FLUIDS AND ELECTROLYTES

1. FLUIDS AND ELECTROLYTES

2. Body Fluid Composition • Water – largest body component • 55-65% total body weight • Solutes –dissolved in body water

3. Solutes • Electrolytes • Cations – positive • Sodium (Na+) • Potassium (K+) • Calcium (Ca+2) • Anions – negative • Chloride (Cl-) • Bicarbonate (HCO3-) • Phosphate (HPO4-) • Non-electrolytes Proteins • Urea • Glucose • Oxygen (O2) • Carbon dioxide (CO2)

4. Body Maintains Charge and Osmolality • Body fluids • Electrically neutral • Osmotically maintained • Specific # solute molecules per volume fluid • Homeostasis of charge, osmolality maintained by • Ion transport • Water movement between fluid compartments • Kidney function

5. Units of Solute Measurement (A Review) • MW (molecular weight) = sum of weights of atoms • mEq (milliequivalents) = MW (in mg) / valence • Valence = # charges of ion • Na+ valence = 1 • Cl- valence = 1 • Ca+2 valence = 2 • Allows comparisons of charge # of solutes in fluids, without molecular wts • Important to monitor overall charge of body fluids • mOsm (milliosms) = # particles in solution • Particles = atoms or molecules, charged or uncharged • Measures concent of overall # of solute particles in fluid • Important to monitor overall concentrations of body fluids

6. Fluid Compartments • ICF = IntraCellular Fluid • Inside cells • 65% total body weight • ECF = ExtraCellular Fluid • Not inside cells • 35% total body weight • Further divided 

7. ECF – cont’d • IVF = IntraVascular Fluid • In blood vessels • 8% total body weight • ISF = InterStitial Fluid • Bathes cells + lymph • 25% of total body weight

8. Movement of Body Fluids (WATER FOLLOWS SALT!) • Solutes may be in higher concentration on one side of the cell membrane • Fluid (water) can move to equilibrate concentration and/or charge on both sides of the membrane

9. Definitions • Diffusion = net movement of particles (solutes) down concentration gradient to establish equilibrium between two sides of membrane • Passive (no energy needed) • Assisted (energy must be added by the cell) • Osmosis = diffusion of water • Freely passes through cell membranes.

10. Movement of Body Fluids – cont’d • ICF to ECF • Osmolality changes in ICF not rapid • Cell strives to maintain fluid and ion concentrations • Cell very dependent on relatively constant water/solute amounts • BUT if ECF osmolality changes so water moves among compartments, both compartments affected and equilibrated over time

11. Movement of Body Fluids – cont’d • IVF to ISF to IVF • Happens constantly due to changes in fluid pressures and osmotic forces at arterial and venous ends of the capillaries • Necessary to move oxygen and nutrients toward metabolizing cells, and wastes and carbon dioxide away from metabolizing cells

13. Movement of Body Fluids – cont’d • Arteriolar end of the capillary: • Highest fluid pressure force -- Blood Hydrostatic Pressure (BHP) • Pressing out against the capillary walls • Direction toward cells • Encourages movement out • Due to fluid pressures and heart contractions • Colloid Osmotic Pressure (COP) • Lower pressure at arteriolar end • Pulls inward from capillary wall • Encourages fluid to stay inside • Due to large proteins, cells in capillary (too large to move through capillary walls, so remain in the capillary), can’t leave the bloodstream • Overall at arteriolar end of capillary, BHP > COP • Greater force encouraging fluid out of capillary than encouraging fluid to stay inside capillary • So fluid (from heart; oxygenated; w/ nutrients) encouraged to move toward metabolizing cells

14. Movement of Body Fluids – cont’d • At the venous end of the capillary: • BHP decreased • Fluid “lost” from vessel • Don’t have same high fluid pressure pushing against vessel walls • COP stays the same • Same amt large proteins, blood cells • Now rel higher pressure “pulling in” away from cells • Overall at venous end of capillary, COP > BHP • Greater force encourages fluid into capillary than encourages fluid out of capillary • Overall, fluid (from around cells; containing wastes and CO2) encouraged to move into capillary • Now returned to lungs to excrete CO2 and to kidneys to excrete wastes

16. Movement of Body Fluids – cont’d • ECF to environment • Fluid intake = fluid output • Intake is -- water, food, beverages • Output -- urine, feces, sweat and water vapor

17. Regulation of Body Water • Works through ADH (AntiDiuretic Hormone) • If there is • Decreased amount water in the body, or • Increased amount Na+ in the body, or • Increased blood osmolality • So the blood is too concentrated, or • Decreased circulating blood volume • All of these lead to:

18. ADH Release – cont’d • Stim’n hypothalamic osmoreceptors,  • Release ADH, and • Stimulation of thirst response • Thirst response  increased drinking • Overall, water volume within the body increases

19. ADH – cont’d • ADH works at kidney •  incr’d permeability of kidney tubules to water •  incr’d reabsorption of water from kidney tubules back into blood vasculature • Water WOULD have been released to urine • So water is conserved, not excreted

