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Fluids and Electrolytes

Overview. Fluid Compartments in the bodyRevisiting Volume of DistributionDetermining distribution of various fluid typesFluids for maintenanceDerived from:Fluid requirements per dayElectrolyte requirements per dayFluids for resuscitationA case of electrolyte abnormality. Fluid Compartments.

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Fluids and Electrolytes

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    1. Fluids and Electrolytes Tad Kim UF Surgery

    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 ˝ NS? Takes 3L of NS, so it should take ~6L of ˝ NS Dextrose is not considered for resuscitation

    8. Fluids for Maintenance D5 ˝NS + 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 20 & 15) 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 ˝NS +20K? 70kg ? Needs 2.5L/day of D5 ˝NS + 20K ˝ 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 ĽNS +10K? 10kg ? Needs 1L/day of D5 ĽNS + 10K ĽNS = 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” 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 Less Na delivered to DCT b/c ?reabsorption 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 ˝ 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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