Title: WATER AND ELECTROLYTE
1WATER AND ELECTROLYTE IMBALANCES
DR JOCELYN NAICKER DEPT. OF CHEMICAL
PATHOLOGY 2008
2DELIVERY CONTENT
33. 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
4HYPONATRAEMIA WHAT ARE COMMON CAUSES?
5- 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
6WATER BALANCE
H2O
Na
INPUT
OUTPUT
7WATER BALANCE 1. INTAKE 2. OUTPUT 3.
FLUID SHIFTS BETWEEN COMPARTMENTS
8 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
9FLUID LOSS (OUTPUT) PURE H2O - urine in
DI ISOTONIC FLUID - blood
- small intestinal
secretions HYPOTONIC FLUID -
vomitus -
diarrhoeal fluid - sweat
10BODY 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
1128 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
12Fluid shifts between the ICF and ECF compartments
are determined by their OSMOTIC
DIFFERENCES This is mainly determined by the ECF
Na
13WATER AND ELECTROLYTE IMBALANCES
depletion excess
WATER
usually euvolaemia
depletion - dehydration excess - oedema
WATER and Na
14OSMOLALITY either MEASURED with an
osmometer or CALCULATED OSMOLARITY 2
Na urea glucose OSMOLAR
GAP Difference between the measured osmolality
and the calculated osmolarity
15OSMOLALITY SERUM - 285 10 mmol / Kg URINE
- no normal range ranges from 50 to1200 mmol
/ Kg
16RENAL COLLECTING DUCT
H2O
H2O
H2O impermeable membrane
H2O
H2O
H2O
H2O
H2O
17ADH
OSMOLALITY
Aquaporins
H2O
H2O
H2O
Concentrated urine
18Osmolality ----gt ADH
No aquaporins
H2O
COLLECTING DUCT
H2O
H2O
H2O
H2O
H2O
H2O
dilute urine
19If despite the OSMOLALITY the
ADH is (as in SIADH)
Aquaporins
H2O
H2O
H2O
Rx Restrict fluid intake
Concentrated urine
20Diabetes Insipidus
ADH DEFICIENCY
H2O
H2O
H2O
Pure H2O deficit
H2O
H2O
H2O
Dilute urine
H2O
21PURE WATER EXCESS
ICF
ECF
Pure H2O
22PURE WATER EXCESS
ICF
ECF
Na
23PURE WATER EXCESS
ICF
ECF
Net effect equal distribution of fluid gained
across both compartments hence no oedema
24PURE WATER DEFICIT
ICF
ECF
H2O
25(No Transcript)
26(No Transcript)
27PURE WATER DEFICIT
ICF
ECF
Replace with H20
Net effect equal distribution of fluid loss
across both compartments
28Hypernatraemia 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
29UNCONSCIOUS
water
H2O
Na
30LOSS OF HYPOTONIC FLUID
ICF
ECF
31LOSS OF BLOOD - ISOTONIC FLUID
ICF
ECF
32Volume depletion gt10 Baroreceptors
ADH RELEASE (fluid retension)
33NA - K ATPase PUMP
CELL
ECF
3Na
2K
Against gradient therefore ENERGY requiring
34Old specimen
Cell
K
K
Na
glucose used up in specimen container
Na-K ATPase pump
35INSULIN DEFICIENCY
Cell
K
K
Na
Na-K ATPase pump
Glucose uptake
36glucose (hyperglycaemia) 23.6
23.6
10mmol/l
K
13.6
Na
glucose
Na
K
osmotic diuresis
37DKA
cell
INSULIN DEFICIENCY
glucose
glucose
glucose
glucose
H2O
glucose
glucose
glucose
glucose
HYPEROSMOLALITY
38CORRECTED Na Na glucose
4
39cell
Na
K
40Serum K levels are related to the ACID-BASE status
ACIDAEMIA HYPERKALAEMIA
N.B. there are exceptions
ALKALAEMIA HYPOKALAEMIA
41ALKALAEMIA ASSOCIATED WITH HYPOKALAEMIA
ECF
CELL
H
H
alkalaemia
to maintain electroneutrality
K
HYPOKALAEMIA
42ALKALAEMIA ASSOCIATED WITH HYPOKALAEMIA
ECF
Tubular lumen
Distal RTC
H
gt
H
gt
K LOSS
K
Na
lt
urine K ?
43 RAS
DEHYDRATION
Renal blood flow (RBF )
Baroreceptors in the JGA of nephrons
RENIN
ACE
ANG I
ANG II
ANGIOTENSINOGEN
442o HYPERALDOSTERONISM ANG II adrenal gland
BP
vasoconstriction
ALDOSTERONE
Na and H2O retention K / H loss
45Distal RTC
ECF
Tubular lumen
H
H
gt
gt
K
K
exchange
Na
lt
Under the influence of Aldosterone
46ACIDAEMIA ASSOCIATED WITH HYPERKALAEMIA
ECF
CELL
H
H for buffering
acidaemia
to maintain electroneutrality
K
HYPERKALAEMIA
47ACIDAEMIA ASSOCIATED WITH HYPERKALAEMIA
ECF
Tubular lumen
Distal RTC
H
gt
H
gt
K
exchange
Na
lt
urine acid