From the Guidelines
Assessing a patient's hydration status in the renal context requires a comprehensive approach combining physical examination, laboratory tests, and clinical history, with a focus on evaluating for signs of dehydration and fluid overload, as well as monitoring urine output and serum electrolytes, as recommended by the most recent guidelines 1. To evaluate hydration status, begin by checking for physical signs of dehydration, including:
- Dry mucous membranes
- Decreased skin turgor
- Sunken eyes
- Orthostatic hypotension
- Tachycardia Also, check for signs of fluid overload, such as:
- Peripheral edema
- Jugular venous distension
- Crackles in the lungs Laboratory assessment should include:
- Serum electrolytes (particularly sodium)
- Blood urea nitrogen (BUN)
- Creatinine
- BUN/creatinine ratio, which typically exceeds 20:1 in dehydration
- Urine specific gravity and osmolality to evaluate urine concentration Urine output should be monitored, with oliguria (less than 0.5 mL/kg/hour) suggesting potential dehydration or acute kidney injury. Weight changes can provide an objective measurement of fluid status, with rapid weight loss indicating fluid deficit and weight gain suggesting fluid retention. These assessments are crucial because the kidneys regulate fluid balance, and improper hydration can lead to acute kidney injury, electrolyte imbalances, or exacerbation of chronic kidney disease, as highlighted in the 2013 ACCF/AHA guideline for the management of heart failure 1. In patients with existing renal impairment, hydration assessment becomes even more critical, as their ability to concentrate or dilute urine may be compromised, and careful management of fluid balance is necessary to prevent complications, as discussed in the context of hyperglycemic crises in patients with diabetes mellitus 1.
From the FDA Drug Label
As with any effective diuretic, electrolyte depletion may occur during furosemide therapy, especially in patients receiving higher doses and a restricted salt intake All patients receiving furosemide therapy should be observed for these signs or symptoms of fluid or electrolyte imbalance (hyponatremia, hypochloremic alkalosis, hypokalemia, hypomagnesemia or hypocalcemia): dryness of mouth, thirst, weakness, lethargy, drowsiness, restlessness, muscle pains or cramps, muscular fatigue, hypotension, oliguria, tachycardia, arrhythmia or gastrointestinal disturbances such as nausea and vomiting. Serum electrolytes, (particularly potassium), CO 2, creatinine and BUN should be determined frequently during the first few months of furosemide therapy and periodically thereafter.
To examine a patient's hydration status in the renal context, monitor for signs and symptoms of fluid or electrolyte imbalance, such as:
- Dryness of mouth
- Thirst
- Weakness
- Lethargy
- Drowsiness
- Restlessness
- Muscle pains or cramps
- Muscular fatigue
- Hypotension
- Oliguria
- Tachycardia
- Arrhythmia
- Gastrointestinal disturbances Laboratory tests should be performed, including:
- Serum electrolytes (particularly potassium)
- CO2
- Creatinine
- BUN These tests should be done frequently during the first few months of furosemide therapy and periodically thereafter 2.
From the Research
Assessing Hydration Status in the Renal Context
To examine a patient's hydration status in the renal context, several methods can be employed, including:
- Bioelectrical impedance vector analysis (BIVA) to estimate body mass and water composition by bioelectrical impedance measurements, resistance, and reactance 3
- Changes in body weight, haematological and urine parameters, bioelectrical impedance, skinfold thickness, heart rate, and blood pressure changes 4
- Plasma osmolality, urine osmolality, and urine specific gravity as markers of hydration 4
- Urine colour as a reasonable indicator of hydration when laboratory analysis is not available or when a quick estimate of hydration is necessary 4
- Assessment of fluid balance and fluid overload, particularly in patients with renal dysfunction 5
- Monitoring of volume status, choice of fluid, and amount of fluid, as well as assessment of fluid status using various monitoring devices 5
Techniques for Assessing Hydration Status
Various techniques can be used to assess hydration status, including:
- Urinary indices (volume, colour, protein content, specific gravity, and osmolality) 4, 6
- Blood-borne indices (haemoglobin concentration, haematocrit, plasma osmolality, and sodium concentration) 6
- Bioelectrical impedance analysis 6, 7
- Pulse rate and systolic blood pressure response to postural change 6
- Isotope dilution, neutron activation analysis, and tracer appearance 7
- Hematologic indices and urinary markers 7
Markers of Hydration Status
Several markers can be used to determine hydration status, including:
- Urinary measures of colour, specific gravity, and osmolality, which are more sensitive at indicating moderate levels of hypohydration than blood measurements 6
- Body mass changes, which can be used to determine hydration status, particularly in an exercise situation 6
- Plasma osmolality, urine osmolality, and urine specific gravity, which are widely used markers of hydration 4