endocrine and metabolic disorders
Volume Depletion
Diagnosis of Volume Depletion
Clinical findings Sometimes serum electrolytes, bloodureanitrogen (BUN), and creatinine Rarely plasma osmolality and urine chemistries Volume depletion is suspected in patients at risk, most often in patients with a history of inadequate fluid intake (especially in comatose or disoriented patients), increased fluid losses, diuretic therapy, and renal or adrenal disorders. Diagnosis is usually clinical. If accurate patient weights immediately before and after fluid loss are known, the difference is an accurate estimate of volume loss; for example, pre- and post-workout weights are sometimes used to monitor dehydration in athletes. When the cause is obvious and easily correctable (eg, acute Overview of Gastroenteritis in otherwise healthy patients), laboratory testing is unnecessary; otherwise, serum electrolytes, BUN, and creatinine are measured. Plasma osmolality and urine sodium, creatinine, and osmolality are measured when there is suspicion of clinically meaningful electrolyte abnormality that is not clear from results of serum tests and for patients with cardiac or renal disease. When Some devices can help assess volume status but are not in widespread use. Point-of-care ultrasonography evaluating inferior vena cava distension is sometimes used to assess volume status when the severity of volume loss is unclear. Also, ultrasonography of the lungs can show findings of pulmonary edema and thus fluid overload. Central venous pressure and pulmonary artery occlusion pressure are decreased in volume depletion, but measurement with an invasive device such as a central venous catheter or pulmonary artery catheter is rarely required, although it is occasionally necessary for patients for whom even small amounts of added volume may be detrimental, such as those with unstable Heart Failure (HF) or advanced The following concepts are helpful when interpreting urine electrolyte and osmolality values: During volume depletion, normally functioning kidneys conserve sodium. Thus, the urine sodium concentration is usually low,<15 mEq/L (< 15 mmol/L); the fractional excretion of sodium (urine sodium/serum sodium divided by urine creatinine/serum creatinine) is usually<1%; also, urine osmolality is often high,>450 mOsm/kg (> 450 mmol/kg). When Metabolic Alkalosis is combined with volume depletion, urine sodium concentration may be high because large amounts of bicarbonate are spilled in the urine, obligating the excretion of sodium to maintain electrical neutrality. In this instance, a urine chloride concentration of Misleadingly high urinary sodium (generally>20 mEq/L [> 20 mmol/L]) or low urine osmolality can also occur due to renal sodium losses resulting from renal disease, diuretics, or adrenal insufficiency. Volume depletion frequently increases the BUN and serum creatinine concentrations; the ratio of BUN to creatinine is often>20:1. Values such as hematocrit often increase in volume depletion but are difficult to interpret unless baseline values are known. 