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                                    Fluids and Electrolyte Therapy in the Paediatric Surgical Patient  25

          before the GFR, and thus serum creatinine levels, approach the levels   intake adjustments. 1
          of a term infant. 1                                    Fluid Requirements
             On a clinical note, the use of gentamicin in the perioperative surgical   Fluid  requirements  in  the  newborn  or  older  child  depend  upon  multiple
          newborn, if the levels of gentamicin are not measured due to resource   factors, but the majority are determined by the insensible water loss and the
          constraints, can potentially increase the amount of renal dysfunction in   newborn’s metabolic rate. The evaporation of water from the skin and the
          this patient population. In a recent study in India, dosing of gentamicin   respiratory tract has environmental factors, such as air and incubator tem-
                                                   2
          with the following neonate weights was considered safe:
                                                                 perature, humidity, and air flow across the child’s body, as well as infant fac-
           • 10 mg every 48 hours for the neonate weighing less than 2000   tors, such as patient position, metabolic rate, and elevation in temperature.
            grams                                                  Many  studies  have  indicated  that  water  loss  from  the  premature
           • 10 mg every 24 hours in the neonate weighing 2000–2249 grams  infant is significantly greater than from the term infant, possibly due
                                                                 to decreased subcutaneous fat and increased permeability through the
           • 13.5 mg every 24 hours for the neonate weighing more than 2500   skin. The combination of increased water loss in the premature infant
            grams
                                                                 and the use of radiant warmers without humidity, which occurs in many
             Gentamicin interval errors are the most common drug error reported   settings, can result in a severely dehydrated premature infant who may
          in a recent neonatal intensive care unit (NICU) study from the United   need  resuscitation.  The  insensible  water  loss  can  increase  50–200%
          States, and certainly the effect on renal function is amplified in a setting   with the use of radiant warmers in the preterm infant. This can have an
                                      3
          where drug levels cannot be measured.  Gentamicin and ampicillin are   significant impact on the intraoperative course, as the patient may arrive
          the two most commonly prescribed antibiotics in the NICU environment,   in the operating theatre dehydrated even though receiving maintenance
          and inappropriate dosing can cause clinically significant renal damage.  fluids in the immediate preoperative period. The low-tech approach to
             Sodium excretion, which is directly correlated to GFR and indirectly   humidity can be achieved merely by keeping an open container of water
          to gestational age, becomes an issue in situations where there is sodium   near the newborn while under warming lights. Fluid chambers need to
          load or the need to retain sodium arises. The kidney’s ability to retain   be cleaned and changed routinely in an effort to decrease infection in
          sodium in preterm infants will not reach the term infant’s level until   the nursery unit, and the fluid level of radiant warmers, which may vary
          they  reach  the  gestational  age  of  a  term  infant.  Clinically,  this  can   depending upon the manufacturer, needs to be monitored.
          produce situations of appropriate release of ADH and reabsorption of   Many  formulas  exist  to  determine  the  maintenance  fluid  levels
          water in a setting where the patient is getting a volume of hypotonic   for the neonate or small child. The formula of the “4-2-1 rule” works
          fluid, such as 0.25% saline in 5% dextrose. If the sodium level goes   well  for  determining  the  maintenance  fluids  for  weight  groups  that
          below  120  mEq/l,  then  the  patient  could  show  signs  of  neurologic   are less than 30 kg. In this formula, the first 10 kg of body weight is
          injury, which can be nonreversible.                    multiplied by 4 ml/hr; the second 10 kg is multiplied by 2 ml/hr; and
             A urinalysis that shows colour (concentration, presence of bilirubin),   any additional kilograms of weight are multiplied by 1 ml/hr.  Table
                                                                                                               4
          red  blood  cells,  white  blood  cells,  protein,  and  glucose  can  help  to   5.3  provides  examples  that  apply  to  newborns  and  older  children  to
          diagnose some renal problems. The observation of protein in the urine   determine  maintenance  fluids.  Intraoperative  fluid  management  is
          can be normal in the first few days of life and then can become expected   discussed in a later section of this chapter that describes translocated
          in  cases  of  hypoxia,  congenital  cardiac  problems,  and  dehydration.   fluid and blood loss. Typically, if one has a 1-ml blood loss, then this
          Small amounts of glycosuria can be detected secondary to a low tubular   1 ml is replaced by 3 ml of crystalloid, which could be normal saline
          reabsorption with a glucose load, and the glucose load can even result   or Ringer’s lactate solution. This amount of replacement allows for the
          in an osmotic diuresis and dehydration. Glucose in the urine may be an   intravascular volume to be maintained, even during times of decreasing
          early sign of sepsis, especially in the presence of other factors.  intravascular volume, which could be surgery.
               Normal Fluid and Electrolyte Metabolism           Table 5.3: Sample 4-2-1 rule for maintenance fluids for newborns and
                                                                 older children.
          Total Body Water
          At birth, the infant is suddenly separated from the source of water found   Child’s body weight  Volume
          in the in utero environment, and now is in an environment with signif-
          cant  water loss from the skin and respiratory tract, thus promoting a                4 × 9 = 36
          potential for early dehydration. During this period of transition, water
          intake and renal conservation of fluids needs to maintain a homeostatic               2 × 0 =   0
          state to survive.                                                9 kg
             Total  body  water  compromises  intracellular  water  (ICW)  and                  1 × 0 =   0
          extracellular water (ECW), with the ECW having an intravascular and                             36 cc/hr
          interstitial  component.  With  advancing  gestational  age,  the  amount
          of  total  body  water  declines  from  94%  of  body  weight  in  the  third        4 × 10 = 40
          trimester  to  approximately  78%  at  term.  In  the  immediate  postnatal
                                                                                               2 × 5 =   10
          period, the amount of extracellular fluid decreases and the percentage
                                                                          15 kg
          of  intracellular  fluid  increases,  although  the  newborn  has  a  large
                                                                                               1 × 0 =     0
          interstitial reserve volume during times of decreased fluid intake. The
          term infant can compensate more than the preterm infant, but newborns                             50 cc/hr
          with a large surface-to-weight ratio, higher total water content, limited
          renal  ability  to  concentrate,  greater  insensible  water  loss  from  thin       4 × 10 = 40
          skin, and high blood flow all can become clinically dehydrated in a
          very short period of time. The added water loss associated with radiant              2 × 10 = 20
                                                                          26 kg
          warmers, which are commonly found in the treatment of the newborn
                                                                                               1 × 6 =     6
          and  especially  preterm  infants,  can  result  in  a  rapid  and  progressive
          level  of  dehydration  without  close  observation  and  appropriate  fluid                      66 cc/hr
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