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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
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