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Fluid and electrolyte balance
This document discusses fluid and electrolyte balance in the human body. It begins by explaining that about 60% of the adult human body is fluid, with most fluid being intracellular fluid inside cells and about a third being extracellular fluid outside cells. Key points covered include the roles of the kidneys in regulating fluid volume and composition, the various fluid compartments in the body, electrolytes such as sodium and potassium, and the mechanisms of fluid and electrolyte movement including diffusion, osmosis, active transport, and filtration. Daily fluid intake and losses are addressed, as well as hormonal regulation of fluid balance by factors like ADH and aldosterone. Causes and signs of dehydration and fluid volume deficit are also summarized.
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Fluid and electrolyte balance
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- 3. CONTENTS INTRODUCTION BODYFLUIDS & ELECTROLYTES METHODS OF FLUID AND ELECTROLYTE MOVEMENTS DAILY INTAKE AND LOSS OF WATER REGULATION OF FLUID EXCHANGE AND OSMOTIC EQUILIBRIUM APPLIED ASPECTS CONCLUSION REFERENCE 3
- 4. INTRODUCTION About 60per cent of the adult human body is fluid, mainly a water solution of ions and other substances. Most of this fluid is inside the cells and is called intracellular fluid, about one third is in the spaces outside the cells and is called extracellular fluid. 4
- 5. The kidneysare essential for regulating the volume and composition of bodily fluids. 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 compartments of the body. 5
- 6. A mostcritical concept to understand is how water and sodium regulation are integrated to defend the body against all possible disturbances in the volume and osmolarity of bodily fluids. In addition to regulating total volume, the osmolarity (the amount of solute per unit volume) of bodily fluids is also tightly regulated. 6
- 7. BODY FLUIDS &ELECTROLYTES BODY FLUIDS - 60% BODY WEIGHT WATER IS LARGEST SINGLE COMPONENT Variations based on age, gender & amt. of body fat 45-50 % body weight in elderly 80% neonate is water
- 8. Major Compartments for Fluids INTRACELLULAR FLUID (ICF) Inside cell Most of body fluid here - 40% weight Decreased in elderly EXTRACELLULAR FLUID (ECF) Outside cell Intravascular fluid - within blood vessels (5%) Interstitial fluid - between cells & blood vessels (15%) Transcellular fluid - cerebrospinal, pericardial , synovial 8
- 9. Distribution of solutesin body Electrolytes Non-Electrolytes - glucose, urea, uric acid - proteins ( albumin ) 9
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- 11. ELECTROLYTES Substance whendissolved in solution separates into ions & is able to carry an electrical current CATION - positively charged electrolyte ANION - negatively charged electrolyte Cations must be equal to anions for homeostatsis to exist in each fluid compartment 11
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- 14. SODIUM (NA+) DominantExtracellular Electrolyte Chief Base Of Blood Serum Level 135-145 m eq/L Main extracellular fluid (ECF) cation Helps govern normal ECF osmolality Helps maintain acid-base balance Activates nerve & muscle cells Influences water distribution (with chloride)
- 15. POTASSIUM (K+) DominantIntracellular Electrolyte Primary Buffer In Cell Serum Level 3.5-5.5 Meq/L Dominant cation in intracellular fluid (ICF) Regulates cell excitability Permeates cell membranes, thereby affecting cell’s electrical status Helps control ICF osmolality & ICF osmotic pressure
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- 17. METHODS OF FLUID& ELECTROLYTE MOVEMENT Diffusion Osmosis Active Transport Filtration
- 18. DIFFUSION Process bywhich a solute in solution moves Involves a gas or substance Molecules move from an area of higher concentration to an area of lower concentration Evenly distributes the solute in the solution Passive transport & requires no energy 18
- 19. OSMOSIS Osmosis isthe net diffusion of water across a selectively permeable membrane from a region of high water concentration to one that has a lower water concentration. 19
- 20. OSMOTIC PRESSURE Pullthat draws solvent through the membrane to the more concentrated side (or side with solute ) Amt. determined by relative number of particles of solute on side of greater concentration Proportional to number of particles per unit volume solvent 20
- 21. COLLOID OSMOTIC PRESSURE ORONCOTIC PRESSURE Special kind of osmotic pressure Created by substances with a high molecular weight (like albumin)
- 22. OSMOLALITY Measure ofsolution’s ability to create osmotic pressure & thus affect movement of water Number of osmotically active particles per kilogram of water Plasma osmolality is 280-300 mOsm/ kg ECF osmolality is determined by sodium MEASURE used in clinical practice to evaluate serum & urine 22
- 23. PLASMA PROTEINS PrimarilyAlbumin Affect serum osmolarity Are main negatively charged intravascular fluid anions Balance the positive charge of sodium in osmolarity Create colloid osmotic pressure which pulls in & holds water in the vascular bed as well as pulling water from interstitial space into vascular bed - “water magnet” 23
