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CHAPTER 5

Fluids and Electrolyte Therapy in

the Paediatric Surgical Patient

Mark W. Newton
Berouz Banieghbal
Kokila Lakhoo

Introduction not number, of the glomeruli after the age of 1 year (Table 5.1). Although
Perioperative fluid and electrolyte management for infants and children the neonate is able to cope with routine fluid and electrolyte require-
can be confusing due the numerous opinions, formulas, and clinical appli- ments, it is during times of dehydration, acidosis, trauma, excessive fluid,
cations, which can result in a picture that is not practical and often mislead- and solute load that the neonate demonstrates immaturity in renal func-
ing. The basic principles of fluid and electrolyte management are similar tion. This immaturity in renal function is even more evident in patients
in the neonate and the paediatric patient if one considers the exceptions, who are less than 34 weeks gestational age at birth; studies demonstrate
which include renal maturity, body composition, physiological losses, that when a newborn is between 25 and 28 weeks gestational age, it takes
delivery issues, and autonomic nervous system differences. Understanding 8 weeks for their GFR to reach that of term infants. 1
the ability of the neonate and older paediatric patient to compensate for The term and preterm neonate will not have a complete diuretic
fluid and electrolyte alterations due to the surgical pathology is addressed response to a water load until after 5 days of age, and the preterm will
here after an overview of normal fluid and electrolyte metabolism. have an even slower response when compared to an adult response.
Perioperative fluid and electrolyte management addresses Newborns may have an altered ability to concentrate urine, tend to have
dehydration, fasting status, intraoperative fluid management, lower thresholds for glucose excretion, have unnecessary excretions
postoperative issues, and transfusion therapy. When practicing in of sodium, and have poor tolerances for fluid loads, all of which are
a resource-limited medical practice setting, one needs to be able to amplified in the preterm infant. By 1 month of age, the full-term
manage extremes of fluid and electrolyte issues with less laboratory infant’s kidney is about 70–80% mature in comparison to that of a
and investigative infrastructure in patients who may have delayed healthy adult patient. One of the primary homeostatic functions of the
presentation after their surgical pathology presented itself. The physician kidney is to maintain proper sodium levels in the body.
who cares for the surgical needs of the neonate and paediatric patient Term infants in nonphysiological stressful situations can maintain
population must be keenly aware of the perioperative needs regarding normal sodium levels, but preterm infants less than 32 weeks gestational
fluid and electrolyte metabolism requirements. This understanding will age would be considered “salt losers”. Their ability to conserve sodium
increase the goal of a successful and safe surgical course for both the is even further altered by hyperbilirubinaemia, hypoxia, and increased
paediatric patient and the patient’s parents. intraperitoneal pressure, which may decrease RBF and thus produce a
state of hyponatraemia. In the desire to replace the sodium that may be
Renal Function lost in the gastric, due to intestinal obstructional loss, or by diarrhoea,
Physiology of the Newborn the physician may give the neonate an excessive load of sodium, which
The neonatal renal function is not at adult levels until after the age of 1–2 may override the tubular functions of the immature renal system and
years due to many factors. The renal blood flow (RBF) reaches adult lev- even produce a state of hypernatraemia. Complications, including
els (20% of cardiac output (CO)) around the age of 2 years, whereas the reopening of the ductus arteriosus and cerebral bleed, can be caused by
glomerular filtration rate (GFR) shows the effects of increasing in size, hypertonicity due to the elevated sodium load.
Table 5.1: Glomerular filtration rate.
GFR by postnatal age (mean ± SD)
Gestational age 1 week 2–8 weeks >8 weeks
Normal GFR (ml/min/1.73 m ) 2 11.0 ± 5.4 a 15.5 ± 6.2 a 47.4 ± 21.5 a,b
25–28 weeks 10 26 9
No. of subjects 6 9 26
Mean – 1 SD c 15.3 ± 5.6 a 28.7 ± 13.8 a,b 51.4
29–34 weeks 27 27 1
No. of subjects 10 15
Mean – 1 SD 40.6 ± 14.8 65.8 ± 24.8 b 95.7 ± 21.7 b
38–42 weeks 26 20 28
No. of subjects

Absolute GFR (ml/min) 0.64 ± 0.33 a 0.88 ± 0.42 a 5.90 ± 5.92 a
25–28 weeks 1.22 ± 0.45 a 2.43 ± 1.27 a,b 10.83
29–34 weeks 5.32 ± 1.99 11.15 ± 5.21 b 20.95 ± 6.40 b
38–42 weeks
a Significantly less than corresponding value in full-term infants.
b Significant increase compared with previous age group.
c Mean – 1 SD represents lower cutoff value.