fluid and electrolyte therapy

1. AKUFFO QUARDE
INTERN (PEDIATRICS, TEMA GEN. HOSP)

2. Fluid and Electrolyte Management

Physiology of water homeostasis

Body Fluid Compartments

Maintenance Fluid Requirements

Dehydration and Fluid therapy

Oral Rehydration Therapy

Practical Examples

3. Physiology of Water Homeostasis

To understand that disorders of sodium balance
are related to conditions that alter extracellular
fluid volume

To recognize clinical signs and symptoms of
the different forms of dehydration.

To appreciate that the management of
hypernatremic dehydration differs from that of
isonatremic/hyponatremic dehydration.

4. Physiology of Water Homeostasis

Osmotic Shifts of water between body fluid
compartments is dependent on the solute
particles within individual body compartments.

Effective osmolarity of body fluid compartments
is contributed to by unique properties of the cell
membranes ( difference in permeability to water
and solutes)

The difference in concentration of impermeable
particles across cell membranes determines
the osmotic movement of water. (effective
osmolarity)

5. Physiology of Water Homeostasis

In a steady state the osmolarity of both
intracellular and extracellular compartments will
remain the same. (approx. 300MOsm)

There is a delicate interaction between
osmolality and water balance.

(movement of water in the initial phase of
compensation for osmolar changes, is to reset
osmolarity either at a higher level or lower level.
i.e. Osmolarity of both intracellular and
extracellular fluids should remain the same

6. Physiology of Water Homeostasis

A complex set of homeostatic mechanisms are
at play, which regulate water intake and water
excretion.

The hypothalamus and surrounding brain
control the sense of thirst and the production
and release of arginine vasopressin (AVP), the
antidiuretic hormone (ADH)

It is the osmolality of plasma and extracellular
fluid which is “sensed” by osmoreceptors in the
anteromedial hypothalamus.

7. Physiology of Water Homeostasis

Non-osmotic stimuli will also cause AVP to be
released. (atrium / large vessels in the chest)

A reduction in “effective circulating volume”
[blood loss, hemorrhage, ECF volume depletion
(dehydration, diuretics, etc.), nephrotic
syndrome, cirrhosis, congestive heart
failure/low cardiac output]

8. Neonatal Physiology

At birth renal function is generally reduced,
particularly in premature neonates.

GFR increases progressively during gestation
particularly in the third trimester. By 1 to 2
years, GFR, Urea clearance and maximum
tubular clearances would have reached adult
levels.

9. Neonatal Physiology

AVP has been measured in amniotic fluid and
is present in fetal circulation by mid-gestation.

At birth, vasopressin levels are high but
decrease into “normal” ranges within 1–2 days

In neonates, AVP responds to the same stimuli
as older children and adults. However, the
ability to concentrate urine to the maximum
achieved by older children or adults does not
occur.

10. Neonatal Physiology

Why a low urine concentrating ability in
neonates?

Decreased glomerular filtration rate (decreased
renal blood flow)

reduced epithelial cell function in the loop of
Henle and collecting duct

reduced AVP receptor number and affinity

reduced water channel number or presence on
the cell surface

11. Neonatal Physiology

Neonates have increased non-urinary water
losses (skin and respiratory) as a function of
weight/BSA, which are greater compared to
older children and adults.

The net effect is that neonates are at greater
risk of dehydration either due to inadequate
water provision or to high osmolar loads

Risk of volume overload (hyponatremia/hypo-
osmolality) if fluids are given too rapidly

12. Body Fluid Compartments

Water accounts for 60% of TBW in men and
50% in women while infants have a higher
proportion of water, 70–80% (due to the lower
proportion of muscle in comparison to adipose)

The higher proportion of TBW to whole body
weight in younger children is mainly due to the
larger ECF volume when compared to adults.

disproportionate weight of brain, skin, and the
interstitium in younger children contributes to
the variability in the ECF volume.

