Dehydration

Initial evaluation of a child with dehydration should be directed towards determining the severity of dehydration and illness. This can be assessed through utilization of the Pediatric Assessment Triangle (PAT):

• Appearance: Tone, interactiveness, gaze, cry, consolability.
• Work of Breathing: Breath sounds, positioning, retractions, nasal flaring.
• Circulation: Pallor, mottling, cyanosis.

In children that are determined to have severe dehydration, correlating with a state of hypovolemic shock, it is important to restore their intravascular volume as quickly as possible, regardless of serum osmolarity or cause of dehydration. Intravenous (IV) access or intraosseous (IO) access should be obtained, and isotonic fluid, typically normal saline, should be infused as 20 mL per kg boluses over 15 – 20 minutes. The child’s degree of hydration and hypovolemia should be clinically reassessed after each fluid bolus.

After primary assessment of the patient, a thorough history is important to give clues to the degree and cause of dehydration. One should focus their questioning on determining whether there is concern for decreased intake or increased output as a general cause. Once it is determined that there is historical concern for possible dehydration, you can probe further into signs of dehydration, and then examine for clinical signs. Historically, it is important to ask about three factors:

• Tiredness or listlessness.
• Absence of tears when crying in an infant.
• Urine output, with decreased output suggesting worse degree of dehydration and increased output suggesting possible cause of dehydration, as seen in diabetes mellitus or insipidus.

From an examination standpoint, it is important to look for seven additional factors:

• Decreased skin elasticity.
• Increased capillary refill > 2 seconds.
• Abnormal respirations.
• Dry mucous membranes.
• Sunken eyes.
• Abnormal pulses.
• Tachycardia.

All ten clinical signs of dehydration need to be assessed in the context of the patient, as none of them individually are both sensitive and specific for degree of dehydration. Tachycardia is often the first sign, however it is neither sensitive nor specific (sen 0.46, sp 0.79) as it can be seen with fever, agitation, or pain. Alternatively, decreased skin elasticity is very specific (0.97) but not sensitive (0.35) as it is found in very few patients unless severely dehydrated. Conversely, parental history of decreased urine output is the most sensitive (0.85) but not specific (0.53). Therefore, the general rule for the degree of dehydration and the number of findings on history/physical exam is listed here:

Depending on the degree of dehydration, therapy consists of either oral or intravenous rehydration. For mild to moderate dehydration, oral rehydration therapy (ORT) is recommended.

• Mild Dehydration: Recommended treatment is oral rehydration.
• Moderate Dehydration: Recommended treatment is oral rehydration. Can consider Ondanestron anti-emetic if nauseated.
• Severe Dehydration: Recommended treatment is intravenous/intraosseous isotonic fluid bolus(es) to stabilize shock state administered in volumes of 20mL/kg up to every 20 minutes. Additional treatment is continued isonatremic glucose containing intravenous fluid replacement.

The oral rehydration solution is half a teaspoon of salt, six teaspoons of sugar, and one liter of clear water.

Calculating the Amount of Fluid Replacement Needed

• Weight (kg) / (1 - % dehydration) = baseline weight.
• Baseline weight - current weight = weight loss (kg) = equivalent to mL's deficit x 1000.

ORT consists of small amounts of solution given orally over a period of time. Goal replacement is to replace half of a patient’s fluid deficit over the first eight hours, and the remaining half over the next 16 hours. Alternatively, a goal of 50-100ml/kg every four hours can be used to guide volume of oral replacement. 

For those who are only mild to moderately dehydrated from vomiting and continue to be nauseated, ondansetron, a serotonin receptor antagonist, can be used at a dose of 0.1-0.15 mg per kg to abate nausea. Note that Zofran cannot be used under the age of six months. As a quick rule of thumb, you can use two mg for younger children under five years of age, and 4mg for older children and adolescents.

For those with severe dehydration, fluid loss should be replaced using IV or IO rehydration. As stated earlier, initial management consists of 20mL/kg boluses of isotonic normal saline solution until a patient’s signs of hypovolemic shock are stabilized. Once hemodynamically stabilized, fluids are adjusted to a maintenance rate, with glucose and potassium added to help replenish losses. Most commonly, patients are started on D5.9 NS with 20 mEq/L of potassium chloride (exceptions are for burn patients who require ongoing NS fluid therapy, diabetic ketoacidosis patients who do not receive any glucose in their fluids initially, or for children with severe electrolyte abnormalities). Fluids can be adjusted as needed after initiating to replete sodium at an appropriate rate.

Calculating Maintenance Fluid Rate: Method 1 - Weight-Based Fluid Replacement

• First 10kg: 4mL/kg/hr
• Second 10kg: 2mL/kg/hr
• Additional kg: 1mL/kg/hr

Example: A 40kg child's maintenance fluid rate would be 80mL/hr (40mL for first 10kg, 20mL for second 10kg, then 20mL for the additional 20kgs).

Calculating Maintenance Fluid Rate: Method 2 - Body Surface Area-Based Fluid Replacement

• Replace 1200 mL per m² over 24 hours.

Example: Average 12-year-old child's weight is 40kg and height is 150cm. BSA = √ (cm x kg) / 3600:  √ (150cm x 40kg)/3600 = 1.3 m². Maintenance fluid rate is 1200mL x 1.3m²/24 hours = 65mL/hr.

• Tachycardia in a calm, comfortable, and afebrile patient should raise concern for dehydration and compensated hypovolemic shock.
• Patients with severe dehydration often have difficult IV access - don't hesitate to utilize IO access for primary bolus rehydration (best placed in proximal tibia, distal femur, or proximal humerus).
• Utilize historical and clinical signs to determine severity of dehydration (mild <5% dehydration, moderate 5-10% dehydration, severe >10% dehydration).
• Urine specific gravity and serum electrolytes can help supplement your clinical decision to determine degree of dehydration and appropriate fluid rehydration.
• In patients with nausea but requiring oral rehydration therapy, consider ondansetron 0.1mg/kg early in the treatment course.
• In patients requiring intravenous fluids, rehydration is initially with 20mL/kg boluses of NS given over 15-20 minutes followed by maintenance fluids.
• Normal minimum urine production for a child is expected to be 1mL/kg/hr. Normal bladder size for children under the age of two is 2x age + 2 (capacity in ounces). For children over the age of two, normal bladder size is age/2 + 6 (capacity in ounces). Using these calculations, children at any age should fill their bladder at least every 12 hours. Thus, it is appropriate to give guidance to return to the emergency department for possible intravenous fluid therapy for dehydration if a child is not urinating at least twice in a 24-hour period.

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