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7 fluid, electrolyte balance
 

7 fluid, electrolyte balance

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    7 fluid, electrolyte balance 7 fluid, electrolyte balance Document Transcript

    • Fluid, Electrolyte, and Acid-Base Balance Distribution of body fluids: The distribution of body fluids, or total body water (TBW), involves the presence of intracellular (ICF) and extracellular (ECF) fluids. Water is the major constitutuent of body tissues, and the TBW in an individual range from 40% to 60% of total body weight. The ICF refers to the fluid contained within the cells and constitues about 2/3 of the total body fluids in adults. ICF contains solutes such as Oxygen, electrolytes and glucose. ICF provides a medium in which metabolic processes of the cell take place. It contain electrolytes as K, Mg, HPO, SO as primary electrolytes (principal electrolytes). ECF is the fluid outside the cells and account for 1/3 of the total body fluids. ECF is the transport system that carries nutrients to and waste products from the cells. It contains electrolytes such as sodium, chloride, bicarbonate that represents the principal electrolytes in this compartment. The ECF is further broken down into several components: intravascular (contained within the blood vessels). It contains electrolytes and a protein-rich fluid (plasma) and large amount of albumin. Interstitial (surrounding the cell and the location of most ECF, 3/4 of ECF), it contains little or no protein. And transcellular (contained within specialized body cavities such as cerebrospinal, synovial, pleural, and so on). In the newborn about 50% of the body fluid is contained within the ECF, whereas 30% of the toddler’s body fluid is contained within the ECF. The importance of body water to body function is related not only to its abundance but also to the fact that it is the medium in which body solutes are dissolved and all metabolic reactions take place. In addition, it is a transporter of nutrients, waste products and other substance, a lubricant, an insulator and shock absorber, and one’s mean of regulating and maintaining body temperature. Composition of Body Fluids ICF and ECF contain oxygen, dissolved nutrients, excretory products as CO2 and charged particles called ions. Ions come from dissolved salts (eg. NaCl; sodium cholride breaks into Na+ (ion) and Cl- (ion) these charged particles are called electrolytes because they can conduct electricity). The positive charge ion called cation ( eg of cations Na+, K+, Mg+2) and the negative charge ion called anion( eg. Cl-, HCO3-, HPO4-). Electrolytes are measured in milliequivalents per liter of water ( mEq/L). Clinically the mEq system is commonly used but not with all electrolytes, because the laboratory tests are usually performed using the blood plasma (ECF) which reflect what is happening in the ECF, not what happens within the cells. * Other body fluids such as gastric and intestinal secretions also contain electrolytes Mechanisms of fluid movement: Water is retained in the body in a relatively constant amount and, with few exceptions, is freely exchangeable among all body fluid compartments. The proximity of the extravascular compartment to the cells allows for continual change in volume and distribution of fluids, largely determined by solutes (especially sodium) and physical forces. Transport mechanisms are the basis for all activity within the cells, and since they have limited ability to store materials, movement in and out of cells must be rapid.
    • Internal control mechanisms (such as thirst, antidiuretic hormone (ADH), and aldosterone(which enhances sodium reabsorption)) are responsible for distribution and maintenance of fluid balance. 1- Diffusion: molecules move from a solution of higher concentration to a solution of lower concentration. This motion affected by temperature, size of molecules and the concentration of the solution. 2- Hydrostatic pressure/ Filtration: movement of fluid and solutes from an area of higher hydrostatic pressure to one of lower pressure. The pressure created by the weight of fluids (increased pressure in the arteries forces fluids through the capillary walls into the interstitial spaces). 3- Active Transport: movement of substance across the cell membrane from a less concentration solution to higher concentrated by active transport (a carrier). 4- Osmotic pressure: water movement across the cell membranes from low solute concentration (low osmotic pressure) to higher concentration of solute (high osmotic pressure). Osmolality is the concentration of solutes in the body fluids, usually reported as milliosmols per kilogram (mOsm/kg). Sodium is the greatest determinant of serum osmolality. Example in hypernatremia where the serum Na results in water movement from ICS to ECS, and the hyponatremia is the opposite. Tonicity refers to the osmolality of solution: 1- Isotonic solution has the same osmolality as body fluids ( eg Normal saline 0.9%). 2- Hypertonic solution has a higher osmolality than body fluids ( eg Normal saline 3%). 3- Hypotonic solution has a lower osmolality than body fluids ( eg Normal saline 0.45%) IMBALANCES It occurs when body fluids are lost in excess of fluid gain. The great majority of disturbances in hydration and electrolytes balance occur secondary to vomiting and diarrhea 1-Fluid Imbalances Causes of dehydration are: I) Lack of oral intake. II) GI ; vomiting, diarrhea, malabsorption III) Burns IV) Fever V) Diabetes mellitus VI) Tachypnea as in bronchiolitis Types of dehydration I. Isotonic /Isonatremic dehydration: occurs when fluids and electrolytes losses are in same proportion as they exist in the body. Fluid osmolarity is not affected. And there is deficit of TBW. This can be seen in 70% of children with diarrhea (plasma Na+ remains normal 130-150 mEq/L).
