|
Course Sample:
Introduction Fluid and electrolyte balance can be altered by pathophysiology. This module will discuss assessing fluid balance, assessing acid-base balance, and other commonly measured electrolytes. FLUID BALANCE Since sodium is the main electrolyte associated with fluid balance, we shall begin our discussion of fluid and electrolyte balance with sodium. FUNCTIONS OF SODIUM The functions of sodium in the body are: - Regulates water and electrolyte balance including: sodium, potassium, calcium, magnesium, hydrogen, chloride, bicarbonate, and phosphate balance.
- Maintains acid-base balance
- Excretes metabolic wastes
- Produces rennin to regulate vascular volume
- Regulates prostaglandins, which in turn regulate the antidiuretic hormone and aldosterone.
Sodium levels are controlled by two hormones - the antidiuretic hormone and aldosterone. The normal serum sodium level is 135 to 147 mEq/dL. Sodium levels over 147 mEq/dL are considered hypernatremia and sodium levels less than 135 mEq/dL are considered hyponatremia (Porth, 1994). SODIUM AND WATER BALANCE Sodium affects water balance by causing water to go into the cell if the sodium concentration of the cell is too high, thereby diluting the sodium content of the cell. If the sodium concentration of the cell is too low, water leaves the cell taking sodium along with it, and decreasing the sodium concentration in the cell. Therefore, serum sodium is the primary electrolyte in maintaining fluid balance. Sodium and water have an intricate relationship resulting in the principle of "salt follows water." Serum sodium is the primary electrolyte in maintaining fluid balance. Most of the sodium found in the body is combined with chloride or bicarbonate in the body. The sodium content of the body primarily controls 90 percent of the osmolality of the extracellular fluid. A quick method to determine serum osmolality is simply to double the serum sodium level. Usually, water and sodium increase at the same time, so an increase in sodium in the body is accompanied by an increase in water. (Porth, 1994; Corbett, 2000). SERUM SODIUM Serum sodium is the principle cation of the extracellular fluid, and the primary electrolyte in maintaining fluid balance. Sodium balance in the body is maintained with an intake of 500 mg/day. The average American eats 6-12 grams of sodium daily. Daily replacement of sodium is necessary, as sodium is lost on a daily basis through urine, sweat, and feces. Factors that lead to an elevated sodium level are an excess sodium intake by parenteral sources or by mouth. An extracellular fluid loss results in hypernatremia. Examples of these losses are diuretic therapy, hypertonic tube feedings, and vomiting. The withholding of water also causes the serum sodium to rise, as in fluid restrictions, as does the inability to take oral fluids, or failure to recognize thirst. Clinically, the symptoms of hypernatremia are caused by the increased serum osmolality. This results in water being withdrawn from body cells. When there is an elevated serum sodium level, hypovolemia (low fluid volume), is expected. For the adult, each three mEq rise in serum sodium above normal, above the reference range (Corbett, 2000), represents a fluid loss of one liter and represents a weight loss of one kilogram (2.2 lbs.). When the serum sodium rises above normal, this indicates a serious water deficit. In the early stages of a fluid deficit, the serum sodium level is not elevated. The symptoms of this intracellular dehydration may include: dry skin and mucus membranes, dry flushed skin, rough and dry tongue, central nervous system changes, an increased body temperature, and signs of a decreased vascular volume with an increased heart rate, and weak pulse. Elevated sodium levels are serious; so are decreased sodium levels. HYPOVOLEMIA The fluid and electrolyte balance of the body is in a delicate arrangement. (Loeb, 1994). During illness, whether acute or chronic, this delicate homeostasis may shift, causing life-threatening problems. Hypovolemia, or a fluid volume deficit, occurs when there are serious losses from the extracellular fluid compartment. This can occur from an inadequate fluid intake, or from excessive fluid losses, or both. Hypovolemia: a fluid volume deficit A fluid volume deficit usually results from excessive gastrointestinal losses such as vomiting, diarrhea, hypertonic tube feedings, surgical drainage, suctioning of the gastrointestinal tract or an ileostomy. Diabetic ketoacidosis or hypertonic hyperglycemic nonketotic coma -- as well as diabetes insipidus, Addison's disease, or diuretic therapy -- can result in hypovolemia. A fever can significantly increase fluid needs: ten percent increase for every one degree Fahrenheit (F.) of temperature rise. A fluid volume deficit may result from an extracellular fluid shift from the general circulation into interstitial or other body spaces, from such diseases as congestive heart failure, liver or renal disease. Crushing injuries, intestinal obstruction, peritonitis and burns can also cause such fluid shifts. A fever can significantly increase fluid needs. TYPES OF DEHYDRATION There are three types of dehydration: isotonic, hypertonic, and hypotonic dehydration (Weinberg, 1995). No exact definition of dehydration exists. A useful definition of dehydration is the rapid loss of more than three percent of body weight. Isotonic dehydration results from a balanced loss of water and sodium. Vomiting and diarrhea occur because of the large amounts of water and electrolytes circulating in the gastrointestinal tract daily. Diuretic use can cause isotonic dehydration. The sodium level remains in the normal range. Hypertonic dehydration results from water losses greater than sodium losses. Sodium levels are greater than 147 mg/dl and hyperosmolarity >300 mmol/kg. Fever results in loss of water through both the lungs and the skin, with limited ability to take in fluids through the gastrointestinal tract. This is the most common cause of hypertonic dehydration. Declining mental status, decreased thirst, weakness, infection and hypertonic saline solution can cause hypertonic dehydration. Hypotonic dehydration occurs when sodium loss exceeds water loss, and the serum sodium is less than 135 mmol/kg with a low serum osmol/kg. This type of dehydration occurs primarily with overuse of diuretics, causing excess loss of sodium due mostly to extracellular fluid depletion. Vomiting, diarrhea, osmotic diuresis and diseases resulting in third spacing -- such as cirrhosis -- can cause this form of dehydration. Volume depletion orthostatic changes, dry mouth and mucous membranes, decreased skin turgor, weakness, anorexia and confusion result. Three types of dehydration: Isotonic, hypertonic, and hypotonic dehydration. SODIUM: Adult: 135-147 mEq/L; Elderly: 138-147 mEq/L;
Critical levels: less than 110 mEq/L or more than 160 mEq/L LAB VALUES ↑ SODIUM | Individual Factors | Disease | Drugs | | | Inadequate fluid intake Neglected or/the Unconscious Loss of fluid due to hypertonic fluid ↑ Protein ↑electrolytes ¯ water ↑Perspiration ↑BUN Fever Labored respiration Stored blood Fistulas Hemorrhage Nasogastric drainage Vomiting Diarrhea Crushing injuries Low albumin levels | Uncontrolled diabetes Diabetes insipidus Advanced renal disease Azotemia Pulmonary |
|
