Edema Defined

Edema is the accumulation of excessive fluid in the intercellular spaces. ^, The process of controlling fluid accumulation involves a variety of factors that influence capillary filtration and lymph drainage. Both vascular and nonvascular processes affect fluid accumulation.

All cells are bathed in extracellular fluid. This fluid can be divided into two main components: the interstitial fluid and the blood plasma. ^, The interstitial fluid is outside of the closed vascular system. Blood plasma is the fluid noncellular component of blood in which red blood cells, white blood cells, and platelets are suspended to collectively form total blood volume. ^, This circulating blood tissue permeates the vascular system and flows through the heart, arteries, capillaries, and veins.

The arterial system brings oxygen and nutrients to the cells, whereas the venous system is responsible for waste and carbon dioxide removal. The exchange of nutrients and cellular waste between the tissues and the circulating blood takes place at the level of the capillaries, primarily through diffusion and filtration. The capillary wall consists of a single layer of highly permeable endothelial cells and is surrounded by a basement membrane. The diameter of the capillary is just large enough for red blood cells and other blood cells to pass through. Blood enters the capillaries through arterioles and metarterioles and exits through venules. It is rare that any single functional cell is more than 20 to 30 µm away from a capillary. ^, Oxygen and glucose are in higher concentration in the bloodstream than in the interstitial fluid and diffuse into the interstitial fluid, whereas carbon dioxide diffuses in the opposite direction. ^, Proteins are too large to diffuse easily through the capillary membrane and primarily flow linearly along the capillary. However, small amounts of proteins leak out of the blood capillaries into the interstitium, where they accumulate in the interstitial fluid. ^, The lymphatic system is responsible for returning proteins that have accumulated in the interstitial spaces back into the venous system until the system is back in balance. Lymph is fluid collected from tissues; it flows via lymphatic vessels through the lymph nodes and drains into the venous system. Figure 63-1 illustrates the exchange process between substances in the interstitial fluid spaces with blood and lymphatic capillaries.

Diffusion of fluid molecules and dissolved substances between the capillary and interstitial fluid spaces.

(From Guyton AC, Hall JE. Textbook of Medical Physiology. 9th ed. Philadelphia: WB Saunders, 1996.)

The spaces between cells are collectively called the interstitium. The fluid between cells (or interstitial fluid) is derived by filtration from the capillaries. There is a constant exchange of fluid between the intercellular tissue spaces and the blood plasma across the capillary membrane. Fluid in the interstitium is trapped by proteoglycan filaments, which cause the fluid to have the characteristics of a gel. ^, This “tissue gel” contains almost the same constituents as plasma, except for proteins, because proteins do not filter out of the capillaries easily. Water molecules, electrolytes, nutrients, and cellular waste diffuse through the interstitium rapidly, although fluid flows very poorly in the tissue gel. ^, Generally, there is only a very slight amount of fluid that is free from these proteoglycan filaments and not trapped in the tissue gel. In normal tissues, the “free” fluid is usually much less than 1%. When tissues start to develop edema, the gel can swell from 30% to 50% to accommodate the increased volume of interstitial free fluid. ^, After this point, the gel cannot accommodate additional fluid, and the amount of free fluid increases. The amount of the free fluid may expand to equal more than half of the interstitial fluid, ^, and the interstitial fluid volume can increase to several hundred percent above normal in seriously edematous tissues. Pitting edema is made up of large amounts of free fluid in the tissues that can be displaced briefly by pressure, leaving a pit that slowly fills with fluid flowing back from the surrounding tissues ( Fig. 63-2 online). Brawny edema results when fluid in the interstitium becomes clotted with fibrinogen, preventing it from moving freely, or when tissue cells rather than the interstitium swells. Brawny edema is firm to the touch.

Patient with pitting edema of the hand. Note the “pit” left by the therapist’s thumb ( arrow ).

Lymphedema refers to the specific type of edema caused by accumulation of protein-rich fluid in the extracellular space of skin and subcutaneous tissue, which results from obstruction of superficial extremity lymphatics. Most edemas are caused by increased capillary filtration, which overwhelms lymph drainage (a condition called “dynamic insufficiency”). Lymphedema represents failure of the lymphatic system to drain lymph from a defined region, usually a limb, a condition called “mechanical insufficiency”. The lymphatic vessels are responsible for resorbing excess fluid as well as cells, proteins, lipids, microorganisms, and debris from tissues. The lymphatic system influences the volume of interstitial fluid and the interstitial fluid pressure as it compensates to balance the rate of protein and fluid leakage from the blood capillaries.

