Fluids

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• Fluids
• and
• Electrolytes
• Basic science course
• Sept. 16th 2004
  Y. Edden MD.

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• This is a dry topic
• but

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We are approximately two-thirds water
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Anatomy of Body Fluids

• Man water constitutes 60 of body weight
• Women water constitutes 50 of body weight
• Functional compartments of body fluids
• Intracellular space 40 of body weight
• Extracellular space 20 of body weight
• Interstital 15
• Plasma 5

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Anatomy of Body Fluids

• Changes with age
• Newborns 75-80 of body weight is water
• One year 65 of body weight is water
• Adult males 60, females 50

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Body Compartments
Dry
40
40
Intracellular
15
Interstitial
Extracellular
5
Plasma
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Intracellular Fluid Space

• 40 of body weight
• Largest proportion is in skeletal muscle
• Larger percentage of water is Intracellular in
  males (large muscle mass)
• Cations Potassium Magnesium
• Anions Phosphates and Proteins

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Extracellular Fluid Space

• 20 of body weight
• Interstitial 15, Plasma 5
• Cations Sodium
• Anions Chloride and Bicarbonate
• Has a small nonfunctioning component
• Connective tissue water
• Transcellular (CSF, Joint fluid, etc)

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Summary of Ionic composition
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Composition of Fluids

• plasma interstitial intracellular
• Cations
• Na 140 146 12
• K 4 4 150
• Ca 5 3 10
• Mg 2 1 7
• Anions
• Cl 103 104 3
• HCO 24 27 10
• SO4 1 1 -
• HPO4 2 2 116
• Protein 16 5 40

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Normal Exchange of Fluid Electrolytes

• Water exchange
• Average adult consumption is 2000 to 2500 mls per
  day. (1500 mls in the form of fluids)
• Losses
• 250 ml in stool
• 800 1500 ml in urine (minimum 500 ml)
• 600 ml in insensible losses
• Skin (75)
• Lungs (25)

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Fluid shifts / intakes
Kidneys Guts Lungs Skin
Intracellular 30 liters
Interstitial9 liters
IV 3 liters
Extracellular fluid - 12 litres
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Osmotic / oncotic pressure
Na
Na
PP
Intracellular
Interstitial
Intravascular
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Osmotic Activity of Fluids

• Osm or mOsm unit for number of particles
• 1 mol of NaCl - 2 osm
• Osmolarity - mOsm/L
• Osmolality - mOsm/Kg water
• Osmolality defines concentration of solution
• Tonicity defines effect of fluid on cell volume

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Osmolality

• Plasma osmolality Posm - measure of body
  osmolality
• Usually Posm(mOsm/l) 2x serum Na

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Calculation of osmolality

• Difficult measure add all active osmoles
• Easy sodium x 2 urea glucose
• Normal 280 - 290 mosm / kg

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Volume Control

• osmoreceptors - day to day control
• baroreceptors - respond to pressure change
• neural output
• hormonal mediators

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Osmoregulation

• osmolality 289 mOsm/kg H20
• osmoreceptor cells in paraventricular/ supraoptic
  nuclei
• osmoreceptors control thirst and ADH
• small changes in Posm - large response

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Osmoregulation

• Excess free water (Posm 280)
• thirst inhibited
• ADH declines
• urine dilutes to Uosm 100

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Osmoregulation

• Decreased free water (Posm 295)
• thirst increased
• ADH increases
• urine concentrates to Uosm 1200

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The role of ADH

• ADH urinary concentration
• ADH secreted in response to ? osmo
• secreted in response to ? vol
• ADH acts on DCT / CD to reabsorb water
• Acts via V2 receptors aquaporin 2
• Acts only on WATER

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Fluid shifts in disease

• Fluid loss
• GI diarrhoea, vomiting, fistula etc.
• renal diuresis
• vascular haemorrhage
• skin burns
• Fluid gain
• Iatrogenic
• Heart / liver / kidney failure

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Prescribing fluids

• Crystalloids
• 0.9 saline - not normal !
• 5 dextrose
• 0.18 saline 0.45 dextrose
• Others
• Colloids
• blood
• plasma / albumin
• synthetics

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The rules of fluid replacement

• Replace blood with blood
• Replace plasma with colloid
• Resuscitate with colloid
• Replace ECF depletion with saline
• Rehydrate with dextrose

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Control of Volume

• Effective circulating volume
• Portion of ECF that perfuses organs
• Usually equates to Intravascular volume
• Third space loss
• Abnormal shift of fluid from Intravascular to
  tissues eg bowel obst, Intra-op, pancreatitis

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• As for intra-op fluids which is correct?
• In a healthy person up to 500cc of blood loss can
  be well tolerated.
• During operation the Functional Extracellular
  Fluid (FEF) volume is related directly to the
  volume lost to suction.
• FEF losses should be replaced with plasma.
• Albumin plays important role in the replacement
  of FEF loss.

