This is a short case study involving the blood. Read the casestudy below, then read the questions following it. Answer thequestions in a short (approx. 1-2 pages), double-spaced report. Tryto make it a story, not just a bunch of individualstatements.
A Case Study in Blood
An ambulance arrives at the scene of an automobile accident,having been summoned by an in-vehicle security system. What theemergency personnel find is like a scene from a horror film. MaggieSilvers, the apparent driver of the car, is sitting, slumped nextto the vehicle, with blood covering her shirt and hands. Her carhas clearly hit a tree: a branch is sticking into the driver’swindow, and the airbag has been deployed. Maggie looks dazed, andas the paramedics approach she says with a mixture of panic andrelief, “There’s blood everywhere!†Maggie is only semi-lucid asshe babbles on about pushing out the broken glass in her carwindow.
Maggie, a 48-year-old woman, is, indeed, bleeding profuselyfrom multiple left-arm cuts and an especially deep laceration onher left upper arm. The paramedics stop the bleeding and move herquickly to the ambulance, after noting no other apparent injury.Her systolic blood pressure is 80 mm Hg (low), and her diastolic isnot audible (too low to hear). Her heart rate is 122 bpm (veryrapid), and her skin is pale and clammy, indicating peripheralvasoconstriction (narrowing of her blood vessels, particularly inthe skin) and circulatory shock-like signs. On the way to thehospital, a paramedic begins transfusing normal saline solution(NSS; water with some NaCl, similar to body fluids, given directlyinto her vein).
A fast hematocrit (HCT) test upon Maggie’s arrival to theemergency department (ED) indicates that her HCT is low, butnormal. Several vials of Maggie’s blood are also sent to the labfor blood tests and typing. Two liters of NSS are transfused overthe next hour while the ED physician sutures her deepest,left-upper-arm laceration. Despite no further bleeding since theparamedics treated her at the scene, Maggie’s next HCT, tested onehour after the original HCT, drops to below normal. Aside from herpresent health problem, Maggie is otherwise healthy. She isadmitted to the hospital for overnight observation.
The “fast hematocrit†involves withdrawing a very small amountof blood via a finger prick into a thin capillary tube, spinningthe sample in a centrifuge so that it separates into itscomponents, and then measuring the components. In Maggie’s case,the total blood volume in the capillary tube is 20 mm, the packedcell volume (red blood cells) is 7.1 mm, and the plasma portionmeasures 12.9 mm. Calculate Maggie’s first hematocrit. What is the\"normal\" range for Maggie?
In the ED, blood is withdrawn from the vein and into a testtube. The packed cell volume (RBCs) is 1.45 ml, and the plasmavolume is 3.55 ml. Calculate Maggie’s hematocrit in the ED. Besidesthe HCT, what other component of blood could be measured in ahospital setting to give a better understanding of oxygen-carryingcapacity? Explain your answer.
Explain why the HCT drops despite no further loss ofblood.
Why do you think paramedics give normal saline solution (NSS)and not blood in the ambulance?
Why might a physician be reluctant to order a bloodtransfusion for Maggie, or for any patient for that matter, unlessabsolutely necessary?
Despite no blood transfusion, Maggie’s hematocrit improves bythe time she visits her physician for the removal of her sutures aweek later. [See multiple choice question 3 for the calculation.]She is adequately hydrated. Explain the physiological mechanism forthe improvement in her hematocrit.
