An ambulance arrives at the scene of an automobile accident, having been summoned by an in-vehicle security system. What the emergency personnel find is like a scene from a horror film. Maggie Silvers, the apparent driver of the car, is sitting, slumped next to the vehicle, with blood covering her shirt and hands. Her car has clearly hit a tree: a branch is sticking into the driver's window, and the airbag has been deployed. Maggie looks dazed, and as the paramedics approach she says with a mixture of panic and relief, "There’s blood everywhere!" Maggie is only semi-lucid as she babbles on about pushing out the broken glass in her car window.
Maggie, a 48-year-old woman, is, indeed, bleeding profusely from multiple left-arm cuts and an especially deep laceration on her left upper arm. The paramedics stop the bleeding and move her quickly to the ambulance, after noting no other apparent injury. Her systolic blood pressure is 80 mm Hg (low), and her diastolic is not audible (too low to hear). Her heart rate is 122 bpm (very rapid), and her skin is pale and clammy, indicating peripheral vasoconstriction (narrowing of her blood vessels, particularly in the skin) and circulatory shock-like signs. On the way to the hospital, a paramedic begins transfusing normal saline solution (NSS; water with some NaCl, similar to body fluids, given directly into her vein).
A fast hematocrit (HCT) test upon Maggie's arrival to the emergency department (ED) indicates that her HCT is low, but normal. Several vials of Maggie's blood are also sent to the lab for blood tests and typing. Two liters of NSS are transfused over the next hour while the ED physician sutures her deepest, left-upper-arm laceration. Despite no further bleeding since the paramedics treated her at the scene, Maggie's next HCT, tested one hour after the original HCT, drops to below normal. Aside from her present health problem, Maggie is otherwise healthy. She is admitted to the hospital for overnight observation.