- 24. ACTIVE TRANSPORT SYSTEM Movesmolecules or ions uphill against concentration & osmotic pressure Hydrolysis of adenosine triphosphate (ATP) provides energy needed Requires specific “carrier” molecule as well as specific enzyme (ATPase) Sodium, potassium, calcium, magnesium, plus some sugars, & amino acids use it 24
- 25. FILTRATION Movement offluid through a selectively permeable membrane from an area of higher hydrostatic pressure to an area of lower hydrostatic pressure Arterial end of capillary has hydrostatic pressure > than osmotic pressure so fluid & diffusible solutes move out of capillary 25
- 26. HYPOTONIC & HYPERTONIC Solution of lower osmotic pressure Less salt or more water than isotonic If infused into blood, RBCs draw water into cells ( can swell & burst ) Solutions move into cells causing them to enlarge Solution of higher osmotic pressure 3% sodium chloride is example If infused into blood, water moves out of cells & into solution (cells wrinkle or shrivel) Solutions pull fluid from cells 26
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- 28. Daily Intake ofWater Water is added to the body by two major sources: (1) it is ingested in the form of liquids or water in the food, which together normally add about 2100 ml/day to the body fluids, and (2) it is synthesized in the body as a result of oxidation of carbohydrates, adding about 200 ml/day. This provides a total water intake of about 2300 ml/day 28
- 29. Daily Loss ofBody Water Insensible Water Loss- Some of the water losses cannot be precisely regulated. For example, there is a continuous loss of water by evaporation from the respiratory tract and diffusion through the skin, which together account for about 700 ml/day of water loss under normal conditions. This is termed insensible water loss because we are not consciously aware of it, even though it occurs continually in all living humans. 29
- 30. The insensiblewater loss through the skin occurs independently of sweating and is present even in people who are born without sweat glands; the average water loss by diffusion through the skin is about 300 to 400 ml/day. This loss is minimized by the cholesterol- filled cornified layer of the skin, which provides a barrier against excessive loss by diffusion. 30
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- 33. Regulation of FluidExchange and Osmotic Equilibrium Between Intracellular and Extracellular Fluid A frequent problem in treating seriously ill patients is maintaining adequate fluids in one or both of the intracellular and extracellular compartments. 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. 33
- 34. For maintenanceof homeostasis, excretion of water and electrolytes must precisely match intake. If intake exceeds excretion, the amount of that substance in the body will increase. If intake is less than excretion, the amount of that substance in the body will decrease. Intake of water and many electrolytes is governed mainly by a person’s eating and drinking habits, requiring the kidneys to adjust their excretion rates to match the intake of various substances. 34
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- 36. REGULATION OF WATER INTAKEAND OUTPUT The hypothalamus in the brain contains osmoreceptors that detect changes in the osmolarity of bodyfluids. Osmolarity is the concentration of dissolved materials present in a fluid. The normal plasma osmolality is 275 to 290 m.mol/kg 36
- 37. The primarystimulus for water ingestion is thirst, mediated either by an increase in effective osmolality or a decrease in ECF volume or blood pressure. Osmoreceptors, located in the anterolateral hypothalamus, are stimulated by a rise in tonicity 37
- 38. The hypothalamusis also involved in water balance because of its production of antidiuretic hormone (ADH), which is stored in the posterior pituitary gland. In a state of dehydration, the hypothalamus stimulates the release of ADH from the posterior pituitary. 38
- 39. Antidiuretic hormonethen increases the reabsorption of water by the kidney tubules. Water is returned to the blood to preserve blood volume, and urinary output decreases. 39
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- 42. THIRST Conscious desirefor water It is the major factor that determines fluid intake The osmo receptors in hypothalamus that are stimulated by increase in osmotic pressure of body fluids initiate thirst. 42
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- 44. ADH (Antidiuretic Hormone) There is a powerful feedback system for regulating plasma osmolarity and sodium concentration that operates by altering renal excretion of water independently of the rate of solute excretion. A primary effector of this feedback is antidiuretic hormone (ADH), also called vasopressin. 44
