Fluid and Electrolyte Therapy in the Very Low birthweight

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Article fluids and electrolytes,Fluid and Electrolyte Therapy in. the Very Low birthweight,John M Lorenz MD, Objectives After completing this article readers should be able to. 1 Characterize insensible water loss in extremely preterm neonates. Author Disclosure 2 Compare the renal function of preterm and term neonates. Dr Lorenz did not 3 Describe the changes in total body water and electrolytes with the transition from fetal. disclose any financial to neonatal life, relationships relevant 4 Use the phases of renal fluid and electrolyte adaptation to determine appropriate. to this article fluid and electrolyte therapy for preterm neonates. The transition from fetal to neonatal life is associated with major changes in water and. electrolyte homeostasis Fluid and electrolyte management is particularly challenging. for very preterm neonates in whom water loss is large highly variable and in large. part not subject to feedback control In addition preterm neonates kidneys have a. more limited ability to compensate for water and electrolyte imbalances than term. neonates Insensible water loss is a much larger component of the total water. requirement in extremely preterm infants than in term infants The weight loss seen in. preterm infants during the first postnatal week results in large part from an abrupt. and absolute decrease in total body water volume and hyperkalemia is a common. finding in the first 24 to 72 hours after birth Fluid and electrolyte adaptation in most. very low birthweight newborns generally occurs in three phases and awareness of the. changes associated with each phase can aid clinicians in determining appropriate. adjustments in fluid and electrolyte therapy,Introduction. Fluid and electrolyte management is an important and challenging part of the initial. management of any very preterm or critically ill newborn The transition from fetal to. neonatal life is associated with major changes in water and electrolyte homeostasis Before. birth the fetus has a constant and ready supply of water and electrolytes from the mother. across the placenta fetal water and electrolyte homeostasis is largely a function of maternal. and placental homeostatic mechanisms After birth the newborn rapidly must assume. responsibility for fluid and electrolyte balance in an environment in which water and. electrolyte availability depends on the knowledge and experience of the physician Fluid. and electrolyte management is particularly challenging for very preterm neonates in whom. water loss is large highly variable and in large part not subject to feedback control and. whose kidneys ability to compensate for water and electrolyte imbalances is more limited. than even the term newborn s Superimposed on these more gradual maturational limita. tions of renal function are acute changes in the first few postnatal days in the ability of the. neonate to excrete water and electrolytes Moreover major changes in total body fluid and. electrolyte balances occur with the transition from fetal to neonatal life in the preterm. infant Thus the goal of fluid and electrolyte therapy in the immediate postnatal period is. not to maintain fluid and electrolyte balance but to allow the appropriate changes to occur. without detrimental perturbations in fluid and electrolyte status. Professor of Clinical Pediatrics College of Physicians and Surgeons Columbia University Morgan Stanley Children s Hospital of. New York New York NY,e102 NeoReviews Vol 9 No 3 March 2008.
