FUNDAMENTALS OF FLUID AND ELECTROLYTE BALANCE

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FUNDAMENTALS OF FLUID AND ELECTROLYTE BALANCE
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FLUID REQUIREMENTS
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FLUID CONTENT OF THE BODY

• Varies with age, sex, adipose tissue
• Females 45-50 TBW
• Males 50-60 TBW
• Infants 77 TBW

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BODY FLUID COMPARTMENTS

• RULE OF THIRDS
• Intracellular 2/3 (40 TBW)
• Extracellular 1/3 (20 TBW)
• Interstitial Lymph 2/3 (15 TBW)
• Intravascular 1/3 (5 TBW)

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ELECTROLYTES IN BODY FLUID COMPARTMENTS
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SOLUTES

• Non-electrolytes
• Dextrose
• Urea
• Creatinine
• Electrolytes
• Anions
• Cations

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IV FLUID DISTRIBUTION IN BODY COMPARTMENTS
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MAINTENANCE vs. REPLACEMENT

• Maintenance
• Provide normal daily requirements Water 2.5 L
• Sodium ½ or ¼ NS
• KCl 40-60 meq/L
• Example
• D5 ½ NS with KCL 20 meq/L running at 100 ml/hr

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MAINTENANCE vs. REPLACEMENT

• Replacement
• Replace abnormal losses with a fluid and
  electrolytes similar to that which was lost.

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OSMOLALITY

• Definition Concentration of particles
  (osmotically active) in solution. It is usually
  expressed in millosmoles of solute per kg of
  solution.
• Osmolality is independant of valence.
• Osmolality (mOsm/Kg) of dilute solutions
  approximate osmolarity (mOsm/L)
• Plasma 280-300 mOsm/Kg
• Same in all body compartments
• Water distribution

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Normal Laboratory Values

• Sodium 135-145 meq/L
• Potassium 3.5-5.0 meq/L
• Chloride 95-105 meq/L
• Bicarbonate 22-28 meq/L
• Calcium 9-11 mg/dL
• Phosphate 3.2-4.3 mg/dL
• Glucose 70-110 mg/dL
• BUN 8-18 mg/dL
• Creatinine 0.6-1.2 mg/dL
• Osmolality (P) 280-295 mOsm/kg
• Osmolality (U) 50-1200 mOsm/kg

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ELECTROLYTE DISORDERSSODIUM

• JO is a 58 year-old male with cirrhosis of the
  liver due to ethanol abuse. Physical examination
  reveals ascites.
• Baseline lab is as follows
• Na 128, K 3.8, Cl 95, CO2 24
• JO is to be started on TPN, Should we request
  additional sodium to correct his hyponatremia?

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ELECTROLYTE DISORDERSSODIUM

• Primary extracellular cation
• Hyponatremia
• Excess of TB water
• Decrease in TB sodium
• Serum sodium primarily reflects water balance,
  not sodium balance.

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ELECTROLYTE DISORDERSSODIUM

• Isotonic hyponatremia (factitious)
• Hypertonic hyponatremia (dilutional)
• Hypotonic hyponatremia

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ELECTROLYTE DISORDERSSODIUMHypertonic
Hyponatremia

Extracellular Fluid BS 400 mg/dl Na
Intracellular Fluid Water
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ELECTROLYTE DISORDERSHypotonic Hyponatremia

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ELECTROLYTE DISORDERSSODIUM

• JO is a 58 year-old male with cirrhosis of the
  liver due to ethanol abuse. Physical examination
  reveal ascites.
• Baseline lab is as follows
• Na 128, K 3.8, Cl 95, CO2 24
• JO is to be started on TPN, Should we request
  additional sodium to correct his hyponatremia?
• JOs is in an edematous state. He has an excess
  of TB water and sodium. The appropriate
  treatment is water and sodium restriction. He
  should also receive diuretic treatment. The drug
  of choice is Aldactone (spironolactone), an
  aldosterone antagonist.