    • II. Hypertonic dehydration/hypernatremia: When the water intake decreases and Na increases. Proportionally greater loss of water than Na. It can occur when insensible loss of water from skin and respiration tract is high. In this case the Na increase the osmotic pressure in the blood vessels that shifts the fluids from the IC to the ECS (plasma Na+ > 150 mEq/L) . 10-20% of children with dehydration have this type. The causes can be i. Administration of hypertonic IV fluids ii. Increase of Na intake iii. Failure of ADH iv. Increase of insensible loss of water as in burn, fever, respiratory infections. The defense mechanisms for this case are: a. stimulation of thirst b. stimulation of ADH. III. Hypotonic/ Hyponatremia dehydration: This type refer to decrease in Na and retention of water. It can be caused by excessive plain water intake and defect in renal water excretion and failure in SIADH ( syndrome of inappropriate antidiuretic hormone).. it can be seen in cystic fibrosis due to excessive lose of Na via sweat. The water shifts from ECS to ICS causing circulatory collapse. This type is occur in 10% of children with dehydration. Infants prone for water loss due to greater volume of extracellular fluid, which can be lost by illness or environmental conditions. The infants and children are more vulnerable to fluid and electrolyte imbalances due to I) greater surface area to body mass (more evaporation) II) higher metabolic rate III) Immature kidneys function. Edema ( increase the interstitial fluid volume) excess interstitial fluid caused by I) Fluid Volume Excess that increase the capillary pressures, pushing fluid into the interstitial tissues by filtration. Which can be seen in heart failure and renal failure. II) Low levels of plasma proteins which will reduce the oncotic pressure so that fluid is not drawn into the capillaries from interstitial tissues. As in nephritic syndrome and malnutrition. III) allergic reaction capillaries become more permeable allowing the fluid to escape into interstitial tissues. The albumin can move easily from the capillaries membrane pulling with it the fluid. This can be seen in burns, truma and allergic reactions IV) increase in interstitial oncotic pressure: the protein enter the interstitial fluid more than they leave causing increase in interstitial oncotic pressure that in turn pull the fluid into tissue as in tumors and hypothyroidism. V) Obstructed lymph flow impairs the movement of fluid from interstitial tissues back into the vascular compartment.
    • Homeostasis: a balance of fluids, electrolytes and acids and bases in the body; that reflects a good health. Acid-Base Balance an acid is the substance releases hydrogen ions (H) Base (alkalis) is the substance that can accept hydrogen ions. pH is the relative acidity or alkalinity of a solution: higher hydrogen ions more acidic which is low pH. And less hydrogen ions more alkaline which is high pH. - Body fluids are slightly alkaline - normal pH of arterial blood is 7.35-7.45 - several body systems including buffers, the respiratory system, and the renal system are maintaining the narrow pH - a drop in pH is called acidosis - a rises in pH is called alkalosis Regulating acid-base balance 1- Buffers: major buffers system in ECF is the bicarbonate ( HCO-3) and carbonic acid ( H2CO3). Besides bicarbonate and carbonic acid buffers, plasma proteins, hemoglobin and phosphates also function as buffers in body fluids. 2- Respiratory Regulation: regulating acid-base balance by eliminating or retaining carbon dioxide (CO2) by altering the rate and depth of respirations. - if the blood level of carbonic acid increase the rate and depth of respirations increase to excrete carbon dioxide to fall the level of carbonic acid - if the blood level of bicarbonate increase the rate and depth of respirations decrease to retained the carbon dioxide and rise the level of carbonic acid. - PCO2 refer to pressure of carbon dioxide in venous blood -PaCO2 refer to pressure of carbon dioxide in arterial blood. Normal PaCO2 is 38-40 mmHg 3- Renal Regulation: kidneys maintain acid-base balance by excreting or conserving bicarbonate and hydrogen ions - if acidity increased the kidneys reabsorb and regenerate bicarbonate and excrete H - in the case of alkalosis excess bicarbonate is excreted and H ion is retained - normal serum bicarbonate level is 22-26 mEq/L Factors Affecting Body Fluid, Electrolytes and Acid-Base Balance 1- age: infant has immature kidneys, rapid respiration and more body surface area than adult which make the infant losses the fluid rapidly. In elderly people the thirst response often is blunted and kidney become less able to conserve water that will affect the fluid balance. 2- Gender and Body Size: people with a higher percentage of body fat have less fluid. 3- Environmental Temperature: both salt and water are lost through sweating in hot climate 4- Lifestyle: diet, exercise, stress and alcohol consumption all affect the fluid and electrolyte balance
