This document discusses various biochemical indices related to water and mineral metabolism in the body. It covers electrolyte abnormalities including hyponatremia, hypernatremia, hypokalemia, and hyperkalemia. For each condition, it describes symptoms, laboratory findings, and approaches to treatment and fluid replacement.

1. • BIOCHEMICAL INDICES
OF WATER-MINERAL
METABOLISM

2. • Patients may develop lethargy,
weakness, confusion, delirium, and
seizures, especially in the presence of
an abnormal serum sodium
concentration.
• Muscle weakness occurs in patients
with severe hypokalemia, hyperkalemia,
and hypophosphatemia;
• Сonfusion, seizures, and coma may
develop in those with severe
hypercalcemia.

3. • In addition to taking a careful history,
the diagnosis and treatment of fluid and
electrolyte disorders are based on:
• 1) assessment of total body water and
its distribution
• 2) serum electrolyte concentrations
• 3) urine electrolyte conntrations
• 4) serum osmolality

4. Body Water
• Two-thirds of total body water (40 % of body
weight) is intracellular fluid (ICF), while one-third
(20 % of body weight) is extracellular fluid
(ECF).
• Water may be lost from either or both of the
fluid compartments.
• One -fourth of extracellular fluid (5% of
body weight) is retained within the blood vessels
as plasma (effective circulating volume)

6. • Effective circulating volume
may be assessed by physical
examination (blood pressure,
pulse rate, jugular vein dilation).

7. Serum Electrolytes

8. Evaluation of Urine
• Fractional excretion (Fe) of an
electrolyte X (Fex) is calculated using a
random urine sample with simultaneously
obtained serum samples for X and cre­atinine
(Cr).
• Fex(%) = UrineX/SerumX × 100
Urine Cr/Serum Cr

9. Serum Osmolality
• Serum osmolality (normally 285-295
mosm/kg) can be calculated from the
following formula:
• Osmolality = 2(Na+ mEq/L) + Glucose mg/dL + BUN
mg/dL
18
2.8

10. • "Osmoles per kilo­gram
of
water" is osmolality; "osmoles
per liter of solution" is
osmolarity.

13. HYPONATREMIA
• Hyponatremia (defined as a serum
sodium concentration less than 130
mEq/L) is the most common elec­trolyte
abnormality observed in a
general hospitalized population, seen
in about 2 % of patients.

15. • Isotonic hyponatremia can be seen with
hyperlipidemia and hyperproteinemia. Because
of marked increases, lipids (chylomicrons,
triglycerides, which make the blood visibly
lipemic, and very occasionally cholesterol,
which may not make the blood visibly lipemic)
and proteins (> 10 g/dL, eg, intravenous
immunoglobulin therapy) occupy a
disproportionately large portion of the plasma
volume.
• Plasma osmolality remains normal because its
measurement is unaffected by the lipids and
proteins.

16. • Because the sodium
concentration in the plasma
water is actually normal,
hyperlipidemia and
hyperproteinemia cause so-called
"pseudohyponatremia."

18. • Hypertonic hyponatremia is most commonly
seen with hyperglycemia.
• When blood glucose becomes acutely elevated,
water is drawn from the cells into the
extracellular space, diluting the serum sodium.
• The plasma sodium level falls 2 mEq/L for
every 100 mg/dL rise when the glucose
concentration is between 200 and 400 mg/dL.
If the glucose concentration is above 400
mg/dL, the plasma sodium concentration falls
4 mEq/L for every 100 mg/dL rise in glucose.

19. HYPERNATREMIA
• An intact thirst mechanism usually
prevents hypernatremia (> 145 mEq/L).
Thus, whatever the underlying disorder
(eg, dehydration, lactulose or mannitol
therapy, central and nephrogenic diabetes
insipidus), excess water loss can cause
hypernatremia only when adequate water
intake is not possible, as with unconscious
patients

20. • A. Symptoms and Signs
• When dehydration exists, orthostatic
hypotension and oliguria are typical
findings. Because water shifts from the
cells to the intravascular space to
protect volume status, these symptoms
may be delayed. Hyperthermia, delirium,
and coma may be seen with severe
hyperosmolality.

21. • B. Laboratory Findings
• 1. Urine osmolality > 400 mosm/kg. Renal
water-conserving ability is functioning.
• a. Nonrenal losses. Hypernatremia will
develop if water ingestion fails to keep up
with hypotonic losses from excessive
sweating, exertional losses from the
respiratory tract, or through stool water.
Lactulose causes an osmotic diarrhea with loss
of free water.
• b. Renal losses. Whereas diabetic
hyperglycemia can cause pseudohyponatremia,
progressive volume depletion from the
osmotic di­uresis
of glycosuria can result in
true hypernatremia. Osmotic diuresis can
occur with the use of mannitol or urea.

22. • 2. Urine osmolality < 250 mosm/kg. A
dilute urine with osmolality less than
250 mosm/kg with hypernatremia is
characteristic of central and
nephrogenic diabetes insipidus.
Nephrogenic diabetes insipidus, seen
with lithium or demeclocycline therapy,
after relief of prolonged urinary tract
obstruction, or with interstitial
nephritis, results from renal
insensitivity to ADH.

23. Choice of Type of Fluid
for Replacement
• Hypernatremia with hypovolemia—
Severe hypovolemia should be treated
with isotonic (0.9%) saline to restore the
volume deficit and to treat the
hyperosmolality, since the osmolality of
isotonic saline (308 mosm/kg) is often
lower than that of the plasma. This
should be followed by 0.45% saline to
replace any remaining free water deficit.

24. • Hypernatremia with euvolemia—Water
drinking or 5% dextrose and water
intravenously will result in excretion of
excess sodium in the urine. If die GFR is
decreased, diuretics will increase
urinary sodium excre­tion
but may
impair renal concentrating ability,
increas­ing
the quantity of water that
needs to be replaced.

25. • Hypernatremia with hypervolemia—
Treatment consists of providing water
as 5% dextrose in water to reduce
hyperosmolality, but this will expand
vascular volume. Thus, loop diuretics
such as furosemide (0.5-1 mg/kg)
should be administered intravenously
to re­move
the excess sodium. In
severe renal insufficiency,
hemodialysis may be necessary.

27. HYPOKALEMIA
• A. Symptoms and Signs
• Muscular weakness, fatigue, and muscle
cramps are frequent complaints in mild to
moderate hypokale­mia.
Smooth muscle
involvement may result in consti­pation
or
ileus. Flaccid paralysis, hyporeflexia,
hypercapnia, tetany, and rhabdomyolysis
may be seen with severe hypokalemia (< 2.5
mEq/L).

28. • B. Laboratory Findings
• The electrocardiogram (ECG) shows
decreased ampli­tude
and broadening of
T waves, prominent U waves, premature
ventricular contractions, and depressed
ST segments. Hypokalemia also
increases the likelihood of digitalis
toxicity. Thus, in patients with heart
dis­ease,
hypokalemia induced by
certain drugs such as β2-adrenergic
agonists and diuretics may impose a sub­stantial
risk

30. HYPERKALEMIA
• Many cases of hyperkalemia are
spurious or associated with acidosis
(Table 21-6). The common practice of
repeatedly clenching and unclenching
a fist during venipuncture may raise
the potassium concentration by 1-2
mEq/L by causing acidosis and
consequent po­tassium
loss from cells