21. ADH – cont’d • Overall: • Incr’d water consumption, and • Incr’d water conservation, so • Incr’d amt water in body • Relieves decr’d water, decr’d circulation blood volume • Decr’d blood osmolality • Relieves increased body Na+, increased blood osmolality • Note: the various conditions leading to ADH release can all be caused by different dysfunctions or traumas, but are all related physiologically • If either hemorrhage (decr’d blood volume) or sweating (decr’d water in body)  decr’d fluid available  decr’d IVF  decr’d blood pressure • Compensation: body tries to increase fluids in body • If endocrine disorder  incr’d Na+  incr’d blood osmolality • Compensation: body tries to increase fluids to bring blood osmolality back to normal range (since body can’t n;ormalize osmolality through solute amount) • So if sodium LOAD has doubled to 290 mEq/L: if fluid VOLUME can double, will now have 290 mEq/2L, which = 145 mEq/L (normal sodium CONCENTRATION is 145 mg/L)

22. ADH – cont’d • Note: conditions ADH release, regardless of cause, related physiologically • Hemorrhage (decr’d blood volume) or sweating (decr’d water in body) •  decr’d fluid available  decr’d IVF  decr’d blood pressure • Compensation: body tries to increase fluids in body • Endocrine disorder  incr’d Na+  incr’d blood osmolality • Compensation: body tries to increase fluids (body can’t normalize osmolality through solute amount) • Ex: Na+ LOAD doubled (290 mEq/L); by doubling fluid VOLUME  290 mEq/2L= 145 mEq/L (normal sodium CONCENTRATION is 145 mg/L)

23. Important Cations Contributing to Body Fluid Osmolality • Sodium (Na+) • About 90% ECF cations • Normal range = 136-145 mEq/L in ECF • Pairs with Cl-, HCO3- to neutralize charge • Low in ICF (~10 mEq/L) • Most impt ion in regulating water balance

24. Sodium – cont’d • Regulation in ECF -- Renal tubule reabsorption, modulated by hormones: • Aldosterone • Rel’d from adrenal gland when body senses decr’d Na+ load • Works at renal tubule to incr renal tubule reabsorption of Na+ • Renin/angiotensin • Affects aldosterone release (also controls Na+ reabsorption) • Natriuretic hormone • Works at kidney •  decr’d renal reabsorption of Na+

25. Potassium • Major INTRAcellular cation • ICF concentration = 150-160 mEq/L • Lower in ECF (3.5-4.5 mEq/L) • K+ concentration INSIDE cells approximates Na+ concentration OUTSIDE • Na+ concentration INSIDE cells approximates K+ concentration OUTSIDE • Body keeps electrical charge constant in ICF and ECF, but uses diff cations inside/outside cells • Cell moves two cations differently, uses each differently • Overall cells strive to maintain high K+ inside and high Na+ outside

26. Potassium – cont’d • Why keep K+ high inside and Na+ high outside cells? • Resting membrane potential in neurons, muscles • Na+, K+ move into/out of these cells  depolarization  action potential • If imbalanced, can  neurological, muscle contraction problems • REMEMBER: heart is an important muscle!

28. Potassium – cont’d • K+ also important: • Regulates fluid, ion balance inside the cell • Sim to Na+ regulation outside the cell • pH regulation • K+ can move across the cell membrane for H+ when H+ is in excess (body fluids are too acidic) • Regulation of body K+ is through the kidney • Aldosterone regulates K+ • If body senses decr’d K+ in plasma  aldosterone release • Works at kidney tubule  incr’d reabsorption of K+ from tubule back to blood (similar to Na+ mechanism) • Insulin  increased K+ taken up by cells • So K+ must be monitored in diabetic patients

29. Isotonic Alterations • Volume of fluid changes, but numbers and types of electrolytes remain at normal levels (Table 4-5) • Loss  volume depletion (hypovolemia); occurs with • Hemorrhage • Severe wound drainage • Excess sweating • Burns • Third spacing

30. Hypovolemia – cont’d • Fluid lost from blood vessels, but remains in body • Receptors in the vessels sensitive to pressure • Interpreted as fluid loss, so decr’d ECF volume  • Decr’d urine output • Weight loss (through fluid weight) • Can  hypovolemic shock • Symptoms of hypovolemia • Decr’d blood pressure • Incr’d heart rate

31. Hypervolemia • Excess body fluid; occurs with: • Excessive IV fluids • Overproduction aldosterone • Why should this lead to hypervolemia? • Some drugs (ex: cortisol) • With incr’d ECF volume  • Weight gain (fluid weight) • Diluted urine • Incr’d blood pressure • Can also  edema

