Fluids and Electrolytes

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Chapter 34 Fluids and Electrolytes

Kathy N. Shaw, MD, MSCE

1 How do you estimate the extent of dehydration in children?

Since serial weights on the same scale are rarely available in the emergency department (ED) setting, rely on the physical examination to estimate the degree of fluid loss (Table 34-1).

Table 34-1 Clinical Findings of Dehydration

2 What are the most reliable clinical examination findings that help you predict how dry a child has become?

An abnormal capillary refill time is probably the most reliable sign for predicting 5% dehydration in children. However, a combination of examination signs is better than any individual sign. The presence of two or more of the following four clinical measures seems most reliable in predicting dehydration:

“Ill” general appearance

Lack of tears

Capillary refill time at the fingertip > 2 seconds

Dry mucous membranes

Gorelick MH, Shaw KN, Murphy KO: Validity and reliability of clinical signs in the diagnosis of dehydration in children. Pediatrics 99:e6, 1997.

Steiner MJ, DeWalt DA, Byerley JS: Is this child dehydrated? JAMA 291:2746–2754, 2004.

3 How does the extent of dehydration translate into fluid lost?

For each kilogram of weight loss, 1 L of fluid was lost. Using weight obtained in the ED and your estimate of the percentage dehydration, you can calculate the “well” or rehydrated weight. The difference between the estimated well weight and current weight is converted into liters or cubic centimeters. For example, a 9-kg, ill-appearing baby presents with dry mucous membranes, crying with no tears, and a capillary refill time of > 2 seconds. She is estimated to have lost 10% of her body weight (severe dehydration).

4 How much fluid and what type do you use for a “bolus” to begin IV hydration?

The first objective in treating a child with dehydration is to restore intravascular volume and treat shock. Isotonic fluid, such as normal saline or Ringer’s lactate, should be used. Give boluses of 20 mL/kg, and reassess the child. The goal is to restore blood pressure, reduce heart rate, restore perfusion to the tissues (return of capillary refill < 2 seconds), improve mental status or general appearance, and produce urine. If initial fluid boluses > 60 mL/kg are needed, reconsider the diagnosis and management plan.

5 Should 5% dextrose in water be used as a fluid bolus for dehydration?

No, 5% dextrose in water (D5W) should not be used to treat dehydration. Only isotonic crystalloid fluid should be used for treatment of dehydration in pediatrics. Giving dextrose along with a large fluid bolus can lead to hyperglycemia.

6 Are there any children who should not receive a rapid fluid bolus?

Children with diabetic ketoacidosis or hypernatremic dehydration (serum sodium level > 150 mEq/dL) who are in a hyperosmolar state require slower and more cautious fluid resuscitation. Clearly, uncompensated shock (hypotension) must be treated rapidly, but 10-mL/kg boluses of normal saline should be used and the child reassessed after each bolus. Also administer fluids more cautiously to children in cardiogenic shock (heart failure).

7 What stock should be used after the initial IV bolus or if the child is not dehydrated?

Generally, D5¼ normal saline (NS) or D5½ NS, with 10 mEq potassium chloride/L added if the child has urinated. Use D5½ NS in children who have had < 20 mL/kg NS boluses or who have hyponatremic dehydration (serum sodium level < 130 mEq/dL). Children with burns, pyloric stenosis with hypochloremia, and diabetic ketoacidosis are usually kept on a normal saline infusion in the ED.

8 At what rate should fluids run on a child who has orders to receive nothing by mouth? How is this maintenance rate adjusted for the dehydrated child?

All children who are unable to drink should receive maintenance fluids, and if they are dehydrated, the rate is higher to replace some of the remaining fluid deficit. Calculate all rates by using the child’s well or rehydrated weight. Increase rates above maintenance if the child is febrile or has increased insensible or gastrointestinal losses.

Example: Maintenance rate for a 16-kg child: 40 mL/h (first 10 kg) + 6 kg × 2 mL = 12 mL/h (next 6 kg) or 52 mL/h (if the child is febrile, add 10% more, or 55–60 mL/h). To determine the rate for the dehydrated child, half of the total fluid deficit (minus the fluid boluses already given) is added to the maintenance rate for the first 8 hours. The other half of the deficit is added to the maintenance rate over the next 16 hours (hopefully outside of the ED!). For children with hypertonic dehydration, the remaining fluid deficit after initial boluses is replaced evenly over the next 48 hours.

