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  • Dehyration: What is it?

    Dehydration describes a state of negative fluid balance that may be caused by numerous disease entities. Diarrheal illnesses are the most common etiologies. Worldwide, dehydration secondary to diarrheal illness is the leading cause of infant and child mortality.

    Pathophysiology

    The negative fluid balance that causes dehydration results from decreased intake, increased output (renal, GI, or insensible losses), or fluid shift (ascites, effusions, and capillary leak states such as burns and sepsis). The decrease in total body water causes reductions in both the intracellular and extracellular fluid volumes. Clinical manifestations of dehydration are most closely related to intravascular volume depletion. As dehydration progresses, hypovolemic shock ultimately ensues, resulting in end organ failure and death.

    Young children are more susceptible to dehydration due to larger body water content, renal immaturity, and inability to meet their own needs independently. Older children show signs of dehydration sooner than infants due to lower levels of extracellular fluid (ECF).

    Dehydration can be categorized according to osmolarity and severity. Serum sodium is a good surrogate marker of osmolarity assuming the patient has a normal serum glucose. Dehydration may be isonatremic (130-150 mEq/L), hyponatremic (< 130 mEq/L), or hypernatremic (>150 mEq/L). Isonatremic dehydration is the most common (80%). Hypernatremic and hyponatremic dehydration each comprise 5-10% of cases. Variations in serum sodium reflect the composition of the fluids lost and have different pathophysiologic effects.

        Isonatremic (isotonic) dehydration occurs when the lost fluid is similar in sodium concentration to the blood. Sodium and water losses are of the same relative magnitude in both the intravascular and extravascular fluid compartments.
        Hyponatremic (hypotonic) dehydration occurs when the lost fluid contains more sodium than the blood (loss of hypertonic fluid). Relatively more sodium than water is lost. Because the serum sodium is low, intravascular water shifts to the extravascular space, exaggerating intravascular volume depletion for a given amount of total body water loss.
        Hypernatremic (hypertonic) dehydration occurs when the lost fluid contains less sodium than the blood (loss of hypotonic fluid). Relatively less sodium than water is lost. Because the serum sodium is high, extravascular water shifts to the intravascular space, minimizing intravascular volume depletion for a given amount of total body water loss.

    Neurologic complications can occur in hyponatremic and hypernatremic states. Severe hyponatremia may lead to intractable seizures, whereas rapid correction of chronic hyponatremia (>2 mEq/L/h) has been associated with central pontine myelinolysis. During hypernatremic dehydration, water is osmotically pulled from cells into the extracellular space. To compensate, cells can generate osmotically active particles (idiogenic osmoles) that pull water back into the cell and maintain cellular fluid volume. During rapid rehydration of hypernatremia, the increased osmotic activity of these cells can result in a large influx of water, causing cellular swelling and rupture; cerebral edema is the most devastating consequence. Slow rehydration over 48 hours generally minimizes this risk.

    Frequency: United States

    Diarrheal illnesses in children causes 3 million physician visits, 220,000 hospitalizations (10% of all children who require hospitalization), and 400 deaths per year. On average, North American children younger than 5 years have 2 episodes of gastroenteritis per year.


    Frequency: International

    Diarrheal illnesses with subsequent dehydration account for nearly 4 million deaths per year in infants and children. The overwhelming majority of these deaths occur in developing nations.

    Mortality/Morbidity

    Mortality and morbidity generally depend on the severity of dehydration and the promptness of oral or intravenous rehydration. If treatment is rapidly and appropriately obtained, morbidity and mortality are low.

    Routine use of hypotonic parenteral fluids in hospitalized children has been associated with hyponatremia and subsequent neurologic complications and death. Monitoring the efficacy and complications of parenteral rehydration with accurate fluid balances and serum electrolytes is crucial.


    Age

    Children younger than 5 years are at the highest risk.

    History

    The following should be considered in patients with dehydration:

        Intake of fluids, including the volume, type (hypertonic or hypotonic), and frequency
        Urine output, including the frequency of voiding (last wet diaper), presence of concentrated or dilute urine, hematuria
        Stool output, frequency of stools, stool consistency, presence of blood or mucus in stools
        Emesis, including frequency and volume and whether bilious or nonbilious, hematemesis
        Contact with ill people, especially others with gastroenteritis, use of daycare
        Underlying illnesses, especially cystic fibrosis, diabetes mellitus, hyperthyroidism, renal disease
        Fever
        Appetite patterns
        Weight loss
        Travel
        Recent antibiotic use
        Possible ingestions
        
    Physical

    A complete physical examination may assist in determining the underlying cause of the patient's dehydration and in defining the severity of dehydration. The clinical assessment of severity of dehydration determines the approach to management. In general, physical signs of dehydration have poor precision and accuracy. Rather than attempting to assign an exact percentage of dehydration, one should attempt to place the child in one of 3 broad categories.

    The determination of dehydration severity should be based on the overall constellation of symptoms. Patients in a given category need not exhibit all the signs and symptoms listed below. Literature reviews have suggested that delayed capillary refill, delayed skin turgor, and abnormal respiratory pattern are the most reliable clinical signs of dehydration in children. Validated clinical dehydration scales may be a useful adjunct to predict need for intravenous fluid and longer stays in the emergency department.

    MEDSCAPE General Abstract

    Created by Rich on 22/12/2012 in Medical Stuff

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