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• As for intra-op fluids
• In a healthy person up to 500cc of blood loss can
  be well tolerated.
• During operation the Functional Extracellular
  Fluid (FEF) volume is related directly to the
  volume lost to suction.
• FEF losses should be replaced with plasma.
• Albumin plays important role in the replacement
  of FEF loss.

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Fluid Replacement

• The solvent (water) will follow the distribution
  of the solute!

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• The most common cause for serum Na of 125 mEq/L
  in a post op patient is
• Water deficit.
• Water excess
• Na excess.
• Na deficit.
• Na within normal limits.

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• The most common cause for serum Na of 125 mEq/L
  in a post op patient is
• Water deficit.
• Water excess
• Na excess.
• Na deficit.
• Na within normal limits.

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Fluid shifts / intakes
Kidneys Guts Lungs Skin
Intracellular 30 liters
Interstitial9 liters
IV 3 liters
Extracellular fluid - 12 litres
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Crystalloids colloids
2 litres of blood
30 litres
Intracellular 30 liters
9 litres
3 litres
Interstitial9 liters
IV 3 liters
IV 3 liters
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Crystalloids colloids
30 litres
Intracellular 30 liters
9 liters
5 litres
Interstitial9 liters
Interstitial9 liters
IV 5 liters
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Crystalloids colloids
2 litres of colloid
30 litres
Intracellular 30 liters
9 litres
3 litres
IV 3 liters
Interstitial9 liters
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Crystalloids colloids
30 litres
Intracellular 30 liters
9 litres
5 litres
Interstitial9 liters
IV 5 liters
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Crystalloids colloids
29 litres
Intracellular 29 liters
8 litres
7 litres
Interstitial8 liters
IV 7 liters
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• Normal saline will distribute throughout the
  extracellular fluid compartment and only 10 will
  remain in the plasma compartment after an hour.

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Crystalloids colloids
2 litres of 0.9 saline
Intracellular 30 liters
IV 3 liters
Interstitial9 liters
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Crystalloids colloids
30 litres
Intracellular 30 liters
9 litres
5 litres
Interstitial9 liters
IV 5 liters
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Osmotic / oncotic pressure
Na
Na
PP
Intracellular
Interstitial
Intravascular
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Crystalloids colloids
29 litres
Intracellular 29 liters
10.5 litres
4.5 litres
Interstitial10.5 liters
IV 4.5 liters
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• Dextrose 5W will distribute throughout all fluid
  compartments and therefore less than 10 will
  remain in the plasma compartment.

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Crystalloids colloids
2 litres of 5 Dextrose
Intracellular 30 liters
IV 3 liters
Interstitial9 liters
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Crystalloids colloids
30 litres
Intracellular 30 liters
9 litres
5 litres
Interstitial9 liters
IV 5 liters
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Crystalloids colloids
31 litres
Intracellular 31 liters
9.7 litres
3.3 litres
IV 3.3 liters
Interstitial9.7 liters
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• Using 5 DW for rapid correction of severe
  symptomatic hypernatremia associated volume
  deficit may result in convulsions and coma.
• True or False?

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• Using 5 DW for rapid correction of severe
  symptomatic hypernatremia associated volume
  deficit may result in convulsions and coma.
• True!

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How much fluid to give ?

• What is your starting point ?
• Euvolaemia ? ( normal )
• Hypovolaemia ? ( dry )
• Hypervolaemia ? ( wet )
• What are the expected losses ?
• What are the expected gains ?

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Signs of hypo / hypervolaemia

• Signs of
• Volume depletion Volume
  overload
• Postural hypotension
  Hypertension
• Tachycardia Tachycardia
• Absence of JVP _at_ 45o Raised JVP / gallop
  rhythm
• Decreased skin turgor
  Oedema
• Dry mucosae Pleural effusions
• Supine hypotension Pulmonary oedema
• Oliguria Ascites
• Organ failure Organ failure

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What are the expected losses ?

• Measurable
• urine ( measure hourly if necessary )
• GI ( stool, stoma, drains, tubes )
• Insensible
• sweat
• exhaled

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What are the potential gains ?

• Oral intake
• fluids
• nutritional supplements
• bowel preparations
• IV intake
• colloids crystalloids
• feeds
• Drugs!