Net Capillary Filtration and Effect on Edema

Net filtration of fluid across the capillary membrane is determined by the balance between the forces that tend to force fluid outward into the interstitial spaces (filtration) and the forces that move fluid inward (resorption). Normally, the filtration pressures slightly exceed the resorption pressures, and the lymphatics balance the system by pulling excess fluid and proteins out of the interstitial spaces and returning them to the blood. ^,

Substances are transferred between the plasma and interstitial fluid primarily by diffusion through the capillary membrane. This diffusion provides continual mixing between the interstitial fluid and the plasma. ^, Lipid-soluble substances such as oxygen and carbon dioxide can diffuse directly through the cell membranes. Lipid-insoluble substances, such as chloride ions, sodium ions, and glucose, as well as water, diffuse through capillary pores or periodic intercellular clefts that connect the interior of the capillary with the exterior. These clefts or slit pores are about 20 times the diameter of a water molecule but slightly less than the diameters of plasma proteins such as an albumin molecule. The net rate of diffusion depends on the concentration difference between the two sides of the capillary membrane.

Minute vesicles are also located on the surface of the endothelial cells. These vesicles transport plasma and extracellular fluid through the capillary wall by imbibing small amounts and then moving slowly through the endothelial cells, releasing the contents to the outer surface. Fluid exchange depends on the properties of the capillary walls and the pressures acting across the capillary membrane. Capillary permeability is selective and is affected by pressures and relative concentrations on either side of the membrane and on the integrity of the membrane itself. Capillary permeability is increased following external injury, operative trauma, and burns.

The primary four pressures that influence net capillary filtration are the capillary (hydrostatic) pressure, the interstitial fluid (hydrostatic) pressure, the plasma colloid osmotic pressure, and the interstitial fluid colloid osmotic pressure. The capillary pressure is the blood pressure in the capillaries that tends to move fluid from the capillary outward through the membrane at any given point. This pressure is greater at the arterial end than at the venous end of the capillary, resulting in fluid filtering out at the arterial end and being reabsorbed at the venous end of the blood capillaries.

The interstitial fluid pressure tends to force fluid inward through the capillary membrane when it is positive but outward when it is negative. This can be subdivided into the pressure of the fluid within the gel (integral pressure) and the free-fluid pressure. There is a slight difference between these pressures caused by the osmotic pressure of the gel. When acute edema develops, the free-fluid portion swells. Normally, in loose tissue, interstitial free-fluid pressure is slightly less than atmospheric pressure and exerts a suction force, drawing fluid out of the capillaries. ^, The direct cause of edema is positive pressure in the interstitial fluid spaces.

Colloid osmotic or oncotic pressures are the pressures created by dissolved proteins, causing osmosis of fluid. The plasma colloid osmotic pressure draws fluid inward through the membrane, whereas the interstitial fluid colloid osmotic pressure draws fluid outward through the membrane. The concentration of protein in the plasma is generally two to three times that of the interstitial fluid. Approximately 75% of the plasma colloid osmotic pressure results from albumin. The plasma colloid osmotic pressure is important in preventing loss of fluid volume from the blood into the interstitial spaces.

The capillary pressure, negative interstitial free-fluid pressure, and interstitial fluid colloid osmotic pressure all tend to force fluid outward, whereas the plasma colloid osmotic pressure causes osmosis of fluid inward. The balance of pressure between these four forces is called the net capillary filtration pressure. There is usually a higher outward force (filtration pressure) at the arterial end of the capillary because of the higher capillary pressure at this end, and a higher inward force, or resorption pressure, is seen at the venous end. About nine-tenths of what is filtered out at the arterial end of the capillary is reabsorbed back in at the venous end, with the remaining fluid going through the lymph vessels. ^, When the net filtration pressure rises excessively, too much fluid is moved outward into the interstitial spaces for the lymphatics to manage, and extracellular edema results.