Example: A 9-kg dehydrated baby was given 400 mL of NS (40 mL/kg) as an initial fluid bolus. The fluid deficit was 1000 mL. Half of the deficit is 500 ML. Since 400 mL was already given, 100 mL of the deficit should be added to the maintenance rate over the next 8 hours. Thus, 100 mL/8 h = 12.5 mL/hr should be added to the maintenance rate of 40 mL/hr (based on 10-kg “well” weight), or 52 mL/hr of D5¼ NS should be ordered.

Shaw KN, Spandorfer P: Dehydration. In Fleisher GR, Ludwig S, Henretig FM (eds): Textbook of Pediatric Emergency Medicine, 5th ed. Philadelphia, Lippincott Williams & Wilkins, 2006, pp 233–238.

KEY POINTS: DEHYDRATION

1 The first objective in treating a child with severe dehydration is to restore intravascular volume and treat shock, regardless of etiology.

2 In all children receiving IV fluids, the serial electrolytes and urine output should be monitored and fluid rates adjusted on the basis of the child’s hydration status, urine output, and presence or absence of increased ADH.

3 Compared with IV therapy, oral rehydration therapy is effective in treating dehydration in most children, has fewer complications, and may be faster.

9 Will use of hypotonic maintenance solutions cause dangerous hyponatremia?

Most children admitted with fever and volume depletion require free water. However, some children are at risk for secretion of antidiuretic hormone (ADH), which may cause retention of free water and hyponatremia. Conditions that have been associated with this state include bronchiolitis, meningitis, pneumonia, and postoperative pain or nausea. These children may require fluid restriction. In all children receiving IV fluids, the serial electrolytes and urine output are monitored and fluid rates adjusted on the basis of the child’s hydration status, urine output, and presence or absence of increased ADH. Keeping children on isotonic parenteral maintenance solution may cause hypernatremia and may not replace insensible water loss; evidence to support its safety is lacking.

Hatherill M: Rubbing salt in the wound. Arch Dis Child 89:414–418, 2004.

Moritz ML, Ayus JC: Prevention of hospital-acquired hyponatraemia: A case for using isotonic saline. Pediatrics 111:227–230, 2003.

10 Which children may be treated with oral rehydration?

Strongly consider oral rehydration in all children with mild or moderate dehydration who do not have uncompensated shock, severe vomiting, high stool output of >20 mL/kg/h, or poor adherence. It is very effective in treating dehydration and has a low failure rate.

Centers for Disease Control and Prevention: Managing acute gastroenteritis in children. MMWR Morb Mortal Recomm Rep 52:1–16, 2003.

11 Then why aren’t more children treated orally rather than with IV fluids?

Oral rehydration therapy takes time, one-to-one care, and patience. Many parents bring the child to the ED because they want a “quick fix.” Nevertheless, recent studies have shown that oral rehydration therapy is as effective as IV rehydration and may require less time with a lower complication rate.

Atherly-John YC, Cunningham SJ, Crain EF: A randomized trial of oral vs intravenous rehydration in a pediatric emergency department. Arch Pediatr Adolesc Med 156:1240–1243, 2002.

Spandorfer PR, Alessandrini EA, Joffe MD, et al: Oral versus intravenous rehydration of moderately dehydrated children: A randomized, controlled trial. Pediatrics 115:295–301, 2005.

12 How do you calculate the fluid and amount to give for oral rehydration?

The fluid deficit is calculated based on the estimate of the degree of dehydration, and the entire deficit is given by mouth over 4 hours. The parent is asked to offer a small amount of fluid every 5–10 minutes. For mild to moderate dehydration, give 1 mL/kg of an oral electrolyte solution every 5 minutes. For moderate to severe dehydration, give 2 mL/kg by mouth every 5 minutes.

Example: A 9-kg dehydrated baby with an estimated “well” weight of 10 kg has a fluid deficit of 1000 mL. We ask the mother to give 60 mL every 15 minutes (2 ounces in a bottle) or to insert via syringe 20 mL (2 mL/kg) into the baby’s mouth every 5 minutes for the next 4 hours (1000 mL/4 h = 250 mL/h; 250 mL/60 minutes = ∼4 mL/minute).

