WATER AND ELECTROLYTE

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WATER AND ELECTROLYTE IMBALANCES
DR JOCELYN NAICKER DEPT. OF CHEMICAL
PATHOLOGY 2008
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DELIVERY CONTENT
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3. Introduction to a practical approach to
management of hypo- and hypernatraemia 4.
Discussion of common causes of hyper- and
hypokalaemia using patient examples and
diagrams
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HYPONATRAEMIA WHAT ARE COMMON CAUSES?
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• HYPONATRAEMIA
• Dilutional hyponatraemia
• ? renal water excretion
• SIADH
• ? H2O intake - psychogenic polydipsia
• - excess IV fluids
• In adults thiazide diuretics
• In infants children due to - GIT loss
• - H2O enemas
• - dilute formula

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WATER BALANCE

H2O
Na
INPUT
OUTPUT
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WATER BALANCE 1. INTAKE 2. OUTPUT 3.
FLUID SHIFTS BETWEEN COMPARTMENTS
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WATER BALANCE Obligatory losses skin
500mls lungs 400 mls gut
100 mls kidney 500 mls 1500
mls Water gain metabolic H2O
400 mls dietary H2O
1100 mls 1500 mls
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FLUID LOSS (OUTPUT) PURE H2O - urine in
DI ISOTONIC FLUID - blood
- small intestinal
secretions HYPOTONIC FLUID -
vomitus -
diarrhoeal fluid - sweat
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BODY WATER
Young Males - 60 BW Young Females - 55 BW
Elderly Males - 50 BW Elderly Females -
45 BW Infants and Children - 75 - 80 BW
BW Body Weight
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28 L
14L
ECF 1/3
ICF 2/3
10.5L
3.5L
VASCULAR COMPARTMENT
INTERSTITIAL FLUID COMPARTMENT
e.g. in a 70 Kg male ?total body water 42 L
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Fluid shifts between the ICF and ECF compartments
are determined by their OSMOTIC
DIFFERENCES This is mainly determined by the ECF
Na
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WATER AND ELECTROLYTE IMBALANCES
depletion excess
WATER
usually euvolaemia
depletion - dehydration excess - oedema
WATER and Na

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OSMOLALITY either MEASURED with an
osmometer or CALCULATED OSMOLARITY 2
Na urea glucose OSMOLAR
GAP Difference between the measured osmolality
and the calculated osmolarity
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OSMOLALITY SERUM - 285 10 mmol / Kg URINE
- no normal range ranges from 50 to1200 mmol
/ Kg
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RENAL COLLECTING DUCT
H2O
H2O
H2O impermeable membrane
H2O
H2O
H2O
H2O
H2O
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ADH
OSMOLALITY
Aquaporins
H2O
H2O
H2O
Concentrated urine
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Osmolality ----gt ADH
No aquaporins
H2O
COLLECTING DUCT
H2O
H2O
H2O
H2O
H2O
H2O
dilute urine
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If despite the OSMOLALITY the
ADH is (as in SIADH)
Aquaporins
H2O
H2O
H2O
Rx Restrict fluid intake
Concentrated urine
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Diabetes Insipidus
ADH DEFICIENCY
H2O
H2O
H2O
Pure H2O deficit
H2O
H2O
H2O
Dilute urine
H2O
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PURE WATER EXCESS
ICF
ECF
Pure H2O

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PURE WATER EXCESS
ICF
ECF
Na

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PURE WATER EXCESS
ICF
ECF

Net effect equal distribution of fluid gained
across both compartments hence no oedema
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PURE WATER DEFICIT
ICF
ECF

H2O
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PURE WATER DEFICIT
ICF
ECF

Replace with H20
Net effect equal distribution of fluid loss
across both compartments
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Hypernatraemia always denotes hypertonicity Occur
s frequently in hospitals Sustained ? Na only
when - thirst is impaired eg elderly - failure
to respond to thirst due to - illness
- infants
- unconsciousness
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UNCONSCIOUS
water
H2O
Na
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LOSS OF HYPOTONIC FLUID
ICF
ECF

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LOSS OF BLOOD - ISOTONIC FLUID
ICF
ECF

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Volume depletion gt10 Baroreceptors
ADH RELEASE (fluid retension)
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NA - K ATPase PUMP
CELL
ECF
3Na
2K
Against gradient therefore ENERGY requiring
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Old specimen
Cell
K
K
Na
glucose used up in specimen container
Na-K ATPase pump
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INSULIN DEFICIENCY
Cell
K
K
Na
Na-K ATPase pump
Glucose uptake
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glucose (hyperglycaemia) 23.6
23.6
10mmol/l
K
13.6
Na
glucose
Na
K
osmotic diuresis
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DKA
cell
INSULIN DEFICIENCY
glucose
glucose
glucose
glucose
H2O
glucose
glucose
glucose
glucose
HYPEROSMOLALITY
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CORRECTED Na Na glucose
4
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cell
Na
K

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Serum K levels are related to the ACID-BASE status
ACIDAEMIA HYPERKALAEMIA
N.B. there are exceptions
ALKALAEMIA HYPOKALAEMIA
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ALKALAEMIA ASSOCIATED WITH HYPOKALAEMIA
ECF
CELL
H
H
alkalaemia
to maintain electroneutrality
K
HYPOKALAEMIA
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ALKALAEMIA ASSOCIATED WITH HYPOKALAEMIA
ECF
Tubular lumen
Distal RTC
H
gt
H
gt
K LOSS
K
Na
lt
urine K ?
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RAS
DEHYDRATION
Renal blood flow (RBF )
Baroreceptors in the JGA of nephrons
RENIN
ACE
ANG I
ANG II
ANGIOTENSINOGEN
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2o HYPERALDOSTERONISM ANG II adrenal gland

BP
vasoconstriction
ALDOSTERONE
Na and H2O retention K / H loss
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Distal RTC
ECF
Tubular lumen
H
H
gt
gt
K
K
exchange
Na
lt
Under the influence of Aldosterone
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ACIDAEMIA ASSOCIATED WITH HYPERKALAEMIA
ECF
CELL
H
H for buffering
acidaemia
to maintain electroneutrality
K
HYPERKALAEMIA
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ACIDAEMIA ASSOCIATED WITH HYPERKALAEMIA
ECF
Tubular lumen
Distal RTC
H
gt
H
gt
K
exchange
Na
lt
urine acid