coagulation profile
  • Urea and Electrolytes
  • Liver function tests

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.

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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.

Imaging Studies
  • X-rays to rule out bowel perforation
  • US to rule out an ectopic pregnancy
  • CT scan to assess for fluid collection in the pelvis, retained byproducts, adnexal mass

Treatment of Uterine Atony

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:

  • 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.
  • Methylergonovine (Methergine) – given IM 0.2 mg. Given every 2 to 4 hours. Should be avoided in patients with hypertension.
  • 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.
  • Misoprostol (Cytotec) – 800 to 1000 mg placed rectally. May cause a low-grade fever. It has a delayed action.
  • Dinoprostone (Prostin E2) 20 mg – vaginal or rectal suppository may be given every 2 hours.
  • Antibiotics – usually a combination of ampicillin (clindamycin if penicillin-allergic) and metronidazole. Gentamicin should be added to the above combination in cases of endometritis (tender uterus) or overt sepsis.
  • Uterotonics – examples include syntocinon (oxytocin), syntometrine (oxytocin+ergometrine), carboprost (prostaglandin F2) and misoprostol (Prostaglandin E1).
  • Oxytocin  A hormone naturally produced by the posterior pituitary works rapidly to cause uterine contraction with no contraindications and minimal side effects.
  • Methylergonovine  Semi-synthetic ergot alkaloid.  Works rapidly for sustained uterine contraction.  Contraindicated in patients with hypertension.
  • Carboprost – Synthetic prostaglandin analog of PGF Contraindicated in severe hepatic, renal, and cardiovascular disease, may cause bronchospasm in asthmatics.
  • Misoprostol – Prostaglandin E1 analog. More delayed onset than the above medications.
Prenatal Readiness
  • If the woman is at 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 gestations, 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 a 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.
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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.

Surgical Treatment

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

Tamponade Techniques
  • 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.
  • Bakri balloon (with vaginal packing to ensure its retention) with Foley catheter insertion to facilitate bladder drainage.
Surgical Management Techniques
  • Uterine curettage for retained products
  • Uterine artery ligation (O’ Leary), with an option to for extending arterial ligation to tubo-ovarian vessels.
  • Compression sutures such as the B-Lynch are typically reserved for clinical scenarios where bimanual compression of the uterus leads to arrest in bleeding.
  • Hypogastric artery ligation (performed by Gyn/Onc)
  • Hysterectomy

Postoperative and Rehabilitation Care

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.

References

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