Abnormal leakage of fluid from the capillaries into the extracellular (interstitial) spaces can be caused by increased capillary pressure (as with arteriolar dilation, venular constriction, increased venous pressure, failure of venous pumps, or lack of active muscular activity), decreased plasma proteins (as with loss of proteins from denuded skin areas in burns and wounds), increased capillary permeability (as results from release of histamine and related substances, from kinins such as bradykinin, or from bacterial infections), or blockage of lymph return. All of these will result in an increased volume of interstitial fluid with subsequent expansion of the extracellular fluid volume. ^,

Widespread edema may be caused by heart failure, loss of proteins in the urine or decreased ability to produce proteins, and excessive kidney retention of salt and water. Trauma can cause venous obstruction or arteriolar dilation and thus result in increased capillary pressure and a higher net filtration pressure. The capillary filtration pressure will also be elevated by local or general heating that causes arterial dilation. Burns not only decrease plasma proteins (as discussed earlier) but also lead to increased capillary permeability and may allow fluid to spill into the tissues as a result of damage to the integrity of the capillary endothelium or enlarged capillary pores. Release of histamine, bradykinin, and substance P is part of an initial inflammatory response and will increase capillary permeability and blood flow, allowing large quantities of fluid and protein, including fibrinogen, to leak into the tissue. This in turn will cause increased interstitial fluid to accumulate.

Intracellular edema can occur in conditions in which the metabolic systems of tissues are depressed or lack adequate nutrition to the cells, and it may occur in inflamed tissue areas as cell membranes increase their permeability to sodium and other ions, with subsequent osmosis of water into the cells. ^,

Edema and Stages of Wound Healing

The nature and treatment of edema differ for the three stages of wound healing. The stages are described here and consist of the inflammatory phase, which usually lasts the first 3 to 5 days; the fibroplastic or proliferative phase, which may last 2 to 6 weeks depending on the nature and degree of injury; and the maturation or remodeling phase, which may last from 6 months to 2 years. ^,

Edema is the first and most obvious reaction of the hand to injury. Most wounds have an excess of fluid content early in the healing process. Release of histamine and bradykinin increases capillary permeability and is part of a normal acute inflammatory reaction that occurs in response to tissue injury from a variety of causes, including trauma, heat, chemicals, and bacteria. Edema in the early phase of wound healing is liquid, soft, and easy to mobilize and reduce. At this stage, the excess fluid or transudate consists mainly of water and dissolved electrolytes. This type of edema should not alarm the therapist as long as the principles of compression, elevation, use of cold, and active motion are observed to minimize pooling of blood in injured areas. ^, However, excessive edema can inhibit wound healing by decreasing arterial, venous, and lymphatic flow.

The primary function of the inflammatory phase is to wall off the injured area, dispose of injury by-products through phagocytosis, and prepare for the fibroplastic repair phase. Chemical mediators initially cause vasoconstriction, followed by vasodilation. Increased cell permeability allows passage of fluid and white blood cells through cell walls to form plasma. Leukocytes and other phagocytic cells accumulate at the site of injury to clean up the debris, and fibrinogen is converted to fibrin. Key to treatment in the inflammatory phase of wound healing is pain control and a balance between gentle active range of motion in an elevated position and rest of the involved structures. Excessive exercise in this phase can delay clot formation and increase inflammation. Heat is also contraindicated in the inflammatory stage, because it will cause further vasodilation and increase membrane permeability, capillary infiltration, and arterial blood flow, which will result in additional edema.

Fibroplasia begins as early as 3 to 5 days after injury and lasts from 2 to 6 weeks, depending on the extent of the wound. ^, During the fibroplastic or repair stage of wound healing, repair of the injured tissue is initiated. Fibroplasia is characterized by increased capillary growth, increased fibroblasts, and new collagen synthesis. Clinically, scar production is heightened, and the wound begins to gain tensile strength.

Edema that persists into the fibroplasia phase is of particular concern to the surgeon and therapist. This edema is likely to become an ongoing problem unless early intervention is applied. The edema fluid becomes more viscous from the elevated protein content, and the excess fluid is called exudate. The protein-rich fluid or exudate associated with edema causes fibrosis and thickening of the tissues, with subsequent shortening of structures such as ligaments and tendons. As fibrin is deposited between tissue layers, organized adhesions result between structures such as tendons and their sheaths, joint capsules, synovial membranes, and fascial layers. ^, Structures will continue to swell, thicken, and shorten, and eventually will be replaced by dense fibrous tissue. ^, The greater the edema and the longer it persists, the more extensive the scarring and the resultant pain, adhesions, disfigurement, and disability. All tissues—vessels, nerves, joints, and intrinsic muscles—become involved in a state of reduced nutrition and inelasticity. The combination of persistent edema with immobilization and poor positioning ultimately results in a stiff hand and must be circumvented.

