How to assess for dehydration?

From the Guidelines

Assessing Dehydration Dehydration should be assessed using a combination of clinical evaluation and laboratory tests, including measuring urine specific gravity, which should be between 1.020-1.030, and urine output, which should be at least 0.5 mL/kg/hour 1.

Clinical Evaluation

• Monitoring serum electrolyte levels, such as sodium and potassium, can help identify dehydration, with abnormal levels indicating potential hypovolemia 1.
• Assessing serum osmolality can also help identify dehydration, with a threshold value of >300 mOsm/kg indicating dehydration 1.

Laboratory Tests

• Measuring urine osmolality can help assess hydration status, with a value of <300 mOsm/kg indicating dehydration 1.
• Monitoring electrolyte levels, such as sodium and potassium, can help identify dehydration, with abnormal levels indicating potential hypovolemia 1.

Rehydration Therapy

• Oral rehydration solution (ORS) is recommended as the first-line therapy for mild to moderate dehydration in infants, children, and adults with acute diarrhea from any cause 1.
• Intravenous fluids, such as 0.9% sodium chloride or lactated Ringer's solution, may be necessary for severe dehydration or when oral rehydration is not possible 1. Some key points to consider when assessing dehydration include:
• Degree of dehydration: Assessing the degree of dehydration is crucial in determining the appropriate treatment, with mild to moderate dehydration typically treated with ORS and severe dehydration requiring intravenous fluids 1.
• Electrolyte imbalance: Monitoring electrolyte levels, such as sodium and potassium, is essential in assessing dehydration, as abnormal levels can indicate potential hypovolemia 1.
• Urine output: Monitoring urine output is critical in assessing hydration status, with a value of at least 0.5 mL/kg/hour indicating adequate hydration 1.

From the Research

Assessment of Dehydration

To assess dehydration, several methods can be employed, including:

• Urine concentration: can be used to assess fluid intake adequacy or to diagnose dehydration, but its use should be approached with caution due to potential misapplication of thresholds 2
• Bioelectrical impedance vector analysis (BIVA): can be used to evaluate hydration status in patients with chronic kidney disease, and has been associated with clinical and biochemical outcomes and mortality 3
• Body fluids: saliva, sweat, and tear can be used as potential markers of hydration status, but their collection and evaluation have limitations and require careful consideration of the setting and method of collection 4
• Serum osmolality, serum sodium concentration, inferior vena cava ultrasonography, and axillary dryness: have been found to have high diagnostic value for assessing hydration status in older patients 5
• Changes in body weight, haematological and urine parameters, bioelectrical impedance, skinfold thickness, heart rate and blood pressure changes: are among the indices that have been developed to assess hydration levels accurately in humans 6

Methods to Assess Hydration Status

Some of the methods used to assess hydration status include:

• Urine osmolality and specific gravity: are widely used markers of hydration 2, 6
• Urine colour: can be used as a quick estimate of hydration, and has been found to be a reasonable indicator of hydration 6
• Plasma osmolality: is a widely used marker of hydration 6
• Biochemical hydration assessment markers: within blood and urine, such as serum and urinary albumin, hematocrit, serum electrolytes and creatinine 3

Limitations of Hydration Assessment Methods

Some of the limitations of hydration assessment methods include:

• Urine concentration: can be misapplied or misinterpreted, leading to dubious conclusions 2
• Body fluids: collection and evaluation of saliva, sweat, and tear have limitations and require careful consideration of the setting and method of collection 4
• Clinical signs: such as skin turgor test, sunken eyes, dry mouth, tachycardia, orthostatic dysregulation, and dark urine, have been found to be of inadequate diagnostic value for assessing hydration status in older patients 5