- 45. Made inhypothalamus; water conservation hormone Stored in posterior pituitary gland Acts on renal collecting tubule to regulate reabsorption or elimination of water If blood volume decreases, then ADH is released & water is reabsorbed by kidney. Urine output will be lower but concentration will be increased. 45
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- 48. ALDOSTERONE Produced byadrenal cortex Released as part of RAA mechanism Acts on renal distal convoluted tubule Regulates water reabsorption by increasing sodium uptake from the tubular fluid into the blood but potassium is excreted Responsible for reabsorption of sodium & water into the vascular compartment 48
- 49. RENIN Released bykidneys in response to decreased blood volume Causes angiotensinogen (plasma protein) to split & produce angiotensin I Lungs convert angiotensin I to angiotensin II Angiotensin II stimulates adrenal gland to release aldosterone & causes an increase in peripheral vasoconstriction 49
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- 52. Dehydration Disturbance ofwater balance Output greater than input Decrease in body water below normal May be the result of – pure water depletion pure salt depletion mixed 52 APPLIED ASPECTS
- 53. 1-Pure water Depletion Occurs when water intake is not there and there is no loss of salts in the secretions. CAUSES --- very weak or ill patient - comatosed patient - mentally upset - dysphagia - total inavailability of water 53
- 54. Pathophysiology and Effects ECFbecomes hypertonic Water flows from ICC to ECC and causes cellular dehydration. There is Thirst, Oliguria due to the release of ADH. BP may drop in late stage. 54
- 55. Biochemical findings ECFis hypertonic Blood urea may be slightly raised Plasma volume decreases in late stage Urine volume is scanty with raised specific gravity Death occurs when water loss amounts to 15% of body weight. 55
- 56. 2- Pure SaltDepletion Due to the loss of fluids of high Na or Cl content and replacement done by salt deficient fluids. CAUSES : excessive sweating, loss of GI fluids, urinary loss of Na, diuretics. 56
- 57. Pathophysiology and effects ECFbecomes hypotonic Decreased release of ADH and thus diuresis Results in decrease in plasma and interstitial fluid volume. Hypotonicity of ECF results in water entry into the cells and further fall in ECF volume. 57
- 58. NO thirst Marked weakness and fainting Loss of interstitial fluid causes sunken eyes and loss of skin elasticity Decreased cardiac output and fall in BP. Decreased glomerular filtration results in raised urea level. 58
- 59. Biochemical findings ECFhypotonic Low plasma volume Decreased plasma sodium Raised blood urea 59
- 60. FLUID VOLUME DEFICIT Hypovolemia or FVD is result of water & electrolyte loss Compensatory mechanisms include: Increased sympathetic nervous system stimulation with an increase in heart rate & cardiac contraction; thirst; plus release of ADH & aldosterone Severe case may result in hypovolemic shock or prolonged case may cause renal failure 60
- 61. CAUSES OF FVD Abnormal GI fluid loss such as N&V or drainage of GI tract Abnormal fluid loss from skin such as high temperature or burns Increased water vapor from the lungs such as hyperpnea Conditions that increase renal excretion of fluids such as diuretics & hypersomolar tube feedings Decrease in fluid intake Third-space shift such as ascites 61
- 62. SIGNS & SYMPTOMSOF FVD Dry mucous membranes Weight loss -mild at 2%,moderate at 5%, & severe deficit at 8% Orthostatic hypotension & increase in pulse rate Body temperature usually subnormal Flat neck veins & decrease in CVP Decreased urinary output & altered sensorium 62
- 63. MONITORING OF FVD Monitoring on a regular schedule depending on the patient If urine output is below 30 mL / hr. notify the physician May check urine specific gravity in 8hrs. Weigh patient daily at the same time & recognize that a change of 2.2 lbs. represents a loss of 1000 mL 63
- 64. FLUID VOLUME EXCESS Hypervolemia or FVE is result of expansion of fluid compartment from an increase in total sodium content Kidney receives signal to save sodium & water to compensate for cirrhosis, CHF, renal failure, excessive Na-containing fluid Labs may show decreased.:hematocrit, serum Na, serum osmolality, urine sp. gravity 64
- 65. SIGNS & SYMPTOMSOF FVE Orthopnea Edema & weight gain Distended neck veins & tachycardia Increased blood pressure Crackles & wheezes Maybe ascites & pleural effusion Increase in CVP 65
- 66. MONITORING OF FVE monitor for physical signs of hypervolemia Check for edema & weigh patient daily Restrict sodium intake as prescribed Limit intake of fluids Watch for signs of potassium imbalance Monitor for signs of pulmonary edema Place patient in semi-Fowler’s position 66
- 67. Clinical Abnormalities of FluidVolume Regulation: Hyponatremia and Hypernatremia The primary 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 (about 142 mEq/L), a person is said to have hyponatremia. When plasma sodium concentration is elevated above normal, a person is said to have hypernatremia. 67
