Fluid and-electrolytes-2010

AKUFFO QUARDE

INTERN (PEDIATRICS, TEMA GEN. HOSP)

Fluid and Electrolyte Management

Physiology of water homeostasis Body Fluid Compartments Maintenance Fluid Requirements Dehydration and Fluid therapy Oral Rehydration Therapy Practical Examples

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.


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)


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


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.


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]

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.

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.

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

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

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.

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

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.


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.

Maintenance Fluid RequirementsTable 3Caloric, Water, and Basic Electrolyte Requirements Based on Weight

Sodium Chloride Potassium mEq/100 mEq/100 mEq/100Body weight (kg) Calories Water mL H2 O mL H2 O mL H2 O3–10 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


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.

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.

Intravenous Fluids

Solutions Used for Intravenous Administration Osmolality Sodium Potassium Chloride DextroseSolution mOsm/L mEq/L Eq/L mEq/L mOsm/L0.9% Isotonic saline 308 154 154(normal saline)

0.45% Isotonic saline 154 77 77∗(1/2 Normal)

5% Dextrose in Water 2785% Dextrose + 0.33% 378 50 50 278isotonic saline

5% Dextrose + 0.45% 432 77 77 278isotonic 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.

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.


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)

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)

Dehydration and Fluid TherapySeverity of DehydrationCharacteristicsInfants 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, weakSystolic BP Normal Normal, Low Very LowUrine output Decreased Decreased Oliguria (<1 mL/kg/h)Buccal mucosa Slightly dry Dry ParchedAnt fontanel Normal Sunken Markedly sunkenEyes Normal Sunken Markedly sunken

Skin turgor/capillary refill Normal Decreased Markedly decreased Cool, mottling,Skin Normal Acrocyanosis


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.


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.


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.


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)


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


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.

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.


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.


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


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.

CONCLUSION

Health & Medicine

Fluid and-electrolytes-2010