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ELECTROLYTE DISORDERSModel for Distribution and
Elimination of Intracellular Ions

Intake
K Phos Mg ICF
ECF
Stomach Intestine
Renal Losses
GI (stool) Losses
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ELECTROLYTE DISORDERSPOTASSIUM

• Primary intacellular cation
• Hypokalemia Causes
• Decreased dietary intake
• Redistribution
• Insulin
• Metabolic Alkalosis
• Dehydration

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ELECTROLYTE DISORDERSPOTASSIUMMetabolic
Alkalosis and Hypokalemia

Extracellular Fluid K
Intracellular Fluid H
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ELECTROLYTE DISORDERSPOTASSIUM

• Hypokalemia Causes
• Increased Urinary or GI Losses
• Diuretics
• NG Suction
• Diarrhea

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ELECTROLYTE DISORDERSPOTASSIUM

• Drugs which may cause hypokalemia
• Urinary wasting aminoglycosides, amphotericin B,
  corticosteroids, diuretics, levodopa, nifedipine,
  penicillins, rifampin
• Gastrointestinal losses laxatives
• Redistribution Beta-2 agonists, lithium

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ELECTROLYTE DISORDERSPOTASSIUM

• Hypokalemia Treatment/Estimation of Deficit
• If serum K gt 3meq/L
• 100-200 meq required per each change in serum K
  of 1 meq/L
• If serum K lt 3 meq/L
• 200-400 meq required per each change in serum K
  of 1 meq/L

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ELECTROLYTE DISORDERSPOTASSIUM

• Hypokalemia Estimation of Deficit
• If serum K gt 3meq/L
• 100-200 meq required per each change in serum K
  of 1 meq/L
• If serum K lt 3 meq/L
• 200-400 meq required per each change in serum K
  of 1 meq/L
• Example Serum K 2.5 How much K is required to
  correct serum K to 4.0?
• Step 1
• To increase from 2.5 to 3.0 200-400 meq X
  0.5100-200meq
• Step 2
• To increase from 3.0 to 4.0 100-200 meq X
  1.0100-200meq
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  Total200-400meq

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ELECTROLYTE DISORDERSPOTASSIUM Hypokalemia
Treatment
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ELECTROLYTE DISORDERSPOTASSIUM

• Mrs D. is a 62 year-old female who is having an
  acute exacerbation of Crohns disease. She
  complains to you of severe and frequent diarrhea
  over the last four days. She experiences
  dizziness when she stands. Your physical
  examination reveals dry mucous membranes. In the
  supine position her BP110/65 and in the upright
  position her BP90/45 and her pulse140. Your
  lab values are as follows
• Na 132, K 2.9, Cl 92, CO2 31, BUN 25, Cr 1.0
• Discuss Mrs. Ds fluid and electrolyte problems.

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ELECTROLYTE DISORDERSCase Study Hypokalemia

• Mrs D. is a 62 year-old female who is having an
  acute exacerbation of Crohns disease. She
  complains to you of severe and frequent diarrhea
  over the last four days. She experiences
  dizziness when she stands. Your physical
  examination reveals dry mucous membranes. In the
  supine position her BP110/65 and in the upright
  position her BP90/45 and her pulse140. Your
  lab values are as follows
• Na 132, K 2.9, Cl 92, CO2 31, BUN 25, Cr 1.0
• Mrs Ds has extracellular volume depletion due
  to prolonged diarrhea. The ECVD is supported by
  her physical assessment and postural hypotension
  and her BUN/Cr is gt 201. The diarrhea has
  resulted in a loss of fluid and sodium chloride.
  Some potassium was lost directly in the stools,
  but the main cause of her hypokalemia is her ECVD
  which has induced a metabolic alkalosis
  (contraction alkalosis.) The alkalosis
  contributed to her hypokalemia by two mechanisms.
  Some potassium has moved to the intracellular
  compartment but much of it has been lost in the
  urine where potassium wasting occurs secondary to
  chloride deficit. Administration of Normal
  Saline with Potassium Chloride will correct her
  fluid and electrolyte problems (and alkalosis.)

