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24 Fluids and Electrolyte Therapy in the Paediatric Surgical Patient
Table 5.2: Clinical significance of newborns’ physiological presentations.

Physiology Clinical significance

Low glomerular filtration due to Poor tolerance volume load
Low perfusion pressure Poor tolerance sodium level
High renal vascular resistance

Only juxtamedullary glomeruli are functional
Fewer and smaller glomeruli
Smaller glomerular pore size

Diminished proximal tubular function
Low blood flow to juxtamedullary nephron tubules Tendency to excrete filtered sodium
Less tubular mass per nephron Low threshold for glucose excretion
Glomerular-tubular imbalance

Diminished proximal tubular function
Low blood flow to juxtamedullary nephron tubules Inability to concentrate urine
Less tubular mass per nephron
Glomerular-tubular imbalance

Potassium balance in the preterm infant can be an issue if the The absence of abdominal wall musculature can indicate prune
excretion of potassium and the extracellular movement of potassium belly syndrome, and the evidence of one umbilical artery connecting
occur after acidosis. This situation can easily be seen in many situations to the placenta correlates with an increased incidence of cardiac and
that would prompt the need for surgical intervention, especially if the renal malformations. The examination of the placenta is an easy task
presentation to a health care facility is delayed. Usually the newborn that could benefit the care of the newborn surgical or nonsurgical
can manage with a potassium level of approximately 6 mmol/l, and the patient when renal function is in question. Oedema in the newborn,
technique of taking the blood sample needs to be determined due the which is abnormal in the term child, can also indicate renal disease
common occurrence of haemolysed blood cells and a falsely elevated related to an underlying cardiac problem, hypoxia due to respiratory
potassium level. insufficiency, or low albumin levels, among the list of causes that may
Additional factors that may influence the renal function include include renal dysfunction. The infant with liver failure may present
maternal oligohydramnios, maternal drug use (indomethacin), with signs of oedema that are unrelated to any renal problems. A
polycystic disease in the family, and some forms of urinary obstruction. history of asphyxia commonly leads to a marked decrease in urine
Any situation whereby the infant has hypoxia, hypotension, or output. Sepsis is the other common cause of acute renal failure in the
haemorrhage may lead to a decreased RBF and a subsequent drop in neonate. A syndrome of inappropriate antidiuretic hormone (ADH)
the normal urine output. All of these factors point toward the reminder may accompany asphyxia, which may lead to fluid and electrolyte
that infants (especially preterm) must have their fluid status closely abnormalities. Once hypotension and oxygen needs are addressed,
monitored so that homeostasis is maintained, or approached, in the fluids may need to be restricted until diuresis occurs with fluids.
circumstance surrounding the need for surgical intervention. The lack The perioperative patient who arrives late in the progression of a
of urine pH monitoring and more extensive laboratory testing abilities surgical disease may present with signs of severe dehydration, and it
should not determine the impact that a detailed history and basic renal often is difficult to get a detailed history regarding urine output in the
function monitoring can have on the improvement of surgical outcome, neonate. The clinical evaluation of the neonate, which would include
which involves renal function immaturity. alertness, skin turgor, anterior fontanelle size or dimensions, heart
Table 5.2 presents the clinical significance of newborns’ rate, blood pressure, and presence or lack of urine, would assist in
physiological presentations. the determination of renal function and fluid status. Routinely, if the
Clinical Evaluation of Renal Function urine output history is questionable, the placement of gauze near the
urethra opening could be weighed to assist in obtaining the objective
The physical characteristics of the newborn may give the exam-
information needed to determine urine output preoperatively.
iner a clue as to a possible renal dysfunction. Low-set ears, flat-
tened nose, and VATER (Vertebrae, Anus, Trachea, Esophagus, and Laboratory Evaluation of Renal Function
Renal) or VACTERAL (Vertebral and spinal cord, Anorectal, Cardiac, Obtaining the serum creatinine level, which is available in most hos-
TracheoEsophageal, Renal and other urinary tract, Limb) syndrome pital settings, is the simplest method of determining the glomerular
may heighten the suspicion of renal function issues. The occurrence of function in the infant. Initially, the creatinine and even sodium level
an elevated systolic blood pressure, or systolic blood pressure greater in the newborn is a representation of the maternal electrolyte balance
than 90 mm Hg in the term infant, may indicate renal insufficiency, but and renal function. A number of factors determine newborn creatinine
usually these findings are associated not with renal problems but with levels such as maternal levels, gestational age, muscle mass, and
other issues such as pain or hunger. An accurate measurement of blood fluid balance. Increasing creatinine levels over the first few days of
pressure is sometimes difficult, but equally necessary, so that the more life indicates some form of renal dysfunction. If an infant is born at
subtle findings can be helpful in the diagnosis of renal disease. a gestational age of 25–28 weeks, it will take approximately 8 weeks