Question

This is a short case study involving the blood. Read the case study below, then read the questions following it. Answer the questions in a short (approx. 1-2 pages), double-spaced report. Try to make it a story, not just a bunch of individual statements.

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 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.

The “fast hematocrit” involves withdrawing a very small amount of blood via a finger prick into a thin capillary tube, spinning the sample in a centrifuge so that it separates into its components, and then measuring the components. In Maggie’s case, the total blood volume in the capillary tube is 20 mm, the packed cell volume (red blood cells) is 7.1 mm, and the plasma portion measures 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 test tube. The packed cell volume (RBCs) is 1.45 ml, and the plasma volume is 3.55 ml. Calculate Maggie’s hematocrit in the ED. Besides the HCT, what other component of blood could be measured in a hospital setting to give a better understanding of oxygen-carrying capacity? Explain your answer.

Explain why the HCT drops despite no further loss of blood.

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 blood transfusion for Maggie, or for any patient for that matter, unless absolutely necessary?

Despite no blood transfusion, Maggie’s hematocrit improves by the time she visits her physician for the removal of her sutures a week later. [See multiple choice question 3 for the calculation.] She is adequately hydrated. Explain the physiological mechanism for the improvement in her hematocrit.

Answer 1

Answer :

Normal range for HCT for Maggie (a female) is 35 % - 45 %. (for males it is a bit higher)

First HCT Reading can be calculated by:
PCV of RBC is 7.1 mm
Plasma volume is 12.9 mm
Total blood volume is 20 mm
HCT = (PCV / total blood vol) x 100 = (7.1 / 20) x 100 = 35.5 %

Second reading will be = (1.45 / 5) x 100 = 29 %

HCT is an RBC Indices. Hence, in hospital set-up a simple test of CBC or just Haemoglobin estimation will give good indicator of oxygen carrying capacity of the blood. After all Haemoglobin is the carrier molecule for oxygen. Alternatively, in more severe cases, directly blood gases will measure pO2 and pCO2 .

Maggie is bleeding through her multiple lacerations and a gape wound in upper arm. Loss of blood is making her go into circulatory shock. But despite blood loss her hematocrit (HCT) value is normal because she is losing the blood as whole i.e.. the plasma as well as the cellular components. Therefore still the ratio between packed cell volume and plasma volume is maintained.

However, after she is transfused with large amount of saline, her repeat HCT test shows a drop. Now, the transfusion of normal physiological saline has replaced her body fluid and loss of plasma is now compensated. The reduced cell numbers are now suspended in normal volume of blood and therefore ratio of packed cells to plasma volume is different and thus she shows a drop in HCT. This is expected value.

Blood Transfusion is not as safe as most of us consider. There are several factors to be considered before transfusion is given. Blood group cross matching is just one of them. There are risks involved in this procedure and hence clinicians should measure the benefits against risks and only if benefits outweigh the risks should they give blood transfusion. Paramedics are support staff and are not given the authority to transfuse blood without first assessment from the clinician in ER and who decided that blood transfusion is the only way left to save patient...

But, without being transfused with blood, her HCT has returned to normal. This is because, once body is recovering, all organs go to their normal work and new RBCs are being made to compensate for the stress body has gone through. Therefore with new blood cells coming back into circulation, the HCT also will move towards normal.