Obstetric Hemorrhage Massive Transfusion

Postpartum hemorrhage is not defined safely by a single number. SOGC retains traditional thresholds of more than 500 mL after vaginal birth and more than 1,000 mL after caesarean birth, but any blood loss that produces hemodynamic instability warrants treatment. A rapidly bleeding patient with a normal blood pressure can already be in serious danger. The four causes are the four T’s: - Tone: uterine atony, the most common cause; the uterus remains soft and fails to compress open spiral arteries. - Trauma: cervical, vaginal, or perineal laceration, uterine rupture, or surgical bleeding. - Tissue: retained placental fragments or abnormal placentation, including accreta-spectrum bleeding. - Thrombin: impaired clot formation from consumption, dilution, or an underlying coagulopathy. After placental separation, contraction of the myometrium functions like a living clamp across the placental bed. With atony, that clamp is loose. With trauma, the uterus may be firm but a lacerated vessel continues to bleed. This distinction changes the treatment: more uterotonic medication will not repair a cervical laceration. Obstetric bleeding accelerates because the term uterus receives approximately 500–700 mL of blood each...