blood homeostasis.
Now to some other basics: The average adult has about 10 pints of blood—and this varies with weight, age, sex, body build, etc., and can lose about a pint without much problem. When one donates a unit of blood it is equal to about a pint. The volume you lose with the donation is made up rapidly with transfer of fluids from one part of your body to the blood stream, so that the total volume remains the same. It takes about two weeks for your body to produce and replace the red blood cells.
The blood circulates through your body in a continuous circular pattern, driven by the contractions of the heart. It goes from the heart through the arteries to the tissues, such as brain, stomach, kidneys, skin, etc., where it gives off oxygen and other nutrients to the cells, and then returns to the heart by the veins. It is pumped into the lungs, where it picks up more Oxygen, returns back to the heart and then starts the trip again. Simply put, the flow of blood, with a certain volume present, gives us our blood pressure. If the amount of fluid in the system falls, as with bleeding, then the blood pressure falls, and the heart beats faster to keep the total amount of blood circulating at a constant number. So when there is hemorrhage, a patient's blood pressure usually goes down and his heart rate or pulse goes up. Those signs, together with measurements of the blood, will let the surgeon know how much a patient is bleeding and how much to replace. We'll talk more about the actual numbers in Chapter 25, when we will also discuss the white blood cell count (WBC) and other blood factors.
When a patient's blood count, amount of blood, or red blood cells falls too low, he may need a blood transfusion. We generally say that 9 grams of hemoglobin is the cutoff level, with normal being between 13 and 15 grams for most healthy people. But for many reasons, including religious (Jehovah Witnesses refuse any blood transfusion), the choice of no blood or of, under certain circumstances, blood be given. Frequently, when a patient knows he will be needing blood, he will give his own blood in advance or have friends or relatives donate for him.
As far as coagulation is concerned, I am going to show you a schematic version of the clotting pathway, which includes factors IV and VII through XIII. I never remember all the specifics myself and always have to refer to specialists or books to understand all the pathways, but I thought you might be interested to see how much is involved in forming a blood clot and stopping bleeding when you get a scratch or cut. The factors and their synonyms are:
| I | = | Fibrinogen |
| II | = | Prothrombin |
| III | = | Tissue Factor |
| IV | = | Calcium Ion |
| V | = | Proaccelerin (labile factor) |
| VII | = | Serum Prothrombin Conversion Accelerator Factor (stable factor) |
| VIII | = | Antihemophilic Factor |
| IX | = | Christmas Factor |
| X | = | StuartPrower Factor |
| XI | = | Plasma Thromboplastin Antecedent |
| XII | = | Hageman Factor |
| XIII | = | Fibrin Stabilizing Factor and then there are platelets. |
We sometimes refer to the expression “consumption coagulopathy,” which means that, because of continued bleeding and the body's attempt at stopping the bleeding by forming blood clots, many clotting factors are used up or consumed, and this must be managed by physicians with in-depth knowledge of the clotting pathways and their replacements.
In certain situations like hemophilia, kidney disease, and Von Willebrand's disease, special factors are needed and must be supplied by the hematologists. Another problem is disseminated intravascular coagulation or DIC, the name for a number of conditions which cause severe problems with coagulation and can lead to death if not rapidly and appropriately corrected. Some of the things that can cause DIC are massive bleeding, problems with labor and delivery, severe infections, burns, liver disease, crush injuries, and malignancies. DIC is a difficult problem to counteract and sometimes results in death, even in the most experienced hands.
Now let us turn to the whole area of transfusions. Blood contains substances which are called antigens, and, without being more specific, we have to receive a blood transfusion with blood containing pretty much the same antigens as our own. Otherwise, severe “allergic” reactions and even death can occur. The first blood group discovery was made in 1901 with the determination of A, B, and O types. Later on, many other subgroups, such as Rh, Kell, Lewis, and Duffy, were discovered, making it much safer to receive blood transfusions. In the early 1980's, with the beginning of the AIDS epidemic, we were unable to identify contaminated blood. Now we can determine contaminated HIV positive or AIDS blood, making the blood supply safe and dependable.
In conclusion, let me review briefly the hemostatic process, or how bleeding stops without our external help. After a minor injury causes an opening in a vein or an artery small artery called an arteriole, the vessel contracts and partially closes off. Then, a mass of platelets join together to form a plug--like a finger in a dike which stops the bleeding and allows the hole to heal with a collagen scar (see Chapter 21). So the next time you have a cut and are bleeding, think about all these considerations I have mentioned, and by the time you have reread this chapter the bleeding had better have stopped; if not see a doctor!
Chapter 19
PULMONARY EMBOLISM
Blood clots in veins where they shouldn't be found,
Can be a great problem if they should abound.
And if they break loose and go to the lung,
A patient may die with the reason unsung.
More than half a million will get this bad disease,
With blood clots from their pelvis, or their ankles to their knees.
And ten percent will die within an hour, sad to say.
So one must make the diagnosis soon, with no delay.
And of the 90% who live beyond the very first hour,
About a third will die in spite of all the medical power.
So face it, blood clots in your veins, are a very serious matter,
And shouldn't be taken lightly or be treated by a Mad Hatter.
If you are diagnosed and treated with the proper drugs
The doctor can dissolve the most pernicious of the clogs.
And using anticoagulants, (blood thinners to the public,)
You'll probably survive to next New Year and be able to
drink
