Replace urine output mL/mL with a solution that is based on the measured urine electrolytes
Output from surgical drains and chest tubes, when significant, should be measured and replaced. Third space lossesmanifest with edema and ascites and are due to a shift of fluid from the intravascular space into the interstitial space. Thirdspace losses cannot be quantitated. Nonetheless, these lossescan be large and lead to intravascular volume depletion, despiteweight gain from edema or ascites. Replacement of third spacefluid is empirical but should be anticipated in patients who areat risk, such as children who have burns or abdominal surgery.Third space losses and chest tube output are isotonic and usually require replacement with an isotonic fluid, such as normal saline or Ringer’s lactate. Adjustments in the amount ofreplacement fluid for third space losses are based on continuing assessment of the patient’s intravascular volume status.
Dehydration, most often due to gastroenteritis, is common in children. The first step in caring for a dehydrated child is to assess the degree of dehydration. The degree of dehydration dictates the urgency of the situation and the volume of fluid needed for rehydration. Table 33-5 summarizes the clinical features that are present with varying degrees of dehydration.
A patient with mild dehydration has few clinical signs or symptoms. The history may describe decreased intake but
Infants and young children Thirsty, alert; restless Thirsty; restless or lethargic; Drowsy; limp, cold, sweaty, cyanotic extremities; may irritable be comatose
Older children Thirsty, alert Thirsty, alert (usually) Usually conscious (but at reduced level), apprehensive; cold, sweaty, cyanotic extremities; wrinkled skin on fingers and toes; muscle cramps
Respirations Normal Deep, may be rapid Deep and rapid
Data from World Health Organization.
more often increased fluid losses. An infant with moderate dehydration has demonstrable physical signs and symptoms. The patient needs fairly prompt intervention. A patient with severe dehydration is gravely ill. The decrease in blood pressure indicates that vital organs may be receiving inadequate perfusion (shock) (see Chapter 40). Such a patient should receive immediate and aggressive intravenous (IV) therapy. Clinical assessment of dehydration is only an estimate; the patient must be continually re-evaluated during therapy. The degree of dehydration is underestimated in hypernatremic dehydration because the osmotically driven shift of water from the intracellular space to the extracellular space helps to preserve the intravascular volume.
Serum blood urea nitrogen (BUN) and creatinine concentrations are useful in assessing a child with dehydration. Volume depletion without renal insufficiency may cause a disproportionate increase in the BUN, with little or no change in the creatinine concentration. This is secondary to increased passive reabsorption of urea in the proximal tubule caused by appropriate renal conservation of sodium and water. This increase in the BUN may be absent or blunted in a child with poor protein intake because urea production depends on protein degradation. Conversely, the BUN may be disproportionately increased in a child with increased urea production, as occurs in a child with a gastrointestinal bleed or a child who is receiving glucocorticoids. A significant elevation of the creatinine concentration suggests renal injury.
The urine specific gravity is usually elevated (≥1.025) incases of significant dehydration but decreases after rehydration.
With dehydration, a urinalysis may show hyaline and granularcasts, a few white blood cells and red blood cells, and 30 to 100 mg/dL of proteinuria. These findings usually are not associatedwith significant renal pathology, and they remit with therapy.Hemoconcentration from dehydration causes an increase inthe hematocrit and hemoglobin.
Calculation of Fluid Deficit