الفهرس | Only 14 pages are availabe for public view |
Abstract The relative constancy of the body fluids is remarkable because there is continuous exchange of fluid and solutes with the external environment, as well as within the different body compartments. Intake of water is highly variable among different people and even within the same person on different days, depending on climate, habits, and level of physical activity. The kidneys are faced with the task of adjusting the excretion rate of water and electrolytes to match precisely the intake of these substances, as well as compensating for excessive losses of fluids and electrolytes that occur in certain disease states. Blood contains both extracellular fluid (the fluid in plasma) and intracellular fluid (the fluid in the red blood cells) . The distribution of fluid between intracellular and extracellular compartments, in contrast, is determined mainly by the osmotic effect of the smaller solutes especially sodium, chloride, and other electrolytes acting across the cell membrane .The osmolal concentration of a solution is called osmolality when the concentration is expressed as osmoles per kilogram of water, it is called osmolarity when it is expressed as osmoles per liter of solution . If a cell is placed into a hypotonic solution, water will diffuse into the cell, causing it to swell; water will continue to diffuse into the cell, diluting the intracellular fluid while also concentrating the extracellular fluid until both solutions have about the same osmolarity. Solutions of sodium chloride with a concentration of less than 0.9 percent are hypotonic and cause cells to swell. If a cell is placed in a hypertonic solution, water will flow out of the cell into the extracellular fluid, concentrating the intracellular fluid and diluting the extracellular fluid. In this case, the cell will shrink until the two concentrations become equal. Sodium chloride solutions of greater than 0.9 percent are hypertonic . A measurement that is readily available to the clinician for evaluating a patient’s fluid status is the plasma sodium concentration. When plasma sodium concentration is reduced more than a few milliequivalents below normal (135 - 145 mEq/L), a person is said to have hyponatremia.When plasmasodium concentration is elevated above normal, a person is said to have hypernatremia . Hyponatremia is the most common electrolyte disorder encountered in clinical practice and may occur in up to 15% to 25% of hospitalized patients . Some IV fluids are designed to stay in the intravascular space to increase the intravascular volume, or volume of circulating blood. Other IV fluids are specifically designed so the fluid leaves the intravascular space and enters the interstitial and intracellular spaces . Echocardiography has the advantage of being noninvasive and it can provide a quick ‗snapshot‘ of the fluid status of the patient . Absence of symptoms does not exclude mild to moderate hypovolemia, especially if the volume loss has occurred gradually . The choice of oral or intravenous replacement fluids (or both) for hypovolemic states is dictated by the integrity of gastrointestinal absorptive function, by the magnitude of the volume deficit, and by the disturbances in other electrolyte and acid-base parameters .In addition to replacement fluids, maintenance fluids must be provided to counteract ongoing losses. Such ongoing losses may be a continuation of the underlying disease state (e.g., continued vomiting, diarrhea, polyuric states, or severe burns). The volume, rate of administration, and composition of these replacement fluids are best determined by actual measurements of the corresponding ongoing fluid losses, with appropriate adjustments for the patient’s clinical assessment parameters . The most important step in hypervolemia management is ameliorating renal sodium retention by recognition and treatment of the underlying disease. Three treatment modalities are available to reduce ECF volume directly by inducing negative sodium balance: dietary sodium restriction, diuretics, and extracorporeal fluid removal by ultrafiltration . |