- 68. Causes of Hyponatremia: ExcessWater or Loss of Sodium Decreased plasma sodium concentration can result from loss of sodium chloride from the extracellular fluid or addition of excess water to the extracellular fluid. A primary loss of sodium chloride usually results in hypo-osmotic dehydration and is associated with decreased extracellular fluid volume. Conditions that can cause hyponatremia owing to loss of sodium chloride include diarrhea and vomiting. 68
- 69. Overuse ofdiuretics that inhibit the ability of the kidneys to conserve sodium and certain types of sodium-wasting kidney diseases can also cause modest degrees of hyponatremia. Finally, Addison’s disease, which results from decreased secretion of the hormone aldosterone, impairs the ability of the kidneys to reabsorb sodium and can cause a modest degree of hyponatremia. 69
- 70. Hyponatremia canalso be associated with excess water retention, which dilutes the sodium in the extracellular fluid, a condition that is referred to as hypoosmotic overhydration. For example, excessive secretion of antidiuretic hormone, which causes the kidney tubules to reabsorb more water, can lead to hyponatremia and overhydration. 70
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- 72. Causes of Hypernatremia: WaterLoss or Excess Sodium Increased plasma sodium concentration, which also causes increased osmolarity, can be due to either loss of water from the extracellular fluid, which concentrates the sodium ions, or excess sodium in the extracellular fluid. When there is primary loss of water from the extracellular fluid, this results in hyperosmotic dehydration. This condition can occur from an inability to secrete antidiuretic hormone, which is needed for the kidneys to conserve water. 72
- 73. As aresult of lack of antidiuretic hormone, the kidneys excrete large amounts of dilute urine (a disorder referred to as diabetes insipidus), causing dehydration and increased concentration of sodium chloride in the extracellular fluid. In certain types of renal diseases, the kidneys cannot respond to antidiuretic hormone, also causing a type of nephrogenic diabetes insipidus. 73
- 74. A morecommon cause of hypernatremia associated with decreased extracellular fluid volume is dehydration caused by water intake that is less than water loss, as can occur with sweating during prolonged, heavy exercise. Hypernatremia can also occur as a result of excessive sodium chloride added to the extracellular fluid. This often results in hyperosmotic overhydration because excess extracellular sodium chloride is usually associated with at least some degree of water retention by the kidneys as well. 74
- 75. For example,excessive secretion of the sodium-retaining hormone aldosterone can cause a mild degree of hypernatremia and overhydration. The reason that the hypernatremia is not more severe is that increased aldosterone secretion causes the kidneys to reabsorb greater amounts of water as well as sodium. 75
- 76. Edema: Excess Fluid inthe Tissues Edema refers to the presence of excess fluid in the body tissues. In most instances, edema occurs mainly in the extracellular fluid compartment, but it can involve intracellular fluid as well. 76
- 77. Intracellular Edema Twoconditions are especially prone to cause intracellular swelling: (1) depression of the metabolic systems of the tissues, and (2) lack of adequate nutrition to the cells. 77
- 78. Extracellular Edema Extracellularfluid edema occurs when there is excess fluid accumulation in the extracellular spaces. There are two general causes of extracellular edema: (1) abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries (2) failure of the lymphatics to return fluid from the interstitium back into the blood. 78
- 79. The mostcommon clinical cause of interstitial fluid accumulation is excessive capillary fluid filtration. 79
- 80. Summary of Causesof Extracellular Edema 80
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- 82. Safety Factors That NormallyPrevent Edema Even though many disturbances can cause edema, usually the abnormality must be severe before serious edema develops. The reason for this is that three major safety factors prevent excessive fluid accumulation in the interstitial spaces: 1. Low compliance of the interstitium when interstitial fluid pressure is in the negative pressure range 82
- 83. 2. The abilityof lymph flow to increase 10- to 50-fold, and 3. washdown of interstitial fluid protein concentration, which reduces interstitial fluid colloid osmotic pressure as capillary filtration increases. 83
- 84. Determination of Volumesof Specific Body Fluid Compartments 84
- 85. Fluid and electrolyte replacement done with 3 types of solutions ISOTONIC HYPOTONIC HYPERTONIC 85
- 86. ISOTONIC SOLUTIONS 0.9%Sodium Chloride Solution Ringer’s Solution Lactated Ringer’s Solution Use- replace fluid losses, usually extracellular losses, and to expand the intravascular volume
- 87. HYPOTONIC SOLUTIONS 5%DEXTROSE & WATER 0.45% SODIUM CHLORIDE 0.33% SODIUM CHLORIDE Use- They are commonly infused to dilute extracellular fluid and rehydrate the cells of patients who have hypertonic fluid imbalances and to treat gastric fluid loss and dehydration from excessive diuresis.
