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  1. 1. Nutrition &Metabolism Fluid, Electrolytes ,and Acid-Base Balance Fluid –is water containing chemical compounds(electrolytes +blood cells+other molecules) 45-80% of the body weight is fluid. 46-52% body wt of female is fluid 52-60% of male body wt is fliud It varies according to :age,fat and sex 1
  2. 2. FLUID AND ELECTROLYTES •Body fluid is located in two fluid compartments • the intracellular space (fluid in the cells) and •the extracellular space (fluid outside the cells). Intracellular space Contains two third of total body fluid 2/3(42) = 28 L Has negative environment Located primarily in the skeletal muscles 2
  3. 3. Fluid and electrolytes….. Extracellular fluid • Contains less than one third of the total body fluid • <1/3(42L) = 11L • Classified in to: • Interstitial fluid • Intravascular (fluid within the blood vessels) • Trans-cellular 3
  4. 4. Fluid and electrolytes….. Interstitial fluid • Fluid out of cell and out of vascular • Contains about 11 to 12 L in an adult • E.g lymphatic fluid Intravascular contains plasma Approximately 3 L of the average 6 L of blood volume is made up of plasma. The remaining 3 L is made up of erythrocytes, leukocytes, and thrombocytes 4
  5. 5. Fluid and electrolytes….. Trans-cellular fluid • the smallest division of the ECF compartment • contains approximately1 L of fluid at any given time • cerebrospinal, pericardial, • synovial, intraocular, and • pleural fluids; sweat; and digestive secretions 5
  6. 6. Fluid and electrolytes….. • Body fluid normally shifts between the two major compartments – equilibrium • Third-space fluid shift: Loss of ECF into a space that does not contribute to equilibrium between the ICF and the ECF • An early clue of a third-space fluid shift is a decrease in urine output despite adequate fluid intake 6
  7. 7. Fluid and electrolytes….. Other signs and symptoms of third spacing that indicate an intravascular fluid volume deficit include:- • increased heart rate • decreased blood pressure • decreased central venous pressure • edema • increased body weight and • imbalances in fluid intake and output (I&O). 7
  8. 8. Fluid and electrolytes….. • Third-space shifts occur in: • Ascites(an accumulation of fluid in the abdomen) • Burns • Peritonitis (inflammation of the peritoneal membrane ) • Bowel obstruction, and • Massive bleeding into a joint or body cavity. 8
  9. 9. Electrolytes • Electrolytes in body fluids are active chemicals. • Are of two types • Cations: positive charges, and E.g. sodium(ECF), potassium(ICF), calcium, magnesium, and hydrogen ions • Anions: negative charges E.g. chloride, bicarbonate, phosphate, sulfate, and proteinate ions 9
  10. 10. REGULATION OF BODY FLUID COMPARTMENTS Osmosis and Osmolality • diffusion of water caused by a fluid concentration gradient is known as osmosis • The magnitude of this force depends on the number of particles dissolved in the solutions, not on their weights • The number of dissolved particles contained in a unit of fluid determines the osmolality of a solution 10
  11. 11. Regulation of body fluid…. • Tonicity is the ability of all the solutes to cause an osmotic driving force that promotes water movement from one compartment to another • The control of tonicity determines the normal state of cellular hydration and cell size • Sodium, mannitol, glucose, and sorbitol are effective osmoles (capable of affecting water movement). 11
  12. 12. Regulation of body fluid…. Three other terms are associated with osmosis • Osmotic pressure is the amount of hydrostatic pressure needed to stop the flow of water by osmosis. • It is primarily determined by the concentration of solutes • Oncotic pressure is the osmotic pressure exerted by proteins(eg, albumin). 12
  13. 13. Regulation of body fluid…. • Osmotic diuresis occurs when the urine output increases due to the excretion of substances such as glucose, mannitol, or contrast agents in the urine. • Diffusion is the natural tendency of a substance to move from an area of higher concentration to one of lower concentration. • It occurs through the random movement of ions and molecules 13
