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Water and Electrolyte Balance

Water and Electrolyte Balance

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Water and Electrolyte Balance

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  1. Water and Electrolyte Balance

  2. Water • 60% - 90% of BW in most life forms • 2/3 intracellular fluid • 1/3 extracellular fluid • plasma • lymph • interstitial fluid • gut

  3. Dehydration • Occurs when fluid loss exceeds intake • sweating vs time • Fluid lost mostly from ECF • decreased circulating blood volume inadequate tissue perfusion, inefficient transport of substrates to muscle, and elevated HR

  4. Clinical Signs persistent elevation of HR and RR weak pulse poor capillary refill muscular weakness, tremors depression weak pulse, staggering muscle cramps Treatment IV or oral fluids and electrolytes Dehydration

  5. Estimates of Fluid Loss • Weigh animal before and after exercise • 1 kg = 1 L • loss of 3% of BW = reduce performance • loss of 10% of BW = serious, possibly life threatening

  6. Estimates of Fluid Loss • Blood analysis • PCV and total plasma proteins • rise indicates dehydration • if PCV > 50% indicates hazardous fluid loss

  7. Detecting Dehydration • Skin pinch test • falls back instantly - normal • 2 - 4 sec - moderate • 4 -6 sec - severe • Capillary refill • press finger on gums above an upper tooth • if it takes longer than 2 seconds for blood to return - dehydration

  8. Electrolytes • Salt that dissociates in solution into electrically charged particles (ions) • cations - positive charge • anions - negative charge • Function in fluid balance, transmission of nerve impulses, and muscular activity

  9. Electrolytes • Na, K, Cl • ICF predominate cation is K • ECF predominate cation is Na • determines water distribution between compartments

  10. Electrolyte Replacement • Sweat is hypertonic • 100 mEq Na:30 mEq K: 130 mEq Cl • small amounts of Ca, Mg, and Zn also lost • Electrolyte loss is easily replaced by dietary means if sweat is sparse or infrequent

  11. Electrolyte Replacement • Electrolyte supplementation recommended if sweating is frequent • also in hot and humid weather • Dietary electrolytes should replace ions lost in sweat in correct proportions • water or feed

  12. Dietary Considerations • Type of hay • legume vs grass • DCAD - dietary cation anion balance • strong and weak cations vs anions

  13. Cations Na+ K+ Ca2+ Mg2+ Anions Cl- SO42- lactic acid Strong Ions

  14. Na/K ATPase Pump Lehninger, 1993

  15. Stewart (1981) • Concept of electrolytes as critical factors in acid/base balance • Strong ion difference (SID) • sum of all strong cations minus sum of all strong anions (NA, K, CL, SO42-) • anions greater = negative SID = H+ > OH- • cations greater = positive SID = OH- > H+

  16. Stewart (1981) • Balance of SID is maintained by the dissociation and reassociation of water

  17. H+ = Dependent Variable • Three independent variables determine the value of H+: • SID • Pco2 • H increases as Pco2 increases • CO2 acts as an acid • Total concentration of weak acids (plasma proteins) • H increases as weak acids increase

  18. Long Term Kidney regulates electrolytes primarily Na GI tract absorption of cations and anions dependent of needs Rapid Lung releases CO2 (HCO3-) Regulation of pH

  19. Altering Acid Base Balance • DCAD diets • Sodium bicarbonate administration • IV vs GI • effect of other sodium forms • Furosemide