The quantity of blood in the body depends on the size of the individual; roughly, it constitutes one thirteenth of the body weight. To study the anatomy of the blood it may be divided into the solid portion and the liquid portion. The solid portion consists of the free-floating cells and comprises almost half (45 per cent) of the blood’s volume. The liquid portion is the plasma, which contains many substances in solution.
The red bood cells (erythrocytes) contain an iron-protein compound, called hemoglobin. This is what gives blood its red color. Hemoglobin readily combines with oxygen in the lungs and gives it up in the tissues; it absorbs the waste gas carbon dioxide in the tissues and expels it in the lungs. The white blood cells (leukocytes) are of several different kinds, and each has a specific role to play in the general functions of defending the body against germs and other inflammatory irritants, and repairing damaged tissues. The platelets are small floating bodies which are important in the clotting of blood. All the cellular elements are microscopic in size and each normally is present in a definite number per unit of volume. Whenever the oxygen-carrying red cells arc decreased in number or have a lowered hemoglobin content, the condition is called anemia. The white cells may greatly increase in total number in inflammatory conditions; the specific type of cell present in greater proportions gives the physician a diagnostic clue as to the type of tissue irritant causing the inflammation and the degree of inflammation produced.
The plasma portion of the blood serves as a medium for the cells to be transported and as a vehicle for many other materials as well. The plasma proteins are albumin, globulin, and fibrinogen. The former two are concerned principally with maintaining the correct consistency of the plasma for osmotic attractions of fluids and salts across capillary and cell membranes, while fibrinogen serves in clot formation whenever blood escapes from the vessels. Plasma with its fibrinogen removed is called serum. (Thus, blood minus its cells is plasma; plasma minus fibrinogen is serum.)
There are numerous other substances in the liquid portion of the blood. Sodium chloride and other salts essential to normal body chemistry make up almost 1 per cent. Glucose which is carried to the tissues for their fuel is present in rather constant solution in normal health; the liver converts glycogen back to glucose and returns it to the blood as the tissues use it up. Similarly, the amino acids from the dietary proteins are carried in the blood plasma to the tissues for their normal structural maintenance and repairs. The tissue waste products are carried to their excretion sites through the blood stream, and can be found in specific normal amounts in health. Other substances of import carried in the plasma are the enzymes and hormones which initiate and control certain chemical processes in the body, and the protective antibodies which aid in the reactions against certain infectious diseases.
Diseases which affect the blood are many. If bacteria gain entrance to the blood stream, the resulting condition is called bacteriemia or septicemia. Almost all other changes in the blood constituents are merely reflection of other diseases. The cellular components arc manufactured principally in the bone marrow, and diseases of this process in the marrow are manifested by changes in the number and quality of cells found in the blood stream. For example, in the disease leukemia, which is actually a cancer of the bone marrow, there is uncontrolled massive production of one of the types of white cells, so that it is found to predominate over the cell’s normal proportions. Other elevations of the normal number of a certain type of white cell are found in inflammatory diseases anywhere in the body, as this is a normal body response to inflammatory processes.
Anemia may be due to such things as recent hemorrhage or continued slow blood loss, or to dietary deficiencies of materials essential to produce normal red cells or hemoglobin, or to diseases which destroy the red cells.
Changes in the plasma elements are similarly only reflections of disease of other tissues. In kidney diseases elevation of the waste substances in the plasma may be found, or salt levels may be upset; in diabetes the glucose level may be greatly altered, and in dietary deficiencies the proteins may be low.
There are many other blood fractions which may be altered in disease, and abnormal substances may be detected. Numerous laboratory blood tests have been devised on these bases to aid in the diagnosis of disease.
Blood clotting is a complicated chemical and physical reaction by which the blood solidifies when it escapes from the vessels, to form a block against further loss of blood. This occurs mainly by the conversion of the liquid blood protein fibrinogen into the solid material fibrin. This process entails the interaction of several agents, some of which are derived from the blood and some of which are exuded from the injured tissues and the platelets. This chain of chemical reactions depends on the presence of fibrinogen, prothrombin, thromboplastin, calcium, and platelets. As the solid fibrin forms, some of the red blood cells are enmeshed within it, sealing off the bleeding area. Impaired clotting mechanism may be due to a deficiency of any one of these vital substances, which could be the result of disease of any tissue responsible for their productions.
As already implied, changes from the normal in the blood are diagnostic adjuncts in all fields of medicine. In surgery the ability of this tissue to perform its functions efficiently is particularly important. Operative treatment depends on the blood and the rest of the cardiovascular system to deliver adequate oxygen to the tissues even under the abnormal state of anesthesia; furthermore, dependence on the blood to carry out its usual roles in inflammation and tissue repair may be greatly enhanced. The blood must be at its most efficient capabilities before operative therapy is entertained. Whenever anemia is present, it must be recognized and corrected before operation, whatever the cause may be. Whenever possible, the treatment is directed at the causative factor. But sometimes this cannot be determined, or, more frequently, is a result of the operative illness; in such instance artificial replacement of blood to the normal levels by transfusions before operation is necessary.