  14. 14. Regulation of body fluid…. E.g. of diffusion • Exchange of oxygen and carbon dioxide between the pulmonary capillaries and alveoli and • The tendency of sodium to move from the ECF to ICF 14
  15. 15. Regulation of body fluid…. Filtration • Hydrostatic pressure in the capillaries tends to filter fluid out of the vascular compartment into the interstitial fluid. • Movement of water and solutes occurs from an area of high hydrostatic pressure to an area of low hydrostatic pressure. • Filtration allows the kidneys to filter 180 L of plasma per day • E.g. the passage of water and electrolytes from the arterial capillary bed to the interstitial fluid 15
  16. 16. ROUTES OF GAINS AND LOSSES Kidneys • The usual daily urine volume in the adult is 1 to 2 L. • A general rule is that the output is approximately 1 mL of urine per kilogram of body weight per hour (1 mL/kg/h) in all age groups. Skin • Sensible perspiration refers to visible water and electrolyte loss through the skin (sweating) 16
  17. 17. Routes… • The chief solutes in sweat are sodium, chloride, and potassium. • Actual sweat losses can vary from 0 to1,000 mL or more every hour, depending on the environmental temperature. • Continuous water loss by evaporation (approximately600 mL/day) occurs through the skin as insensible perspiration, a nonvisible form of water loss 17
  18. 18. Routes… Lungs • The lungs normally eliminate water vapor at a rate of approximately 400 mL every day. • The loss is much greater with increased respiratory rate or depth, or in a dry climate. 18
  19. 19. Routes… GI Tract • The usual loss through the GI tract is only 100 to 200 mL daily • approximately 8 L of fluid circulates through the GI system every 24 hours (called the GI circulation). 19
  20. 20. Average Daily Intake and Output in an Adult 20
  21. 21. LAB. TESTS FOR EVALUATING F LUID STATUS Osmolality  reflects the concentration of fluid that affects the movement of water between fluid compartments by osmosis.  measures the solute concentration per kilogram in blood and urine.  It is also a measure of a solution’s ability to create osmotic pressure and affect the movement of water 21
  22. 22. Lab. Tests… • Serum osmolality primarily reflects the concentration of sodium. • Urine osmolality is determined by urea, creatinine, and uric acid • When measured with serum osmolality, urine osmolality is the most reliable indicator of urine concentration. • Osmolality is reported as milliosmoles per kilogram of water (mOsm/kg). 22
  23. 23. Lab. Tests… • Normal serum osmolality is 280 to 300mOsm/kg • normal urine osmolality is 250 to 900mOsm/kg. Osmolarity, describes the concentration of solutions measured in milliosmoles per liter (mOsm/L). 23
  24. 24. Lab. Tests… Factors increasing osmolality • Serum osmolality • Free water loss • Diabètes insipides • Sodium overload • Hyperglycemia(elevated blood glucose level) • Uremia (blood poisenening) 24
  25. 25. Lab. Tests… Factors increasing osmolality • Urine osmolality • Fluid volume deficit • SIADH(Syndrome of inappropriate antidiuretic hormone) • HF • Acidosis 25
  26. 26. Lab. Tests… Factors decreasing osmolality • Serum osmolality • SIADH • Renal failure • Diuretic use • Adrenal insufficiency 26
  27. 27. Lab. Tests… Factors decreasing osmolality • Urine osmolality • Fluid volume excess • Diabetes insipidus 27
  28. 28. Lab. Tests… Urine specific gravity measures the kidneys’ ability to excrete or conserve water. Compared to the weight of distilled water, which has a specific gravity of 1.000. The normal range of specific gravity is 1.010 to 1.025. varies inversely with urine volume; normally, the larger the volume of urine, the lower the specific gravity 28
  29. 29. Lab. Tests… • Specific gravity(relative density) is a less reliable indicator of concentration than urine osmolality • increased glucose or protein in urine can cause a falsely high specific gravity. 29
  30. 30. Lab. Tests… Blood urea nitrogen (BUN) • made up of urea, an end product of metabolism of protein by the liver • The normal BUN is 10 to 20 mg/dL (3.5–7 mmol/L) • The BUN level varies with urine output Factors that increase BUN include: • decreased renal function, GI bleeding, dehydration, increased protein intake, fever, and sepsis 30
