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Fluids and Electrolytes

Fluids and Electrolytes. Elizabeth A. Beierle Tad Kim, M.D. UF Surgery tad.kim@surgery.ufl.edu (c) 682-3793; (p) 413-3222. Overview. Fluid Compartments in the body Revisiting Volume of Distribution Determining distribution of various fluid types Fluids for maintenance Derived from:

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Fluids and Electrolytes

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  1. Fluids and Electrolytes Elizabeth A. Beierle Tad Kim, M.D. UF Surgery tad.kim@surgery.ufl.edu (c) 682-3793; (p) 413-3222

  2. Overview • Fluid Compartments in the body • Revisiting Volume of Distribution • Determining distribution of various fluid types • Fluids for maintenance • Derived from: • Fluid requirements per day • Electrolyte requirements per day • Fluids for resuscitation • A case of electrolyte abnormality

  3. Fluid Compartments • Total Body Water (TBW) = 0.65 x Wt male • 0.5 x Wt female • Intracellular Fluid (ICF) = 2/3 TBW • Extracellular Fluid (ECF) = 1/3 TBW • Interstitial Fluid (ISF) = 2/3 ECF • Intravascular Fluid = 1/3 of ECF

  4. Exercise in Fluid Compartments • 70kg Male • What is his approximate blood volume? • TBW = 0.65 x 70kg = 45L • ECF = 1/3 x TBW = 15L • Blood volume = 1/3 x ECF = 5L • Typical vascular volume is ~5L • Remember: Blood volume = ~1/9 of TBW or ~1/3 of ECF. ECF is ~1/3 of TBW

  5. Distribution of Various Fluids • Membrane barriers btw compartments • Infusions are introduced into plasma / vessel • Will distribute until impermeable barrier • Plasma & Interstitial fluid separated by capillary endothelium permeable to all ions, but not to plasma proteins (i.e. albumin) • Albumin will stay intra-vascular • ECF & ICF separated by cell membrane impermeable to electrolytes • electrolytes will distribute throughout ECF • TBW: free water, urea distribute everywhere

  6. Distribution of Various Fluids • Give a 70kg male 3L of Free water • Will distribute throughout TBW (Vd = 45L) • Hematocrit will drop only 3/45th (hemodilution) • Give a 70kg male 3L of NS • Will distribute throughout ECF (Vd = 15L) • Hematocrit will drop 3/15th or 1/5th • 70kg male loses 1L of blood, why do you give 3L NS? (Why the “3:1” rule?) • Because 3L NS will distribute throughout ECF • Plasma is 1/3rd of ECF, so effectively only 1/3rd of that NS will distribute to the plasma

  7. Distribution of Various Fluids • So if a 70kg male (with TBW 45L) lost 1L of blood, how much to replace using: • Free water? (Recall: Plasma is 1/9 of TBW) • Takes 9L free water to replace 1L of plasma • NS? (Recall 3-to-1 rule: Plasma is 1/3 ECF) • Takes 3L of NS to replace 1L of plasma • Albumin? or Blood? (1:1 replacement) • Takes 1L of 5% albumin or 3 Units = 1L PRBC • ½ NS? • Takes 3L of NS, so it should take ~6L of ½ NS • Dextrose is not considered for resuscitation

  8. Fluids for Maintenance • D5 ½NS + 20KCl • What does this mean? • D5 = 5% glucose = 5g dextrose per 100mL of solution or 50g per Liter bag • Prevents mobilization of protein as fuel source • NS = 154mEq Na & 154mEq Cl per Liter • 20KCl = 20mEq KCl per 1L bag

  9. Fluid Requirements per day • 100 / 50 / 25 or the 4 / 2 / 1 rule (per hour) • First 10kg → 4mL/kg/hr • 10-20kg → 2mL/kg/hr • >20kg → 1mL/kg/hr • Easy way to remember: • At 10kg, you need 40mL/hr • At 20kg, you need 60mL/hr • Anything over 20kg, it’s 60 + (1 per extra kg)