13. Body Fluid Compartments

Water is distributed between two main
compartments, the intracellular fluid
compartment (ICF) and extracellular fluid
compartment (ECF)

The intracellular compartment makes up
approximately 2/3 of the TBW. The ECF
constitutes 1/3 of the TBW composed of
plasma and interstitial fluid

14. Maintenance Fluid Requirements

Maintenance requirements are related to
metabolic rate and affected by body
temperature.

Insensible losses account for about half of
maintenance requirements.

Volume must rarely be exactly determined, but
generally should aim to provide an amount of
water that does not require the kidney to
significantly concentrate or dilute the urine.

15. Maintenance Fluid Requirements

The Holliday-Segar method remains the
simplest in approximating maintenance fluid
requirements.

It is based on caloric requirement each day and
the amount of fluid needed based on caloric
expenditure.

16. Maintenance Fluid Requirements
Table 3
Caloric, Water, and Basic Electrolyte Requirements Based on Weight
Sodium Chloride Potassium
mEq/100 mEq/100 mEq/100
Body weight (kg) Calories Water mL H2 O mL H2 O mL H2 O
3–10 kg 100/kg 100/kg 3 2 2
11–20 kg 50/kg 1000 mL + 3 2 2
50 mL/kg for
each kg above
>20 kg 20/kg 1500 mL + 3 2 2
20 mL/kg for
each kg above
20

17. Maintenance Fluid Requirements

5% dextrose is provided to deliver 5 g of
carbohydrate per 100 mL of solution or 50 g/L

For a limited period of time (generally under 5–
7 days) this amount of carbohydrate will be
sufficient to prevent protein breakdown.

If it is anticipated that there will be a need for
prolonged parenteral therapy, a higher dextrose
solution will be required.

18. Intravenous Fluids

Intravenous fluids that are safe to administer
parenterally based on their osmolality

Each solution is selected based on the clinical
status of the patient. Solutions without dextrose
(0.45% isotonic saline) or without electrolytes
5% dextrose in water are only administered
under special clinical situations.

19. Intravenous Fluids
Solutions Used for Intravenous Administration
Osmolality Sodium Potassium Chloride Dextrose
Solution mOsm/L mEq/L Eq/L mEq/L mOsm/L
0.9% Isotonic saline 308 154 154
(normal saline)
0.45% Isotonic saline 154 77 77∗
(1/2 Normal)
5% Dextrose in Water 278
5% Dextrose + 0.33% 378 50 50 278
isotonic saline
5% Dextrose + 0.45% 432 77 77 278
isotonic saline
∗ The lowest intravenous solution that can be used safely is 0.45% isotonic saline with an
osmolality of 154 mOsm/L or approximately 50% of plasma. Any solution with an osmolality
under this value will result in cell breakdown with a large potassium load to the extracellular
space resulting in severe hyperkalemia leading to cardiac arrhythmias and possibly death.

20. Dehydration and Fluid Therapy

Dehydration is significant depletion of body
water and electrolytes

Dehydration usually due to gastroenteritis
remains a major cause of morbidity and
mortality in infants and young children
worldwhile.

Infants are particularly susceptible on account
of their greater baseline fluid requirements
and higher evaporative losses. (High surface
area) and their inablity to communicate thirst.

21. Dehydration and Fluid Therapy
Aetiology and Pathophysiology

It results from increased fluid loss or a
decrease intake or both

Fluid is always lost with accompanying
electrolytes, in varying concentrations.

Common causes include (gastroenteritis, DKA,
burns, 3rd
space losses eg. I/O)

22. Dehydration and Fluid therapy
Symptoms and Signs

They vary based on the fluid deficit.

