Inflammation is the most important of all pathological processes, as it is the most universal. Inflammation is a local reaction of living tissues to something which irritates them. Any tissue which is subjected to the action of an irritant reacts with some degree of inflammatory change. The process of inflammation is actually the body’s attempt to fight off the irritating agent. In this attempt there are certain changes in the tissues, all directed at fighting off or eliminating the offending agent. The final step of inflammation is healing of the tissues which were injured and took part in warding off the irritant. Therefore, inflammation is the body’s attempt to eliminate the irritant and dead tissue preparatory to healing the damaged structures. Every step in the process is directed toward this goal.
Irritants to the tissues may be infective, physical, or chemical. Infective irritants include all germs; i.e., bacteria, viruses, and fungi. The physical irritant includes all injuries to tissues by any means, including the necessary cutting of tissues by operation. In this case the irritant is no longer present but the final stage of inflammation (i.e., healing) must take place. Other examples of physical irritants are heat burns; wounds by sharp or blunt objects; foreign bodies imbedded in tissues; frost bite, and substances to which the patient is allergic, such as pollens and dusts. The degree of inflammation, of course, varies with the irritant; the simple laceration caused by a knife will have little reaction, while a deep burn with much dead tissue may have a prolonged severe inflammatory reaction. Chemical irritants affect the skin, mouth, eye, and other body covering tissues. With any irritant the inflammatory reaction of the body is dependent on the degree the tissues are irritated. In some diseases the irritant is unknown, but the process is the same.
The cardinal signs of inflammation are redness, swelling, pain and tenderness, and increased heat. These are due largely to the increased size of the blood vessels in the area. The first response to the tissue irritant is the dilatation of the blood vessels in the area. This is due to a local reaction and involves the small arteries, veins, and capillaries. This step allows greater blood supply to the region for greater oxygen and nutriment supply. The redness and increased heat are directly due to this increase in the supply of blood to the area, and the swelling is also due in part to this phenomenon. The pain and tenderness are a result of the local action on the fine nerves in the vicinity.
The second step in inflammation is the collection of an exudate in the region. The exudate is cells and fluid, and is liberated into the area for the purpose of neutralizing and/or eliminating the irritant and dead tissue in preparation for repair of the tissues. White blood cells from the blood stream actually pass out through the wall of the small dilated blood vessels to take part in the battle. There are several kinds of white blood cells, each with a special talent, and they are called into the area according to their need. At the same time, the total number of the specific type of cell in the blood stream is increased by a greater production of these cells in the bone marrow.
This serves as a diagnostic aid to the surgeon (the white blood cell count) to determine the degree of inflammation in nonvisible structures, the type of inflammation, and the body’s ability to combat the process. The role of the white cells may be to devour particles of the irritant or dead tissue, to carry particles away, or to produce a substance to neutralize the irritant. After the cells have accomplished their part of the mission, they die and disintegrate. The white cells constitute the chief element of the pus so often seen in an area of inflammation. A drop of pus contains millions of white blood cells, most of which are fragmented and no longer living.
Another component of the inflammatory exudate is the mobile cells which arise out of the tissues in the vicinity of the irritant. These have roles similar to those of the white blood cells, and their fate is the same, but again each type of cell seems to have definite skills and specializes in combating a specific type of irritant.
The liquid portion of the exudate is the blood plasma. It, too, actually passes out of the dilated vessels to collect in the area of inflammation. In the plasma are found antibodies which also join in the battle against the irritant. Fibrin is produced from plasma elements which is very important in inflammation, for it “walls off” the process to keep the irritant from extending, and to limit the reaction to the vicinity around the irritant. The entire exudate, but mostly the plasma portion, is responsible for the greater part of the swelling in an inflammatory area.
Inflammation is essentially, then, a struggle between two forces—the irritant, the agent of destruction; and the body’s defense mechanisms, the representatives of conservation. The end results depend on which is the stronger and on the degree of destruction incurred before repair begins. In any case, the termination may be either
- resolution of the process with healing
- extension of the destructive process and widespread tissue death.
Fortunately, the former most often occurs.
The final phase of inflammation is healing or repair of all the injured tissue. In some cases this may begin immediately, but in other cases it takes a long period of time before healing starts. In the case of tissue injured by operation there is no irritant remaining and little dead tissue to be eliminated, so the processes of repair begin immediately; but, in the case where the tuberculosis germ is the irritant, it may take months before the irritant is eliminated so that the tissues may heal. In many cases, however, the processes may overlap or go on side by side; as the irritant is eliminated in one area, repair begins, even though the irritant is still present in another area.
