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Fluids and Electrolytes
Disorders affecting the body fluids and electrolytes are treated by supplying maintenance requirements, correcting volume and electrolyte deficits, and by replacing ongoing abnormal losses dehydration, fluids, electrolytes.
Dehydration
Maintenance fluid and electrolytes
Sensible losses, primarily urinary, account for approximately 50% of daily fluid requirements. Caloric requirements for growth can be estimated as equivalent on a kcal-for-mL basis to water requirements.
Factors that increase the requirements for calories and water are fever (10% for each degree), physical activity, ongoing gastrointestinal losses, hyperventilation, and hypermetabolic states. Anuria, oliguria, and
Maintenance Requirements for Fluid and Electrolytes
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Body Weight
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0 to 10 kg
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10 to 20 kg
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>20 kg
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Water Volume
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100 mL/kg
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1000 mL + 50 mL/kg for each kg >10 kg
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1500 mL + 20 mL/kg for each kg >20 kg
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Sodium
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3 mEq/kg
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3 mEq/kg
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3 mEq/kg
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Potassium
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2 mEq/kg
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2 mEq/kg
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2 mEq/kg
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Chloride
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5 mEq/kg
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5 mEq/kg
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5 mEq/kg
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Abnormal losses, such as those arising from nasogastric aspiration, prolonged diarrhea or burns, should be measured, and replaced on a volume for
Estimation of deficit
Estimation of volume depletion should assess fever, vomiting, diarrhea, and urine output. Recent feeding, including type and volume of food and drink, and weight change should be
Estimation of Dehydration
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Degree of Dehydration
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Mild
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Moderate
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Severe
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Weight Loss--Infants
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5%
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10%
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15%
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Weight Loss--Children
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3-4%
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6-8%
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10%
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Pulse
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Normal
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Slightly increased
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Very increased
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Blood Pressure
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Normal
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Normal to orthostatic, >10 mm Hg change
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Orthostatic to shock
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Behavior
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Normal
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Irritable
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Hyperirritable to lethargic
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Thirst
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Slight
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Moderate
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Intense
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Mucous Membranes
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Normal
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Dry
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Parched
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Tears
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Present
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Decreased
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Absent tears, sunken eyes
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Anterior Fontanelle
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Normal
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Normal to sunken
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Sunken
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External Jugular Vein
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Visible when supine
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Not visible except with supraclavicular pressure
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Not visible even with supraclavicular pressure
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Skin
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Capillary refill <2 sec
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Delayed capillary refill, 2-4 sec (decreased turgor)
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Very delayed capillary refill (>4 sec), tenting; cool, acrocyanotic, or mottled skin
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Urine Specific Gravity (SG)
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>1.020
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>1.020; oliguria
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Oliguria or anuria
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The percent dehydration is used to calculate the milliliters of body water deficit per kilogram of body weight.
Isonatremic dehydration
The most common cause of dehydration in infants is diarrhea. Children who have a brief illness and anorexia usually present with isotonic dehydration.
Oral rehydration
Moderate volume depletion should be treated with oral fluids. The majority of patients who have gastroenteritis can be treated with oral rehydration therapy.
Small aliquots of oral hydration solution ( Ricelyte, Pedialyte, Resol, Rehydralyte) are
Parenteral rehydration
Parenteral fluids should be given for severe volume depletion, altered states of consciousness, intractable vomiting, and abdominal distention or ileus.
The first phase of treatment rapidly expands the vascular volume. Intravenous normal saline or Ringers lactate (10-20 mL/kg) should be given over 1 hour.
The next phase of treatment is aimed at correcting the deficit, providing maintenance, and replacing ongoing abnormal losses. In severe depletion, half of the calculated deficit is
Hyponatremia and hyponatremic dehydration
The signs and symptoms of hyponatremia correlate with the rapidity and extent of the fall in serum Na+ concentration. Symptoms include apathy, nausea, vomiting, cramps, weakness, headache, seizures, and
Management of hyponatremia
Hypovolemic patients who have hyponatremia first require volume repletion with normal saline, then a solution containing salt is given to correct the Na+ deficit (10 to 12 mEq/kg of body weight or 15 mEq/kg in severe hyponatremia) and to provide the
Symptomatic hyponatremia (headache, lethargy, disorientation) requires urgent therapy to prevent seizures or coma.
Hypertonic saline (3% saline solution), with or without a loop diuretic and water restriction, should be used to raise the serum Na+ by 1 to 2 mEq/L per hour or halfway toward normal during the
Hypernatremia and hypernatremic dehydration
The hypernatremic patient is usually also dehydrated. Total body Na+ most commonly is decreased. Affected patients frequently exhibit lethargy or confusion, muscle twitching, hyperreflexia, or
Differential Diagnosis
Diarrhea, which usually results in isonatremic or hyponatremic dehydration, may cause hypernatremia in the presence of persistent fever, anorexia, vomiting, and decreased fluid
Potassium disorders
Abnormalities of serum K+ are potentially life-threatening because of effects on cardiac function.
Hypokalemia
Hypokalemia (serum K+ concentration <3 mEq/L) is most frequently caused by gastrointestinal K+ losses or renal losses (nasogastric suction, protracted vomiting, diuretics, renal tubular disease).
Hyperkalemia
The most common cause of hyperkalemia (K+ >5.5 mEq/L) is "pseudohyperkalemia" from hemolysis of the blood sample. This cause should be excluded by repeating the measurement on a free-flowing venous sample. Children may display hyperkalemia in metabolic acidosis, tissue catabolism, renal failure, volume depletion, or hypoaldosteronism.
In salt-losing congenital adrenal hyperplasia, due to complete deficiency of the enzyme 21-hydroxylase, the symptoms in affected male infants appear in the first weeks of life and include dehydration and failure
Acid-base disorders
The pH of the body fluids normally is between 7.35 and 7.45.
Metabolic acidosis
Acidosis results from the addition of acid or the removal of alkali from body fluids, and it causes a compensatory increase in ventilation (respiratory alkalosis) and a fall in Pco2. Manifestations of acidosis include depressed myocardial contractility, arrhythmias, hypotension, and pulmonary edema.
Diagnosis
Addition of a fixed acid to the extracellular fluid causes the formation of unmeasured anions. These unmeasured anions are referred to as the anion gap, which can be estimated as:
Normal anion gap (hyperchloremic) acidosis
This disorder occurs when HCO3- is lost from the body, either through the
Metabolic alkalosis
Alkalosis results from a gain of base or a loss of acid. The common clinical manifestations are lethargy, confusion, neuromuscular irritability, arrhythmias, and
Respiratory acidosis
Respiratory acidosis is induced by an increase in Pco2, which lowers plasma pH. Causes of respiratory acidosis include airway obstruction, and
Respiratory alkalosis
Respiratory alkalosis is caused by a decrease in Pco2, secondary to hyperventilation, resulting in dizziness, confusion, and
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