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ELECTROLYTE DISORDERSPOTASSIUM

• Hyperkalemia Causes
• Decreased Renal Excretion
• CRF and ARF
• Drug induced
• K-sparing diuretics (spironolactone,
  triamterine, amiloride)
• Angiotensin converting enzyme inhibitors
• NSAIDS

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ELECTROLYTE DISORDERSPOTASSIUM

• Hyperkalemia Causes
• Redistribution
• Trauma, burns
• Acidosis
• Hyperosmolar states
• Increased intake
• Salt substitutes
• Blood transfusions
• K salts of antibiotics

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ELECTROLYTE DISORDERSPOTASSIUMMetabolic
Acidosis and Hyperkalemia

Extracellular Fluid H
Intracellular Fluid K
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ELECTROLYTE DISORDERSPOTASSIUM

• Hyperkalemia Treatment
• Potassium Antagonist
• Calcium Chloride
• Redistribution
• Insulin dextrose
• Sodium bicarbonate
• Cationic binding resins
• Kayexalate (polystyrene sulfonate)
• Renal Elimination/dialysis

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ELECTROLYTE DISORDERSMAGNESIUM

• Hypomagnesemia Causes
• Decreased Intake
• Malnutrition
• Alcoholism
• Decreased Absorption
• Increased Losses
• GI losses
• Renal losses

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ELECTROLYTE DISORDERSMAGNESIUM

• Drug Induced Hypomagnesemia
• GI Losses
• Laxatives
• Renal Losses
• Diuretics, cisplatin, aminoglycosides,
  amphotericin B

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ELECTROLYTE DISORDERSMAGNESIUM

• Hypomagnesemia Treatment
• IV Magnesium Sulfate
• Replace over several days
• Renal threshold for reabsorption of Mg
• 1 mEq/kg on day 1
• 0.5 mEq/kg on days x 3-5 days
• Oral replacement
• Mylanta

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ELECTROLYTE DISORDERSMAGNESIUM

• Hypermagnesemia Causes
• Exogenous ingestion
• Impaired renal excretion
• Treatment Eliminate exogenous source of Mg

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ELECTROLYTE DISORDERSPHOSPHOROUS

• Hypophosphatemia usually asymptomatic until lt1
  mg/dL
• Causes
• Impaired absorption
• Aluminum or calcium binding
• Redistribution
• Respiratory alkalosis
• Glucose insulin
• Increased Excretion

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ELECTROLYTE DISORDERSPHOSPHOROUS

• Hypophosphatemia Treatment
• Oral Fleets Phosphosoda
• IV Replace cautiously

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ELECTROLYTE DISORDERSPHOSPHOROUS

• Hyperphosphatmeia Causes
• Renal impairment
• Increased intake
• Treatment
• Phosphate binders Alternagel, Amphojel,
  Calcium Suppliments

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ELECTROLYTE DISORDERSPHOSPHOROUS

• M.T. is a 55 year-old female with a history of
  chronic renal failure who is admitted to the SICU
  following a motor vehicle accident. She is
  started on a TPN solution with minimal K, no Mg
  and no Phos. She also receives Mylanta II 30 ml
  per NG tube every four hours. Although her
  baseline labs were normal on day six her labs are
  as follows
• K 4.3, Mg 2.6, Phos 1.6
• What role did the antacid play in her electrolyte
  abnormalities?
• What role did the TPN play?

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ELECTROLYTE DISORDERSPHOSPHOROUS

• M.T. is a 55 year-old female with a history of
  chronic renal failure who is admitted to the SICU
  following a motor vehicle accident. She is
  started on a TPN solution with minimal K, no Mg
  and no Phos. She also receives Mylanta II 30 ml
  per NG tube every four hours. Although her
  basline labs were normal on day six her labs are
  as follows
• K 4.3, Mg 2.6, Phos 1.6
• M.Ts K is normal, but she has hypermagnesemia
  and hypophosphatemia. The antacid contributed to
  both of these abnormalities. It provided a
  significant source of Mg this patient with
  impaired excretion. Also the aluminum in the
  antacid acted a phosphate binder contributing to
  the hypophosphatemia.
• The TPN could have contributed to the
  hypophosphatemia by inducing an intracellular
  shift of phosphate (refeeding.) The potassium
  probably remained normal because some was being
  provided. Mg was being provided enterally.

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