Clinical meaning
Postpartum hemorrhage (PPH) is defined as cumulative blood loss of 1000 mL or more, or blood loss accompanied by signs and symptoms of hypovolemia, within 24 hours of birth regardless of delivery method. This updated definition from the American College of Obstetricians and Gynecologists (ACOG) replaced the previous threshold of 500 mL for vaginal delivery and 1000 mL for cesarean delivery. PPH is classified as primary (early), occurring within 24 hours of delivery, or secondary (late), occurring between 24 hours and 12 weeks postpartum. Primary PPH accounts for approximately 70-80% of all PPH cases. The pathophysiology of PPH is organized using the 4 Ts mnemonic: Tone, Trauma, Tissue, and Thrombin. Uterine atony (Tone) is the most common cause, accounting for approximately 70-80% of all PPH cases. After placental delivery, the myometrium must contract firmly to compress the spiral arteries at the former placental site. These blood vessels, which carried 500-700 mL/min of blood flow to the placental bed during pregnancy, rely entirely on myometrial contraction (physiological ligatures of Pinard) for hemostasis. When the uterus fails to contract adequately (atony), these vessels remain open, resulting in rapid, life-threatening hemorrhage. Risk factors for uterine atony include overdistended uterus (multiple gestation, polyhydramnios, macrosomia), prolonged labor, rapid labor, chorioamnionitis, use of tocolytic agents (magnesium sulfate, terbutaline), general anesthesia, and high parity. Trauma accounts for approximately 20% of PPH and includes lacerations of the cervix, vagina, or perineum, uterine rupture, and hematoma formation. Tissue retention (retained placental fragments or membranes) prevents complete uterine contraction and accounts for approximately 10% of cases. Retained tissue provides a surface that prevents the myometrium from contracting around the spiral arteries. Thrombin disorders (coagulopathies) are the least common cause but the most dangerous, including disseminated intravascular coagulation (DIC), pre-existing bleeding disorders (von Willebrand disease, thrombocytopenia), and anticoagulant therapy. During pregnancy, blood volume increases by 40-50% (physiological hypervolemia), which provides a compensatory buffer against blood loss. However, this also means that clinical signs of hypovolemia may not appear until blood loss exceeds 15-20% of total blood volume. The practical nurse must be vigilant in monitoring blood loss, fundal tone, and vital signs because tachycardia (the earliest compensatory sign) may be masked by epidural anesthesia or beta-blocker use.