  31. 31. Lab. Tests… • Factors that decrease BUN include: • end-stage liver disease • a low-protein diet • starvation, and • any condition that results in expanded fluid volume(e.g, pregnancy). 31
  32. 32. Lab. Tests… Creatinine • The end product of muscle metabolism. • It is a better indicator of renal function than BUN because it does not vary with protein intake and metabolic state. • The normal serum creatinine is approximately 0.7 to 1.5 mg/dL; however, its concentration depends on lean body mass and varies from person to person 32
  33. 33. Lab. Tests… • Serum creatinine levels increase when renal function decreases Hematocrit • measures the volume percentage of red blood cells(erythrocytes) in whole blood • normally ranges from 44% to52% for males and 39% to 47% for females. 33
  34. 34. Lab. Tests… • Conditions that increase the hematocrit value are • dehydration and • Polycythemia(increase in the red blood cell • concentration in the blood) • Those that decrease hematocrit are: • over hydration and • anemia 34
  35. 35. Lab. Tests… • Urine sodium values change with sodium intake and the status of fluid volume • Normal urine sodium levels range from 50 to 220 mEq/24 h(50–220 mmol/24 h). • Urine sodium levels are used to assess volume status and are useful in the diagnosis of hyponatremia(sodium depletion) and acute renal failure 35
  36. 36. HOMEOSTATIC MECHANISMS • Organs involved in homeostasis include: • Kidneys • Lungs • Heart • Adrenal glands • Parathyroid glands, and • Pituitary gland. 36
  37. 37. Kidneys functions • kidneys normally filter 170 L of plasma everyday in the adult, while excreting only 1.5 L of urine Major functions of the kidneys in maintaining normal fluid balance include the following: • Regulation of ECF volume and osmolality by selective retention and excretion of body fluids 37
  38. 38. Kidneys… • Regulation of electrolyte levels in the ECF by selective retention of needed substances and excretion of unneeded substances • Regulation of pH of the ECF by retention of hydrogen ions • Excretion of metabolic wastes and toxic substances 38
  39. 39. Pituitary Functions • The hypothalamus manufactures ADH • ADH is sometimes called the water-conserving hormone because it causes the body to retain water. • Functions of ADH include maintaining the osmotic pressure of the cells by controlling the retention or excretion of water by the kidneys and by regulating blood volume 39
  40. 40. Adrenal Functions Aldosterone • has a profound effect on fluid balance. • Increased secretion of aldosterone causes sodium retention (and thus water retention) and potassium loss. • Conversely, decreased secretion of aldosterone causes sodium and water loss and potassium retention 40
  41. 41. Adrenal Functions… Cortisol • has only a fraction of the mineralocorticoid potency of aldosterone. • When secreted in large quantities, however, it can also produce sodium and fluid retention and potassium deficit. 41
  42. 42. Baroreceptors  are small nerve receptors that detect changes in pressure within blood vessels and transmit this information to the central nervous system.  responsible for monitoring the circulating volume, and  they regulate sympathetic and parasympathetic neural activity as well as endocrine activities 42
  43. 43. Baroreceptors… • They are categorized as: Low-pressure: located in the cardiac atria, particularly the left atrium High-pressure: nerve endings in the aortic arch and in the cardiac sinus • Also located in the afferent arteriole of the juxtaglomerular apparatus of the nephron 43
  44. 44. Renin–Angiotensin–Aldosterone System • Rennin is released by the juxtaglomerular cells of the kidneys in response to decreased renal perfusion. Angiotensinogen angiotensin I Ang.II • Ang.II with its vasoconstrictor properties, increases arterial perfusion pressure and stimulates thirst Rennin ACE 44
