Fluid management in infants

Published on 07/02/2015 by admin

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Last modified 07/02/2015

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Fluid management in infants

William Shakespeare, MD and Randall P. Flick, MD, MPH

The normal newborn is particularly prone to developing derangements in fluids and electrolyte concentrations. In the face of significant illness or injury or in the setting of an invasive surgical procedure, fluid balance becomes even more precarious. This propensity arises from several factors that are unique to the neonate and infant. Total body water in neonates and infants makes up a substantially larger proportion of body mass than in the older child or adult (80% vs. 60%). Body surface area, when compared with body mass, is also much larger in neonates and infants, leading to greater insensible fluid losses, especially when a major body cavity is opened. Finally, limited ability to communicate hunger and thirst makes the young child dependent on thoughtful fluid and electrolyte management by a vigilant clinician throughout the perioperative period.

Maintenance fluids

Reliance on the method of Holliday and Segar continues despite concern regarding its relevance to the perioperative care of young children. In their seminal 1957 paper, the authors provided a simplified method for estimating maintenance fluids and electrolytes based on energy requirements: 1-kg to 10-kg infants need about 100 cal·kg⁻¹·24 h⁻¹; each kilogram over 10 kg and up to 20 kg requires an additional 50 cal·kg⁻¹·24 h⁻¹; after 20 kg, each additional kilogram requires 20 cal·kg⁻¹·24 h⁻¹. Approximately 1 mL of water is needed for each calorie expended. This method can be simplified (Table 194-1). These recommendations were intended to guide maintainence fluid therapy for hospitalized children, however, and not for intraoperative care.

Table 194-1

Maintenance Fluid Therapy for Hospitalized Neonates and Infants *

Weight (kg)	Fluid Needed (mL • kg⁻¹ • h⁻¹)
< 10	4
10-20	2
> 20	1

Note: These recommendations are NOT intended to be used intraoperatively.

^*Based on the method of Holliday and Segar.

Fluid replacement

The fluid deficit in a patient receiving nothing by mouth can be calculated by multiplying the number of hours that the patient is not receiving anything by mouth by the maintenance fluid requirement. Although a scientific basis for the following recommendation is lacking, common practice is to not only provide maintenance requirements, but also replace half of the fluid deficit in 1 h, one fourth of the deficit in the second hour, and the final one fourth of the deficit in the third hour. Likewise, limited data exist to support the practice of replacing third-space losses, as has been described in most standard texts of pediatric anesthesia (Table 194-2). Many factors may influence fluid requirements in the very young, making the use of simplified formulas problematic and potentially dangerous. In the neonate, insensible water loss is increased by fever, crying, sweating, hyperventilation, bilirubin lights, and radiant heaters. Adequacy of fluid therapy is best monitored by clinical signs (heart rate, blood pressure, urine output, capillary refill, central venous pressure) rather than by blind adherence to a poorly validated formula. A few simple rules that will help to avoid problems occasionaly encountered in fluid management:

Table 194-2

Guidelines for Third-Space Fluid Replacement

Probability of Fluid Translocation	Example Procedure	Additional Fluid Replacement (mL • kg⁻¹ • h⁻¹)
Little or no	Craniotomy	0
Mild	Inguinal hernia	2
Moderate	Thoracotomy	4
Severe	Bowel obstruction	6

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