If the lymphatic system becomes blocked or metabolites are allowed to accumulate in the interstitial spaces, colloid osmotic pressure is increased by the relative increase in concentration of proteins, again resulting in a higher capillary net filtration pressure. The coagulating effect of tissue exudates causes the interstitial and lymphatic fluid to clot, preventing the fluid from being expelled by pressure and resulting in brawny edema in the spaces surrounding the injured cells. Brawny or nonpitting edema can also be caused by swelling of the tissues cells from trauma, disease, or inadequate nutrition.

The final phase of healing is called the maturation or remodeling phase; it is initiated as fibroplasia subsides. In this stage, tissue remodeling and realignment are achieved by placing tensile stresses on collagen fibers. At this point, persistent, stagnant edema may have led to fibrosis with elevated protein content. Chronic edema will result in stretching of the tissue spaces, necessitating long-term use of continuous-compression garments to maintain gains made in edema reduction. If allowed to progress to the maturation phase, edema will become hard, thick, and brawny as the result of connective tissue infiltration and fibrosis. In the worst scenario, edema compromises arterial flow, causing anoxia and impaired metabolic circulation and cellular nutrition, and necrosis of tissues may ensue.

Prevention of Edema

The prevention and treatment of edema are of paramount importance during all phases of management of the injured hand . Measures must be taken before edema is visible, because interstitial fluid volume will increase 30% above normal before detection. According to Brand and Thompson, as much as 50 ml of edematous fluid can accumulate in the hand without being noticed “by a busy therapist dealing with a succession of patients.” More recently, Kelly also comments that “a 30% fluid overload may occur before swelling is visible.”

After surgery or trauma, the extremity should be positioned above the heart as much of the time as possible except following arterial injury/repair. In this case the hand should be slightly below the level of the heart to prevent undue pressure on the repaired artery. If the hand must be immobilized, when possible it should be positioned in the intrinsic-plus position of flexed metacarpophalangeal (MCP) joints (to 70 degrees) and extended interphalangeal (IP) joints to prevent shortening of the MCP joint collateral ligaments and IP volar plates. The wrist should be positioned in neutral or slight extension. The first webspace also must be maintained via thumb abduction and extension. This is particularly true with burn patients, whose wounds will contract as they heal. If the intrinsic-plus position is not feasible, the patient’s hand should be positioned in the best approximation and the orthosis adjusted when feasible. In some cases injured and repaired structures of the hand may require alternative positioning.

Active ROM and tendon gliding exercises are especially important in the fibroplasia stage of healing to prevent the development of adhesions. Orthotic positioning will help to maintain and increase ROM. All joints that are not required to be immobilized should be able to move freely in the cast or orthosis and taken through their full ROM.

Edema in its early stages is reversible. If edema can be controlled early, subsequent scar formation is minimized in comparison with the scar that forms if edema is prolonged and brawny. Postoperative efforts are directed toward minimizing edema and promoting uncomplicated wound healing. Patient education is vital. Beginning with the initial treatment in the hospital or clinic, the patient must be made aware of the factors that can exacerbate or alleviate edema.

Assessment of Edema

As discussed previously, a significant amount of edema may accumulate in a hand without visible detection. For this reason, the ability to establish and measure changes in edema with standardized and reliable procedures is critical for the effective management of edema. Edema will fluctuate daily with changes in diet, activity level, water retention, temperature, and time of day. Therefore, it is important to measure both the involved and uninvolved extremities to obtain a relative comparison between the two, ideally at the same time of day and in the same position. Measures should be taken at the initial evaluation and routinely thereafter with one of the three techniques described below.

The volumeter, figure-of-eight method, and truncated circumferential method of measuring edema are all reliable techniques to measure edema. A high correlation between water displacement and geometric (truncated) formulas has been well documented. Studies are also available that assess volumetry and truncated measures as a tool to look at change in edematous arms over a period of time. Both measures have been found to be accurate, although the methods are not interchangeable. Total volumes for both of these measures are provided in units of cubic centimeters, which can be converted directly to milliliters. The figure-of-eight method provides a final measure in centimeters. A high correlation between the figure-of-eight method and volumetry has been established in three separate studies, as well as in a study by Maihafer et al. that used slightly different landmarks.

The volumeter is a standardized tool that allows the therapist to measure hand edema by measuring the amount of water the limb displaces. ^, Waylett-Rendall and Seibly have shown that the volumeter is reliable within ± 10 mL (1%) if successive measures are performed by the same examiner. A subsequent study done by King assessed the effect of water temperature on hand volume during volumetric measurement. Although there was a significant difference in volumes using extreme temperatures (41°F versus 113°F; 5°C versus 45°C), it was found that the use of “cool” (68°F; 20°C) versus “tepid” (95°F; 35°C) water does not appear to alter hand volume readings sufficiently to be of concern.