32. Edema -- ECF Isotonic Volume Excess • Accum’n isotonic fluid in interstitial space (incr’d ISF) • Forces that favor incr’d ISF also favor edema: • Incr’d BHP, if • Chronic hypertension • Venous obstruction • Water retention • Decr’d COP if • Not enough proteins/cells in the blood: • Protein synthesis disorders of liver • Blood cell disorders  decreased # of blood cells

33. Edema – cont’d • Increased capillary permeability, which can occur with • Trauma • Inflammation • Decreased lymph drainage with • Blocked lymph node • Surgical removal of lymph vessels • REMEMBER: ISF drains into lymph vessels, which returns ISF to the bloodstream

34. Edema – cont’d • Clinical • Pitting • Weight gain (water weight) • Neck vein distension • Incr’d blood pressure • Treatment • Treat underlying conditions (tumor, blood cell disorder, etc.) • Relieve symptoms

35. Electrolyte Imbalances (Table 4-6): Sodium • Hypernatremia (a hypertonic imbalance) • Plasma Na+ > 145 mEq/L • Too much Na+ or too little water • “Tonicity”: # of solute particles in solution • Hypertonic -- high amt solute • Hypotonic = dilute • Characteristics of hypernatremia: •  movement of water from ICF to ECF, so • Cells dehydrate  • Overall incr’d ECF vol (at expense of the cell vol)

36. Sodium Imbalances – cont’d • Hypernatremia – cont’d • Due to • Admin hypertonic IV sol’ns • Oversecretion aldosterone • Loss of pure water • Long term sweating w/ chronic fever • Respiratory infection  water vapor loss • Diabetes  polyuria • Insufficient water ingested

37. Sodium Imbalances – cont’d • Hypernatremia – cont’d • Clinical • Thirst • Lethargy • Neurological dysfunction (dehydration of brain cells) • Treatment • Lower serum Na+ • Use isotonic salt-free IV fluid (5% glucose) to replace body water; returns Na+ concentration to normal levels

38. Sodium Imbalances – cont’d • Hyponatremia • Overall Na+ decr ECF • Two types • Depletional: Too little Na+ • Dilutional: Too much water • Causes of each type • Depletional (Na+ lost out of body or insufficient) • Diuretics • Chronic vomiting • Chronic diarrhea • Though electrolytes loss • Decr’d aldosterone • Decr’d Na+ intake

39. Sodium Imbalances – cont’d • Hyponatremia – cont’d • Dilutional • Renal dysfunction w/ incr’d hypotonic fluid intake • Excessive sweating  increased thirst  intake excessive pure water • Syndrome of Inappropriate ADH (SIADH)  impaired renal excretion of water • Excessive beer drinking (???) • Clinical • Neurological symptoms • Now improper Na+ concentration outside cell  improper depolarization/action potential/neuron conduction • Seizures possible • Treatment • Restrict water, or • Administer Na+

40. Electrolyte Imbalances: Potassium • Hypokalemia • Characteristics • Serum K+ < 3.5 mEq/L • Beware if diabetes: • Insulin plays a role in K+ into the cell • Ketoacidosis  incr’d H+ in ECF (so ECF too highly + charged) • H+ enters cells • Body tries to equilibrate + charges by moving K+ out of cells • Now ECF high in K+ (lost through urine) • Overall whole body K+ deficit

41. Potassium Imbalances – cont’d • Hypokalemia – cont’d • Causes • Decr’d K+ intake (rare) • Incr’d K+ loss • With chronic diuretics, g.i. disturbance • Acid/base imbalance  K+ out of cells into ECF, then lost through urine • Clinical • Neuromuscular disorders • Cardiac arrest • REMEMBER: Na+/K+ gradient for proper action potentials in neurons/muscles • Treatment • Increase K+ intake • BUT slowly to avoid abrupt Na+/K+ gradient change

42. Potassium Imbalances – cont’d • Hypokalemia – cont’d • Clinical • Neuromuscular disorders • Cardiac arrest • REMEMBER: body maintains Na+/K+ gradient for proper action potentials in neurons/muscles so proper neuron/muscle function • Treatment • Increase K+ intake • BUT must be increased slowly to avoid abrupt Na+/K+ gradient change

43. Potassium Imbalances – cont’d • Hyperkalemia • Serum K+ > 5.5 mEq/L • Importance/causes/when to check • Renal disease (kidney regulates K+) • Massive cellular trauma • High intracellular K+ is released into ECF • Insulin deficiency • Insulin plays a role in K+ uptake into cells • Addison’s disease  altered aldosterone secretion • Decr’d blood pH (high blood acidity) •  H+ into cells •  K+ out of cells  ECF •  High K+ in ECF • BUT over time K+ will be lost to urine  overall decrease in body K+

44. Potassium Imbalances – cont’d • Hyperkalemia – cont’d • Clinical • Muscle weakness, paralysis • Change in ECG pattern • Treatment • Insulin + glucose  K+ taken into the cells (out of ECF) • Bicarbonate – buffers H+ ions if hyperkalemia due to acidosis • Ca+2 counteracts K+ effects on heart