Renal Hemodynamics: After birth, renal blood flow increases in response to increased blood pressure (renin-angiotensin) with a secondary increase in glomerular filtration rate.AVP secretion is increased in response to stress, such as birth, asphyxia, RDS, positive pressure ventilation, pneumothorax and intracranial hemorrhage. Arginine vasopressin (AVP, ADH) levels rise after birth.Increased aldosterone levels enhance distal tubular reabsorption of sodium resulting in an impaired ability to excrete a large, or acute, sodium load.The Renin-angiotensin system is very active in the first week of neonatal life resulting in increased vascular tone and elevated levels of aldosterone.Therefore, insensible water losses will be greatest with small size and decreased gestational age. The surface area of the newborn is relatively large and increases with decreasing size. A proportion of the diuresis observed in both term and preterm infants during the first days of life should be regarded as physiologic.After birth this excess water must be mobilized and excreted. The preterm fetus or neonate is in a state of relative total body water and extracellular fluid excess.The body composition of the fetus changes during gestation with a smaller proportion of body weight composed of water as gestation progresses.A rational approach to the management of fluid and electrolyte therapy in term and preterm neonates requires the understanding of several physiologic principles. Excess fluid administration in the very low birth weight infant is associated with patent ductus arteriosis and congestive heart failure, intraventricular hemorrhage, necrotizing enterocolitis and bronchopulmonary dysplasia. In the near term and term neonate excess fluid administration results in generalized edema and abnormalities of pulmonary function. Inadequate administration of fluids can result in hypovolemia, hypersomolarity, metabolic abnormalities and renal failure. mm/L = micromol/litre.Fluid and electrolyte management in the newbornĬareful fluid and electrolyte management is essential for the well being of the sick neonate. If your laboratory does not provide reference ranges for newborns or subsets thereof, the following may be helpful. This is particularly important, for example, with respect to coagulation profiles. It is always advisable to keep in mind the reference ranges from your own laboratory as they will be analyser or population-specific. Is there any risk or danger in correcting an abnormal result?.What is the evidence that correcting the abnormality is beneficial?.Is this due to sampling or laboratory error?.In most cases, when considering the correction of ‘abnormal’ values, it is wise to consider the following: As (extreme) prematurity is a pathological condition in itself, be cautious when using the concept of ‘normal’. In general, normal pathology values are readily available for healthy term infants. Normal laboratory values are reference ranges used by clinicians to interpret results of laboratory tests. We recommend that you also refer to more contemporaneous evidence in the interim. Please note that all guidance is currently under review and some may be out of date.
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