The difference in volume of dominant versus nondominant hands was studied by Van Velze et al. for 263 male laborers. They concluded that, on average, the left nondominant hand was 3.43% smaller (16.9 mL) than the right dominant hand for male laborers.

The effect of exercise of the asymptomatic hand on volumetric and sensory status has been studied by McGough and Surwasky. Their results on 20 subjects suggest that exercise influences volumetric measurements. Specifically, females in the study demonstrated a 3.6% increase in volumetrics immediately after exercise, with a decline in volume at 10 minutes after exercise to 2.4%. The males in the study demonstrated a 5.2% volume increase immediately after exercise, with a decline in volume at 10 minutes after exercise to 5%. McGough and Surwasky encourage further statistical investigation on a larger scale of the role of hand dominance, gender, and age on hand volume.

It is important to follow the standardized procedure for the volumeter and to standardize alternative techniques as much as possible. The volumetric kit includes the volumeter, the 800-mL collection beaker, and a 500-mL graduated cylinder ( Fig. 63-3A online). Instructions for the standardized procedure to use with the commercially available volumeters accompany each volumeter purchased from equipment companies. The volumeter should be placed on exactly the same spot on the same level surface for each use. Readings should also be taken on exactly the same spot, since most floors and tables are not completely level. The volumeter should be filled with room temperature water (68°F to 95°F) until it overflows, the overflow discarded, and the beaker placed under the volumeter’s spout. Once all jewelry has been removed from the patient’s hand, the hand should be lowered into the volumeter with the thumb facing the spout and the forearm in pronation until the webspace between the middle and ring fingers firmly straddles the rod ( Fig. 63-3B online). The sides of the hand should not come into contact with the sides of the volumeter. Any variations in this position should be documented. Water will overflow into the beaker. This position must be maintained until water stops spilling from the spout. The water from the beaker can than be poured into the graduated cylinder and measured. This same process is then completed with the other hand. Both hands should always be measured.

A , The volumeter, beaker, and graduated cylinder used to collect and measure the amount of water displaced by an edematous hand. B , The hand placed in pronation inside the volumeter, with the ring and middle fingers straddling the rod and the webspace in contact with the bar.

Truncated surface measures are derived by dividing the arm into cones, determining the volume of each cone, and summing these to determine total arm volume. There are two basic formulas for this, depending on whether measures are taken every 4 cm (or less) or every 10 cm (or less) ( Box 63-1 ). Commercial computer programs are available that automate the computations once the therapist has determined the landmarks and circumferences, or the formulas can be entered into a spreadsheet program, such as Microsoft Excel. Landmarks are recorded as the distance in centimeters measured from the third fingertip or nail bed ( Fig. 63-4A ) with the first landmark being at the MCP, all joints neutral as able, and the arm pronated. Additional landmarks should be taken every 4 to 10 cm. as well as anywhere that the shape of the arm changes significantly, such as the wrist and elbow. The same landmarks should be used on the uninvolved arm and in all subsequent reassessments. It is important to use the same measuring tape and to apply consistent tension. One way to accomplish this is to have the tape straddle the landmark with the larger number always proximal, and with the ball of the tape always hanging just inside and below the arm where it is being measured ( Fig. 63-4B ). The tape should be taut and lay flat against the skin, without being so tight as to wrinkle the skin.

Box 63-1

Formulas for Calculating Limb Volume from Truncated Surface Measures

• 
  

  Formula for every 4 cm: Volume = circumference ² /π for each segment

  
  
• 
  

  Formula for every 10 cm: Volume = h [( C _t × C _t ) + ( C _t × C _b ) + ( C _b × C _b )]12π

  
  
• 
  

  Where h is the height of the cone, C _t is the circumference at the top of the cone, and C _b is the circumference at the bottom of the cone, for each segment.

For example, the first cone could be the area between the MCP joints and wrist. Assuming these are 8 cm apart (height), the MCP joints (top of cone) measure 16 cm, and the wrist (bottom of cone) measures 18 cm, the formula for this segment would be:

<SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='8[(16×16)+(16×18)+(18×18)]12π’>8[(16×16)+(16×18)+(18×18)]12π8[(16×16)+(16×18)+(18×18)]12π
8 [ ( 16 × 16 ) + ( 16 × 18 ) + ( 18 × 18 ) ] 12 π

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

No related posts.

Stay updated, free articles. Join our Telegram channel

Join