Introduction

Fluid and electrolyte requirements / 24 hours:

• 100 cc/kg first 10 kg

• 50 cc/kg second 10 kg

• 20 cc/kg additional kg

Examples: 10 kg patient = 1000 cc/24h; 20 kg patient = 1500 cc/24h; 50 kg patient = 2100cc/24h

Electrolyte requirements / 24 hours

• Na⁺ 3 mEq/kg

• K⁺ 2 mEq/kg

Types of Dehydration

Principles of Therapy for Fluid and Electrolyte Losses

Assess the degree of dehydration (see the following chart):

• Look for a recent weight change, it available.

• Gauge clinical appearance.

For most patients, while you're waiting for lab results, it is appropriate to begin fluid resuscitation with 0.33% NaCl, 0.45% NaCl, or even 0.9% NaCl solution at a 1.5 x maintenance rate. When laboratory information is available, calculations for volume and electrolytes losses can take into account what has already been given to the child.

Important point: If a child is in shock, give volume (crystalloid: 0.9% NaCl or Ringer's Lactate as a bolus of 20 mL/kg) irrespective of the serum sodium level.

Management of mild dehydration

• Oral hydration is usually adequate in the child that is less than 5 percent dehydrated if the patient can tolerate oral intake.

• If oral fluids are not retained, parenteral fluids should be given. Many children can tolerate fluids after an initial IV bolus of 10-20 mL/kg of normal saline. However, if the child continues to vomit, then consider fluid resuscitation as outlined below.

• Patients require careful monitoring of intake, output and weight (or change in weight). If initial labs are normal and if the child continues to improve, then additional lab studies may not be necessary.

• Orally, use clear fluids (i.e., Pedialyte, Lytren, Resol). In a child whose emesis is abating or who is being managed as an outpatient, drinking an ounce an hour of a rehydration fluid will often prevent significant dehydration. Do not use tea or boiled milk. Fruit juices may worsen the diarrhea secondary to their hyperosmolarity.

• Once ongoing losses have ceased, diet may be advanced. Recommend do not prescribe the BRAT (bread, rice, applesauce, and toast) diet. See the section on pediatric diarrhea for a discussion on this subject.

Examples

• Isotonic Dehydration: Normal serum sodium. Calculations of deficit and maintenance requirements require three variables: wet weight; water deficit; and sodium deficit

• 10 kg child: 10 percent dehydrated. Wet weight (i.e. weight if fully hydrated) = (Current weight / 100 - percent dry) x 100. Thus the wet weight for this child would be 10 kg /0.9 = 11.1 kg. The fluid deficit then would be 11.1 kg, 10.0kg + 1.1 kg = 1100mL.

Some practitioners use a simpler method, skipping the calculation of wet weight and calculating the deficit based on the dry weight. In this example then, the deficit, using the simpler method would be 1000 mL (10 percent of 10 kg). While this method is a bit quicker, it does underestimate the deficit by a small amount. In practice, this usually is not significant, since fluid resuscitation is a dynamic process of checking and rechecking the patient's clinical status.

After calculating the fluid deficit, next calculate the Na+ deficit. In isotonic dehydration, the patient has lost water and sodium in such a way that the serum sodium remains normal. However, some sodium has been lost and must be replaced. A simple approach is demonstrated in the following table:

Since this patient is 10 percent dehydrated, the Na+ deficit is 8 mEq per kg of wet weight or 8 x 11.1 or 89 mEq.

Thus the three required variables for calculating fluid resuscitation in this patient are:

• Wet weight 11.1 kg

• Water deficit 1100 mL

• Sodium deficit 89 mEq

There are two phases to the resuscitation; (1) an initial phase, lasting 8 hours, in which 50 percent of the deficit is replaced and standard maintenance fluid and electrolytes are provided. The second phase lasts 16 hours (total 24 hours), and the remaining deficit as well as maintenance fluid and electrolytes are given. For ease of calculation, assume that you are almost always going to use a glucose-containing solution (D5W) with added electrolytes (exception: DKA). This allows you to skip calculations for glucose. Further assume that you are going to provide K+ at 2 mEq per 100 mL (20 mEq/L) in most cases. This allows you to skip calculations for potassium. Many practitioners choose to add the potassium only after the patient's first void.