- 88. HYPERTONIC SOLUTIONS 3% SODIUMCHLORIDE 5% SODIUM CHLORIDE WHOLE BLOOD ALBUMIN TOTAL PARENTERAL NUTRITION TUBE FEEDINGS CONCENTRATED DEXTROSE (>10%) Use- to treat patients who have severe hyponatremia. Depending on the type of hypertonic fluid infused, it can provide patients with calories, free water, and some electrolytes.
- 89. Oral rehydration therapy Oral rehydration therapy (ORT) is a type of fluid replacement used to prevent or treat dehydration especially that due to diarrhoea. It involves drinking water with modest amounts of sugar and salt added (an oral rehydration solution or ORS) while continuing to eat. Oral rehydration solution is on WHO's list of essential medicines. 89
- 90. WHO andUNICEF jointly have developed official guidelines for the manufacture of ORS and describe acceptable alternative preparations, depending on material availability. Commercial preparations are available as either pre-prepared fluids or packets of oral rehydration salts (ORS) ready for mixing with water. 90
- 91. The formulafor the current WHO-ORS (also known as low-osmolar ORS or reduced-osmolarity ORS) is 2.6 grams (0.092 oz) salt (NaCl), 2.9 grams (0.10 oz) trisodium citrate dihydrate (C 6H5Na3O7,2H2O), 1.5 grams (0.053 oz) potassium chloride (KCl), 13.5 grams (0.48 oz)anhydrous glucose (C 6H12O6) per litre of fluid. 91
- 92. It canbe made using 6 level teaspoons (25.2 grams) of sugar and 0.5 teaspoon (2.1 grams) of salt in 1 litre of water. 92
- 93. Fluid and electrolyte replacementin Dentistry In dentistry fluid and electrolyte replacement implication is mainly related to oral and maxilla facial surgery. Usually it is administered in clinical conditions like Trauma During and after surgeries under GA Hypovolemic shock during minor surgical procedures (eg - Injury to any artery) Hypogycemic shock during procedures 93
- 94. Conclusion To achievehomeostasis, the body maintains strict control of water and electrolyte distribution and of acid-base balance. Methods of fluid & electrolyte movement are diffusion, osmosis, active transport & filtration 94
- 95. The kidneyis the primary organ that maintains the total volume, pH, and osmolarity of the extracellular fluid within narrow limits. The kidney accomplishes this by altering urine volume and osmolarity. The kidney, in turn, is regulated by neural, hormonal, and local factors. 95
- 96. Hormones likeRenin, Angiotensin, Aldosterone & Vassopressin play a key role in regulation Assessment of body fluid is important to determine causes of imbalance Interventions for imbalances are based on the cause 96
- 97. REFERENCE GUYTON &HALL, TEXTBOOK OF MEDICAL PHYSIOLOGY, ELEVENTH EDITION, ELSEVIER PUBLISHERS K SEMBULINGAM, ESSENTIALS OF MEDICAL PHYSIOLOGY, SIXTH EDITION, JAYPEE PUBLISHERS N GEETHA, TEXTBOOK OF MEDICAL PHYSIOLOGY, THIRD EDITION, PARAS BOOKS LEONARD JOHNSON, ESSENTIAL MEDICAL PHYSIOLOGY, THIRD EDITION THE TREATMENT OF DIARRHOEA, A MANUAL FOR PHYSICIANS AND SENIOR HEALTH WORKERS- WORLD HEALTH ORGANIZATION, 2005. 97
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