In the lowest forms of animal life entire organs or parts may be replaced by healing, but this is not so in humans; missing parts are forever gone. Moreover, some simple cells may regenerate but the more complex cells of man will not be replaced. It seems that, the more highly specialized the tissue’s cells, the less power it has for regeneration. Bone and certain other connective tissues are relatively simple cells and tend to be replaced, but specialized cells, such as those of the brain or the kidney, arc replaced only by simple scar cells.
The processes of repair are seemingly quite simple. When the wound is free of all irritants and dead tissue, the exudate of cells and plasma has passed in to fill the gaps in the tissues. The fibrin in the plasma coagulates so that the tissues are literally glued together by the interlacing strands of fibrin. Throughout the body tissues there are cells which may lie quiescent for years just to join in the process of repair. These we may call repair cells (actually fibroblasts), and, when healing begins, they spring to life. In the fibrin they reproduce many-fold and develop branching processes which interlock with the fibrin and with each other. At the same time, the capillaries around the area begin to form buds which grow out into the area. These develop a canal within them and fill with blood. Thus, a network of new blood vessels is formed in the area. As these processes go on, the fibrin is absorbed, so that the entire region becomes replaced by new vessels and repair cells. This fills in all gaps in the wound.
Grossly, this newly formed tissue looks quite rough and velvety and has acquired the name of granulation tissue (commonly called “proud flesh”). The process is called granulation. As the process goes on, the repair cells become more mature and their appearance changes to the cell called a scar cell (fibrous cell). The new blood vessels gradually obliterate as they are no longer needed. So in the area remain only the scar cells, which gradually lose their outlines and blend together to become quite indistinct. The homogeneous new tissue remaining is called fibrous tissue or scar tissue.
The scar tissue is all that remains forever after in most tissues, but with certain tissues the original cells may gradually replace the scar cells. On the skin, if the area is no larger than a half dollar, the adjacent skin will regenerate with normal skin cells to cover the area void of skin. In bone the fibrous tissue is substituted by regenerating bone cells, and calcium is deposited to make the region as strong as before. A few other connective tissues are likewise reverted back to normal.
This process of healing is the same for all wounds, whether it be the fine slit left by the surgeon or a wide, open ulcer. In the former, the amount of granulation tissue will not be visible to the naked eye, but in the latter, tremendous attempts at granulation will be made. In wounds where there is a blood clot formed over the lesion, the same process takes place beneath the clot, and finally the clot is released.
Defective healing may occur when there are adverse conditions. Healing is delayed, of course, when any irritant remains; foreign particles, dead tissue, and infection slow the usual progression to repair. When there is an interference in the blood supply to the part from any source, the process of healing is slower. In patients where there are vitamin deficiencies, especially vitamin C, and in patients debilitated from disease or malnutrition, the healing course may be prolonged.
Varieties of Inflammation
There are slight variations in the course of inflammations, mostly dependent on the specific irritant. In all, however, the body’s attempts are the same:
- to eliminate the irritant and dead tissue
- to heal the damaged area.
Infective irritants are the most common offenders. Infection means the presence of germs. It may be bacteria, virus, or fungus. These are living creatures, microscopic in size and parasitic in want.
It is not the author’s purpose in this book to present a course in bacteriology (the study of germs), but its relationship to surgery must be mentioned. Germs are present everywhere, in the air and on all objects, except where sterilization procedures have been performed. The human skin is covered with germs, and the mouth is teeming with many different varieties. Fortunately, the skin and mouth coverings afford excellent protection against the invasion of germs, and only occasionally are the germs able to penetrate these structures.
There are numerous species of each of the types of micro-organisms, and each has its own living habits. Many germs are not at all harmful to man; moreover, some types are beneficial. One specific type enters the digestive tract of man soon after birth and remains there for the remainder of the individual’s life to aid in the digestion of food. Some germs may join in the fight against other harmful germs. Germs have been found to have specific preferences in their habitat. This is true not only in their outside environment, but also in the tissues they attack after they have gained entrance into the body. This is a peculiar but important point to the physician. Certain germs attack certain body tissues only; i.e., specific organisms cause specific diseases. Volumes have been written on this subject for each disease, and the role of bacteriology in surgical inflammations cannot be overemphasized.
Today we have excellent means of combating most infections by use of the antibiotic (against [germ] life) drugs. But there is a specific choice drug for each type of germ. In the case where more than one type germ can cause the same disease, the physician must determine the offending type to select the most effective drug. Bacteriological procedures, such as wound cultures, and other laboratory tests often are needed in conjunction with the physical findings to ascertain the germ type.