    • Disturbances in Fluid Volume, Electrolyte, and Acid-Base Balances Many factors affect the fluid and electrolyte balance such as illness, surgery, medications, burns, vomiting, diarrhea and nasogastric suction. The majority of childhood illnesses that caused imbalances they occur secondary to vomiting and diarrhea. The imbalances can be: I) total body deficit or excess of fluid and electrolyte and the osmolality of the body is not affected. II) when relationship between fluid and electrolyte has been altered and the osmolality is altered. III) or both a and b. 2- Electrolyte Imbalances 1- Potassium ( 95% of K of body in IC fluid) Hypokalemia: K < 3.5 mEq/L caused by vomiting, diarrhea and gastric suction diuretics, alkalosis. The K shifts from EC to IC space and also insulin promotes K to enter skeletal muscles and hepatic cells. CM are; cardiac arrhythemia, muscle weakness, shallow breathing, polyuria Hyperkalemia : K > 5.0 : most commonly occur in children as a result of too rapid administration of IV potassium chloride, and caused by renal failure, shift of K from IC to EC by tissue damage, and metabolic acidosis. CM are malaise, muscle weakness, oliguria to anuria, abnormal cardiac function and diarrhea 2- Calcium ( required for activation of numerous enzymes, cardiac and neural and muscular functions hypocalcemia : Ca < 4.0 mEq/L, caused by hypoparathyroidism, Vit D deficiency,burns, infections diarrhea, renal failure. CM tetany, when giving cow’s milk early in infancy so that the milk is high conc of phosphate which drops the Ca level, laryngospasm, numbness and seizures. hypercalcemia : Ca > 5.5 mEq/L, caused by increase administration of Vit Aand D, prolonged immobilization and hyperparathyroidism. CM; nausea, vomiting, constipation and flank pain 3-Acid-Base Imbalances The abnormalities in PCO2 increase or decrease is called respiratory alkalosis or acidosis because PCO2 regulated by respiration i. Increase in PCO2 —————- respiratory acidosis ii. Decrease in PCO2—————-respiratory alkalosis. The abnormalities of plasma bicarbonate concentration refer to metabolic process I) Increase in HCO3———————metabolic alkalosis II) Decrease in HCO3——————- metabolic acidosis
    • 1- Respiratory Acidosis Hypoventilation and CO2 retention cause carbonic acid level to increase which will drop the pH level below 7.35. This can be casued by I) asthma, II) central nervous system depression III) anesthesia, alcohol , IV) aspiration of foreign body. V) Pneumonia When respiratory acidosis occur the kidneys will retain bicarbonate to restore the normal ratio of bicarbonate:carbonic acid (20:1) in order to restore the normal pH. S&S I) headache II) blurred vision III) restlessness IV) anxiety V) tremors 2- Respiratory Alkalosis Hyperventilation the CO2 is exhaled causing the carbonic acid to fall and rise the pH above 7.45. This can be caused by I) Tetany II) fever, III) anxiety, IV) respiratory infection. With respiratory alkalosis the kidneys will excrete bicarbonate to return normal pH. S&S I) increase irritability of central and peripheral nervous system. II) Light headache III) Altered consciouness IV) Paresthesia of extremities V) arrhythmias 3-Metabolic Acidosis (Diarrhoea) when bicarbonate is low in relation to the carbonic acid in the body , causing the pH to fall. This can be caused by I) renal failure II) inability of the kidneys to excrete H ions. III) Increase of anaerobic metabolism IV) Decrease in blood volume causing the kidney to function less effectively Metabolic acidosis will stimulate the respiratory center causing the rate and depth of respiration to increase ( in which the CO2 is eliminated and the carbonic acid is fall). S&S I) Increase depth of respiration II) Arrhythmia
    • III) Lethargy—-coma IV) Impaired growth (rickets) V) Wt loss VI) Anorexia VII) Muscle weakness and listlessness. 4- Metabolic Alkalosis (vomiting) When the amount of bicarbonate in the body exceeds the normal 20:1 ratio. This can be caused with ingestion of antacid, vomiting which causing losing in H. Causes are I) Muscles hypertonic II) vomiting III) nasogastric suctioning IV) diuretics; decrease the ECF leaving HCO3 uncharged V) Hypokalemia The metabolic alkalosis will stimulate the respiratory center to slow and shallow the breathing (causing to retain CO2 which will increase the carbonic acid level). VI) HCO3 retention may result from, massive blood transfusion, excessive administration of sodium bicarbonate S&S i. Weakness ii. Muscle cramp iii. Dizziness glucose facilitates the absorption of sodium (and hence water) on a 1:1 molar basis in the small intestine; �sodium and potassium are needed to replace the body losses of these essential ions during diarrhoea (and vomiting); �citrate corrects the acidosis that occurs as a result of diarrhoea and dehydration. �