Fluids and Electrolytes

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Fluids and Electrolytes

• Elizabeth A. Beierle
• Tad Kim, M.D.
• UF Surgery
• tad.kim_at_surgery.ufl.edu
• (c) 682-3793 (p) 413-3222

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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

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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

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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

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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

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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 31 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

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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? (11 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

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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

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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
• gt20kg ? 1mL/kg/hr
• Easy way to remember
• At 10kg, you need 40mL/hr
• At 20kg, you need 60mL/hr
• Anything over 20kg, its 60 (1 per extra kg)

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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

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Electrolyte Requirements

• For Adults
• Sodium 2-3mEq/kg/day
• Chloride similar to sodium
• Potassium 0.5-1mEq/kg/day

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Review of Fluids/Lytes Reqs

• 70kg patients requirements
• Maintenance IVF 110mL/hr 2.5L/day
• Sodium Needs 140-210mEq/day
• Potassium Needs 35-70mEq/day

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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)

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Infants

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

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Review in 10kg infant

• 10kg infant
• Maintenance Needs 40mL/hr 1L/day
• Sodium Needs 30-50mEq/day
• Potassium Needs 10mEq/day

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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

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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 ABCs
• 2 large bore IVs, 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)

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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?

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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 gt lose H

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Case

• Metabolic disturbance due to volume depletion in
  the face of hypochloremia
• Management of HPS
• D5 ½ NS 20K _at_ 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

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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