Dehydration without hemodynamic changes
represents mild dehydration (5% body weight
or 3% bw in adolescents)

Tachycardia represents moderate dehydration.
(10% body weight or 6% bw in adolescents)

Hypotension with impaired perfusion means
severe dehydration. (15% body weight in
infants or 9% in adolescents)

23. Dehydration and Fluid Therapy
Severity of Dehydration
Characteristics
Infants Mild – 1–5% Moderate – 6–9% Severe – >10%
(=> 15% =
shock)
Older Children Mild – 1–3% Moderate – 3–6% Severe – >6% (=>
9% = shock
Pulse Full, normal Rapid Rapid, weak
Systolic BP Normal Normal, Low Very Low
Urine output Decreased Decreased Oliguria
(<1 mL/kg/h)
Buccal mucosa Slightly dry Dry Parched
Ant fontanel Normal Sunken Markedly sunken
Eyes Normal Sunken Markedly sunken
Skin turgor/
capillary refill Normal Decreased Markedly
decreased
Cool, mottling,
Skin Normal Acrocyanosis

24. Dehydration and Fluid Therapy

Treatment

Treatment is best approached by considering
an estimated fluid deficit, ongoing losses and
maintenance requirements

The volume, composition and rate of infusion of
replacement fluids differs for each.

Most importantly, monitoring the vital signs,
clinical appearance and urine output, serves as
an appropriate guide.

25. Dehydration and Fluid Therapy

Treatment

Children with evidence of circulatory
compromise – severe dehydration, should be
given IVFs in the initial resuscitation

Those unable or unwilling to drink or having
repetitive vomiting should receive fluids IV,
through an NG tube or by administering
repeated small amounts orally.

26. Dehydration and Fluid Therapy
Resuscitation

Patients with symptoms and signs of
hypoperfusion, should receive fluid
resuscitation with boluses of isotonic fluid (e.g.
0.9% Saline or Lactated Ringers)

Resuscitation phase should reduce moderate
or severe dehydration to a deficit less than 8%
body weight.

20ml/kg (2% body weight) is given IV over 20-
30 minutes.

27. Dehydration and Fluid Therapy

Most importantly response of the patient to
resuscitation determines the endpoint of fluid
resuscitation.

This includes (Restoration of tissue perfusion
and BP and return of increased heart rate
toward normal)

28. Dehydration and Fluid Therapy
Deficit Replacement

The resuscitation phase should have reduced
moderate or severe dehydration to a deficit of /
about 8%.

The remaining deficit can be replaced by
providing 10ml/kg (1% body weight) per hour
over the next 8hours.

Deficits in total body potassium is usually
began after urine output has improved (restored
tissue perfusion) . 2-3mEq/24hrs

29. Dehydration and Fluid Therapy
Ongoing losses

Volume of ongoing losses should be measured
directly (eg. NG tube aspirates, catheter ,
stools) or estimated e.g. 10ml/kg per diarrheal
stool.

30. Oral Rehydration Therapy

Oral Fluid Therapy is effective, safe,
convenient and effective compared with IV
therapy.

It should be used for children with mild to
moderate dehydration who are accepting fluids
orally.

Contraindications to ORT is incessant copious
vomiting, surgical abdomen, I/O.

Soda, juice and fizzy drinks generally have too
little sodium and too much carbs.

31. Oral Rehydration Therapy

ORS is effective in patients with dehydration
regardless of age, cause or type of electrolyte
imbalance. [in the presence of unimpaired renal
function]

If ORS is unavailable, a sodium/glucose
solution can be used.

SSS are prepared by adding 1tbsp of sugar to
½ tsp of salt in 1L of water. Though less
effective, it can be used for treating diarrhea.

32. Oral Rehydration Therapy
Administration

Mild dehydration – 50ml/kg over 4hours

Moderate dehydration – 100ml/kg over 4hours

10ml/kg for each diarrheal stool (up to a max of
240mls)

Patient should be reassessed after 4hours.

N.B – Patients with cholera may require many
gallons of fluid per day

33. Oral Rehydration Therapy

Vomiting is not a contraindication to oral
rehydration. Small frequent volumes should be
given. (e.g 5ml every 5mins and increased
gradually as tolerated)

Importance of encouraging oral feeds.

34. CONCLUSION