13 What type of fluid should be used for oral rehydration?

Use an oral rehydration solution. These have the correct proportion of dextrose and salt to allow for maximal absorption of electrolytes. Although solutions with higher concentrations of sodium (75–90 mEq/dL) are recommended initially (Rehydralyte [manufactured by Ross], ORS packets [Jaianas]), solutions with lower sodium content (40–60 mEq/dl) may be used and are more readily available (Pedialyte [Ross], Infalyte [Mead Johnson]).

14 Why can’t I mix half juice and half rehydration solution to make it taste better?

Juice and soda have high sugar contents, and a 50% mixture raises the sugar content above the amount that allows for maximum sodium/glucose transport across the cell membrane in the gastrointestinal tract. Use flavored solutions or add only a small amount (1:8 solution) to the rehydration solution.

15 When should oral rehydration not be used?

Severe dehydration

Inability to tolerate oral fluids because of vomiting

Altered mental status with risk of aspiration

Ileus

Short gut or carbohydrate malabsorption, which limit absorption

Batra B, Stanton B: Oral rehydration therapy, 2006. Available at www.uptodate.com.

16 What concerns should I have about a child with hypertonic dehydration?

The deficit in children with hypertonic dehydration may be underestimated because they appear less dry since their intravascular space is maintained longer. Additionally, rapid rehydration can cause cerebral edema, hemorrhage, or thrombosis. Hyperglycemia or hypocalcemia may also occur.

17 How do I treat hyponatremia?

Treat the patient, not the laboratory value. Treat children with seizures, severe lethargy, hypoventilation, coma, or shock immediately. For children with dehydration and low serum sodium, a fluid bolus of 20–40 mL/kg NS quickly corrects symptomatic hyponatremia. For water-intoxicated children or those with syndrome of inappropriate antidiuretic hormone secretion—-in whom sodium, not fluid, is needed—give 2–4 mL/kg of 3% saline to stop seizures, followed by 6–12 mL/kg of 3% saline over the next 2–4 hours.

18 How do I treat hypoglycemia?

A 0.5-gm/kg bolus is adequate to treat most cases of hypoglycemia. This can be given as 5 mL/kg of D10 or 2 mL/kg of D25. D50 is not used in children.

19 How and when do I treat metabolic acidosis?

Give sodium bicarbonate to children with a pH < 7.1 who are critically ill or are unable to compensate. Most children with dehydration whose serum bicarbonate level is > 8 correct their metabolic acidosis with fluid resuscitation and do not require bicarbonate. Bicarbonate should be given only for metabolic acidosis, not respiratory acidosis. Children with respiratory insufficiency should not receive bicarbonate. Also, bicarbonate should be given slowly because it does not cross the blood–brain barrier. However, its byproduct, carbon dioxide, does cross this barrier and may cause cerebral acidosis. Usually 1–2 mEq/kg is given over a minimum of 30–60 minutes. Administration of bicarbonate is the only treatment factor found to be associated with development of cerebral edema in patients with diabetic ketoacidosis.

Glaser N, Barnett P, McCaslin I, et al, for the Pediatric Emergency Medicine Collaborative Research Committee of the American Academy of Pediatrics: Risk factors for cerebral edema in children with diabetic ketoacidosis. N Engl J Med 344:264–269, 2001.

20 How do I treat hypercalcemia?

Give furosemide, 1–2 mg/kg, and address the etiology.

21 How do I treat hyperkalcemia?

The type and speed of treatment depend on the potassium levels and electrocardiogram changes. Potassium may be forced out of the cell by acidosis. Treatment of the acidosis causes potassium to return to the cell and out of the serum (Table 34-2).

Table 34-2 Treatment of Hyperkalemia

Potassium Level (mEq/dL)	ECG Finding	Treatment
<7.0	Peaked t waves only, or normal	Remove K source, treat acidosis, Kayexalate (1g/kg orally or rectally) every 4–6 hr
7.0	Widespread ECG changes without arrhythmia	Glucose (0.5 g/kg or 5 mL/kg of D10 over 30–60 minutes) and insulin (0.1 U/kg over 30–60 minutes) plus bicarbonate (2 mEq/kg over 30–60 minutes)
8.0	Arrhythmia	10% calcium gluconate (0.5 mL/kg over 2–5 minutes with ECG monitoring, discontinue if heart rate <100 beats per minute) plus glucose and insulin, bicarbonate as above