  10. Exercise in Maintenance Reqs • 50kg → 60 + (difference btw 50 & 20) • 60 + 30 = 90mL/hr maintenance fluids • 70kg → 60 + (difference btw 70 & 20) • 60 + 50 = 110mL/hr • 100kg → 60 + (difference btw 70 & 20) • 60 + 80 = 140mL/hr • 15kg → 40 + 2x (difference btw 15 & 10) • 40 + 10 = 50mL/hr

  11. Electrolyte Requirements • For Adults: • Sodium = 2-3mEq/kg/day • Chloride = similar to sodium • Potassium = 0.5-1mEq/kg/day

  12. Review of Fluids/Lytes Req’s • 70kg patient’s requirements: • Maintenance IVF: 110mL/hr = 2.5L/day • Sodium: Needs 140-210mEq/day • Potassium: Needs 35-70mEq/day

  13. Revisit: Why D5 ½NS +20K? • 70kg → • Needs 2.5L/day of D5 ½NS + 20K • ½ NS = 77mEq Na per L • 2.5 x 77 = 190mEq Na (falls in the 140-210 range) • 20K = 20mEq KCl per L • 2.5 x 20 = 50mEq K (falls in the 35-70 range)

  14. Infants • Same maintenance rate requirements • Slightly altered electrolyte needs • Sodium → 3-5mEq/kg/day • Chloride → similar • Potassium → 1mEq/kg/day

  15. Review in 10kg infant • 10kg infant • Maintenance: Needs 40mL/hr = 1L/day • Sodium: Needs 30-50mEq/day • Potassium: Needs 10mEq/day

  16. Why use D5 ¼NS +10K? • 10kg → • Needs 1L/day of D5 ¼NS + 10K • ¼NS = 39mEq sodium (falls in 30-50 range) • 10K = 10mEq potassium (exactly right) • Around 10kg is the cutoff after which you can use adult-type maintenance fluids

  17. Fluids for Resuscitation • For hypovolemic or dehydrated patients • Vomiting, sepsis, pancreatitis, burns, etc • Signs: dry mucous membranes, poor skin turgor, skin tenting, no axillary sweat, pt is “thirsty”, weight loss • Tachycardia (before hypotension), oliguria • This is the “C” in ABC’s • 2 large bore IV’s, Foley and continuous monitor • Isotonic crystalloid fluids (LR, NS, plasmalyte) • Bolus IVF: 20mL/kg in peds, 2L in adults • Assess response and re-bolus until patient responds. If no response, then think fast about reasons for hypoTN (tension, tamponade, bleed)

  18. Case • 6wk old baby presents with projectile nonbilious emesis after meals, then is immediately hungry. • Palpable olive on exam of epigastrum • Ultrasound: 4mm pyloric muscle thickness • What is the diagnosis? • What is the metabolic/electrolyte abnormality associated with this dx? • What is the management?

  19. Case • Dx: Hypertrophic pyloric stenosis (HPS) • Metabolic abnormality: • Hypochloremic, hypokalemic metab alkalosis • Lose chloride when vomiting • Proximal convoluted tubules (PCT) reabsorb sodium w chloride to preserve volume • Runs out of chloride, reabsorbs bicarbonate • More Na delivered distally b/c above is limited • Aldosterone acts to promote Na/K exchange • Lose potassium, then K/H exchange => lose H+

  20. Case • Metabolic disturbance due to volume depletion in the face of hypochloremia • Management of HPS: • D5 ½ NS + 20K @ 1.5-2x maintenance • Alkalosis resolves via both: volume repletion and chloride replacement • Alkalosis is a/w ↑risk of post-op apnea, so you must correct alkalosis before OR • Pyloromyotomy: laparoscopic vs open

  21. Take Home Points • Understand body compartments • Understand volume of distribution of types of fluids: crystalloid vs colloid vs free water • Be able to figure hemodilution after fluids • Justify the use certain maintenance IVF • Know what fluids are for resuscitation • Understand the metabolic derangement of HPS and its treatment

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