Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3825_Библиотеки_им_академика_М_И_Перельмана

Colloidal proteins are in random motion in solution and exert a pressure (π) at any surface that reects them. The asymmetry in pressure results in free water move­ment. A solute dissolving in a solvent causes disruption of order resulting in an increase in entropy (S), a decrease in free energy (G), and a decrease in activity coefcient (γ). The decrease in G results in less random thermal movement and col­lisions which results in relatively more movement of solute-free solvent across membranes until a new equilibrium of G and S is reached. The osmotic pressure of a solution contained in a beaker open to the atmosphere is not a pressure which it actually exerts; it is in fact to be regarded as one of the thermodynamic properties of this solution similar to, say, its freezing point. For example, when a solution is said to have an osmotic pressure of 20 atmospheres, this does not mean that the solution necessarily exerts this pressure, but only that the solution would be in equilibrium with pure solvent through a semi-permeable membrane, if an excess pressure of this amount was applied to the system. In his now classic observation, van’t Hoff noted that osmotic pressure for an ideal solution acted like a gas according to the ideal gas law, PV = nRT. So, the question arises whether alterations can be made to the plasma to restore free entropy and avoid the need for diuretics or albumin infusions? Theoretically, some day we could treat edema of nephritic syndrome by restoring free entropy to the plasma rather than through the use of diuretic, avoiding their well-known complications.

Elevation of an extremity after musculoskeletal injury is a universal treatment aimed at decreasing effusion and edema formation. It is generally accepted that elevation affects edema formation by altering the inuences of gravity. When the position of an extremity is along the gravity, the force of gravity increases hydrostatic pressure in the peripheral blood vessels while also increasing resistance to venous and lym­phatic ow. This results in an increase in uid movement into the tissues, thereby increasing extremity volume. By placing the injured extremity in an elevated posi­tion, the force of gravity assists the return of uids back to the heart via the venous and lymphatic systems and decreases hydrostatic pressure by resisting ow into the elevated peripheral vessels [3, 20].

Marked reductions in the circulating levels of proteins, especially albumin, are another cause of edema relating to intravascular factors. Hypoproteinemia may result from rapid loss of proteins across a compromised glomerular barrier in dis­eased kidneys, impaired hepatic synthesis of plasma proteins in liver disease, severe malnutrition or protein-losing enteropathy (which limits the availability of substrate for protein synthesis), or from infusion of intravenous uids lacking macromole­cules. The ensuing reduction in the colloid osmotic pressure gradient (πc − πt), which favors reabsorption in the non-steady state and opposes the hydrostatic pres­sure gradient that favors ltration, induced by hypoproteinemia can result in a large transcapillary ux of protein-poor uid into the interstitial spaces. Like capillary hypertension, this effect is opposed by elevations in tissue hydrostatic pressure, which increases lymph ow, both of which serve to limit the accumulation of tissue uid. Edema is also seen commonly in overweight and obese individuals. The causes are not always clear and can be multifactorial. Chronic venous insufciency, lymphatic system impairment, as well as defective cardiac, respiratory, or renal functions can be attributed to obesity-related oedema.

Leg swelling is considered to be blocked by leg exercise, because muscle activity pumps lymph and maintains a high interstitial pressure, but the effect depends on the type of exercise. Intermittent heel-up and stepping exercises could not prevent leg swelling. Continuous pedaling reduced leg swelling according to the power

Rapidly ascending to higher altitudes exposes individuals to hypoxic environments. The response of systemic vessels to hypoxia is vasodilation that increased the capil­lary hydrostatic pressure in the peripheral circulation leading to peripheral edema (high-altitude peripheral edema—HAPE). In contrast to this, lower limb edema can also occur at low altitudes (low-altitude peripheral edema—LAPE). Millions of permanent high-altitude residents, born at high altitude occasionally descend to sea level, for work or leisure. This is a change where the organism perfectly adapted to chronic hypoxia is suddenly exposed to a hypertoxic environment and needs to adapt to the new circumstance. One of the most striking symptoms that occur in these people is edema of lower limbs that can become more pronounced at 2weeks of stay. A positive Godet sign develops in these individuals. The Godet sign is elic­ited by pressing for few seconds in front of the tibia bone. This displaces excessive uid found in the interstitial subcutaneous spaces and gives rise to the formation of an evident concave impression. This sign is usually found in patients suffering from cardiac insufciency, renal insufciency, anasarca with low blood protein levels, or inammation. Upon ascent to high altitude, there is central edema and that is why acute mountain sickness, high-altitude pulmonary edema, and high-altitude cerebral edema occur. Conversely, on descending to sea level, peripheral edema occurs. Going higher, oxygen needs to be transported preferably to the life-sustaining organs: brain, heart, and lungs, whereas going lower there is excessive amounts of oxygen and peripheral edema occurs possibly as a defense mechanism to reduce oxygen transport to the life-sustaining organs, as it is sensed toxic.