Downloaded from http neoreviews aappublications org by Jeffrey Merrill on August 5 2011. fluids and electrolytes fluid and electrolyte therapy. Table 1 Insensible Water Loss in Appropriate for gestational Age Newborns. Gestational Postnatal Age days,Age wk 1 1 3 5 7 14 21 28. 25 to 27 57 to 214 62 to 171 59 to 96 43 to 72 31 to 68 18 to 59 14 to 55 8 to 53. 28 to 30 22 to 75 23 to 68 20 to 57 19 to 48 16 to 45 12 to 37 9 to 34 9 to 34. 31 to 36 8 to 29 8 to 28 10 to 27 10 to 27 10 to 27 9 to 22 10 to 19 11 to 16. 37 to 41 8 to 18 11 to 14 11 to 14 11 to 14 11 to 14 11 to 14 12 to 13 11 to 16. Ninety five percent confidence limits for infants nursed naked in an incubator with 50 ambient humidity ambient air temperature in the neutral thermal. range and constant air flow of 8 L min, Reprinted with permission from Lorenz JM Fluid and electrolyte therapy in the newborn infant In Burg FD Polin RA Ingelfinger JR Gershon A eds. Current Pediatric Therapy 17 Philadelphia Pa WB Saunders 2002 Calculated from the data of Hammarlund K Sedin G Stro mberg B Transepidermal. water loss in newborn infants VIII Relation to gestational age and post natal age in appropriate and small for gestational age infants Acta Paediatr Scand. 1983 72 721 728 and Riesenfeld T Hammarlund K Sedin G Respiratory water loss in relation to gestational age in infants on their first day after birth Acta. Paediatr Scand 1995 84 1056 1059, Special Considerations compensate for changes in water and electrolyte intake is. Insensible Water Loss IWL limited Glomerular filtration rate is lower in the preterm. IWL is a major consideration in fluid and electrolyte than the term neonate It increases with gestational and. therapy of extremely preterm neonates First it repre postnatal age 9 The sodium reabsorptive capacity of. sents a much larger component of the total water re the proximal nephron is limited in the preterm infant. quirement than in term infants Second it is highly thereby limiting the ability to conserve sodium with a. variable IWL occurs transepidermally and across upper normal extracellular volume compared with term infants. airway epithelium Transepidermal loss is the larger and is and adults This capacity is related directly to gestation. affected principally by gestational and postnatal age 1 9 10. and ambient water vapor pressure 2 Antenatal steroids Even low birthweight and presumably preterm in. also decrease IWL at any given gestational age 3 Upper fants are capable of urinary potassium excretion at a rate. airway epithelial loss is a function of minute ventilation in excess of the rate of potassium filtration across the. independent of maturity 4 and the water vapor pres glomerulus during potassium or sodium bicarbonate. sure of inspired gas Third the infant has no ability to loading in the first postnatal month indicating net tubu. modulate IWL in response to water balance Therefore lar potassium secretion 11 However the rate of potas. IWL is obligate free water loss sium excretion per unit body or kidney weight during. Table 1 describes IWL as a function of gestational and exogenous potassium loading is lower in the immature. postnatal age from the first day after birth No compara. than mature animal 12 In general the limited potas. ble data are available for neonates of 23 to 24 weeks of. sium secretory capacity of the immature distal nephron is. gestation or for neonates under radiant warmers How. clinically relevant only under conditions of potassium. ever IWL surely is higher in neonates of 23 to 24 weeks. excess or when potassium shifts from the intracellular. gestation at any given postnatal age and higher in ambi. fluid ICF space to the extracellular fluid ECF space. ent humidity as is typical under radiant warmers The. in the immediate period after birth in extremely preterm. same group of investigators whose data were used to. infants On the other hand potassium reabsorption in. construct Table 2 found IWL to be 15 to 35 higher, creased in parallel with the increase in the filtered potas. during the first 3 postnatal weeks under a radiant warmer. sium load with increasing gestational age in a study of. 5 compared with the humidified environment specified. infants of 23 to 31 weeks of gestation on postnatal days. in Table 2, 4 to 5 with urinary potassium excretion remaining low.
and unchanged over this period of gestation 13, Renal Function Although preterm infants can dilute their urine. Although even the very preterm neonate can maintain nearly as much as term infants and adults can they. water and sodium balance within a relatively narrow cannot concentrate their urine to nearly the same de. range over a relatively broad range of water and sodium gree Adults can achieve a maximum urine osmolality of. intakes 6 7 8 the ability of the immature kidney to 1 500 mOsm L term infants concentrate their urine to. NeoReviews Vol 9 No 3 March 2008 e103, Downloaded from http neoreviews aappublications org by Jeffrey Merrill on August 5 2011. fluids and electrolytes fluid and electrolyte therapy. Postnatal Renal Fluid and Electrolyte Adaptation in Very Low. birthweight Infants, Phase Prediuretic Diuretic Natriuretic Homeostatic. Age Birth to 2 days 1 to 5 days After 2 to 5 days, Urine output Low Abrupt increase Decreases then proportional to. Sodium excretion Minimal Abrupt increase Decreases then proportional to. Potassium excretion Minimal Abrupt increase Decreases then proportional to. Water balance Less than intake minus IWL Markedly negative Approximately proportional to. sodium balance, Sodium balance Slightly negative Markedly negative Stable then positive with growth.