First phase:

Maintenance for 8 hours plus replacement of half of the deficits.

Thus, in the first 8 hours of resuscitation, this patient needs a total of 900 mL of water and 55 mEq of sodium. To convert this into a liter-based equivalent, divide both the volume and the sodium by 0.9, yielding a sodium concentration of ~ 60mEq/L. There is no standard off-the-shelf solution with this concentration, but note that a 0.33% NaCl solution has 57 mEq of sodium per liter - close enough so that you don't have to break the seal on the sterile IV solution and add sodium. Your rate of administration will be 900 mL/ 8 hrs or 112 mL/ hr. Your order for this first phase would then read:

IV with D5 + 0.33% NaCl at 112 mL / hr for 8 hrs. Add KCl 20 mEq / L after first void.

Maintenance solutions for 16 hours plus replacement of the remaining deficit.

Thus, in the second phase of resuscitation, this patient needs a total of 1250 mL of water and 66 mEq of sodium. To convert this into a liter-based equivalent, divide both the volume and the sodium by 1.25, yielding a sodium concentration of ~ 50 mEq/L. There is no standard off-the-shelf solution with this concentration, but note that a 0.33% NaCl solution has 57 mEq of sodium per liter again, close enough, and you don't have to prepare a special solution. Your rate of administration will be 1250/ 16 hrs or 78 mL/hr. Your order for this second phase would then read:

After 8 hours, decrease IV rate to 78 mL / hr.

Writing these orders is not enough. Reassess the patient periodically based on clinical appearance and urine output.

When the serum sodium is low in a dehydrated patient, the patient has lost more sodium than water. In addition to the predicted sodium loss based on the percent dehydration, there have been additional losses, calculated as:

Additional sodium deficit = Wet weight in kg x 0.6 x 135 - measured sodium

Given a 10 kg child who is 10 percent dry with a sodium of 120 mEq/ L, the calculation variables for resuscitation are:

• Wet weight 11.1 kg

• Water deficit 1100 mL

• Sodium deficit 89 mEq + (11.1) (0.6) (135-120) = 89 + 99 = 188 mEq

In treating a patient with hypotonic dehydration, most practitioners will use a 24-hour treatment period rather than a 2-phase approach. Calculations would be as follows:

Thus, in this example, the patient needs a total of 2150 mL of water and 221 mEq of sodium over a 24-hour period. To convert this into a liter-based equivalent, divide both the volume and the sodium by 2.15, yielding a sodium concentration of ~ 103 mEq /L. There is no standard off-the-shelf solution with this concentration, but note that a 0.45% NaCI solution has 77 mEq of sodium per liter - not quite close enough, so you'll have to prepare a special solution. Add 26 mEq of NaCl to each liter of fluid, and you have a sodium concentration of 103 mEq/ L. Your rate of administration will be 2150 mL/ 24 hrs or 90 mL/ hr. Your order for this patient would then read:

IV D5 + 0.45% NaCI at 90 mL/hr. Add NaCl 26 mEq / L Add KCl 20 mEq/ L after first void.

Again, simply writing these orders is not enough. Reassess the patient periodically based on clinical appearance and urine output.

Warning: Correcting hyponatremia too quickly, especially in adults, can result in central pontine myelinolysis leading to virtual destruction of the central pons. Go slow with sodium replacement. The only exception would be in the patient who is having seizures related to the hypernatremia.

Hypertonic Dehydration:

• Elevated serum sodium

• Water loss in excess of sodium loss

This type of dehydration requires skill and experience in management. Discussion is beyond the scope of this manual. If you encounter this type of dehydration in a pediatric patient, in the absence of shock (requiring a fluid bolus), start an IV with D5 + 0.2 % NaCl at a 1.5 x maintenance rate and refer or transport.