One of the most important factors in operating room techniques is the sterilization of everything that may come in contact with the incised area. Sterilization means to render free of all forms of life. Various heating methods and germicidal (germ-killing) solutions kill all the germs on all the equipment to be used. Wounds produced in any other way will contain numerous organisms and are called contaminated wounds. If the processes of inflammation do not quickly destroy the organisms, they will multiply prolifically and penetrate the deeper tissues, so that an obvious infected wound is manifested. The initial treatment of a wound must be directed at ridding it of all irritants, especially germs, and eliminating all obviously dead tissue; then surgical repair may be done.
All inflammations are variants of the same process. The variations depend in part on the organ affccted, on the irritant, and on the relative strength of the attacking and protective forces. Pus is a collection of dead disintegrated white cells, dead tissue particles, and other byproducts from inflammation which have not been carried away or absorbed. Any wound containing pus is called a purulent wound.
An abscess is an infected wound which has developed a pocket or cavity of pus surrounded by a wall of inflamed tissue. An abscess may recover, remain stationary, or advance. A small abscess may go through the processes of inflammation and finally repair by scar tissue, but this is not common, unless antibiotic medications are employed early. Rarely does one remain stationary, but if it should and if all the germs in it are killed, it is called a sterile abscess. Without intervention an abscess usually advances so that there is progressive destruction of cells, and more of the wall becomes liquefied and added to the central pus. As it progresses, the abscess burrows its way through tissues, following the lines of least resistance, finally opening on a surface. Often the surgeon can minimize the process by opening the abscess to the nearest surface earlier than the process would take by itself, and thereby lessen the amount of tissues destroyed and hasten recovery. Needless to say, pus may contain millions of germs still alive, and precautions must be taken not to infect other tissues or other persons. A typical example of an abscess is the boil, which starts its infectious process in a hair follicle or skin gland.
An ulcer is an inflammatory lesion with an interruption of the continuity of a surface. This may occur on the skin, in the mouth, in the digestive tract, or in any area where there is a surface membrane. There are many different kinds of infected ulcers, each with characteristic features.
A sinus is a tubular ulcer. It usually heals with difficulty due to the presence of dead tissue or infection. It is lined by granulation tissue.
A fistula is a similar passage between two surfaces. It may be between skin and intestine, the bladder and skin, two loops of intestine, or any two body surfaces. A sinus most often occurs by an abscess discharging to a surface, and a fistula by the discharging of an abscess to two surfaces. When germs from an inflammatory process gain entrance to the blood stream and thrive to reproduce, the condition is callcd septicemia or bacteremia. This is, of course, a serious situation, for infections may be set up in many other parts of the body.
Mechanical irritants may produce closed or open wounds. The closed wound is a contusion. It is the result of the impact of blunt objects which crush some of the tissues beneath the skin although the skin itself is not penetrated. There may be any degree of injury to the soft tissues under the skin, and this is always associated with some degree of hemorrhage under the skin due to rupture of blood vessels. Contusion is also called a “bruise.” If a large amount of blood escapes out of the blood vessels into the tissues, there is swelling and bluish discoloration which is called a hematoma (blood-swelling). With contused wounds the process of inflammation is directed at eliminating the dead tissue and the red blood cells in the area. The red cells act as a tissue irritant and must be excluded before the healing processes may begin. With the dissolution of the red cells the wound may pass through stages of bluish to yellowish discoloration. Bacteria thrive on dead red blood cells, so treatment must include efforts to preclude bacteria gaining entrance to the area. In some cases the hematoma may be so large that the surgeon must evacuate it.
Open wounds include the abrasion, the incised or lacerated wound, the penetrating wound, and the perforating wound. The abrasion is a superficial wound of the skin without penetration of all layers of the skin. It is a scratching or scraping of the skin. A clot usually forms over the area and the process of inflammation with ultimate healing takes place beneath the clot, and, when completed, the clot is released.
The incised wound is made by a sharp object. The severed edges are smooth, with little tissue damage, but, if the incision is deep, important structures such as large blood vessels and nerves may be divided. This wound usually bleeds freely because of cut blood vessels, and usually requires surgical repair. The lacerated wound is the same as the incised wound except that the edges are more jagged. It may require debridement (operational removal of the dead debris) before surgical repair.
The penetrating wound is a puncture with penetration of the skin and tissues beneath it. The damage of the penetration depends, of course, on the depth of the stab and the organs involved. Usually this is difficult to determine from the appearance of the wound. Needless to say, penetrating wounds of the chest, abdomen, and head may be very serious.
A perforating wound is similar to the penetrating wound, but it goes completely through a structure, such as the through-and-through wound of the hand which goes in the palm and comes out the back side.
