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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.
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