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Normal Exchange of Fluid Electrolytes

• Salt exchange
• Average adult consumption varies between 50 to 90
  meq of Sodium Chloride per day. Balance is
  maintained by renal excretion of excess salt.
• Losses occur mostly from the GI tract
• GI losses are usually isotonic or slightly
  hypotonic and should be replaced by an isotonic
  salt solution.
• Note losses of extracellular fluid represents
  isotonic losses of salt and water

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Extracellular Fluid Loss

• Most common cause is GI losses!
• Vomiting, diarrhea, NG losses, Fistula drainage,
  GI bleed
• Third space losses
• Peritonitis, bowel obstruction, burns, etc
• Renal losses
• Diuretics, Osmotic diuresis, etc

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Gastrointestinal Secretions
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• 62M patient with HTN on Hydrochlorothiazide 50mg
  BID. Pre-Op bowel preparation with Golytely.
• Na 141 mEq/L K 2.6 mEq/L. The hypokalemia is
  due to?
• Loss of electrolytes from prep.
• Water and lytes loss from prep.
• Two days clears diet.
• Thizide diuretics.
• Lytes intake with prep.

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• 62M patient with HTN on Hydrochlorothiazide 50mg
  BID. Pre-Op bowel preparation with Golytely.
• Na 141 mEq/L K 2.6 mEq/L. The hypokalemia is
  due to?
• Loss of electrolytes from prep.
• Water and lytes loss from prep.
• Two days clears diet.
• Thizide diuretics.
• Lytes intake with prep.

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• This degree of low potassium (K 2.6) represents
  loss of?
• 25-50 mEq/L.
• 50-100 mEq/L.
• 100-200 mEq/L.
• 200-300 mEq/L.
• 300-600 mEq/L.

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• This degree of low potassium represents loss of?
• 25-50 mEq/L.
• 50-100 mEq/L.
• 100-200 mEq/L.
• 200-300 mEq/L.
• 300-600 mEq/L.

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Clinical Assessment of Dehydration

• History
• Vomiting, diarrhea, IV fluids (type, duration),
  surgery (type, duration)
• Physical examination
• Vitals, skin turgor, tears, fontanelle, cap
  refill, JVP, Hypotension
• Urine output
• Volume, colour

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Estimation of Deficit
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Laboratory Assessment of Dehydration

• CBC
• Elevated hematocrit, hemoconcentration of indices
• Electrolytes
• Sodium?, Potassium?, etc
• Urine
• Sodium concentration (lt10 mEq/l), Osmolality,
• Other
• BUN, Creatinine (Prerenal azotemia), Weight

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Intravenous Fluids
Note Glucose can be added to any crystalloid
solution.
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• A good heart and kidneys can surmount all but the
  most willfully incompetent fluid regimen.

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Normal Intake of Water

• 2000cc 1300 - free water
• 700 cc bound to food
• additional water comes from catabolism

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Normal Water Exchange

• daily ml
• Sensibleurine 800-1500
• intestinal 0-250 sweat 0
• Insensiblelungs/skin 600-900 600-900
• ? 10/ o rise in Temp

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Maintenance Requirements

• This includes
• insensible
• urinary
• stool losses

Body weight Fluid required0-10Kg 100ml/kg/dne
xt 10-20kg 50 ml/kg/dsubsequent 20
Kg 20ml/kg/d 15ml/Kg/d for elderly
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70 Kg Man Needs

• 10 x 100 1000
• 10 x 50 500
• 50 x 20 1000
• 2500 cc/d or 104cc/h

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Fluid Replacement

• Example
• 60 Kg woman who is estimated to be 10
  dehydrated.

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• Maintenance
• 100 X 10 for first 10 Kgs 1000 ml
• 50 X 10 for second 10 Kgs 500 ml
• 20 X 40 for the remaining wt 800 ml
• Total 2300cc/24h 95 ml/hr

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• Deficit
• 10 of 60 kg is 6 Kg 6 L
• Give ½ in first 8 (3000 cc 375cc/h) hrs and ½ in
  next 16 hrs (187cc/h).

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Water and Eletrolyte Exchange

• Surgical patients prone to disruption
• nil orally
• anesthesia
• trauma
• sepsis

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Fluid and Electrolyte Therapy

• Surgical patients have
• Maintenance volume requirements
• On going losses
• Volume excess/deficits
• Maintenance electrolyte requirements
• Electrolyte excess/deficits

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On Going Losses

• NG
• drains
• fistulae
• third space losses
• Concentration is similar to plasma
• Replace with isotonic fluids

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Volume Deficit - Acute

• vital signs changes
• Blood pressure
• Heart rate
• CVP (less used than before)
• ECHO!
• tissue changes not obvious
• urine output low

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Fluid and Electrolyte Therapy

• Goal
• normal homodynamic parameters
• normal electrolyte concentration
• Method
• replace normal maintenance requirements
• ongoing losses
• deficits

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Fluid and Electrolyte Therapy

• The best estimate of the volume required
• is the patients response!