All of the mechanical wounds, except those performed in the operating room under aseptic (without-germs; i.e., sterile) technique, are associated with some degree of contamination with micro-organisms. Usually within a short time the inflammatory processes have eliminated the germs, but frequently the wound becomes quite infected. Initial treatment must be directed at eliminating as much of all the irritants as possible, as well as the reconstruction of tissues.
With many mechanical wounds there are foreign bodies left in the tissues. Sand particles may be ground into the abrasion; a knife blade may chip in the laceration, or a bullet may lodge in the tissues after its penetration. The most common foreign body left in tissue is the simple wood splinter of the fingers. The inflammatory response to the foreign body is dependent on the nature of the substance. Many of them will cause no irritation to the tissues at all; others cause a marked reaction. The body attempts to remove them all by moving the inflammation forces into the area and surrounding it. In many cases, where the substance is metallic, the germs are destroyed and a wall of scar tissue is built around the metal. It causes no more irritation and may remain in this state in the tissues forever after without detriment. Contrary to the conception disseminated by movies and books, it is by no means always necessary to remove bullets. Only those lying in or near vital body structures need be removed. To be sure, more damage is done by the missile entering the body than by the bullet’s lodgment in the tissue. In some cases, however, an abscess may develop around a foreign body due to the germs brought in with it and the irritation of the tissues from the substance. These must be removed. In general, the harder the material, the more likely it is to be walled off by scar tissue and rendered inert; while softer substances such as wood, clothing, and paper cause a greater inflammatory response and are better removed. But frequently the latter substances may be completely disintegrated by the inflammatory phase and go on to complete healing.
Heat as a mechanical irritant need be in contact for only a few seconds to produce a severe thermal burn. As the area cools, the irritant is automatically eliminated. The inflammatory processes are then directed at the removal of the dead tissues in preparation for healing. Frost bite is similar. The irritant is soon removed, but the destroyed tissue must be eliminated by inflammation, preparatory to the body’s reconstruction of the part by scar tissue production. Chemical irritants must be neutralized by the inflammatory reaction and the removal of dead tissues, so healing may begin.
Gangrene is death of a part of the body. It may affect a small area on one of the digits, an entire extremity, a loop of bowel, or any other anatomical structure. Gangrene in most cases is primarily due to interference of the blood supply to the part so that adequate oxygen and nutriments are not afforded the tissues. It may also rarely be due primarily to certain toxins from bacteria acting on the tissues. Gangrene may appear spontaneously from sudden cessation of the blood supply by mechanical interference of the blood flow, severing an artery, clot formation within the blood vessels, or marked constriction of the vessels from severe cold. In patients with diabetes and those with diseases of the arteries, gangrene is common; this is due to loss of the vessels’ elasticity through hardening of the arteries, thereby rendering them unable to carry adequate blood to the part.
After gangrene has once begun, germs usually invade the area and live on the dead tissues, so there is superimposed an infection. The inflammatory process then becomes more complex, for this new irritant must be fought and eliminated as well as the dead tissue particles. Since the circulation is already deficient, the full forces of inflammation cannot be provided. Before infection the area of dead tissue is called dry gangrene, and after the new irritant (germ) enters it becomes a wet gangrene. Chances for revitalization of the tissues is lessened in the latter type. There may also be a disturbance of the flow of unoxygenated venous blood away from the area in the moist type.
Nomenclature in medical language applicable to inflammation is quite simple. The suffix -itis implies inflammation; for example, inflammation of the appendix is called appendic/f/s and inflammation of the tonsils is called tonsill/f/jr. This suffix always means inflammation of its prefix, regardless of the irritant stimulating the inflammatory process. The term acute implies a rapidly developing process of short duration, while the word chronic means a slower process of long duration. An intermediate term is subacute. An acute proccss may develop into a chronic one, but either may start as such from the onset. Both have a typical microscopic appearance insofar as the type of white cells involved. When a disease occurs once, is cured, and then strikes again in the same tissues, it is called a recurrence.
Summary of Inflammation and Healing
Inflammation is the commonest of all pathological processes. It is the body’s response to a tissue irritant which may take any form, the most important being germs. The aim of inflammation is to rid the tissues of the irritant and all dead tissue, preparatory to the process of healing. Inflammation may be acute or chronic. Several different specific varieties of inflammations occur. Inflammation and healing pass through various specific phases in their processes. The shortest period of inflammation is the incision made by the surgeon’s knife where the irritant is eliminated as soon as it strikes so that healing may begin immediately; whereas, an example of prolonged inflammation is the tissue infected with the tuberculosis germ. Inflammation is the struggle between two forces representing destruction and conservation. Fortunately, the latter most often wins, and the healing processes then ensue.