Potassium balance Slightly negative Markedly negative Stable then positive with growth. Extracellular fluid volume Stable or slightly decreases Abruptly decreases Proportional to sodium balance. increases with growth, Glomerular filtration rate Low Abruptly increases Decreases then gradually. increases with maturation, Fractional excretion of Variable Increased Gradual decrease. Fractional excretion of Variable No change No change. Urine osmolality Moderately hypo osmotic Moderately hypo osmotic Moderately hypo osmotic. Common Problems Water intoxication with Hypernatremia Water and sodium retention. lower IWL than Hyperglycemia with chronic lung disease. anticipated patent ductus arteriosus, Hypernatremia with higher Water and sodium depletion. IWL than anticipated with or without hyponatremia,Hyperkalemia Hypokalemia. IWL insensible water loss, Adapted from Lorenz JM Fluid and electrolyte management in the first week of life In Polin RA Yoder MC Burg FD eds Workbook in Practical.
Neonatology 3rd ed Philadelphia Pa WB Saunders Company 2001. only approximately 600 mOsm L and preterm infants ure 14 15 16 17 18 19 20 The decrease in. concentrate it to only approximately 500 mOsm L As a ECF volume is the result of a decrease in interstitial fluid. result the minimal water requirement to excrete a given ISF volume without a change in plasma volume 16. solute load is greater in the preterm than term infant The reason for this contraction is not understood The. Thus the preterm infant has a limited ability to conserve magnitude of the contraction of the ECF space is roughly. free water inversely proportional to gestational age. Although physiologic correlates of postnatal diuresis. Changes in Total Body Water and Electrolytes and natriuresis have been described 20 21 22 23. With the Transition from Fetal to Neonatal 24 25 26 the reason for this phenomenon is un. Life known The disproportionate decrease in ECF precludes. A 10 to 20 weight loss is common in preterm in ascribing this decrease solely to catabolism That it is. fants during the first postnatal week Although inade physiologic is suggested by several observations First. quate caloric intake may contribute somewhat to this relatively large differences in water and caloric intake are. weight loss it results in large part from an abrupt and required to moderate this weight loss 6 7 8 Further. absolute decrease in total body water volume in the first higher caloric intake has been correlated with less post. few days after birth 14 15 16 17 18 19 The best natal weight loss but no difference in the magnitude of. evidence suggests that a disproportionate loss of this ECF contraction 18 Moreover increases in ICF and. water occurs from the ECF compartment in appropriate body solids per kilogram of body weight but not in ECF. for gestational age very low birthweight infants Fig per kilogram body weight occur with subsequent weight. e104 NeoReviews Vol 9 No 3 March 2008, Downloaded from http neoreviews aappublications org by Jeffrey Merrill on August 5 2011. fluids and electrolytes fluid and electrolyte therapy. Phases of Renal Fluid and Electrolyte,Adaptation, In most preterm infants the excretion of water and. sodium that occurs as the result of contraction of the. ECF space in the first few postnatal days does not occur. gradually In fact a characteristic pattern of fluid and. electrolyte adaptation which is largely independent of. fluid and electrolyte intake is observed in the first post. natal week in most very low birthweight and probably. most newborns Usually three phases can be distin, guished 25 27 Awareness of these phases is helpful in. anticipating changes in fluid and electrolyte homeostasis. and guiding fluid and electrolyte therapy Table 2 sum. marizes the changes in fluid and electrolyte balances. ECF volume and renal function associated with each. phase their implications for fluid and electrolyte man. agement and common fluid and electrolyte problems to. anticipate during each phase, Figure Body weight g and extracellular water volume vol. ume of distribution of sucrose mL in 13 preterm,Fluid and Electrolyte Guidelines.
appropriate for gestational age infants within the first Guidelines for initiating and subsequently adjusting fluid. Fluid and electrolyte adaptation in most very low birthweight newborns generally occurs in three phases and awareness of the changes associated with each phase can aid clinicians in determining appropriate adjustments in uid and electrolyte therapy Introduction Fluid and electrolyte management is an important and challenging part of the

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