All the various functions of the blood are evaluated and placed in efficient working order in the initial stages of surgical therapy. In modern times, the occasions for denial of operative treatment because of blood deficiencies are rare. The administration of blood or plasma infusions preoperatively, operatively, and/or postopera- tively have been made safe procedures.
With the vast number of accidents today, the sudden loss of blood becomes a more frequent problem. The amount of blood which could be lost without impairment of life varies greatly from person to person, depending on the size of the individual and the age and general physical state of health. The primary concern in the face of hemorrhage is life itself, and attention must be directed first at controlling the bleeding and then toward replacement of the lost blood volume.
In hemorrhage, all fractions of the blood are lost; it is a loss of entire volume rather than a shortage of any one component. But the greatest immediate disturbance is the insufficient supply of oxygen to the tissues. The loss of other functions of the blood can be temporarily tolerated by the tissues, but an inconstant oxygen supply is not compatible with the life of any body organ. The oxygen is carried by the red blood cells, and they are very efficient. The problem of transporting oxygen in the face of an insufficient blood volume is actually not the decrease in the number of red cells, but in their flow back and forth between the lungs and the tissues. The cardiovascular system does not have sufficient fluid to pump the remaining cells about fast enough.
After the bleeding has been stopped, plasma or a fluid substitute may be given until the whole blood transfusion is ready. Other immediate treatment may include oxygen therapy to insure an adequate supply with less work on the part of the respiratory organs, and sedation to further minimize the immediate need of oxygen. Such treatment is continued until the cardiovascular system can function efficiently enough to allow operation for the repair of the damaged tissues.
Minor injuries which sever only the capillaries stop bleeding within a few minutes spontaneously; when the larger vessels are injured, the bleeding may be difficult to control. Whenever the bleeding is such that it cannot be immediately controlled, such as within the body trunk, operative intervention and the re-establishment of blood volume in the cardiovascular system may have to be carried out simultaneously.
With minor losses of blood the body has certain mechanisms which compensate for the loss and soon replace the lost volume. The blood vessels constrict to maintain the necessary pressure within the vessels; the heart pumps faster, and breathing is increased. Then, more liquid portions are absorbed into the vascular tree to replace the lost volume within a short period. The replacement of cells takes considerably longer, however. Losses of one to two pints of blood in the adult are compensated in this manner. Greater losses require artificial replacements.
Whenever there is a disease which permits a chronic slow loss of blood, the compensatory powers maintain the required blood volume but a condition of anemia results; that is, there are fewer red blood cells than normal, or they have an abnormally low content of hemoglobin. This, of course, demands correction of the primary disease and then either medication to promote greater cell and hemoglobin production, or whole blood transfusions, or both. Frequently the anemia has to be corrected as a preparatory step for operation.
A sudden upset in the normal physiology of the cardiovascular system often occurs after injury. This is called shock. It almost always accompanies severe hemorrhage; it occurs frequently after severe physical injury to any part of the body, and may even appear after emotional injury. Formerly this condition had been poorly understood and constituted one of the most difficult emergencies to confront. But today the changes in the circulatory tree in shock are better understood and managed.
The major physical change which occurs to produce shock takes place in the blood vessels, especially the small arteries. It appears that the normal control of the vessels is lost. Under normal conditions the blood vessels dilate (enlarge) and constrict (tighten) to change the size of their openings, in accord with the various tissue’s needs for blood and the over-all pressure required within the circulation system. With loss of this control in shock, the blood vessels lose their ability to remain properly constricted, and they simply relax. These flaccid vessels then pool with blood, and the necessary pressure within the entire system is diminished. Since the capacity of the circulatory system is increased through the many miles of relaxed dilated vessels, the usual blood volume is not of sufficient quantity to keep the circulatory tree distended; many of the vessels therefore collapse. Furthermore, some of the fluid portions of the blood can more easily escape from the relaxed vessels through their walls into the tissues, further decreasing the blood volume and making the blood a more concentrated mixture. There is also an inefficient return of blood to the heart, so each beat has less thrust to mobilize the blood throughout the body. The findings in shock are, therefore, a lowered blood pressure, a rapid but feeble pulse, rapid respirations, and collapsed surface blood vessels. The individual is pale, weak and exhausted, thirsty, and in a cold profuse sweat. Blood analysis shows it to contain diminished fluid proportions.
The emergency treatment of shock includes placing the patient in a reclining position with the brain below the heart level, since the brain can tolerate oxygen deficiency very poorly and gravity may assist the flow to this vital organ. Drugs to alleviate pain are administered, since pain contributes to the intensity of shock. Stimulant drugs which will increase the heart’s actions and constrict the vessels are given. And infusions of plasma or liquid substitutes are employed to increase the blood volume. If hemorrhage has been severe, its control and replacement of lost blood by transfusion may be needed.
After the cardiovascular system has been returned to an efficient state of function, the necessary operative repair of the injured structures may be undertaken.