Uterine Atony

Preop risk stratification - Prolonged or precipitous labor, multifetal gestation, polyhydramnios, macrosomia, fibroid uterus, chorioamnionitis, prolonged oxytocin augmentation, magnesium infusion, and BMI over 40 all predict atony. Get large-bore access and a type and screen before you need them.

First response is mechanical - Fundal and bimanual massage comes before any drug, along with IV access and labs. Uterotonics do not fix a uterus nobody is rubbing.

Oxytocin first line - Dilute infusion, 20-40 units per liter. A direct IV bolus causes tachycardia, vasodilation, and hypotension, so run it rather than push it.

Methylergonovine second line - 0.2 mg IM, repeatable at 2 to 4 hour intervals, onset 2 to 5 minutes. The label contraindicates hypertension, toxemia, and pregnancy, and says not to give it IV routinely because of sudden hypertensive and cerebrovascular accidents — if IV is essential as a lifesaving measure, push it over no less than 60 seconds with the cuff cycling. Coronary artery disease or its risk factors raise the odds of vasospasm-driven myocardial ischemia and infarction.

Carboprost third line - 250 mcg deep IM, repeatable at 15 to 90 minute intervals, label maximum 2 mg (8 doses). It raises cardiac output and pulmonary vascular resistance. The label contraindicates active cardiac, pulmonary, renal, or hepatic disease and lists a history of asthma as use-with-caution — carboprost both incites and worsens bronchospasm, so in an asthmatic reach for misoprostol instead. Expect transient pyrexia; temperature rose more than 2°F in about one in eight patients.

Misoprostol as an add-on - PGE1, 600 mcg oral, sublingual, or rectal. No bronchospasm risk, but expect fever, nausea, and hypotension.

Turn off what relaxes the uterus - The uterus contracts through alpha receptors and relaxes through beta-2, so beta-2 agonists and magnesium work against you. Under GA, volatile agents markedly worsen uterine tone once the fetus is out — convert to TIVA with propofol, or to nitrous with a reduced volatile.

Watch the numbers, not the drape - Atony declares as hypotension, tachycardia, oliguria, and falling saturation, with pallor, restlessness, confusion, and air hunger in the awake parturient. Estimated blood loss at the drape is routinely underestimated.

Tranexamic acid - TXA is a lysine analog that blocks plasminogen conversion to plasmin, peaks almost immediately, and has a 2-hour half-life. Evidence for prophylactic use at cesarean is low to moderate quality, and a large retrospective high-risk cohort found no reduction in PPH, so treat it as an adjunct, not the plan.

When uterotonics fail - The obstetric team moves to invasive control while you run the resuscitation. Anticipate a general anesthetic in a patient who is now hypovolemic with a full stomach, and get blood products in the room rather than ordered.

Uterine atony is failure of the corpus uteri myometrium to contract adequately in response to the endogenous oxytocin released during delivery. Hemostasis at the placental bed is mechanical: the spiral arteries are uniquely devoid of musculature and depend on contracting myometrium to squeeze them shut. A uterus that stays boggy keeps bleeding from open spiral arteries. Atony is the most common cause of postpartum hemorrhage (PPH) — it complicates roughly 1 in 40 US births and accounts for at least 75% of PPH cases, and PPH sits among the top five causes of maternal mortality worldwide.

Risk factors cluster around an overworked or overstretched uterus: prolonged or precipitous labor, multifetal gestation, polyhydramnios, macrosomia, fibroid uterus, chorioamnionitis, prolonged oxytocin augmentation, magnesium sulfate infusion, retained placental tissue, abnormal placentation, uterine inversion, and BMI above 40.