  45. 45. ADH AND THIRST • ADH and the thirst mechanism have important roles in maintaining sodium concentration and oral intake of fluids • Oral intake is controlled by the thirst center located in the hypothalamus. • As serum concentration or osmolality increases or blood volume decreases, neurons in the hypothalamus are stimulated by intracellular dehydration; thirst then occurs, and the person increases oral intake of fluids 45
  46. 46. Osmoreceptors • Located on the surface of the hypothalamus • Sense changes in sodium concentration. • As osmotic pressure increases, the neurons become dehydrated and quickly release impulses to the posterior pituitary, which increases the release of ADH • ADH travels in the blood to the kidneys, where it alters permeability to water, causing increased reabsorption of water and decreased urine output 46
  47. 47. Release of Atrial Natriuretic Peptide • ANP is released by cardiac cells in the atria of the heart in response to increased atrial pressure. • Any disorder that results in volume expansion or increased cardiac filling pressures (eg, high sodium intake, heart failure, chronic renal failure, atrial tachycardia, or use of vasoconstrictor agents) will increase the release of ANP 47
  48. 48. Release of Atrial…. • The action of ANP is the direct opposite of the RAA system and decreases blood pressure and volume • The ANP measured in plasma is normally 20 to 77 pg/mL. • This level increases in acute heart failure, paroxysmal atrial tachycardia, hyperthyroidism, subarachnoid hemorrhage, and small cell lung cancer. • The level decreases in chronic heart failure and with the use of medications such as urea and prazosin 48
  49. 49. FLUID VOLUME DEFICIT • occurs when loss of extracellular fluid volume exceeds the intake of fluid • water and electrolytes are lost in the same proportion as they exist in normal body fluids • should not be confused with the term dehydration 49
  50. 50. Causes of FVD abnormal fluid losses, such as those resulting from: vomiting diarrhea GI suctioning sweating, and decreased intake, as in nausea or inability to gain access to fluids (Beck, 2000). 50
  51. 51. Third-space fluid shifts  Burn, edema, ascites Additional risk factors include: diabetes insipidus adrenal insufficiency osmotic diuresis hemorrhage and coma 51
  52. 52. Clinical Manifestations • acute weight loss • decreased skin turgor • oliguria • concentrated urine • postural hypotension • a weak • rapid heart rate • flattened neck veins • increased temperature 52
  53. 53. • decreased central venous pressure • cool, clammy skin related to peripheral vasoconstriction • thirst • anorexia • nausea • muscle weakness and • cramps. 53
  54. 54. Diagnostic Findings • Elevated BUN • Hematocrit level is greater than normal • Hypokalemia • Hypernatremia • Increased urine specific gravity • Urine osmolality is greater than 450 mOsm/Kg 54
  55. 55. Medical Management • When the deficit is not severe, the oral route is preferred • When fluid losses are acute or severe, however, the IV route is required • Isotonic electrolyte solutions are frequently used to treat the hypotensive patient with FVD because they expand plasma volume • E.g. lactated Ringer’s or 0.9% sodium chloride 55
  56. 56. • As the patient becomes normotensive, a hypotonic electrolyte solution is often used to provide both electrolytes and water for renal excretion of metabolic wastes • E.g. 0.45%sodium chloride 56
  57. 57. • If the patient with severe FVD is not excreting enough urine and is therefore oliguric, the health care provider needs to determine whether the depressed renal function is the result of reduced renal blood flow secondary to FVD (prerenal azotemia) or, more seriously, to acute tubular necrosis from prolonged FVD. The test used in this situation is referred to as a fluid challenge test. During a fluid challenge test, volumes of fluid are administered at specific rates and intervals while the patient’s hemodynamic response to this treatment is monitored (ie, vital signs, breath sounds, sensorium, central venous pressure, urine output). 57

Notas del editor

  • hematocrit =percentage of total blood volume consisting of RBCs
  • Loss of ECF into a space that does not
    contribute to equilibrium between the ICF and the ECF is referred
    to as a third-space fluid shift, or “third spacing” for short.